The efficency of a turbine engine, as with any internal combustion engine, is a function of compression ratio. A single stage compressor is very limited. To gain efficiency a multi stage compressor is required and axial flow is the best way to do that. The very first (WWII) jet engines used a single stage centrifugal compressor which is why the first generation jet planes had relatively large diameter fuselages though the Germans did develop an multi stage axial flow engine (Jumo 004) used in the ME 262. Its smaller diameter allowed an underwing twin engine layout not practical for the fat, barrel shaped centrifugal engines used by the allies. Axial flow engines required many years of developing advanced machining processes and metallurgy to take advantage of the higher forces and temperatures (and thus efficiency) of the axial flow designs. The big fan with bypass airflow can make use of excess power from the power turbine section but adding a fan to a single stage compressor and single stage power turbine engine is not going to do much for overall efficiency but will increase diameter and weight which is not desirable in most applications. Modern turbine engines have compression ratios of about 30:1 and acheive very high efficency as a result. That requires extremely accurately made parts in the compressor and turbine stages as well as benefitting from the larger diameter of the full scale engines. A small scale turbine, even with multiple stages, would be very difficult (and expensive) to fabricate and would be limited in the peak compression ratio and efficiency simply because of the small size of the components. Despite such limitations, some efficiency gain is possible and Williams Advanced Engineering was developing a small scale, multiple stage axial flow turbine to power a generator for a proposed hybrid vehicle application for the now discontinued Jaguar car company C-X75 project. It is doubtful that such an engine could be made at a price realistic for recreational RC applications.
In order to reduce the temperature of the exhaust which hits the turbine blades, I imagine that we should convert temperature to a swirl of almost the speed of sound at that temperature. Then a converging nozzle as in a turbo could even increase the velocity using the cyclone effect. To reduce the velocity on the way to the compressor blades, the compressor radius needs to be smaller. For some reason RC engines and APUs barely swirl the flow?
there are turbines (turbofan cores...) that reach 60:1 compression ratio, but their limits are with hot section temps...as for the single stage compressors - take a look at the russian VK-650V. It's a modern design turboshaft, the compressor looks like an automotive one, just...big...
or the engines it's designed to replace - Pratt & Whitney Canada PW200 or Turbomeca Arrius families, all single stage radial compressors with competitive efficiency
@@AKAtheA I guess I have a problem with the names. I thought that first there was the water turbine. A turbine converts fluid energy onto a shaft. See : work turbine in a turbo shaft . Or turbine boosted in contrast to gear driven compressor. I only talk about the hot section. Compressor is just CFD and aluminum.
Please note that when the fan is placed IN FRONT of the compressor intake as suggested in this video, it would further raise overall pressure ratio. For example, the centrifugal compressor has maximum pressure ratio of 4, while the fan with stator can deliver 1.5 pressure ratio, thus boosting pressure ratio to 4 x 1.5 = 6, thus will cause additional gain in power and thermal efficiency INDEPENDENT of the gain in thrust and propulsion efficiency from the big fan disc. And this is not difficult to do, as is suggested in the video. Hopefully, some companies will take up on this to make turbofans for bigger RC models, for fast military drones and UAV and even for some man-carrying gliders powered by big RC turbojets, as well as for ultra-light turbojets like the BD5 and the Sonex jet...since big turbojets consume a lot of fuel thus reduce range and payload considerably due to the massive weight of the fuel.
Model turboprops are already on the market. They run a power takeoff turbine that drives the propeller. Changing the design of this turbine section would make it suitable for a direct fan drive. The fan would be at the rear of the engine with current designs, but that should still work. A redesign with a hollow main shaft would allow the fan to be in the front if desired.
I have exactly this idea in mind. Would work best in a fighter jet model with air scoops directing the air toward the aft fan. The exhaust would be routed to enter behind the fan to mix with cool air aft of the fan for more thrust. Would need 1 fewer stage of reduction gearing because the ducted fan would spin faster, thus would be less expensive, while the fan should cost comparable with the propeller on the turboprop model. However, for more power and efficiency gain, the fan should be placed IN FRONT of the compressor intake as suggested in this video, in order to further raise pressure ratio. For example, the centrifugal compressor has maximum pressure ratio of 4, while the fan with stator can deliver 1.5 pressure ratio, thus boosting pressure ratio to 4 x 1.5 = 6, thus will cause additional gain in power and thermal efficiency independent of the gain in thrust and propulsion efficiency from the big fan disc. And this is not difficult to do, as is suggested in the video. Hopefully, some companies will take up on this to make turbofans for bigger RC models, for fast military drones and UAV and even for some man-carrying gliders powered by big RC turbojets, as well as for ultra-light turbojets like the BD5 and the Sonex jet...since big turbojets consume a lot of fuel thus reduce range and payload considerably due to the massive weight of the fuel.
its always been known that the smaller the turbine, the more inefficient it becomes. you cant scale air down. and you cant scale CLEARANCES down. as sizes reduce, clearances, remaining constant, become a much larger percentage of total area. air likes to sneak past those gaps that are required. you cant SEAL high speed shafts. labyrinth glands are only so effective... shafts and bearings have to have clearance, and that adds to the clearance required at blade tips, where all the leakage occurs... the higher the pressure difference across a turbine blade, the more the air tries to sneak past rather than do anything useful. on the compressor side, a single stage centrifugal can get far higher pressure ratios with only one set of clearances to deal with, versus a multistage axial compressor that has to deal with more bearings, more clearances, and has to be ASSEMBLED. let alone MADE. that leads into mass manufacturing tolerances, interchangeability and selective assemblies... cost... weight. material strengths. heat flow. that blade material that could deal with combustion temperatures at full size no longer holds together when 1/10th the size, volume, and spinning 15X as fast... have a set of plans with a revision involving NOT boring out the inconel turbine disc, a redesigned two-part shaft, more akin to how de laval was doing it with his turbines... that a hole, a press-fit on a shaft, tends to expand and no longer be a press fit at high RPM, and the wheel itself would expand until it seized in the housing. a two part shaft bolted to hubs either side of a solid wheel doesnt expand... as much. there are several TONNES acting on those blades at full speed... the design of the wheel itself to deal with the forces occupies space, and determines certain aspects of blade geometry... everythings a compromise. when theyre running at partial load, low speed, the clearances are larger... they only become "efficient" at full power, full gas flow... when everythings hot and clearances are minimised... surface areas to volume of gas, everything changes. a small combustion chamber has far less gas in it burning and producing heat, with far more surface area to absorb and conduct that heat away, than its full scale counterpart... that is, the small engine is losing a large portion of its heat through the body itself, and cannot be utilised. the fullscale engine with far less surface area but far more volume keeps the air hotter for longer so it can perform more useful work. so many un-considered aspects in this simplistic attitude that axial compression and "turbopropping" is merely a matter of "adding parts" to "increase efficiency"... its easier to make a working centrifugal turbine. and with turbo-charger compressors being so cheap and accurate now... noones making axial superchargers or turbochargers... and in that regard, small turbos are always more inefficient than large turbos... any axial superchargers have been a niche one-off... nothing really large-scale or we would see more of them. RC jets are about the sound and ego more than anything. give us ten minutes of flight time with lots of noise, and we're happy... we dont care about efficiency, it was the fact that someone actually managed to get one this small to even work, let alone make thrust thats amazing. theres still no RC jet plane breaking the sound barrier... a glider can be sneaky and go supersonic, a jet plane cant... ha ha.
Agree a smaller turbine is less efficient then a bigger engine. However we are not comparing a turbojet vs a turbojet. We are comparing a turbojet vs a turbofan. Agree on efficiency and the intended market, this was covered in the video too.
Whilst certainly one could make the powerplant _more_ efficient, it won't be "efficient" in the way that we like to think. I just retired from a company that makes the largest turbofans on the planet, and, in general, the larger, the more efficient (BSFC-wise.)
But that’s only true to a point. There is a cut off where efficiency declines drastically with the increase in size. So there’s a sweet spot. So to speak.
All modern turboJET engines in the world are AXIAL FLOW turbojets. Basically the exact same multi-stage design of the turbofan shown in this video but with smaller compressor blades that don't bypass air around the engine but all the compressed air goes straight into the multi-stage compressor. The axial turbojets used in the RC industry are primitive designs first developed in the 1930's. It's like comparing 2-stroke RC glow engines with carburetors to modern 4 cycle engines with fuel injection used in full size cars.
its a lot easier to get a higher compression ratio from a centrifugal compressor, and the blade clearances arent so critical. gas, air, it doesnt scale down. clearances become greater percentages of total area as size reduces. thermal losses through surface to area volumes increase as size reduces. the bigger the turbine, the better.
the big problems are it would double the weight and tripple the cost, and most of the people that use these engines these days would look no further than that. As a 40 year gas turbine building veteran i have seen and tried this from every angle. for model and hobby sizes, forget it. for the bigger sizes yes, but not planetary box type. that would become the new life limiting section as opposes to bearings. much more to say on this but im not going to. its already being taken care of
Kurt Schreckling the author of "homebuild turbo engine" wrote a second book on turbo props and turbo fan. He designed, built and flown a twin spool turbo fan in the 90s. He also discussed many different designs and the need for a separate power turbine in either cases. Highly recommend the book. "the model turbo-prop engine for home construction.
Since I probably don't get to buying that book, I wonder if a fan for a (medium or rather low) bypass centrifugal compressor should not also be centrifugal ( or at least diagonal? ). We only have this small anular bypass. The nacelle still has to direct a lot of air around the engine. Though, I guess at slow model speeds, the bypass does not choke, so, we still can have a large frontal area. But still (second negation) , the fan could just as well sit on a wide hub which ends almost in the diameter of the core engine. So centrifugal forces are at play. A lot of low bypass military engines have multiple stages on the fan. So it is not uncommon to have quite a pressure on the bypass, which again increases efficiency overall if we feed this pressure into the second stage.
@@ArneChristianRosenfeldtHi Arne, not sure if I understood your question. In order to make an efficient engine, it's important to have both the fan and core running in their efficient zone. So how much shaft power there is available to run the fan at which rpm will all need to be factored in regardless of the types. The core wants to spin fast but not too fast for fuel efficiency but the fan cannot spin too fast to the point that the tip starts to stall or goes supersonic. A gear box capable of high reduction with a low profile, being light weight and can tollerate the shaft rpm is not that easy to make. In comparison, a concentric double shaft engine with free rotating power turbine is easier to achieve. There is also a limit to where the compression ratio of model jet turbine can go. With increased compression goes the temp raise for feed air and temperature of turbine. So we can't exceed the limit of turbine material without blade cooling or using the ceramic matrix ceramic fiber stuff as turbine.
It also came to me that centrifugal turbines are good for pressure with trade offs for speed and flow rate. it makes little sense to have centrifugal bypass fans because we want to generate thrust which is F=mv^2 .
clearances dont reduce with scale... surface areas dont decrease proportional to volume... material properties dont always scale... combustion takes a certain amount of time... its amazing an RC turbine can even run, really.
You can do it but the turbine core needs to be the same size so you end up with an engine with at least twice the diameter depending on the bypass ratio. That is not great for an RC turbine
@@paradiselost9946 Even more impressive are nitro engines. I mean: with the tolerances at such scale you woul expect them to have bad hp/L ratios, but these things put out 600hp/L without forced induction. Thats about twice as much as the F1 NA engines had.
Why more reading? I didn't enjoy reading when getting my engineering degree and probably still won't enjoy it today. :) There are already much smaller turbines on the market then what I use. And these much smaller turbines are used as turbo props too. For example a 210N turbojet vs a 45N turbojet used in turboprop form, outputs the same static thrust. The fuel consumption rate is 180g / min vs 600g / min at full power. Massive difference.
@@RCexplained it is clear turbojets are the least efficient, but they are cheaper and smaller. For the same reason small turboprop engines use centrifugal compressors, cheaper and smaller
A better idea is to stick a generator onto the RC jet engine's shaft. The current from the generator can then be used to spin the fan. This allows you to modulate the fan speed in manner that is decoupled from the shaft speed of the turbine. For starting purposes that generator can also be used as a motor to spin the turbine up to self-sustaining speeds.
I read your statement like 5 times and still didn’t understand one word what your saying , what I will say is there is auto starts, where there is a electric motor that spins the engine up to speed and starts based off running a pre programmed file programed in the engine start sequence
@@stevennagley3407 What I am saying is that you can use the electric motor (which also serves to start the turbine) as a generator. Then use the power taken off the shaft by that generator to drive another another electric motor that runs the big fan. -- This way the fan speed does not have to be a fixed ratio of the turbine shaft speed and you are not relying on something like an 8:1 reduction gear to get that 200,000 rpm turbine to spin a fan at 25,000 rpm. Reduction gears will need lubrication, and quarter filling the housing with vat of oil like in a car's rear axle wouldn't work at 200,000 rpm. The oil will atomize, aerate and basically do nothing while the gears grenade. Pratt & Whitney had all kinds of problems with their PW1000G geared turbofans. And that only has an input shaft speed of 10,500 rpm with the fan is running at about 3,500.
I think what would make more sense than an electric powered fan and generator or the gearbox solution in this video it would be simpler to just make it a two spool engine. Basically have the core of a current style engine but use a hollow shaft. Put a second shaft inside this with the front side of the shaft driving the fan and the back side as a 2nd stage in the hot end driven but the gas generated in the primary core. This is basically how a full size high bypass turbine and turboprop engine works with the engine core mostly being a gas generator to power the prop or fan but extracting very little thrust from the core itself. The open fan engine like the UDF engines demonstrated and tested in the late 1980s are likely going to make a comeback in the next 10-20 years which will basically operate like a high speed turboprop engine with hardly any thrust at all from the engine core.
@@larrybremer4930 Not exactly the same value proposition. A two spool engine's ONLY advantage is to optimize the compressor speed by allowing the fan to spin at a much lower rpm without slowing down the compressor spool. Both the fan and the compressor are both most efficient at just under transonic speeds. That however is not possible on a single spool with the dramatic difference in fan vs compressor diameter. -- However, this only solves half the problem. The turbine driving the fan is still much slower than optimal. This is we have gered turbofans -- all the ones I know are two spool engines to begin with. This is also why, if you look at the cutaways of most modern high bypass engines you will notice that low pressure turbine stages get progressively larger in diameter so as to speed up the blade speeds. -- An electric transmission allows for a simple single spool design spinning very fast for efficient compressor operation. Instead of taking off additional power with a 2nd spool, you take off power with a generator. You can then drive the fan at whatever speed you want and hence have as big a fan as you want. In fact, you can put the fan somewhere else too. The engine can be in the wing and the fan can be in the nose if you like. -- Efficient wise, a planetary reduction drive is about 90~92% efficient. A generator or a motor at their optimal speed and load are both about 95% efficient. So it's about wash. The only penalty is weight. But for RC planes and drones at least the self-starting capability is at least worth the weight of the starter motor.
@@dwightlooi The issue with this is weight. Generators and motors are heavy, and weight is critical in aircraft. There's a very good reason that the majority of modern jet engines use air starters rather than electric starters.
Or could build a hybrid. The advantage of a centrifugal compressor is that it compresses air a little more efficiently than the axial flow (AF is a 1:1.1 compression ratio where a CF compressor is 1:1.2 compression ratio). For a single stage compressor it's definitely the way to go. However even a hybrid is still going to need two turbine wheels, the first to power the compressor, the second to power the fan. I wouldn't mess around with a gearbox though that is an option, but it works much better for a turboprop. That in turn is going to add weight and complexity to the engine. It can definitely be done though, the question is how much is a hobbyist willing to pay for it? In fact come to think of it, Wren built the engine for my father's Bergen R/C helicopter. It was constructed much like the Pratt and Whitney PT-6 in that the driveshaft that turned the heli's transmission was not mechanically connected to the turbine shaft. That concept could definitely be done to turn a bigger fan and create a true turbofan engine. The only thing is that I do recall the Wren being a bit more expensive than the Jetcat engine he was also considering. Oh, and as far as sound... Yes it would sound different, but not necessarily bad. Fighters like the F-16 and Phantom use low bypass turbofan engines, whereas airliners use a high bypass fan. Oh, something else to consider is that you could mount the fan on the rear of the engine. That's what Convair did with the 990 Coronado airliner when they used the GE CJ805 engines. It was the fastest airliner of the bunch. The concept worked obviously! Sorry, I'm thinking aloud! LOL!
I also think that a hybrid axial-radial fan is the way to go for the fan. RC planes are well below the speed of sound, and we need to pass around this wide centrifugal core engine. So we should compress air into that annular ring. The outer part of the fan blades move fast and can create a lot of pressure axially. Still it might be a good idea to slightly tighten the intake and have a conical "diffuser" duct around the fan.
Excellent video my friend. Congratulations! There is a 150kg/f thrust turbo fan from FrankTurbine that is under development. I would like to add one more point. What if, in addition to the fan, an afterburner is added to increase thrust even more? Obviously it would cost more, but the gain in thrust is exponential.
Interesting theories.. 🤔but I think you pretty much covered it at the end. It's such a niche field of the RC world and not really affordable for the every-man.. so it's basically unknown territory at this point. A large scale airliner with real turbofans would be really cool, though! ✈
One easy way to add a fan without making cost go up would be to do it all in the rear. In your mock up the center of the fan was removed. In the real world Turbo Fans, the fan also helps get the air goin into the first stage and thus needs to be in the front. You don't need to do that. If you move the fan and turbine for it in the rear. you can delete the center shaft and it's complexity and delete the planetary gear. Simply design the Turbine to be correct for the rpm/torque you need to drive the fan efficiently. Putting it in the rear means you make the bearings there and vastly reduce complexity and cost. And it should still work good enough for the RC world.
What you are talking about is an AftFan Turbofan, it uses a Freepower turbine coupled to a radially mounted fan and shroud behind the existing turbine to push more aire through. I'm currently working on a prototype but it's much more complicated to make than it sounds, hot gas sealing being a major challenge as labyrinth seals are not easy to get right. There's also the fact that you may need a secondary NGV which could cut down massively on the overall efficiency although it may not be necessary if we use a counter rotating fan, overall I'll keep you updated if I manage to do it
@@guillaumineliott6649 awesome! Don’t let the complexity get to you. I get lost a lot in my projects and in the end the simple solution always ended up being the best. You can do it simple and affordable for the rc guys.
In very simple terms and excluding the combustion process, the compressor in the RC Jet engine is designed to spin the turbine wheel which is in turn is designed to spin the compressor. It is a delicate balance between the two and if you ad a fan load to the front two things will happen. First EGT will shoot through the roof and it will melt your hot section. Second the fan RPM needs to be much lower than the compressor due to tip speed. So in summary this simple design will not work. If you wanted to build a turbofan with the fan up front then you need a second stage turbine with a second shaft running through the center of the main shaft and at the proper RPM for the fan. Your second option is to use a second stage turbine and have the fan at the rear. This is a much easier design and can "almost" be a bolt on to the rear of the RC jet in place of the tail cone. For the record, this is Albert from the original RA Microjets. We tried all this way back. The RC jet industry has made great progress since we started this in the mid 90s. Add a few more ounces of fuel and keep it simple.
This turbofan is not optimized in any form and leaves a lot to be desired. I'll leave the optimization to those building and manufacturing model engines.
I don't think what you are proposing hasn't been thought out by the engine manufacturers. They do anything to increase their profit. I just don't think this would be cost effective. These micro turbines are already selling for a few thousand dollars with the super simple design they have. Converting these to a simple and single-stage turbofan (I am not even getting into multi-stage axial flow design) would probably easily double the price of these engines and most people wouldn't pay this. This said, I have seen a turbofan micro turbine on TH-cam. It has been done already, and it sounds awesome. Thank you for your time.
Doubling complexity for 20% efficiency improvement seems like a bad tradeoff. Have you considered an aft turbine directly coupled to an aft fan? Maybe retrofit to an existing engine?
As a DIY starting point, I think a turboelectric design might work. If you "encase" a normal rc jet engine in an EDF you could get all the benefits of a turbofan but with the adjustability of having the fan independently driven from the turbine. Thus it can act almost as a CVT where it can fine tune the fan RPM to the air speed. The EDF can then just run off the jet's alternator to not need big LiPo batteries on board. With the EDF pushing air around the jet it gets heated by the losses of the jet which adds to its thrust too. There is a commercial concept being tested similar to this by Astro Mechanica if you're interested.
@@paradiselost9946 So you genuinely think that having an alternator (which already comes stock on RC jet engines btw) and a BLDC with a 3D printed fan, is somehow overcompicated when compared to completely modifying the internals of an RC jet to accomodate a turbine-driven fan that would require tight tolerance machining, balancing and stress testing to make sure it's not going to remain intact at 10kRPM? Apart from that, do you know how much electronics are already present in RC jet engines? There's no way you can start and sustain the operation of one without their ECU. At least the addition that I am proposing are off the shelf parts that a 5 year old can figure out how to put together.
@atrumluminarium I have no problem understanding simple or complex sentences. The idea of coupling the electrical output of the generator to drive a Dan is dumb. It's actually ignorant. The power required to drive the compressor in a turbojet is enormous. Coupling the tiny electric generator would not produce enough power (watts) to drive a fan. In an RC sized jet it's something like 50shp. 30-50% is used to drive the compressor so that's roughly 15-25hp or 11kw-18kw. Yes 11,000 watts to 18000 watts. Running a fan via electricity from the turbine generator on the nose isn't going to cut it. Large diameter fans require high power consumption to generate appreciable thrust. The alternator doesn't put out enough power to do this... it's like 500 watts tops. Armchair engineers need to educate on reality-based engineering principles. This just isn't possible. A cars alternator strapped to the front of the jet engine would still only privide about 500-1000 watts.
It would be better to house the reduction gear in the hub of the fan, with just a simple shaft extension from the compressor. 1) less restriction on air flow. 2) more modular design. The fan assembly and shroud could an optional add on to any engine.
Making and lubricating/cooling that reduction gear is likely the hard part, given the scale and tolerances involved. Also any torque loading on something that small may present some material issues. Might need to change things and make an enclosed impeller on the compressor with gear teeth on its outer diameter and do the reduction gearing there. (Planetary ring?) Having lash and lubrication just right still seems like a headache (gland seals?), even if you did that to reduce any torque loading. Not saying impossible, just tricky which would make that kind of thing even more expensive. I'd be curious as to what the military has with its smallest fan jets. (Something like this must already exist if you think about it.) But one also has to consider most of those applications are one-time-use, probably not something a hobbyist would be thrilled with given the initial cost.
F=MA tells us that flow speed or flow mass are interchangeable and indistinguishable from a performance standpoint so half the mass at twice the flow, or twice the mass with half the flow are equal.
Completely missed the dual shaft with separate high and low pressure systems. That omission led to the necessity for a really dodgy (failure prone) reduction gear.
"This ONE Change!" :: Goes on to describe a completely new clean-sheet design that would maybe have 2-3 parts interchangeable with the old engine, at best :: This is nearly impossible, and it would be better to start designing a small turbofan from scratch. What you could do however, is use KJ66 (minus the exhaust nozzle at the back) as a gas generator for another separate module consisting of a free power turbine, a gearbox and a prop, making for a quick and dirty makeshift turboprop. It would be considerably more fuel efficient.
Search around on TH-cam a bit, there are a few homebrew jets with multi stage axial compressors, and and at least one turbofan. Nothing commercially available I don't think. The level of complexity and precision is much higher for axial flow engines, the math for designing multi-stage compressors is a lot harder too. Also I suspect that many of the RC model engines cut costs by using off the shelf turbocharger parts.
Efficiency isn't the goal with model turbines though, it's cost. All model turbines manufacturers know how to design small turbofan but the cost would double or triple and simply drive people out of thr market. Also, model turbines do not scale very well, it would ve easier adding another compression stage to increase compression ratio run on the same common sahft, something you can't do with a turbofan as the turbine-conpressor cannot run at thebliw speed a fan requires, so it would need to be a twin shaft of planetary gear driven fan which is just too much engineering for a model that needs to run for 30 minutes every other weekend
It seems like you are describing more of a turboprop hybrid by driving the fan directly from the main spool via a gearbox. In most actual turbofan jet engines the fan is driven by its own low pressure turbine which is independent of the core, or high pressure compressor and turbine. N1 (fan and low pressure turbine) is the low pressure spool and N2 (high pressure compressor and turbine) is the high pressure spool. The fan (N1) is only turned by the hot gasses from the core (N2) moving trough the low pressure turbine blades.
6:34 every turbo fan engine I know of, don't power the fan from the centre core drive shaft, no physical transmission between the two, the suction from the centre core spin the fan. I think your design with the reduction gear box may increase lag in throttle response, I could be wrong, but we won't know until someone builds one.
"the suction from the centre core spin the fan" - Can you give an example of at least one engine that has this? Sounds crazy to me. And there are plenty of geared turbofans, for example PW1000G.
First of all, I don't know of a single turbo fan engine that is powered "by the suction of the center core". All turbo fan engines are powered by a shaft that goes through the center of the engine and is connected to either one or multiple stages of turbines in the rear of the motor. Some engines are dual, or even triple spool engines, which in essence means there are separate turbine sections that all spin free from each other and power their respective compressor or fan section(s). By the way, geared turbo fans are not necessarily new concepts, but they are new to being more frequently used as they had proven to be unreliable when first designed. Now, Pratt has their geared turbo fan there might be one more but not many of them. Rolls Royce is currently testing their new Ultra fan which will be the world's largest geared turbo fan engine as well as largest turbo fan engine in general. -currently build Rolls Royce Trent XWB engines... which are (almost) the same size as the current largest turbo fan (GE) in the world.
@@Positive_Altitude there isn't a single engine that is "powered by the suction from the center core" that doesn't exist. No clue where that info is coming from. All turbo fan engines are essentially ducted turbo prop engines. Which is also why they CFM is working on that they call a ductless turbo fan engine which is literally a turbo prop.
You are correct that it would make the engine more efficient and quieter. Both of these attributes would be great in military, UAV, applications. But I see several huge problems. Firstly the cost of R&D, this gets passed onto the modellers, as does the increased manufacturing costs so they get to the point where modellers can't afford them and unit sale are low. Then there is the question of do you keep the same core size and end up with an engine that is twice the diameter. Or, you keep the same overall size and miniaturise the core, again costs have gone up exponentially. The current engines are the best thrust from the simplest design for the minimum cost using current components. Definitely keep on looking into ways to improve things in the RC world, you will find areas that can be improved.
Several huge problems, that's why in 25+ years of model jet engines, it's never really been done. But I still would love to see and hear one and believe eventually it's going to be done.
I recall spending $5 for plans to construct John Savoy's Screamin Demon Jet Engine. Many say it was a scam. Back in 1974, I was young and wanted a Jet Powered Racing Kart. The plans were given away, so who knows?
RC turbines likely don't have the torque to spin a large fan and gain any efficiency. They are relatively low compression ratios in the world of jets. Drag and material weights unfortunately scales in favor of larger machinery.
You can stick an afterburner on anything BUT turbofans typically DO NOT HAVE AFTERBURNERS. Only military fighter jets use afterburners. The Concorde and the Soviet's version the Tu-144 were the only airliners to have ever used afterburners. They were turboJET engined planes.
You're talking about scaling down a commercial turbo fan. While most of it is possible, some crucial parts are not (primarily the gear reduction for the induction fan). Beyond this, the cost would be inhibitive, to say the least.
No need to scale down air. There are much smaller turbine in model form flying model airplanes then the one shown in the video both in model 3D form and in the model jet airplane.
I really don’t get this sentiment… like fan propelled aircraft work at so many scales, from 100mm to as low as 50… a fan isn’t some experimental tech, this vid is just suggesting to actually combine a fan with a jet.
A century is a very simple sistem tu convert air speed into trust, another cheap alternative is a electric air compressor electric motors can be place with opposite spin thus no need for fix blades in between stages.....
There may be national security issues with making RC jet engines too efficient or too powerful. You don't need to match an F112 to power a really nasty missile. Adding an inch or two to the outsides of current model jets would put them in the same size bracket as the TJ-150. A P550 is already 33% of the way there. It may also be the case that the RC jet companies actively don't want to get too close to that line, least they wake up one morning and find that their engines are being used for nefarious purposes.
Man, you need a gas turbine at the exhaust to drive the fan in front, and a concentric independent shaft. There is not enough power in the regular central turbine used for the compressor.
Can it be done, yeah. But to what end? How much bigger would it make it? Heavier for sure. How much wider. And how much more will it cost? What's the market for it? Does a RC plane need a state of the art turbojet? It may be nice if you're building a RC airliner but don't see this being used in most RC Sport Jets or RC Military Jets. Current RC jets are based on 1940s tech and are perfectly adequate for what they're used for. The hobby can be expensive as it is, throwing in a $20k turbojet isn't needed or wanted
Just one question, have you ever considered the effort needed to make that gear box? As least for GE PW1000G, last time I check it tooked them 5 years! Are you willing to invest that much money into it?
A better fan drive would be an inner/outer shaft running off a low pressure turbine wheel. I'm not in the model turbine manufacturing business, I just want to see a model turbofan that we can drop in our model jets.
They also need air-bearings 25hr overhauls are terrible. And sadly Turbofan doesn’t help me improve fuel consumption on my turboprop based Mini APU. But cool idea!
APU's are well suited for direct attached loads.. I wouldn't be using a free turbine for that design. Sinc it's stationary, and you can spare space, you could also look at a recourperator design.
The planetary gearbox would scream at those rpms. I'm not sure if it could fit in the container that you drew. A double shafted engine might be better with another stage to turn the fan.
So this video was pretty much, modify a turbo jet to be a turbo fan? The main reason for the reduction in sound of current day turbo fans, is the thrust of the fan helps muffle the sound of the exhaust, further more nothing was mentioned on the outer and inner shaft …
Considering a main point of RC models is to, well, model full-scale aircraft, it's a cool idea, because it adds more realism. But let's be honest - efficiency is basically irrelevant in this space. Most models employing RC size jet engines cost five figures (the engine alone costs ~$3k last I checked), and as such, are flown maybe a few times a year. I'd be surprised if they burned more than $50 worth of fuel in a year, so the cost of fuel here is negligible. A more efficient design might save you enough to buy a cup of coffee or two over the course of a year. Efficiency is much more important in the commercial aviation world where jet liners fly hours each day, every day, to make money for their owners, and a 10% savings translates to millions of dollars over the life of the plane.
TL;DR: Find more CR first. You'll find 20% efficiency increase with just getting the pressure ratio up 1. This.. is a bad idea from the start. Model turbines tend to run in the 2-3:1 compression ratio range. This is WAAAY down at the 20% efficiency end of the brayton cycle. Get that up to 5:1 (do-able, but difficult in a single stage) and you'd see a 50% increase in efficiency. Better sealing, a longer combustion chamber, better turbine design.... all things you can do without completely coming up with a new format, would net you more than your proposed design would do. Model turbine engines "barely" run. There's so much more to do to them before considering adding complexity. There are massive difficulties in your chosen method of driving a turbofan. Most important is you're taking shaft torque from a 150krpm shaft to drive that fan. Every gear interface has ~some~ loss of torque, and at 150krpm input, that's going to be a wildly unpleasant amount of energy. The bearings in your model engines are cooled by fuel in a large part because they too have some loss of torque, and because they're going 150krpm, that ads up to a lot of energy. Your fan design is a poor choice. Or at minimum the air path is. Since turbines are driven by compression ratios, any, and i mean any, additional pressure before the centrifugal stage is of monumental importance. Why you'd give up even the slightest input pressure has my head spinning. You're also proposing a direct power turbine, and those are .. tricky to manage at best. You see them really only in very specialized applications where changes in power state aren't needed quickly. They really only work at their design rpm, which is fine for a turboprop with variable pitch blades, or an apu that can idle at run rpm until a load is applied, but that wont work for a model airplane that needs to throttle. So lets talk parts count. At minimum your design is going to need a fan, two support bearings, a pinion, a spur, and at least two planet gears, a new exhaust turbine, a new support bracket to hold the gearbox and fan. So.... we're talking a minimum of a dozen new parts? And a few of them are going to be pretty complex. Lets say you just want a turbofan. A dual shaft setup, with a fan on one end, and a second turbine on the other would get the same results without needing a gearbox, get you around the problems of doing direct power take off from the gas generator, and present many fewer engineering problems. But... we can do it even simpler. The first turbofans had rear mounted fans, with the turbine and fan being the same part. That gets us down to bearings, a carrier, and the turbine/fan assembly. If you could figure out bearing cooling, it would be just one precision part. This is why you were told you need to read more. To be a good engineer you need to know what came first, why it came first, why what came later, and why things happened in the order they did.
I think you missed the point of the video. Making a mock up model for a youtube video is not an optimized engineering project. This model performs exceptionally well for its intended purpose. I'm happy to see that you went deep into the details of turbofan design. I can only hope that a manufacturer is able to give a turbofan design a chance so that we can hear one of these in our models.
Let's don't get too focused on centrifugal jet bad, multistage axial good, There's good and bad examples of both in the full scale realm. Some of the most efficient full scale jet and turboshaft engines made are combined axial dual or triple shafts driven by multiple combustion exit turbines powering combinations of bypass fans and internal centrifugal/axial compressors. The more compression achieved in the combustion chamber, the better and more efficient the engine is overall. Making this complexity into an RC model engine is going to be the difficult thing because jet model engines, like their piston engine counterparts tend to require simplicity, lightness and ruggedness. This is why the old Rolls Royce style of centrifugal compressor model jet is more widely made as a model jet engine, and this also applies to turboshaft engines. When you can make a pretty exact copy of a Garret type of multishaft/ centrifugal-axial/compressor jet or turboshaft, maybe we'll have something to discuss.
The compressor itself is not bad, despite what many claim. A centrifugal compressor simply does not fit into many planes. It does not fit into engine nacelles of Me-262. It does not fit into an F-22 . I may fit into a trainer jet with their relative weak engines. It does fit into a helicopter -- especially if you have the space for example a single engine behind the cabin (where it would replace a piston engine) or in the nose of this pink Magnum PI helicopter. It looks a bit more ugly in nacelles.
you lack an understanding of turbomachinery and thermodynamics: Brayton Cycle efficiency depends on compression ratio, more is better. radial compressors can reasonably have a compression ratio of maybe 6:1 per stage, though typically they are closer to the 3.5-4 mark. Axial compressors are around the 1.1 to 1.2 range per stage. the reason airplanes use axial compressors is because of the frontal area presented to the airflow is lower, making the overall system more aerodynamic.
That's an interesting take on my understanding of turbomachinery. However, your entire comment seems to address something I never mentioned in the video. I didn't recommend, use, or show an axial compressor. I'm a bit puzzled about how your better understanding misidentified the highlighted component featured in the video.
would be interesting to see how good it is on fuel those standard RC Jet engine can eat up to 15L an hour that's more then my land cruiser driving at highway speeds and that thing weights 2.5 tonne. those jet engines have to be the most inefficient thing ever.
Yes, exactly. Was just speaking to a fellow club member about this. He was buying $20-$25 CAD worth of fuel per weekend and flies every weekend possible. It adds up for sure.
Another commenter claiming to know someone's level of knowledge based on a playful TH-cam video? That kind of negativity doesn't benefit the community.
@@RCexplained Another U Tuber who thinks he knows everything ...There's a very good reason MODEL Gas Turbines use centrifugal compressors....You could no doubt research it....🤔😏
I have not seen the video yet as I have to go to bed, but from the thumbnail, I think you're trying to make it into a turbofan engine, right? They are efficient. I'll check out the video tomorrow 😊😊
@@RCexplained I work for the biggest Deference Contractor in the USA.(for over 21 years now) I've been to Europe to teach the Italian's what our system is. We use Pound force for our jet engines not Kilonewton or the like.
I don't think a gearbox is practical or necessary. Most traditional Turbofan engines don't have a gearbox, and neither do Helicopter engines. A completely free fan shaft should work just fine.
It appeared your diagram had the planetry set sitting off the Inlet Compressor end of the shaft, that's a perfomance limitation. The shaft for the main High Bypass fan should run from the gearbox through the center of the shaft for the Compressor and Impellor, and then in to a Drive Fan. That way the gas turbine isn't using Shaft Power to turn the fan, instead the turbine is just there as a Gas Generator, and it is the hot exhaust turning the drive fan, which turns the gearbox and provides and overdrive to the main High Bypass Fan. The thrust pushing the aircraft comes from the Fan, not the turbine. That poorly keyed animated background, is really distracting and lowers the quality of the vision. You're wasting bandwidth that the CoDec should be using for the part of the vision you want the viewer to concentrate on - You. The wasted bandwidth will be making your edited file size larger, and also reducing the quality once TH-cam recompresses it again.
First build your own model conventional jet turbine before making a video on it. The very first problem I see with the design is that it will not be self sustaining because the first stage will be too heavy. This really is a case of Dunning-Kruger effect.
Actually, the first problem in design with this playful video is that the transmission is impossible to manufacture at this size and RPM. Also, stage 1 being too heavy is not the specific issue with this design. Assuming it is weightless, the fan would consume too much power from the turbine and must be on a separate stage. Lastly, while it seems you missed the point of the video, I do appreciate hearing from those more knowledgeable than most.
I want 10 minutes of my life back. This is little more than a clickbait plug for that crappy overpriced 3D printed engine which that company is selling ILLEGALLY and handing out to any random youtubers lately from what I've seen, that design is blatant copyright violation from the original designer who posted that 3D printable STL almost 8 years ago. Nothing explained here is not something nobody that's been paying attention already doesn't know, and that proposed turbofan design is laughably useless, and RC turbofans have been made but they are largely one-off experiments. The technology/demand just isn't there yet and just may never be since there's too many tradeoffs at these scales. Furthermore just look at all the problems a the Pratt and Whitney geared turbofans have created for their operators. They are absolutely horrid in reliability. I fly both full scale jets for work and RC turbines for fun and you just can't transfer the many of technologies from one to the other. Simplicity and lightness are key in the RC world. If people want efficiency, they just need to buy better engines. For example my Xicoy engines are far far more efficient that the equivalent chinese branded ones in my clubs and I'm flying significantly longer times with my Xicoys despite having smaller tanks sometimes than people do with Kingtechs or Swiwins. Those are guzzlers are are much bulkier engines, they're cheap for a reason.
The efficency of a turbine engine, as with any internal combustion engine, is a function of compression ratio. A single stage compressor is very limited. To gain efficiency a multi stage compressor is required and axial flow is the best way to do that. The very first (WWII) jet engines used a single stage centrifugal compressor which is why the first generation jet planes had relatively large diameter fuselages though the Germans did develop an multi stage axial flow engine (Jumo 004) used in the ME 262. Its smaller diameter allowed an underwing twin engine layout not practical for the fat, barrel shaped centrifugal engines used by the allies. Axial flow engines required many years of developing advanced machining processes and metallurgy to take advantage of the higher forces and temperatures (and thus efficiency) of the axial flow designs. The big fan with bypass airflow can make use of excess power from the power turbine section but adding a fan to a single stage compressor and single stage power turbine engine is not going to do much for overall efficiency but will increase diameter and weight which is not desirable in most applications. Modern turbine engines have compression ratios of about 30:1 and acheive very high efficency as a result. That requires extremely accurately made parts in the compressor and turbine stages as well as benefitting from the larger diameter of the full scale engines. A small scale turbine, even with multiple stages, would be very difficult (and expensive) to fabricate and would be limited in the peak compression ratio and efficiency simply because of the small size of the components. Despite such limitations, some efficiency gain is possible and Williams Advanced Engineering was developing a small scale, multiple stage axial flow turbine to power a generator for a proposed hybrid vehicle application for the now discontinued Jaguar car company C-X75 project. It is doubtful that such an engine could be made at a price realistic for recreational RC applications.
In order to reduce the temperature of the exhaust which hits the turbine blades, I imagine that we should convert temperature to a swirl of almost the speed of sound at that temperature. Then a converging nozzle as in a turbo could even increase the velocity using the cyclone effect.
To reduce the velocity on the way to the compressor blades, the compressor radius needs to be smaller.
For some reason RC engines and APUs barely swirl the flow?
there are turbines (turbofan cores...) that reach 60:1 compression ratio, but their limits are with hot section temps...as for the single stage compressors - take a look at the russian VK-650V. It's a modern design turboshaft, the compressor looks like an automotive one, just...big...
or the engines it's designed to replace - Pratt & Whitney Canada PW200 or Turbomeca Arrius families, all single stage radial compressors with competitive efficiency
@@AKAtheA I guess I have a problem with the names. I thought that first there was the water turbine. A turbine converts fluid energy onto a shaft. See : work turbine in a turbo shaft . Or turbine boosted in contrast to gear driven compressor. I only talk about the hot section. Compressor is just CFD and aluminum.
Please note that when the fan is placed IN FRONT of the compressor intake as suggested in this video, it would further raise overall pressure ratio. For example, the centrifugal compressor has maximum pressure ratio of 4, while the fan with stator can deliver 1.5 pressure ratio, thus boosting pressure ratio to 4 x 1.5 = 6, thus will cause additional gain in power and thermal efficiency INDEPENDENT of the gain in thrust and propulsion efficiency from the big fan disc. And this is not difficult to do, as is suggested in the video.
Hopefully, some companies will take up on this to make turbofans for bigger RC models, for fast military drones and UAV and even for some man-carrying gliders powered by big RC turbojets, as well as for ultra-light turbojets like the BD5 and the Sonex jet...since big turbojets consume a lot of fuel thus reduce range and payload considerably due to the massive weight of the fuel.
Model turboprops are already on the market. They run a power takeoff turbine that drives the propeller. Changing the design of this turbine section would make it suitable for a direct fan drive. The fan would be at the rear of the engine with current designs, but that should still work. A redesign with a hollow main shaft would allow the fan to be in the front if desired.
Definitely doable, in the early 1960's General Electric stuck an aft-fan on the CJ610 turbojet to make the CF700 turbofan.
This would be a good alternate design 👌
There is no thing like power takeoff turbine, only power turbine!
I have exactly this idea in mind. Would work best in a fighter jet model with air scoops directing the air toward the aft fan. The exhaust would be routed to enter behind the fan to mix with cool air aft of the fan for more thrust. Would need 1 fewer stage of reduction gearing because the ducted fan would spin faster, thus would be less expensive, while the fan should cost comparable with the propeller on the turboprop model.
However, for more power and efficiency gain, the fan should be placed IN FRONT of the compressor intake as suggested in this video, in order to further raise pressure ratio. For example, the centrifugal compressor has maximum pressure ratio of 4, while the fan with stator can deliver 1.5 pressure ratio, thus boosting pressure ratio to 4 x 1.5 = 6, thus will cause additional gain in power and thermal efficiency independent of the gain in thrust and propulsion efficiency from the big fan disc. And this is not difficult to do, as is suggested in the video.
Hopefully, some companies will take up on this to make turbofans for bigger RC models, for fast military drones and UAV and even for some man-carrying gliders powered by big RC turbojets, as well as for ultra-light turbojets like the BD5 and the Sonex jet...since big turbojets consume a lot of fuel thus reduce range and payload considerably due to the massive weight of the fuel.
its always been known that the smaller the turbine, the more inefficient it becomes.
you cant scale air down.
and you cant scale CLEARANCES down.
as sizes reduce, clearances, remaining constant, become a much larger percentage of total area. air likes to sneak past those gaps that are required. you cant SEAL high speed shafts. labyrinth glands are only so effective... shafts and bearings have to have clearance, and that adds to the clearance required at blade tips, where all the leakage occurs... the higher the pressure difference across a turbine blade, the more the air tries to sneak past rather than do anything useful. on the compressor side, a single stage centrifugal can get far higher pressure ratios with only one set of clearances to deal with, versus a multistage axial compressor that has to deal with more bearings, more clearances, and has to be ASSEMBLED. let alone MADE.
that leads into mass manufacturing tolerances, interchangeability and selective assemblies... cost...
weight. material strengths. heat flow. that blade material that could deal with combustion temperatures at full size no longer holds together when 1/10th the size, volume, and spinning 15X as fast...
have a set of plans with a revision involving NOT boring out the inconel turbine disc, a redesigned two-part shaft, more akin to how de laval was doing it with his turbines... that a hole, a press-fit on a shaft, tends to expand and no longer be a press fit at high RPM, and the wheel itself would expand until it seized in the housing.
a two part shaft bolted to hubs either side of a solid wheel doesnt expand... as much.
there are several TONNES acting on those blades at full speed... the design of the wheel itself to deal with the forces occupies space, and determines certain aspects of blade geometry... everythings a compromise.
when theyre running at partial load, low speed, the clearances are larger... they only become "efficient" at full power, full gas flow... when everythings hot and clearances are minimised...
surface areas to volume of gas, everything changes. a small combustion chamber has far less gas in it burning and producing heat, with far more surface area to absorb and conduct that heat away, than its full scale counterpart... that is, the small engine is losing a large portion of its heat through the body itself, and cannot be utilised. the fullscale engine with far less surface area but far more volume keeps the air hotter for longer so it can perform more useful work.
so many un-considered aspects in this simplistic attitude that axial compression and "turbopropping" is merely a matter of "adding parts" to "increase efficiency"...
its easier to make a working centrifugal turbine. and with turbo-charger compressors being so cheap and accurate now...
noones making axial superchargers or turbochargers... and in that regard, small turbos are always more inefficient than large turbos... any axial superchargers have been a niche one-off... nothing really large-scale or we would see more of them.
RC jets are about the sound and ego more than anything. give us ten minutes of flight time with lots of noise, and we're happy... we dont care about efficiency, it was the fact that someone actually managed to get one this small to even work, let alone make thrust thats amazing.
theres still no RC jet plane breaking the sound barrier... a glider can be sneaky and go supersonic, a jet plane cant... ha ha.
Agree a smaller turbine is less efficient then a bigger engine. However we are not comparing a turbojet vs a turbojet. We are comparing a turbojet vs a turbofan.
Agree on efficiency and the intended market, this was covered in the video too.
Whilst certainly one could make the powerplant _more_ efficient, it won't be "efficient" in the way that we like to think. I just retired from a company that makes the largest turbofans on the planet, and, in general, the larger, the more efficient (BSFC-wise.)
But that’s only true to a point. There is a cut off where efficiency declines drastically with the increase in size. So there’s a sweet spot. So to speak.
All modern turboJET engines in the world are AXIAL FLOW turbojets. Basically the exact same multi-stage design of the turbofan shown in this video but with smaller compressor blades that don't bypass air around the engine but all the compressed air goes straight into the multi-stage compressor.
The axial turbojets used in the RC industry are primitive designs first developed in the 1930's. It's like comparing 2-stroke RC glow engines with carburetors to modern 4 cycle engines with fuel injection used in full size cars.
its a lot easier to get a higher compression ratio from a centrifugal compressor, and the blade clearances arent so critical.
gas, air, it doesnt scale down. clearances become greater percentages of total area as size reduces.
thermal losses through surface to area volumes increase as size reduces.
the bigger the turbine, the better.
Actually no, the Garret ATF3 is a combined centrifugal/axial multishaft engine that works quite well.
the big problems are it would double the weight and tripple the cost, and most of the people that use these engines these days would look no further than that. As a 40 year gas turbine building veteran i have seen and tried this from every angle.
for model and hobby sizes, forget it. for the bigger sizes yes, but not planetary box type. that would become the new life limiting section as opposes to bearings. much more to say on this but im not going to. its already being taken care of
I thought the life of an RC turbine is limited by the frequent crashes I seen on TH-cam.
Kurt Schreckling the author of "homebuild turbo engine" wrote a second book on turbo props and turbo fan. He designed, built and flown a twin spool turbo fan in the 90s. He also discussed many different designs and the need for a separate power turbine in either cases. Highly recommend the book. "the model turbo-prop engine for home construction.
Since I probably don't get to buying that book, I wonder if a fan for a (medium or rather low) bypass centrifugal compressor should not also be centrifugal ( or at least diagonal? ). We only have this small anular bypass. The nacelle still has to direct a lot of air around the engine. Though, I guess at slow model speeds, the bypass does not choke, so, we still can have a large frontal area. But still (second negation) , the fan could just as well sit on a wide hub which ends almost in the diameter of the core engine. So centrifugal forces are at play. A lot of low bypass military engines have multiple stages on the fan. So it is not uncommon to have quite a pressure on the bypass, which again increases efficiency overall if we feed this pressure into the second stage.
is that the same guy who got arrested for sleeping with his sister?
@@AFourthPosition couldn't be. He is a retired German engineer.
@@ArneChristianRosenfeldtHi Arne, not sure if I understood your question. In order to make an efficient engine, it's important to have both the fan and core running in their efficient zone. So how much shaft power there is available to run the fan at which rpm will all need to be factored in regardless of the types. The core wants to spin fast but not too fast for fuel efficiency but the fan cannot spin too fast to the point that the tip starts to stall or goes supersonic. A gear box capable of high reduction with a low profile, being light weight and can tollerate the shaft rpm is not that easy to make. In comparison, a concentric double shaft engine with free rotating power turbine is easier to achieve. There is also a limit to where the compression ratio of model jet turbine can go. With increased compression goes the temp raise for feed air and temperature of turbine. So we can't exceed the limit of turbine material without blade cooling or using the ceramic matrix ceramic fiber stuff as turbine.
It also came to me that centrifugal turbines are good for pressure with trade offs for speed and flow rate. it makes little sense to have centrifugal bypass fans because we want to generate thrust which is F=mv^2 .
You have to do a bit more reading. Look for boundary layer scaling and reynolds nrs. Ie air molecules dont scale well.
clearances dont reduce with scale... surface areas dont decrease proportional to volume... material properties dont always scale... combustion takes a certain amount of time...
its amazing an RC turbine can even run, really.
You can do it but the turbine core needs to be the same size so you end up with an engine with at least twice the diameter depending on the bypass ratio. That is not great for an RC turbine
@@paradiselost9946 Even more impressive are nitro engines. I mean: with the tolerances at such scale you woul expect them to have bad hp/L ratios, but these things put out 600hp/L without forced induction. Thats about twice as much as the F1 NA engines had.
Why more reading? I didn't enjoy reading when getting my engineering degree and probably still won't enjoy it today. :)
There are already much smaller turbines on the market then what I use. And these much smaller turbines are used as turbo props too. For example a 210N turbojet vs a 45N turbojet used in turboprop form, outputs the same static thrust. The fuel consumption rate is 180g / min vs 600g / min at full power. Massive difference.
@@RCexplained it is clear turbojets are the least efficient, but they are cheaper and smaller. For the same reason small turboprop engines use centrifugal compressors, cheaper and smaller
Well done. I like the concept
All jet powered airliners first used turbo jets. The Concorde was the last airliner to use turbojets. It also had afterburners.
A better idea is to stick a generator onto the RC jet engine's shaft. The current from the generator can then be used to spin the fan. This allows you to modulate the fan speed in manner that is decoupled from the shaft speed of the turbine. For starting purposes that generator can also be used as a motor to spin the turbine up to self-sustaining speeds.
I read your statement like 5 times and still didn’t understand one word what your saying , what I will say is there is auto starts, where there is a electric motor that spins the engine up to speed and starts based off running a pre programmed file programed in the engine start sequence
@@stevennagley3407 What I am saying is that you can use the electric motor (which also serves to start the turbine) as a generator. Then use the power taken off the shaft by that generator to drive another another electric motor that runs the big fan.
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This way the fan speed does not have to be a fixed ratio of the turbine shaft speed and you are not relying on something like an 8:1 reduction gear to get that 200,000 rpm turbine to spin a fan at 25,000 rpm. Reduction gears will need lubrication, and quarter filling the housing with vat of oil like in a car's rear axle wouldn't work at 200,000 rpm. The oil will atomize, aerate and basically do nothing while the gears grenade. Pratt & Whitney had all kinds of problems with their PW1000G geared turbofans. And that only has an input shaft speed of 10,500 rpm with the fan is running at about 3,500.
I think what would make more sense than an electric powered fan and generator or the gearbox solution in this video it would be simpler to just make it a two spool engine. Basically have the core of a current style engine but use a hollow shaft. Put a second shaft inside this with the front side of the shaft driving the fan and the back side as a 2nd stage in the hot end driven but the gas generated in the primary core. This is basically how a full size high bypass turbine and turboprop engine works with the engine core mostly being a gas generator to power the prop or fan but extracting very little thrust from the core itself. The open fan engine like the UDF engines demonstrated and tested in the late 1980s are likely going to make a comeback in the next 10-20 years which will basically operate like a high speed turboprop engine with hardly any thrust at all from the engine core.
@@larrybremer4930 Not exactly the same value proposition. A two spool engine's ONLY advantage is to optimize the compressor speed by allowing the fan to spin at a much lower rpm without slowing down the compressor spool. Both the fan and the compressor are both most efficient at just under transonic speeds. That however is not possible on a single spool with the dramatic difference in fan vs compressor diameter.
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However, this only solves half the problem. The turbine driving the fan is still much slower than optimal. This is we have gered turbofans -- all the ones I know are two spool engines to begin with. This is also why, if you look at the cutaways of most modern high bypass engines you will notice that low pressure turbine stages get progressively larger in diameter so as to speed up the blade speeds.
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An electric transmission allows for a simple single spool design spinning very fast for efficient compressor operation. Instead of taking off additional power with a 2nd spool, you take off power with a generator. You can then drive the fan at whatever speed you want and hence have as big a fan as you want. In fact, you can put the fan somewhere else too. The engine can be in the wing and the fan can be in the nose if you like.
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Efficient wise, a planetary reduction drive is about 90~92% efficient. A generator or a motor at their optimal speed and load are both about 95% efficient. So it's about wash. The only penalty is weight. But for RC planes and drones at least the self-starting capability is at least worth the weight of the starter motor.
@@dwightlooi The issue with this is weight. Generators and motors are heavy, and weight is critical in aircraft. There's a very good reason that the majority of modern jet engines use air starters rather than electric starters.
Or could build a hybrid. The advantage of a centrifugal compressor is that it compresses air a little more efficiently than the axial flow (AF is a 1:1.1 compression ratio where a CF compressor is 1:1.2 compression ratio). For a single stage compressor it's definitely the way to go. However even a hybrid is still going to need two turbine wheels, the first to power the compressor, the second to power the fan. I wouldn't mess around with a gearbox though that is an option, but it works much better for a turboprop. That in turn is going to add weight and complexity to the engine. It can definitely be done though, the question is how much is a hobbyist willing to pay for it?
In fact come to think of it, Wren built the engine for my father's Bergen R/C helicopter. It was constructed much like the Pratt and Whitney PT-6 in that the driveshaft that turned the heli's transmission was not mechanically connected to the turbine shaft. That concept could definitely be done to turn a bigger fan and create a true turbofan engine. The only thing is that I do recall the Wren being a bit more expensive than the Jetcat engine he was also considering.
Oh, and as far as sound... Yes it would sound different, but not necessarily bad. Fighters like the F-16 and Phantom use low bypass turbofan engines, whereas airliners use a high bypass fan. Oh, something else to consider is that you could mount the fan on the rear of the engine. That's what Convair did with the 990 Coronado airliner when they used the GE CJ805 engines. It was the fastest airliner of the bunch. The concept worked obviously!
Sorry, I'm thinking aloud! LOL!
I also think that a hybrid axial-radial fan is the way to go for the fan. RC planes are well below the speed of sound, and we need to pass around this wide centrifugal core engine. So we should compress air into that annular ring. The outer part of the fan blades move fast and can create a lot of pressure axially. Still it might be a good idea to slightly tighten the intake and have a conical "diffuser" duct around the fan.
Excellent video my friend. Congratulations! There is a 150kg/f thrust turbo fan from FrankTurbine that is under development. I would like to add one more point. What if, in addition to the fan, an afterburner is added to increase thrust even more? Obviously it would cost more, but the gain in thrust is exponential.
Thanks for the comment. I'd love an afterburner too, just for the added realism.
I’ve wondered if a low-bypass type turbofan could be achieved by building a turbojet with a larger (mismatched) compressor and jetting off bleed air.
Interesting idea!
Interesting theories.. 🤔but I think you pretty much covered it at the end. It's such a niche field of the RC world and not really affordable for the every-man.. so it's basically unknown territory at this point. A large scale airliner with real turbofans would be really cool, though! ✈
One easy way to add a fan without making cost go up would be to do it all in the rear. In your mock up the center of the fan was removed. In the real world Turbo Fans, the fan also helps get the air goin into the first stage and thus needs to be in the front. You don't need to do that. If you move the fan and turbine for it in the rear. you can delete the center shaft and it's complexity and delete the planetary gear. Simply design the Turbine to be correct for the rpm/torque you need to drive the fan efficiently. Putting it in the rear means you make the bearings there and vastly reduce complexity and cost. And it should still work good enough for the RC world.
That idea makes it much more simpler.
What you are talking about is an AftFan Turbofan, it uses a Freepower turbine coupled to a radially mounted fan and shroud behind the existing turbine to push more aire through.
I'm currently working on a prototype but it's much more complicated to make than it sounds, hot gas sealing being a major challenge as labyrinth seals are not easy to get right.
There's also the fact that you may need a secondary NGV which could cut down massively on the overall efficiency although it may not be necessary if we use a counter rotating fan, overall I'll keep you updated if I manage to do it
@@guillaumineliott6649 awesome! Don’t let the complexity get to you. I get lost a lot in my projects and in the end the simple solution always ended up being the best. You can do it simple and affordable for the rc guys.
In very simple terms and excluding the combustion process, the compressor in the RC Jet engine is designed to spin the turbine wheel which is in turn is designed to spin the compressor. It is a delicate balance between the two and if you ad a fan load to the front two things will happen. First EGT will shoot through the roof and it will melt your hot section. Second the fan RPM needs to be much lower than the compressor due to tip speed. So in summary this simple design will not work. If you wanted to build a turbofan with the fan up front then you need a second stage turbine with a second shaft running through the center of the main shaft and at the proper RPM for the fan. Your second option is to use a second stage turbine and have the fan at the rear. This is a much easier design and can "almost" be a bolt on to the rear of the RC jet in place of the tail cone. For the record, this is Albert from the original RA Microjets. We tried all this way back. The RC jet industry has made great progress since we started this in the mid 90s. Add a few more ounces of fuel and keep it simple.
There are videos on TH-cam of a working two spool fanjet with centrifugal compressor. It has too much thrust for RC.
I had this idea for along time 😃
Nice! I hope to see someone do it.
great video ask mike Burlington to show you his bypass r/c turbine he built and demonstrated over thirty years ago .
Will do!
you should also provide a cfd analysis for the turbine .
This turbofan is not optimized in any form and leaves a lot to be desired. I'll leave the optimization to those building and manufacturing model engines.
Very good idea 💡
Many many thanks!
I don't think what you are proposing hasn't been thought out by the engine manufacturers. They do anything to increase their profit. I just don't think this would be cost effective. These micro turbines are already selling for a few thousand dollars with the super simple design they have. Converting these to a simple and single-stage turbofan (I am not even getting into multi-stage axial flow design) would probably easily double the price of these engines and most people wouldn't pay this.
This said, I have seen a turbofan micro turbine on TH-cam. It has been done already, and it sounds awesome.
Thank you for your time.
Doubling complexity for 20% efficiency improvement seems like a bad tradeoff.
Have you considered an aft turbine directly coupled to an aft fan?
Maybe retrofit to an existing engine?
As a DIY starting point, I think a turboelectric design might work. If you "encase" a normal rc jet engine in an EDF you could get all the benefits of a turbofan but with the adjustability of having the fan independently driven from the turbine. Thus it can act almost as a CVT where it can fine tune the fan RPM to the air speed. The EDF can then just run off the jet's alternator to not need big LiPo batteries on board.
With the EDF pushing air around the jet it gets heated by the losses of the jet which adds to its thrust too.
There is a commercial concept being tested similar to this by Astro Mechanica if you're interested.
Dumb
@@kraftwurx_Aviation no, modern "genius engineering" has to rely on over complicated concepts with electric bits... you GOTTA have electric bits!
@@paradiselost9946 So you genuinely think that having an alternator (which already comes stock on RC jet engines btw) and a BLDC with a 3D printed fan, is somehow overcompicated when compared to completely modifying the internals of an RC jet to accomodate a turbine-driven fan that would require tight tolerance machining, balancing and stress testing to make sure it's not going to remain intact at 10kRPM?
Apart from that, do you know how much electronics are already present in RC jet engines? There's no way you can start and sustain the operation of one without their ECU. At least the addition that I am proposing are off the shelf parts that a 5 year old can figure out how to put together.
@@kraftwurx_Aviation you not being capable of understanding simple sentences is not my problem.
@atrumluminarium I have no problem understanding simple or complex sentences. The idea of coupling the electrical output of the generator to drive a Dan is dumb. It's actually ignorant. The power required to drive the compressor in a turbojet is enormous. Coupling the tiny electric generator would not produce enough power (watts) to drive a fan. In an RC sized jet it's something like 50shp. 30-50% is used to drive the compressor so that's roughly 15-25hp or 11kw-18kw. Yes 11,000 watts to 18000 watts.
Running a fan via electricity from the turbine generator on the nose isn't going to cut it.
Large diameter fans require high power consumption to generate appreciable thrust.
The alternator doesn't put out enough power to do this... it's like 500 watts tops.
Armchair engineers need to educate on reality-based engineering principles.
This just isn't possible. A cars alternator strapped to the front of the jet engine would still only privide about 500-1000 watts.
It would be better to house the reduction gear in the hub of the fan, with just a simple shaft extension from the compressor. 1) less restriction on air flow. 2) more modular design. The fan assembly and shroud could an optional add on to any engine.
Making and lubricating/cooling that reduction gear is likely the hard part, given the scale and tolerances involved. Also any torque loading on something that small may present some material issues. Might need to change things and make an enclosed impeller on the compressor with gear teeth on its outer diameter and do the reduction gearing there. (Planetary ring?) Having lash and lubrication just right still seems like a headache (gland seals?), even if you did that to reduce any torque loading. Not saying impossible, just tricky which would make that kind of thing even more expensive.
I'd be curious as to what the military has with its smallest fan jets. (Something like this must already exist if you think about it.) But one also has to consider most of those applications are one-time-use, probably not something a hobbyist would be thrilled with given the initial cost.
Very good ideas and points! Thanks for your input.
F=MA tells us that flow speed or flow mass are interchangeable and indistinguishable from a performance standpoint so half the mass at twice the flow, or twice the mass with half the flow are equal.
Completely missed the dual shaft with separate high and low pressure systems.
That omission led to the necessity for a really dodgy (failure prone) reduction gear.
Kurt streckling released a book with working turboshaft design & drawings
"This ONE Change!"
:: Goes on to describe a completely new clean-sheet design that would maybe have 2-3 parts interchangeable with the old engine, at best ::
This is nearly impossible, and it would be better to start designing a small turbofan from scratch. What you could do however, is use KJ66 (minus the exhaust nozzle at the back) as a gas generator for another separate module consisting of a free power turbine, a gearbox and a prop, making for a quick and dirty makeshift turboprop. It would be considerably more fuel efficient.
Agreed, but this is old news been done years ago already...This guy doesn't know the subject matter at all..😳😳🙄🇬🇧
Search around on TH-cam a bit, there are a few homebrew jets with multi stage axial compressors, and and at least one turbofan. Nothing commercially available I don't think. The level of complexity and precision is much higher for axial flow engines, the math for designing multi-stage compressors is a lot harder too. Also I suspect that many of the RC model engines cut costs by using off the shelf turbocharger parts.
Efficiency isn't the goal with model turbines though, it's cost. All model turbines manufacturers know how to design small turbofan but the cost would double or triple and simply drive people out of thr market. Also, model turbines do not scale very well, it would ve easier adding another compression stage to increase compression ratio run on the same common sahft, something you can't do with a turbofan as the turbine-conpressor cannot run at thebliw speed a fan requires, so it would need to be a twin shaft of planetary gear driven fan which is just too much engineering for a model that needs to run for 30 minutes every other weekend
It seems like you are describing more of a turboprop hybrid by driving the fan directly from the main spool via a gearbox. In most actual turbofan jet engines the fan is driven by its own low pressure turbine which is independent of the core, or high pressure compressor and turbine. N1 (fan and low pressure turbine) is the low pressure spool and N2 (high pressure compressor and turbine) is the high pressure spool. The fan (N1) is only turned by the hot gasses from the core (N2) moving trough the low pressure turbine blades.
Yes, this would be a great method to use too. I really just want to see and hear the sound of a model turbofan engine.
6:34 every turbo fan engine I know of, don't power the fan from the centre core drive shaft, no physical transmission between the two, the suction from the centre core spin the fan. I think your design with the reduction gear box may increase lag in throttle response, I could be wrong, but we won't know until someone builds one.
"the suction from the centre core spin the fan" - Can you give an example of at least one engine that has this? Sounds crazy to me. And there are plenty of geared turbofans, for example PW1000G.
First of all, I don't know of a single turbo fan engine that is powered "by the suction of the center core". All turbo fan engines are powered by a shaft that goes through the center of the engine and is connected to either one or multiple stages of turbines in the rear of the motor. Some engines are dual, or even triple spool engines, which in essence means there are separate turbine sections that all spin free from each other and power their respective compressor or fan section(s). By the way, geared turbo fans are not necessarily new concepts, but they are new to being more frequently used as they had proven to be unreliable when first designed. Now, Pratt has their geared turbo fan there might be one more but not many of them. Rolls Royce is currently testing their new Ultra fan which will be the world's largest geared turbo fan engine as well as largest turbo fan engine in general.
-currently build Rolls Royce Trent XWB engines... which are (almost) the same size as the current largest turbo fan (GE) in the world.
@@Positive_Altitude there isn't a single engine that is "powered by the suction from the center core" that doesn't exist. No clue where that info is coming from. All turbo fan engines are essentially ducted turbo prop engines. Which is also why they CFM is working on that they call a ductless turbo fan engine which is literally a turbo prop.
You are correct that it would make the engine more efficient and quieter. Both of these attributes would be great in military, UAV, applications.
But I see several huge problems. Firstly the cost of R&D, this gets passed onto the modellers, as does the increased manufacturing costs so they get to the point where modellers can't afford them and unit sale are low. Then there is the question of do you keep the same core size and end up with an engine that is twice the diameter. Or, you keep the same overall size and miniaturise the core, again costs have gone up exponentially. The current engines are the best thrust from the simplest design for the minimum cost using current components.
Definitely keep on looking into ways to improve things in the RC world, you will find areas that can be improved.
Several huge problems, that's why in 25+ years of model jet engines, it's never really been done. But I still would love to see and hear one and believe eventually it's going to be done.
excellent
Many thanks
Put the fan at the back, mechanically much simpler.
Absolutely
I recall spending $5 for plans to construct John Savoy's Screamin Demon Jet Engine. Many say it was a scam. Back in 1974, I was young and wanted a Jet Powered Racing Kart.
The plans were given away, so who knows?
Id like to see an edf coupled to a combustion can.
RC turbines likely don't have the torque to spin a large fan and gain any efficiency. They are relatively low compression ratios in the world of jets. Drag and material weights unfortunately scales in favor of larger machinery.
Actually, smaller jets have a better thrust to power ratio. See this iron man / rocket man all up to F22 vertical climb ( but only F35 can hover ).
A turbofan would also give us the ability to have afterburners 🔥
You can stick an afterburner on anything BUT turbofans typically DO NOT HAVE AFTERBURNERS. Only military fighter jets use afterburners. The Concorde and the Soviet's version the Tu-144 were the only airliners to have ever used afterburners. They were turboJET engined planes.
You're talking about scaling down a commercial turbo fan. While most of it is possible, some crucial parts are not (primarily the gear reduction for the induction fan). Beyond this, the cost would be inhibitive, to say the least.
Yes the market can not absorb the cost for sure.
Axil flow.....instead of centrifugal flow.
The main problem is you can scale down the engine, but you cand scale down air to match.
No need to scale down air. There are much smaller turbine in model form flying model airplanes then the one shown in the video both in model 3D form and in the model jet airplane.
I really don’t get this sentiment… like fan propelled aircraft work at so many scales, from 100mm to as low as 50… a fan isn’t some experimental tech, this vid is just suggesting to actually combine a fan with a jet.
You know they already sell conversion kits with transmissions to use them as turboprops, right?
The model turboprops use a secondary turbine wheel. No transmission, and this is naturally a more effective method to drive a prop or fan.
DST-Engines already created the miniature turbofan and had gone through some revisions but has since then not shown anything new since (?)
A century is a very simple sistem tu convert air speed into trust, another cheap alternative is a electric air compressor electric motors can be place with opposite spin thus no need for fix blades in between stages.....
There may be national security issues with making RC jet engines too efficient or too powerful. You don't need to match an F112 to power a really nasty missile. Adding an inch or two to the outsides of current model jets would put them in the same size bracket as the TJ-150. A P550 is already 33% of the way there.
It may also be the case that the RC jet companies actively don't want to get too close to that line, least they wake up one morning and find that their engines are being used for nefarious purposes.
Man, you need a gas turbine at the exhaust to drive the fan in front, and a concentric independent shaft. There is not enough power in the regular central turbine used for the compressor.
Agree. This is how it is done for the turboprop engines.
Can it be done, yeah. But to what end? How much bigger would it make it? Heavier for sure. How much wider. And how much more will it cost? What's the market for it? Does a RC plane need a state of the art turbojet? It may be nice if you're building a RC airliner but don't see this being used in most RC Sport Jets or RC Military Jets. Current RC jets are based on 1940s tech and are perfectly adequate for what they're used for. The hobby can be expensive as it is, throwing in a $20k turbojet isn't needed or wanted
Just one question, have you ever considered the effort needed to make that gear box? As least for GE PW1000G, last time I check it tooked them 5 years! Are you willing to invest that much money into it?
A better fan drive would be an inner/outer shaft running off a low pressure turbine wheel. I'm not in the model turbine manufacturing business, I just want to see a model turbofan that we can drop in our model jets.
They also need air-bearings 25hr overhauls are terrible. And sadly Turbofan doesn’t help me improve fuel consumption on my turboprop based Mini APU. But cool idea!
APU's are well suited for direct attached loads.. I wouldn't be using a free turbine for that design. Sinc it's stationary, and you can spare space, you could also look at a recourperator design.
The planetary gearbox would scream at those rpms. I'm not sure if it could fit in the container that you drew. A double shafted engine might be better with another stage to turn the fan.
I agree. A double shafted engine would be simpler really.
So this video was pretty much, modify a turbo jet to be a turbo fan? The main reason for the reduction in sound of current day turbo fans, is the thrust of the fan helps muffle the sound of the exhaust, further more nothing was mentioned on the outer and inner shaft …
Is still don't understand why they don't make an RC Turbofan. It's not like it wouldn't sell!
Tldw; make a small scale rc turbofan.
Considering a main point of RC models is to, well, model full-scale aircraft, it's a cool idea, because it adds more realism. But let's be honest - efficiency is basically irrelevant in this space. Most models employing RC size jet engines cost five figures (the engine alone costs ~$3k last I checked), and as such, are flown maybe a few times a year. I'd be surprised if they burned more than $50 worth of fuel in a year, so the cost of fuel here is negligible. A more efficient design might save you enough to buy a cup of coffee or two over the course of a year.
Efficiency is much more important in the commercial aviation world where jet liners fly hours each day, every day, to make money for their owners, and a 10% savings translates to millions of dollars over the life of the plane.
TL;DR: Find more CR first. You'll find 20% efficiency increase with just getting the pressure ratio up 1.
This.. is a bad idea from the start.
Model turbines tend to run in the 2-3:1 compression ratio range. This is WAAAY down at the 20% efficiency end of the brayton cycle. Get that up to 5:1 (do-able, but difficult in a single stage) and you'd see a 50% increase in efficiency. Better sealing, a longer combustion chamber, better turbine design.... all things you can do without completely coming up with a new format, would net you more than your proposed design would do. Model turbine engines "barely" run. There's so much more to do to them before considering adding complexity.
There are massive difficulties in your chosen method of driving a turbofan. Most important is you're taking shaft torque from a 150krpm shaft to drive that fan. Every gear interface has ~some~ loss of torque, and at 150krpm input, that's going to be a wildly unpleasant amount of energy. The bearings in your model engines are cooled by fuel in a large part because they too have some loss of torque, and because they're going 150krpm, that ads up to a lot of energy.
Your fan design is a poor choice. Or at minimum the air path is. Since turbines are driven by compression ratios, any, and i mean any, additional pressure before the centrifugal stage is of monumental importance. Why you'd give up even the slightest input pressure has my head spinning.
You're also proposing a direct power turbine, and those are .. tricky to manage at best. You see them really only in very specialized applications where changes in power state aren't needed quickly. They really only work at their design rpm, which is fine for a turboprop with variable pitch blades, or an apu that can idle at run rpm until a load is applied, but that wont work for a model airplane that needs to throttle.
So lets talk parts count. At minimum your design is going to need a fan, two support bearings, a pinion, a spur, and at least two planet gears, a new exhaust turbine, a new support bracket to hold the gearbox and fan. So.... we're talking a minimum of a dozen new parts? And a few of them are going to be pretty complex.
Lets say you just want a turbofan. A dual shaft setup, with a fan on one end, and a second turbine on the other would get the same results without needing a gearbox, get you around the problems of doing direct power take off from the gas generator, and present many fewer engineering problems. But... we can do it even simpler. The first turbofans had rear mounted fans, with the turbine and fan being the same part. That gets us down to bearings, a carrier, and the turbine/fan assembly. If you could figure out bearing cooling, it would be just one precision part.
This is why you were told you need to read more. To be a good engineer you need to know what came first, why it came first, why what came later, and why things happened in the order they did.
I think you missed the point of the video. Making a mock up model for a youtube video is not an optimized engineering project. This model performs exceptionally well for its intended purpose. I'm happy to see that you went deep into the details of turbofan design. I can only hope that a manufacturer is able to give a turbofan design a chance so that we can hear one of these in our models.
Let's don't get too focused on centrifugal jet bad, multistage axial good, There's good and bad examples of both in the full scale realm. Some of the most efficient full scale jet and turboshaft engines made are combined axial dual or triple shafts driven by multiple combustion exit turbines powering combinations of bypass fans and internal centrifugal/axial compressors. The more compression achieved in the combustion chamber, the better and more efficient the engine is overall.
Making this complexity into an RC model engine is going to be the difficult thing because jet model engines, like their piston engine counterparts tend to require simplicity, lightness and ruggedness. This is why the old Rolls Royce style of centrifugal compressor model jet is more widely made as a model jet engine, and this also applies to turboshaft engines.
When you can make a pretty exact copy of a Garret type of multishaft/ centrifugal-axial/compressor jet or turboshaft, maybe we'll have something to discuss.
The compressor itself is not bad, despite what many claim. A centrifugal compressor simply does not fit into many planes. It does not fit into engine nacelles of Me-262. It does not fit into an F-22 . I may fit into a trainer jet with their relative weak engines. It does fit into a helicopter -- especially if you have the space for example a single engine behind the cabin (where it would replace a piston engine) or in the nose of this pink Magnum PI helicopter. It looks a bit more ugly in nacelles.
What if jet engines was giving litle water in burnchamber so more expansion
Hi Ryan. You missed a great day of flying. Sorry you have to work on such a nice day.
Saturday looked pretty windy but Sunday looked good 👍
More bypass!
Absolutely
In short, he says with so many words, make the change to turbofan engine, by the 3d model, I would say mid-bypass turbofan.
I don't think the market can absorb the costs for a turbofan. I would really just like to see one made. Jet engines are really cool in all forms.
Turbofans are big for a reason
you lack an understanding of turbomachinery and thermodynamics: Brayton Cycle efficiency depends on compression ratio, more is better. radial compressors can reasonably have a compression ratio of maybe 6:1 per stage, though typically they are closer to the 3.5-4 mark. Axial compressors are around the 1.1 to 1.2 range per stage. the reason airplanes use axial compressors is because of the frontal area presented to the airflow is lower, making the overall system more aerodynamic.
That's an interesting take on my understanding of turbomachinery. However, your entire comment seems to address something I never mentioned in the video. I didn't recommend, use, or show an axial compressor. I'm a bit puzzled about how your better understanding misidentified the highlighted component featured in the video.
would be interesting to see how good it is on fuel those standard RC Jet engine can eat up to 15L an hour that's more then my land cruiser driving at highway speeds and that thing weights 2.5 tonne. those jet engines have to be the most inefficient thing ever.
Yes, exactly. Was just speaking to a fellow club member about this. He was buying $20-$25 CAD worth of fuel per weekend and flies every weekend possible. It adds up for sure.
I'm confused. You're comparing. Jet turbine with turbofan? Jet engines are different for different uses.
No, I'm comparing a turbojet with a turbofan. Both are jet engines. Modern Military and commercial engines all use turbofan engines.
You have no idea of how miniature Gas Turbines work...😏🇬🇧
Another commenter claiming to know someone's level of knowledge based on a playful TH-cam video? That kind of negativity doesn't benefit the community.
@@RCexplained Another U Tuber who thinks he knows everything ...There's a very good reason MODEL Gas Turbines use centrifugal compressors....You could no doubt research it....🤔😏
You still don't get it.
@@RCexplained Nope, it's you matey.....I've forgot more about this than you'll ever know.....😏
My point, you have proven. Good luck.
I have not seen the video yet as I have to go to bed, but from the thumbnail, I think you're trying to make it into a turbofan engine, right? They are efficient.
I'll check out the video tomorrow 😊😊
You are correct, a turbofan of any design would be cool to see for model jets. 😎
Kilometeres/hour VS what we use i in the USA. We are not in Europe.
I am not in Europe either?
@@RCexplained EXACTLY!
No idea what your point is. You must be the first from USA to watch the video?
@@RCexplained I work for the biggest Deference Contractor in the USA.(for over 21 years now) I've been to Europe to teach the Italian's what our system is. We use Pound force for our jet engines not Kilonewton or the like.
Start to use science @@randyhager2054
Several vendors have tried true axial engines....
Easy to talk about it. Do it.
I'm not in the model turbine manufacturing business.
I don't think a gearbox is practical or necessary. Most traditional Turbofan engines don't have a gearbox, and neither do Helicopter engines. A completely free fan shaft should work just fine.
It appeared your diagram had the planetry set sitting off the Inlet Compressor end of the shaft, that's a perfomance limitation. The shaft for the main High Bypass fan should run from the gearbox through the center of the shaft for the Compressor and Impellor, and then in to a Drive Fan. That way the gas turbine isn't using Shaft Power to turn the fan, instead the turbine is just there as a Gas Generator, and it is the hot exhaust turning the drive fan, which turns the gearbox and provides and overdrive to the main High Bypass Fan.
The thrust pushing the aircraft comes from the Fan, not the turbine.
That poorly keyed animated background, is really distracting and lowers the quality of the vision. You're wasting bandwidth that the CoDec should be using for the part of the vision you want the viewer to concentrate on - You.
The wasted bandwidth will be making your edited file size larger, and also reducing the quality once TH-cam recompresses it again.
Thanks for the editing pointers. I have trouble with the background and I think a green screen can help make this easier for me to edit.
First build your own model conventional jet turbine before making a video on it. The very first problem I see with the design is that it will not be self sustaining because the first stage will be too heavy. This really is a case of Dunning-Kruger effect.
Actually, the first problem in design with this playful video is that the transmission is impossible to manufacture at this size and RPM. Also, stage 1 being too heavy is not the specific issue with this design. Assuming it is weightless, the fan would consume too much power from the turbine and must be on a separate stage. Lastly, while it seems you missed the point of the video, I do appreciate hearing from those more knowledgeable than most.
Just jump to 1:20 The first 14% of the video is the usual fluff from people who can't just launch on a topic.
Just have to get a dig in there.
@@RCexplained It is my crusade to save thousands of man-years of viewer lifetimes. Check "Project Farm" or "Scotty Kilmer" for a masterclass.
Your background is nauseating. Other wise great video..
I want 10 minutes of my life back. This is little more than a clickbait plug for that crappy overpriced 3D printed engine which that company is selling ILLEGALLY and handing out to any random youtubers lately from what I've seen, that design is blatant copyright violation from the original designer who posted that 3D printable STL almost 8 years ago. Nothing explained here is not something nobody that's been paying attention already doesn't know, and that proposed turbofan design is laughably useless, and RC turbofans have been made but they are largely one-off experiments. The technology/demand just isn't there yet and just may never be since there's too many tradeoffs at these scales. Furthermore just look at all the problems a the Pratt and Whitney geared turbofans have created for their operators. They are absolutely horrid in reliability.
I fly both full scale jets for work and RC turbines for fun and you just can't transfer the many of technologies from one to the other. Simplicity and lightness are key in the RC world. If people want efficiency, they just need to buy better engines. For example my Xicoy engines are far far more efficient that the equivalent chinese branded ones in my clubs and I'm flying significantly longer times with my Xicoys despite having smaller tanks sometimes than people do with Kingtechs or Swiwins. Those are guzzlers are are much bulkier engines, they're cheap for a reason.
Lol i made a similar observation but my comment here was deleted - they also have ericthepoolguy's engines for ssale :(
If you can afford a turbine RC jet, you’re already on a level most of us can’t afford 🤣. Still love discussing theory though!
True, I look at it as spend $5k less on a car, now I have a budget.