I love the ball park numbers you guys use. So many places shy away and just say “it depends on multiple variables” which I imagine is true but gives no perspective for reference or insight to the bigger picture.
Within the first 20 seconds you cleared up my biggest worry about split flaps-the turbulence-without saying one word about it. Awesome storytelling and lead-in guys!
it's obvious that you guys are making this aircraft as simple and reliable as possible while also maximizing its speed and performance. Such an awesome plane.
Thanks for adding in the extra clips from within the cabin! Have a merry Christmas and a happy new year guys! Hope to see this beauty flying next year!
It's interesting that the B-52 and B-29 are listed as examples for the Fowler flap, given that it normal practice for modern airliners that are much more familiar to viewers
Modern airliners have another variation of Fowler flaps with multiple elements and slots for the most part. Useing the B-52 is an example of a simple Fowler flap as drawn vs todays flaps.
I love your videos! So cool as both a systems engineer and an aero nerd to see the decisions being made and why. And the engineering explanations are just fantastic. Can't wait to see this thing in the air!
@@ammerudgrenda If you learn how the flap handle moves with relation to the detent, and how the airplane feels with different flap settings+airpseed+power settings, you don't have to stare at the indicator.
Great video, you fixed my misconception that split flaps are more draggy than plain flaps. I hate to be ‘that guy’ but the actuation linkage builds in the opportunity for a linkage failure to give asymmetric flap deployment. If you are able to put the torque tube on the hinge line of the flaps then you could have a single linkage from the flap handle to the torque tube rather than two, meaning that if any articulated joint in the system failed you would be left with a symmetrical failure rather than an asymmetrical one. Please keep the videos coming, you’re doing incredible work.
smart to make the failure mode symmetric. let em know. this is the kind of stuff that next time will appear in an air crash investigation. they should fix it now.
@@daviddavids2884 You got things mixed up. Stationary air does not exist, which is the reason why wind tunnel testing does not conclusively simulate flying, but it's still usefull.
Soon this newborn will be taking its first flight. What a journey this is. Awesome engineering from you boys and good luck with the test flight. Merry Christmas and a Happy new Year!
You've got four potential failure points at the rod ends at either end of the two pushrods travelling aft from the main torques tube where, if you were to lose any of them, you'd risk ending up with a differential flap deployment - a catastrophic condition. One tube traversing from flap to flap with a single input pushrod would solve this. Same geometry in a side-on view, single centerline pushrod in a top-down view. Not sure if there is some other system taking the space that would otherwise prevent the cross tube at the flap hinge position, but I'd strongly recommend against the actuation configuration shown here. Split flap concept though - I like your choices here!
Another exemple of a fast light aircraft using split flaps is the JMB VL3. Also, some flaps are more easily mixed as flaperons to inmprove low speed handling, which is the important limiting factor besides stall speed and stall characteristic. Looking forward to first flight !
I thought most Cessnas have Fowler flaps not slotted flaps? Can’t wait to see this bird fly! I just finished my RV-6A a couple of months ago. First flight was an incredible experience! However the first flight of a new clean sheet design has to be the pinnacle of home building. Congratulations on your success so far!
I agree. The Cessna 172 flaps move down and back which increases the wing chord. Which is a Fowler flap. However, The 172 manual that I have refers to the flaps as the single-slot type.
Nope. Just a slotted flap, which DOES move back and down, just not nearly as far. A Fowler flap is characterized by being RETRACTABLE in operation. Meaning a large section of it slides UNDER the top surface of the wing. To see one in operation just look out the window over or just behind the wing of any airliner during landing. Fowler flaps are usually accompanied by rather large fairings extending aft of the trailing edge to hold the complex tracking, linkage, and actuators that operate them.
In order for a slot to open, the flap has to move aft. A fowler flap has the leading edge of the flap nearly reaching the trailing edge of the basic wing. It also translates aft a significant distance, without deflecting any noticeable amount. Where position 1 flaps is just an increase in wing area Cessnas definitely deflect downward as much or more than they translate aft. Which at most might be 4-6" rearward. And the flaps trailing edge still remains within the basic wing planform as viewed from above, when fully deflected.
The Cessna flap is slotted when half way out, but Fowler fully extended. The slotted / Fowler flap is like a new biplane wing, tilted to catch the airflow deflected by the “upper wing” and deflecting it some more.
Merry Christmas Riley, River and Keegan from Sydney Australia. Thank you for your time and commitment to education. Each time I receive a Dark arrow video, I think... Holy sh#t and then: great it's learning time. Love the British spitfire flap info and "possible to manufacture split flaps"- in aluminium with ribs for strength. Merry Christmas and peace of the lord be with you. 🌏🇭🇲🌲
You guys are my favorite TH-cam Channel. I think you are doing a wonderful job here of building a fan base to help launch the DarkAero 1. I have no doubt you guys will be very successful in time.
Fowler and split flaps have one disadvantage which is the inability to use negative deflection in cruise. You have a good, simple and reliable design, well done!
As a pilot I much prefer manually actuated flaps. Have you done some design analysis on the mechanical advantage of your flap lever? It looks a little short compared to other aircraft of similar size I have flown with manual flaps.
Split flaps just need to be released and fall down via gravity, now the UP and REMAIN up/sealed with less drag is the actual problem. So springs etc are often employed here.
@@w8stralgravity will overcome the airflow? Ever try to open the door of a Cessna in flight or your car door while driving down the highway? I’m not so sure that would work.
Bottom rear half of airfoils have downward suction. I do not believe they went with a reflex airfoil so there should be downward suction. Now will they FULLY deploy? Nope. But flaps 10 or flaps 15? Yup. Spitfire flaps for instance fully deployed to Flaps ~20 with zero input from pilot other than: deploy. Where Cessna door is a compression zone. Same Cessna door on rear half of fuselage is a SUCTION zone and would auto open partially(one reason P51 was faster than Spitfire for instance. It dumped its higher pressure heat into a suction zone decreasing fuselage drag and decreasing drag of the radiator(p47) partially did this as well(though by default rather than on purpose). Cheers @@rnordquest
All this time I thought the purpose of wings was to provide lift, but there's actually a region of downward suction, amazing lol. And I thought that the purpose of extending flaps was to gain lift by deflecting more air, which should give an equal and opposite force on the actuating linkages, boy was I a dummy lol.
I like the mechanism attached to the flap itself especially. The geometry of it means that you're increasing the force you can apply to the flap as it extends further out into the airflow (and so would be harder to move manually).
One thing that's great about aero is that butt math and intuitions conceal the actual complexity of what's involved (leading to myths and misconceptions). I'm impressed at your guys' ability to condense these really complicated subjects down to something digestible and understandable.
One of the advantages of the split flap is that the separation bubble stably extends the pressure recovery aft of the airfoil trailing edge into the freestream, allowing the upper surface pressure to stay below static as opposed to having to recover to near stagnation. We (NASA) used this aspect to design a wing for a glider for Mars exploration; it was to be folded up in an entry capsule, then released to fall away and unfold. The flowfield conditions presented during pullout were challenging - transonic Mach and low Reynolds number. We found that a split-flap design maintained the high CL capability needed to achieve the pullout maneuver even under these conditions. Of course, the relatively high drag was also advantageous, as it would slow the glider and give more time for the pullout to occur.
Fowler flaps: we have them guite often on ultralight airplanes in Europe, for instance Risen. In Italy they make the ultrafast two seat aircraft called Risen. Please note, with 100hp Rotax they guarantee the top speed at sea level 320km/h (173knots) and with turbocharged Rotax 915 -142hp they guarantee maximum cruising speed at 16 thousands feet 450km/h !!! (243 knots ) !!! Will Dark Aero be able to achieve the same velocity with much stronger engine ??? Risen has got the ultimate aerodinamics IMHO. Extreemly efficient and it is all carbon fiber too. What I like about Risen compare to Dark Aero, that Risen is not using any metal(aluminum) honeycomb, but rather materials which can never ever rust.... On the other hand what I like about Dark Aero is the gear(looks strong) and the 2 baggage compartments.
Flap position 1 is 10 degrees deflection. It is the only flap position that extends the flaps trailing edge outside of the basic wing planform. At full 40 degrees, the flaps are definitely not projecting past the trailing edge. A true fowler translated the leading edge of the flap rearward to the trailing edge of the basic wing. Which is about 300% farther aft than a Cessna. All slotted-flaps must translate aft to open the slot. As the slot gap has to remain about the same for each deflection angle, it cannot simply open more and more with angular deflection. It has to open the slot rapidly to its defined point before deflecting. The proper technical term for Cessna flaps is "Slotted Flaps with Fowler Action".
@@Triple_J.1 You are just making stuff up. The definition of Fowler flap is that the flap moves rearward as well as downward. There is no requirement that it move to the trailing edge of the wing. Slotted flaps rotate, but don’t translate. Fowler flaps translate and rotate. Cessna 182 flaps are Fowler flaps. End of story.
@@LTVoyager It looks like Cessna has used Fowler flaps (with rearward translation, although not much) since the 170B of 1952... and the same design continued through the 172 and 182.
I have seen almost all of your videos and they make me glad and amazed,as making an aircraft needs to know several fields of science and knowledge's and you have all of them together. Your job tells me that you were good students and are very qualified engineers now. Congratulate.
Hi. One thing you mentioned was sealing. The gliding community have always been ahead in this area and use Mylar sealing and turbulating tapes. I have an 18 metre flapped Schempp-Hirth Ventus and it is sealed and turbulated within an inch of its life. A gliding buddy of mine has an RV in which he set various records in, including the elapsed time London-Cape Town-London record for a 200 hp aircraft. That is beautifully taped; everywhere! Have you considered what tapes you will use? I’ve attached a link to the first glider supplier I found. I live in the U.K. and have no connection with the company, but their site has a great selection for you to browse. Just a thought. My mate’s RV is impressively fast with a stock engine. But there’s not a gap an air molecule could squeeze through! I notice that the ailerons don’t yet seem to be sealed.
One of my biggest surprise when transitionning to the PA-28 Archer was my intstructor asking me to do a flaps up circuit and landing. He asked me at what speed I would fly the circuit and landing and I was all bent to say for sure faster than the regular speeds used traditionally. That's when he told me just fly the same speed as normal no need to fly faster just the attitude will be more nose up and power setting would be different. The "flaps enable slower speed" is really only true for the stall speed (a few knots of difference as per POH) but as you would never fly that slow anywhere in normal flight that wouldn't do any difference.
Another aspect of the marvel that Concord was is that it had no lift augmentation devices at all, neither leading or trailing edge. Low speed flight was achievable because of the double delta wing, same as the Space Shuttle.
Interesting and informative explanations. You might consider getting rid of any background 'music' or soundtrack. It is really distracting, serving only to make it a little harder to concentrate on, and understand, the narration.
Are you sure? I’ve ever been up close and personal with a single DC-3- and it didn’t have flaps. Looking at photos of planes on the web, and I don’t see any indications of flaps- but, admittedly, all those photos are from the top, so for a split flap, wouldn’t see anything!
With a little change in geometry you could have gotten more leverage at the handle over the flap as it approaches full deployment rather than less. As it is, you have most leverage when it's not needed, and least when it would be nice to have. We do this on big heavy RC sailplanes to avoid breaking the servos when the flaps are fully deployed just in case we don't get them up before touchdown. For you it'll just be a matter of the flaps feeling really heavy at full deployment.
That was one of my thoughts - a 30cm deflection of the flap handle has to extend a relatively large chunk of wing into high speed wind. Gonna be tricky for sure to balance the forces with any possible spring assist.
@@frollard I'm not talking so much about the simple flap lever to flap angle ratio, but the way they've clocked the positions of each end of the linkage relative to each other. There are ways to set it so that you start with more leverage over the flap and end with less (control lever initially moves faster than surface, then slows down to match its speed) which is what they've done, or you can set their relative positions so that you start with less leverage (when you don't need it at low flap deflection) and gain leverage as you move it further (moving arm faster than flap).
Riley's presentation was great. Although I don't usually get much fired up about the new composite airplanes, I wish you guys well on this venture (certainly no pun intended!) I hope that handling qualities are as important as performance to you guys.
Is there a concern about the force required on that short handle to activate the flaps? Just looking at it has me a little concerned if there is an attempt to open the flaps at any relevant speed. (Even at a 50kt airspeed, there would be a pretty high torque because of the surface area of the flap.) It seems to me that this is also why most older aircraft I have seen with manual flaps have relatively long handles.
Fowler flaps are often on Ultralight aircrafts In Europe. For instance in Italy they make the ultrafast two seat aircraft called Risen with fowler flaps.. Please note, with 100hp Rotax they guarantee the top speed at sea level 320km/h (173knots) and with turbocharged Rotax 915 -142hp they guarantee maximum cruising speed at 16 thousands feet 450km/h !!! (243 knots ) !!! Will Dark Aero be able to achieve the same velocity with much stronger engine ??? Risen has got the ultimate aerodinamics IMHO. Extreemly efficient and it is all carbon fiber too. What I like about Risen compare to Dark Aero, that Risen is not using any metal(aluminum) honeycomb, but rather materials which can never ever rust.... On the other hand what I like about Dark Aero is the gear(looks strong) and the 2 baggage compartments.
Two comments, 1) A big disadvantage to fowler flaps is the change in the center of lift. That can be mostly mitigated by adding leading edge devices. Of course that adds complexity but worth it on some aircraft. 2) Aluminum structure complexity can be greatly simplified especially for a simple part like a split flap by using a foam core and bonding aluminum sheets for skin. I've done this a lot and it's much more simple than a composite layup or molded composite part.
Fowler flaps are often on Ultralight aircrafts In Europe. For instance in Italy they make the ultrafast two seat aircraft called Risen with fowler flaps.. Please note, with 100hp Rotax they guarantee the top speed at sea level 320km/h (173knots) and with turbocharged Rotax 915 -142hp they guarantee maximum cruising speed at 16 thousands feet 450km/h !!! (243 knots ) !!! Will Dark Aero be able to achieve the same velocity with much stronger engine ??? Risen has got the ultimate aerodinamics IMHO. Extreemly efficient and it is all carbon fiber too. What I like about Risen compare to Dark Aero, that Risen is not using any metal(aluminum) honeycomb, but rather materials which can never ever rust.... On the other hand what I like about Dark Aero is the gear(looks strong) and the 2 baggage compartments.
There are a lot of wanna-be engineers out here on youtube, but you guys seem to really know your stuff. You showed the pros and cons and your choice makes completly sense to me. It would have been nice to hear an opinion why the big 2 choose fowler flaps for their big birds (I'm just a regular mechanical engineer for farm equipement; this topic is really interesting, but I have no idea what to make of all the possible choices). again: great video! loved it!
Airliners need far more effective flaps with substantial chord extension and effective wing area increase to create viable configurations for takeoff and landing from a wing optimized for their cruise speed. The speed range of anything with a piston engine - even the DarkAero - is much narrower so less effective flaps are viable.
I’ve seen plenty of discussion about that online. We were taught they were “slotted Fowler flaps”, I think the manual only refers to them as slotted flaps. A quick google says the wing are increase is only just over 4%. I guess it’s one of those topics to throw into a group of pilots then sit back and watch the arguments lol
I see most of what you are getting at, It depends on the intended type of field used by the aircraft. If you will always be at runways with nice clearways then you may only care about getting maximum lift to reduce touchdown speeds and reduce stress on tires and gear, drag can be modest. If you plan on locations with steep final approaches to shorter runways, then energy management is more of a concern than minimum touchdown speed and adjusting drag is more important than lift. A generally versatile behavior is for a small deflection to add some lift with minimal change in L/D (Maybe even a slight improvement over the clean wing.). Then as flap angle increases a rapid increase in drag relative to lift. (Gliders take it to the extreme of adding spoilers to the top of the wing.) This doesn't require ideal flap behavior of course, as long as the flap design is "good enough" then the cruise and manufacturing concerns, that were mentioned in the video, become major factors.
There is a great version of the legendary Libelle glider with those flaps. With the additional airbrakes it had a maximum descent angle of 1:4, strong ground effect and strong deceleration it was great to land on very short strips. I loved it!
Thank you! All the modeling work has been an endeavor of its own. Not certain on the total number of hours put into that effort but it’s on the order of 1000’s.
@@DarkAeroInc. Hi from across the pond. I graduated 51 years ago in Aero Eng and Design. My final year project was Foam Stabilised Compression Panels. I used used 20 gauge Al skins and a 1 inch polyurethane core . I wrote to De Havilland for advice and they supplied the adhesive free !! Subsequently I proved mathematically that the Southwell Plot could be used to predict the failing load , in compression, for this “weak in shear” structure. My tests indicated that this could be the case , but at a review in front of the whole course, I was rubbished by a lecturer , that my results were a coincidence and the Southwell Plot only applied to structures in compression which were weak in bending. This humiliation triggered me big time, and after a struggle I proved mathematically that I was correct. So…..how have you tested that your design is structurally sound. And….your design looks really “hot”. How do you propose to conduct stall and spinning trials ? Are you going to fit an anti spin chute during these trials, just in case !! You would be wise to do so. Do you intend to fit leading edge “triangles” inboard , to ensure you get tail buffet stall warning ? Great video by the way. Such a clean design will produce a very flat glide angle I imagine. If you have a flap linkage failure say, will you investigate during flight testing , the use of sideslip to increase your descent rate ?
Great flap discussion. Just a minor nit: "The split flap comes out on top of the split flap when it comes to drag for a particular lift". The graph shows you mean the split flap has a better (ie lower) drag/lift ratio, so it's "on top" in performance, ie desired. However, the statement, especially if the graph were not there, could also imply the opposite: that the split flap has a higher drag/lift ratio (numerically "on top" of the simple flap) and thus is less desirable than the simple flap.
Yes, the split rudder is intended to be used as a speed brake,@@minorlion1327. If drag is needed, it has the advantage of causing minimal pitch change... unlike the split flaps.
Working on getting my ppl and I dream to one day get a experimental kit aircraft and I’m definitely keeping my eyes on you guys! A zenith is cool but I’m honestly a low wing type of guy and I love the design, look, and performance of this aircraft. Keep it up guys 😎
,any decades ago I worked a lockheed with early composite materials and some I suspect are not open source as yet but I'm glad they are in wide use today so widely I always thought them quite amazing in testing !😊
I noticed the projected rated speed of the aircraft will be around 230knots, will you need static whicks with this composite flap aircraft for less noise, interference in your electronics and in comms?
I'm curious if you'd taken a look at assymetric flap deployment versus aileron authority. If any of the linkages were to fail in the flap system, is there sufficient aileron authority to counter the roll until the other flap can be retracted? I don't think it's a likely failure mode but with you attention to detail I'm just wondering if you've examined it.
One does this in VERY high speed aircraft where flutter is the biggest problem, or sometimes in sailplanes where once again, flutter is the biggest problem. In low speed aircraft this is not a problem. In civilian aircraft with their wings full of fuel, once again, flutter is a big problem and due to $$$ of such aircraft, they can afford to have multiple roll capabilities. In their case, they LOCK OUT aileron movement except at LARGE stick deflections and they still allow down aileron, it is not just UP aileron. Of course swept back wings helps here as well so... This is essentially impossible to do on a mechanical only simple aircraft design. Even the commercial boys have a SMALL flap behind the engines providing roll controll and the main flaps DO NOT move for roll control.
@@w8stralNot sure what flutter has to do with any of this. Nor was I suggesting using the flaps for roll control. I was asking that, if in the event of a linkage failure resulting in an asymmetric flap deployment, was aileron authority sufficient to maintain control.
I'm guessing that wouldn't be a high priority design consideration. I know from my flight training on a C172 to expect that an asymmetrical full flap deployment would too severe to fight with aileron control at all. I doubt many other pilots received training quite as terrifying as mine was but it should be pretty well ingrained that the pilot should undo the last flap adjustment if that failure happens.
I thought that was obvious so answered you in a different way. Ok, here goes, basic algebra time and WHY flaps are NOT considered primary flight control and why aircraft can LOSE a flap and still land with flaps down. Aileron CL max is? ~2.5 or so(tip stall territory and you die anyways so... not cool), but when problems occur is possible. Percentage of wing ==? Looks roughly 30% Flap Cl goes to max of? 2.3 percentage of wing = ~60%. Wing CLmx ~0.8-->1. Lets call it 0.9. Lever arm length to CG Moment Flap = 2.3-0.9 = 1.4* center of flap lift @30% or ~0.42. Moment aileron = 2.5-0.9 = 1.6* center of aileron lift @75% = 1.2 1.2 Aileron >> 0.42 Flap Losing a flap or one flap stuck down is ANNOYING, no question, and you will have to LAND faster to compensate for loss of lift, but it is not a death inducing event like losing an Aileron. If you lose an aileron: Bail out because if you are in the aircraft when it crashes--> You are dead 100% of time, if you bail you have a 0.00001% chance of living but slightly possible if over water, or fly with a parachute. @@billstrahan4791
Yup, decreasing the half flaps deployed that are down will decrease your landing speed as one has less downward lift from ailerons on opposite side. @@waywardscythe3358
Krueger flaps. They increase camber too, like all other flaps. They just do it at the leading edge. This is not to be confused with things like Slats and Slots that do not increase camber. There can also be a hybrid Slat/Krueger flap. More types are probably out there that are only found on certain aircraft for unique circumstances or situations like flaperons. Ailerons that also function as flaps.
In applications such as gliders, where drag minimization is most critical, the plain flap can be reflexed, thereby reducing the drag at the best glide speed.
Guys, did you consider placing the torque tube coaxial to the flap pivot? In this case it seem to have more reliable mechanics. At least now if one of the links fail there would be differential lift created, which could be very dangerous obviously
Excellent video. I don't quite get to the "biggest myth" part, - I suppose it's the high drag assumption - but I love the factual nature of the presentation.
Aerodynamics tells me with the hinge point fixed at the front of the flap, when the flaps come down the trailing edge will effectively come forward thereby decreasing the mean chord. CoP will come forward (relative to CoG) reducing the relative moment arm and inducing a pitch-down tendency requiring nose up trim. That will be interesting to see confirmed during flight testing.
Nice update gents! Does the center of lift move back when the split flaps are deployed? (A Mooney characteristic) If no…. No trim change required with deployment. If yes…. Trimming while deploying flaps at the same time and rate, is nice… Safety opportunity…. Nothing worse than flaps accidentally retracting. Fast uncommanded retractions can be extra hazardous, as the stall speed may exceed the current airspeed without warning! (Hand slips off the handle, position lock not engaged) Split deployment… is there a way that the flaps can accidentally deploy or not retract on one side and not the other? A few minutes during the transition training should cover how best to use the flaps, trim, and what to avoid during slow flight. 😃
For fighter aircraft a lot of designs had maneuvering flap position so the split flap would be at low deflection and cause drag. Hurricane and Spitfire only had two flap positions - extended and up and predictably used split flap.
In terms of slipperiness, the closest thing to your design I've flown is the Comanche (not that aerodynamically clean). With the Comanche I'll take all the drag I can get for descents. You are coming towards you destination at cruise altitude, say 12K feet. In the western US the airport is often located on the valley floor and surrounding hills limit your ability to descend early. You start your decent at say 500- 1000 fpm. But your air speed starts to approach VNE limiting your decent rate. You end up having to fly longer patterns aligned with the terrain to loose altitude. That sort of defeats the purpose of flying a fast plane to arrive sooner. Anyway, I wish the Comanche had drag devices I could deploy at higher speeds. The gear helps once you get slowed to a speed you can deploy it. but there you are again fly a fast plane slowly.
I have an AMD CH2000 with split flaps. It is not a lift device. It is a drag device. POH calls for zero flaps on short-field. A few times I’ve forgotten to retract flaps after landing and I can feel the drag on takeoff; the controls become very heavy. If you stop by Houston, I’d be happy to let you fly it to see what I mean.
Fowler flaps are often on Ultralight aircrafts In Europe. For instance in Italy they make the ultrafast two seat aircraft called Risen with fowler flaps.. Please note, with 100hp Rotax they guarantee the top speed at sea level 320km/h (173knots) and with turbocharged Rotax 915 -142hp they guarantee maximum cruising speed at 16 thousands feet 450km/h !!! (243 knots ) !!! Will Dark Aero be able to achieve the same velocity with much stronger engine ??? Risen has got the ultimate aerodinamics IMHO. Extreemly efficient and it is all carbon fiber too. What I like about Risen compare to Dark Aero, that Risen is not using any metal(aluminum) honeycomb, but rather materials which can never ever rust.... On the other hand what I like about Dark Aero is the gear(looks strong) and the 2 baggage compartments.
Fowler flaps: we have them guite often on ultralight airplanes in Europe, for instance Risen(from Italy) , or Stream(from Czech Republic). In Italy they make the ultrafast two seat aircraft called Risen. Please note, with 100hp Rotax they guarantee the top speed at sea level 320km/h (173knots) and with turbocharged Rotax 915 -142hp they guarantee maximum cruising speed at 16 thousands feet 450km/h !!! (243 knots ) !!! Will Dark Aero be able to achieve the same velocity with much stronger engine ??? Risen has got the ultimate aerodinamics IMHO. Extreemly efficient(crossed Atlantic from Africa to South Anerica using 200l tank only) and it is all carbon fiber too. What I like about Risen compare to Dark Aero, that Risen is not using any metal(aluminum) honeycomb, but rather materials which can never ever rust.... On the other hand what I like about Dark Aero is the gear(looks strong) and the 2 baggage compartments.
Looks like the individual cranks for the flaps are at the root of the wings. What about locating them at the center of the flaps so there would be less twist force on the flaps (and their hinges) and also have half as much of a longitudinal chord in the flap which may help with flutter from such a long span.
The flaps are stupid lightweight. Probably five pounds, at most. The heaviest parts of the flap mechanism are all internal to the fuselage, so leverage is still as high as possible while minimizing the moment of inertia in the wings themselves.
@@davidchow9528 that's the question though - will it be, really? Even if it's five hundred newtons per flap, I doubt it would be an issue. And I don't think anybody has ever done a full carbon fiber flap with carbon fiber IN the linkage - it will likely be more than stiff enough to prevent torquing in any way.
@@spdcrzythe concern is not just the force but also flutter. the carbon fiber for sure is stiff enough but what about the hinges and bond points. the greater the chord the higher the likelihood of flutter especially at lower speeds. to me attaching the crank mid cord makes the most sense. But what do I know I didn't do any analysis. Just bringing up an idea for the dark arrow team.
Thank you for the excellent synopsis on Flap types. Might you know if split-flap designs might be inherently different at high extension angles to Fowler design as far as L/D? I was reciently chatting online with other pilots about the how the early model Cessna 310s had a pronounced loss of lift (not stall) on landing if throttles were reduce below zero thrust, and the Beech Barons like the B55 model with Fowler flaps much less. Both were similar wing-area, airfoils and weights.
I know by "deflection" you mean that the flap is angled downwards ... However, I wish people addressed how it manipulates the airflow: It must also deflect air as a lift source & can't just be pressure differentials.
Beautiful plane, best wishes to you for success. Just some thoughts. Your video shows a flap actuator attached only at the inboard, with no attachments or push rods along the span of the flap. I suggest looking at significantly beefing up (metal Plate) the flap control surface, especially in the zone where debris could be kicked up from the wheels into the flap control surface. perhaps a torque tube extending the length of the flap with multiple attach points. Also, if the flaps get stuck down, is there sufficient power and control authority to execute a go-around? If one flap control surface broke and retracted with the other extended, is there sufficient control authority to manage?
A question if I may! On the split flaps. Technically you have two cord lines when the flaps are lowered? How is that affecting the flight characteristics.
How about stall speed for each flap design in same wing and AoA? Is there any different. And what DA1 project design landing speed and runway requirement?
wait..... that wasn't very specific about what was nest at the end lol. so what exactly are you going to ground test first? I am very curios and excited for your project!!
Interesting that you would look at the reduced drag in a split flap verses the plain flap as a goal, when one of the goals with flaps, I thought was to increase lift and drag? Cheers!
@@watashiandroid8314most light aircraft can take off less distance then landing. And in a slippery plane like this one you want to be able to increase drag for landing and easier approach, for example in gliders using airbrakes.
@@electricalmayhem of the 6 light aircraft I have flown enough to be familiar with, maybe one could take off in a shorter distance than it could land. Brakes tend to be far more powerful than the engine in a light aircraft, and from what I recall, most light aircraft can land in a shorter distance than they can take off in. The 6 aircraft I've flown enough to talk about: Cessna 150M, 152, 172M, Aeronca Champ (O-200), Bellanca Citabria (O-235), Super Decathlon. The one aircraft which I think can take off in less distance than land is the Super Decathlon.
@@watashiandroid8314 Hmm you are right for GA aircraft, looks like I've been spoiled with microlight/Sports aircraft which are fibreglass with Rotax 912's giving a good power to weight ratio! (WT9 Dynamic, Rans, Vans etc) Been a while since I flew a cessna.
If the split flap has both less drag (both in cruise and deflected) and more lift... what's the advantage of the plain flap? It doesn't seem simpler. What is the area of the flap, and what is the expected torque and force that you have to apply to the flap handle?
Is there eventually going to be a flap indicator for the split flap similar to the spitfire since you cant see the flap position from the cockpit? Incase of malfunctions l.
I love the ball park numbers you guys use. So many places shy away and just say “it depends on multiple variables” which I imagine is true but gives no perspective for reference or insight to the bigger picture.
This is SO true. Gets my goat everytime.
Agreed! So much better to say, "Hey we did the math comparing each of these under the same conditions, on the same equipment, and this is the result."
Within the first 20 seconds you cleared up my biggest worry about split flaps-the turbulence-without saying one word about it. Awesome storytelling and lead-in guys!
It also eliminates any chance of control surface flutter.
Oh thank God they were able to clear up your confusion.
Turbulence (ride quality) was your biggest worry?
@@36thstreethero no, efficiencies of their flap design was my worry. I incorrectly assumed this type would create more turbulence and thus drag.
it's obvious that you guys are making this aircraft as simple and reliable as possible while also maximizing its speed and performance. Such an awesome plane.
@@timcross2510 Seems like a simple and reliable design to me.
I like that the design is optimized for being efficient at speed.
no gaps, and as simple as possible.
Thanks for adding in the extra clips from within the cabin!
Have a merry Christmas and a happy new year guys!
Hope to see this beauty flying next year!
It's interesting that the B-52 and B-29 are listed as examples for the Fowler flap, given that it normal practice for modern airliners that are much more familiar to viewers
Modern airliners have another variation of Fowler flaps with multiple elements and slots for the most part. Useing the B-52 is an example of a simple Fowler flap as drawn vs todays flaps.
Also, the P-38 is another glaring omission.
Modern airliners are using mostly slotted or double slotted fowler flaps.
I love your videos! So cool as both a systems engineer and an aero nerd to see the decisions being made and why. And the engineering explanations are just fantastic. Can't wait to see this thing in the air!
I agree. You just don’t see videos of people designing aircraft and telling you why. Usually you have to infer
Really happy you guys are staying simple with manual bar for flaps. Easier build, less failure points over time, simple.
More enjoyable experience flying imho. I always love the manual flaps in the piper over the Cessna electric flaps as I continue to learn to fly.
Better ergonomics too. No need to stare at the flap indicator.
@@ammerudgrenda If you learn how the flap handle moves with relation to the detent, and how the airplane feels with different flap settings+airpseed+power settings, you don't have to stare at the indicator.
Great video, you fixed my misconception that split flaps are more draggy than plain flaps.
I hate to be ‘that guy’ but the actuation linkage builds in the opportunity for a linkage failure to give asymmetric flap deployment. If you are able to put the torque tube on the hinge line of the flaps then you could have a single linkage from the flap handle to the torque tube rather than two, meaning that if any articulated joint in the system failed you would be left with a symmetrical failure rather than an asymmetrical one.
Please keep the videos coming, you’re doing incredible work.
air is Stationary wind tunnel testing is NOT conclusive.
smart to make the failure mode symmetric. let em know. this is the kind of stuff that next time will appear in an air crash investigation. they should fix it now.
@@daviddavids2884 You got things mixed up. Stationary air does not exist, which is the reason why wind tunnel testing does not conclusively simulate flying, but it's still usefull.
The linkage is not a very elaborate design. Complicated sure, and fancy too, but not elaborate. Maybe somebody is running out of time.
Soon this newborn will be taking its first flight. What a journey this is. Awesome engineering from you boys and good luck with the test flight.
Merry Christmas and a Happy new Year!
You've got four potential failure points at the rod ends at either end of the two pushrods travelling aft from the main torques tube where, if you were to lose any of them, you'd risk ending up with a differential flap deployment - a catastrophic condition. One tube traversing from flap to flap with a single input pushrod would solve this. Same geometry in a side-on view, single centerline pushrod in a top-down view. Not sure if there is some other system taking the space that would otherwise prevent the cross tube at the flap hinge position, but I'd strongly recommend against the actuation configuration shown here.
Split flap concept though - I like your choices here!
You guys have put so much work and love and energy into this aircraft. I wish stuff like this didn't end up in bankruptcy most of the time.
Another exemple of a fast light aircraft using split flaps is the JMB VL3. Also, some flaps are more easily mixed as flaperons to inmprove low speed handling, which is the important limiting factor besides stall speed and stall characteristic. Looking forward to first flight !
I thought most Cessnas have Fowler flaps not slotted flaps? Can’t wait to see this bird fly! I just finished my RV-6A a couple of months ago. First flight was an incredible experience! However the first flight of a new clean sheet design has to be the pinnacle of home building. Congratulations on your success so far!
I agree. The Cessna 172 flaps move down and back which increases the wing chord. Which is a Fowler flap. However, The 172 manual that I have refers to the flaps as the single-slot type.
Congratulations on your build completion and flight. That’s quite an accomplishment!
Nope. Just a slotted flap, which DOES move back and down, just not nearly as far. A Fowler flap is characterized by being RETRACTABLE in operation. Meaning a large section of it slides UNDER the top surface of the wing. To see one in operation just look out the window over or just behind the wing of any airliner during landing. Fowler flaps are usually accompanied by rather large fairings extending aft of the trailing edge to hold the complex tracking, linkage, and actuators that operate them.
In order for a slot to open, the flap has to move aft.
A fowler flap has the leading edge of the flap nearly reaching the trailing edge of the basic wing. It also translates aft a significant distance, without deflecting any noticeable amount. Where position 1 flaps is just an increase in wing area
Cessnas definitely deflect downward as much or more than they translate aft. Which at most might be 4-6" rearward. And the flaps trailing edge still remains within the basic wing planform as viewed from above, when fully deflected.
The Cessna 150 and 152 had Fowler flaps. The 150 will drop down to 40 degrees and is like a barn door
The Cessna flap is slotted when half way out, but Fowler fully extended. The slotted / Fowler flap is like a new biplane wing, tilted to catch the airflow deflected by the “upper wing” and deflecting it some more.
Merry Christmas Riley, River and Keegan from Sydney Australia. Thank you for your time and commitment to education. Each time I receive a Dark arrow video, I think... Holy sh#t and then: great it's learning time. Love the British spitfire flap info and "possible to manufacture split flaps"- in aluminium with ribs for strength.
Merry Christmas and peace of the lord be with you.
🌏🇭🇲🌲
You guys are my favorite TH-cam Channel. I think you are doing a wonderful job here of building a fan base to help launch the DarkAero 1. I have no doubt you guys will be very successful in time.
There is so much educational value in your videos ♠️
Fowler and split flaps have one disadvantage which is the inability to use negative deflection in cruise. You have a good, simple and reliable design, well done!
Most Cessna singles have slotted Fowler flaps. --- 140A 150 152 170B 172 175 180 182 185 205 206 207 210 --- to name a few
As a pilot I much prefer manually actuated flaps. Have you done some design analysis on the mechanical advantage of your flap lever? It looks a little short compared to other aircraft of similar size I have flown with manual flaps.
Split flaps just need to be released and fall down via gravity, now the UP and REMAIN up/sealed with less drag is the actual problem. So springs etc are often employed here.
@@w8stral The flap seems very light, will gravity be much help in this case?
@@w8stralgravity will overcome the airflow? Ever try to open the door of a Cessna in flight or your car door while driving down the highway? I’m not so sure that would work.
Bottom rear half of airfoils have downward suction. I do not believe they went with a reflex airfoil so there should be downward suction. Now will they FULLY deploy? Nope. But flaps 10 or flaps 15? Yup. Spitfire flaps for instance fully deployed to Flaps ~20 with zero input from pilot other than: deploy. Where Cessna door is a compression zone. Same Cessna door on rear half of fuselage is a SUCTION zone and would auto open partially(one reason P51 was faster than Spitfire for instance. It dumped its higher pressure heat into a suction zone decreasing fuselage drag and decreasing drag of the radiator(p47) partially did this as well(though by default rather than on purpose). Cheers @@rnordquest
All this time I thought the purpose of wings was to provide lift, but there's actually a region of downward suction, amazing lol. And I thought that the purpose of extending flaps was to gain lift by deflecting more air, which should give an equal and opposite force on the actuating linkages, boy was I a dummy lol.
I like the mechanism attached to the flap itself especially. The geometry of it means that you're increasing the force you can apply to the flap as it extends further out into the airflow (and so would be harder to move manually).
Love the shared decision making process and explanation on the "why" about this channel.
One thing that's great about aero is that butt math and intuitions conceal the actual complexity of what's involved (leading to myths and misconceptions). I'm impressed at your guys' ability to condense these really complicated subjects down to something digestible and understandable.
This is a fantastic learning opportunity for all of us.
One of the advantages of the split flap is that the separation bubble stably extends the pressure recovery aft of the airfoil trailing edge into the freestream, allowing the upper surface pressure to stay below static as opposed to having to recover to near stagnation. We (NASA) used this aspect to design a wing for a glider for Mars exploration; it was to be folded up in an entry capsule, then released to fall away and unfold. The flowfield conditions presented during pullout were challenging - transonic Mach and low Reynolds number. We found that a split-flap design maintained the high CL capability needed to achieve the pullout maneuver even under these conditions. Of course, the relatively high drag was also advantageous, as it would slow the glider and give more time for the pullout to occur.
Fowler flaps: we have them guite often on ultralight airplanes in Europe, for instance Risen. In Italy they make the ultrafast two seat aircraft called Risen. Please note, with 100hp Rotax they guarantee the top speed at sea level 320km/h (173knots) and with turbocharged Rotax 915 -142hp they guarantee maximum cruising speed at 16 thousands feet 450km/h !!! (243 knots ) !!! Will Dark Aero be able to achieve the same velocity with much stronger engine ??? Risen has got the ultimate aerodinamics IMHO. Extreemly efficient and it is all carbon fiber too. What I like about Risen compare to Dark Aero, that Risen is not using any metal(aluminum) honeycomb, but rather materials which can never ever rust.... On the other hand what I like about Dark Aero is the gear(looks strong) and the 2 baggage compartments.
My Cessna 182 had Fowler flaps. They moved rearward significantly before descending downward.
Flap position 1 is 10 degrees deflection. It is the only flap position that extends the flaps trailing edge outside of the basic wing planform. At full 40 degrees, the flaps are definitely not projecting past the trailing edge. A true fowler translated the leading edge of the flap rearward to the trailing edge of the basic wing. Which is about 300% farther aft than a Cessna.
All slotted-flaps must translate aft to open the slot. As the slot gap has to remain about the same for each deflection angle, it cannot simply open more and more with angular deflection. It has to open the slot rapidly to its defined point before deflecting.
The proper technical term for Cessna flaps is "Slotted Flaps with Fowler Action".
@@Triple_J.1 You are just making stuff up. The definition of Fowler flap is that the flap moves rearward as well as downward. There is no requirement that it move to the trailing edge of the wing. Slotted flaps rotate, but don’t translate. Fowler flaps translate and rotate. Cessna 182 flaps are Fowler flaps. End of story.
@@LTVoyager It looks like Cessna has used Fowler flaps (with rearward translation, although not much) since the 170B of 1952... and the same design continued through the 172 and 182.
I'm excited for flight testing, and I'll be interested to hear how the flap deployment feels in flight.
It's been a long time but the finish line is in sight.
this channel is top notch. what you all have built is so impressive
I have seen almost all of your videos and they make me glad and amazed,as making an aircraft needs to know several fields of science and knowledge's and you have all of them together.
Your job tells me that you were good students and are very qualified engineers now.
Congratulate.
I’d always thought that split flaps just created more drag versus lift when extended. Thanks so much for this detailed explanation!
Hi. One thing you mentioned was sealing. The gliding community have always been ahead in this area and use Mylar sealing and turbulating tapes. I have an 18 metre flapped Schempp-Hirth Ventus and it is sealed and turbulated within an inch of its life. A gliding buddy of mine has an RV in which he set various records in, including the elapsed time London-Cape Town-London record for a 200 hp aircraft. That is beautifully taped; everywhere! Have you considered what tapes you will use? I’ve attached a link to the first glider supplier I found. I live in the U.K. and have no connection with the company, but their site has a great selection for you to browse. Just a thought. My mate’s RV is impressively fast with a stock engine. But there’s not a gap an air molecule could squeeze through! I notice that the ailerons don’t yet seem to be sealed.
One of my biggest surprise when transitionning to the PA-28 Archer was my intstructor asking me to do a flaps up circuit and landing. He asked me at what speed I would fly the circuit and landing and I was all bent to say for sure faster than the regular speeds used traditionally. That's when he told me just fly the same speed as normal no need to fly faster just the attitude will be more nose up and power setting would be different. The "flaps enable slower speed" is really only true for the stall speed (a few knots of difference as per POH) but as you would never fly that slow anywhere in normal flight that wouldn't do any difference.
Another aspect of the marvel that Concord was is that it had no lift augmentation devices at all, neither leading or trailing edge. Low speed flight was achievable because of the double delta wing, same as the Space Shuttle.
Interesting and informative explanations. You might consider getting rid of any background 'music' or soundtrack. It is really distracting, serving only to make it a little harder to concentrate on, and understand, the narration.
DC3 had split flaps as well. Very informative video.
Are you sure? I’ve ever been up close and personal with a single DC-3- and it didn’t have flaps. Looking at photos of planes on the web, and I don’t see any indications of flaps- but, admittedly, all those photos are from the top, so for a split flap, wouldn’t see anything!
@@dphuntsman Plenty of photos of the DC3 flaps extended on the web. Unusual in they extended under the fuselage as well as the wing.
With a little change in geometry you could have gotten more leverage at the handle over the flap as it approaches full deployment rather than less. As it is, you have most leverage when it's not needed, and least when it would be nice to have. We do this on big heavy RC sailplanes to avoid breaking the servos when the flaps are fully deployed just in case we don't get them up before touchdown. For you it'll just be a matter of the flaps feeling really heavy at full deployment.
That was one of my thoughts - a 30cm deflection of the flap handle has to extend a relatively large chunk of wing into high speed wind. Gonna be tricky for sure to balance the forces with any possible spring assist.
@@frollard I'm not talking so much about the simple flap lever to flap angle ratio, but the way they've clocked the positions of each end of the linkage relative to each other. There are ways to set it so that you start with more leverage over the flap and end with less (control lever initially moves faster than surface, then slows down to match its speed) which is what they've done, or you can set their relative positions so that you start with less leverage (when you don't need it at low flap deflection) and gain leverage as you move it further (moving arm faster than flap).
Riley's presentation was great. Although I don't usually get much fired up about the new composite airplanes, I wish you guys well on this venture (certainly no pun intended!)
I hope that handling qualities are as important as performance to you guys.
When will you fly? It seems like progress has been very slow of late. Can’t wait to see your fantastic aircraft airborne.
Is there a concern about the force required on that short handle to activate the flaps? Just looking at it has me a little concerned if there is an attempt to open the flaps at any relevant speed. (Even at a 50kt airspeed, there would be a pretty high torque because of the surface area of the flap.) It seems to me that this is also why most older aircraft I have seen with manual flaps have relatively long handles.
Fowler flaps are often on Ultralight aircrafts In Europe. For instance in Italy they make the ultrafast two seat aircraft called Risen with fowler flaps.. Please note, with 100hp Rotax they guarantee the top speed at sea level 320km/h (173knots) and with turbocharged Rotax 915 -142hp they guarantee maximum cruising speed at 16 thousands feet 450km/h !!! (243 knots ) !!! Will Dark Aero be able to achieve the same velocity with much stronger engine ??? Risen has got the ultimate aerodinamics IMHO. Extreemly efficient and it is all carbon fiber too. What I like about Risen compare to Dark Aero, that Risen is not using any metal(aluminum) honeycomb, but rather materials which can never ever rust.... On the other hand what I like about Dark Aero is the gear(looks strong) and the 2 baggage compartments.
Love the simple and elegant design.
Design simplification is an art form.
The most common Cessnas, like the 172 series use Fowler flaps, not slotted flaps. However, the Piper Cherokee series has slotted flaps.
When do you expect first flight
Two comments, 1) A big disadvantage to fowler flaps is the change in the center of lift. That can be mostly mitigated by adding leading edge devices. Of course that adds complexity but worth it on some aircraft. 2) Aluminum structure complexity can be greatly simplified especially for a simple part like a split flap by using a foam core and bonding aluminum sheets for skin. I've done this a lot and it's much more simple than a composite layup or molded composite part.
Fowler flaps are often on Ultralight aircrafts In Europe. For instance in Italy they make the ultrafast two seat aircraft called Risen with fowler flaps.. Please note, with 100hp Rotax they guarantee the top speed at sea level 320km/h (173knots) and with turbocharged Rotax 915 -142hp they guarantee maximum cruising speed at 16 thousands feet 450km/h !!! (243 knots ) !!! Will Dark Aero be able to achieve the same velocity with much stronger engine ??? Risen has got the ultimate aerodinamics IMHO. Extreemly efficient and it is all carbon fiber too. What I like about Risen compare to Dark Aero, that Risen is not using any metal(aluminum) honeycomb, but rather materials which can never ever rust.... On the other hand what I like about Dark Aero is the gear(looks strong) and the 2 baggage compartments.
This is good, and explains DarkAero's reasoning well. For a extensive overview of flaps, Wikipedia has a good article under "Flap (aeronautics)".
There are a lot of wanna-be engineers out here on youtube, but you guys seem to really know your stuff.
You showed the pros and cons and your choice makes completly sense to me.
It would have been nice to hear an opinion why the big 2 choose fowler flaps for their big birds (I'm just a regular mechanical engineer for farm equipement; this topic is really interesting, but I have no idea what to make of all the possible choices).
again: great video! loved it!
Airliners need far more effective flaps with substantial chord extension and effective wing area increase to create viable configurations for takeoff and landing from a wing optimized for their cruise speed. The speed range of anything with a piston engine - even the DarkAero - is much narrower so less effective flaps are viable.
I have always thought of most Cessnas having Fowler flaps as they extend as well as droop.
I’ve seen plenty of discussion about that online. We were taught they were “slotted Fowler flaps”, I think the manual only refers to them as slotted flaps. A quick google says the wing are increase is only just over 4%. I guess it’s one of those topics to throw into a group of pilots then sit back and watch the arguments lol
Yes, @@electricalmayhem, it is a short-travel design in those Cessnas.
I see most of what you are getting at, It depends on the intended type of field used by the aircraft. If you will always be at runways with nice clearways then you may only care about getting maximum lift to reduce touchdown speeds and reduce stress on tires and gear, drag can be modest.
If you plan on locations with steep final approaches to shorter runways, then energy management is more of a concern than minimum touchdown speed and adjusting drag is more important than lift.
A generally versatile behavior is for a small deflection to add some lift with minimal change in L/D (Maybe even a slight improvement over the clean wing.). Then as flap angle increases a rapid increase in drag relative to lift. (Gliders take it to the extreme of adding spoilers to the top of the wing.)
This doesn't require ideal flap behavior of course, as long as the flap design is "good enough" then the cruise and manufacturing concerns, that were mentioned in the video, become major factors.
Interesting! Another composite plane that has a split flap is the TL-Sport Sting!
Always excited to see more DarkAero progress!
There is a great version of the legendary Libelle glider with those flaps. With the additional airbrakes it had a maximum descent angle of 1:4, strong ground effect and strong deceleration it was great to land on very short strips. I loved it!
The CAD work is super impressive. Can you estimate how many hours you've spent building the assembly of the whole plan in on shape?
Thank you! All the modeling work has been an endeavor of its own. Not certain on the total number of hours put into that effort but it’s on the order of 1000’s.
@@DarkAeroInc. Hi from across the pond. I graduated 51 years ago in Aero Eng and Design. My final year project was Foam Stabilised Compression Panels. I used used 20 gauge Al skins and a 1 inch polyurethane core . I wrote to De Havilland for advice and they supplied the adhesive free !! Subsequently I proved mathematically that the Southwell Plot could be used to predict the failing load , in compression, for this “weak in shear” structure. My tests indicated that this could be the case , but at a review in front of the whole course, I was rubbished by a lecturer , that my results were a coincidence and the Southwell Plot only applied to structures in compression which were weak in bending. This humiliation triggered me big time, and after a struggle I proved mathematically that I was correct.
So…..how have you tested that your design is structurally sound.
And….your design looks really “hot”. How do you propose to conduct stall and spinning trials ? Are you going to fit an anti spin chute during these trials, just in case !! You would be wise to do so. Do you intend to fit leading edge “triangles” inboard , to ensure you get tail buffet stall warning ?
Great video by the way. Such a clean design will produce a very flat glide angle I imagine. If you have a flap linkage failure say, will you investigate during flight testing , the use of sideslip to increase your descent rate ?
Great flap discussion. Just a minor nit: "The split flap comes out on top of the split flap when it comes to drag for a particular lift". The graph shows you mean the split flap has a better (ie lower) drag/lift ratio, so it's "on top" in performance, ie desired. However, the statement, especially if the graph were not there, could also imply the opposite: that the split flap has a higher drag/lift ratio (numerically "on top" of the simple flap) and thus is less desirable than the simple flap.
Sees like high drag flaps would be desireable on an airframe this light and streamlined, it's always good to be able to get down when you want to
They have a split rudder so there is a little bit braking in the air, and you can control how much you want
Yes, the split rudder is intended to be used as a speed brake,@@minorlion1327. If drag is needed, it has the advantage of causing minimal pitch change... unlike the split flaps.
Working on getting my ppl and I dream to one day get a experimental kit aircraft and I’m definitely keeping my eyes on you guys! A zenith is cool but I’m honestly a low wing type of guy and I love the design, look, and performance of this aircraft. Keep it up guys 😎
This information was very useful for me. Thank you very much.
,any decades ago I worked a lockheed with early composite materials and some I suspect are not open source as yet but I'm glad they are in wide use today so widely I always thought them quite amazing in testing !😊
I noticed the projected rated speed of the aircraft will be around 230knots, will you need static whicks with this composite flap aircraft for less noise, interference in your electronics and in comms?
I'm curious if you'd taken a look at assymetric flap deployment versus aileron authority. If any of the linkages were to fail in the flap system, is there sufficient aileron authority to counter the roll until the other flap can be retracted? I don't think it's a likely failure mode but with you attention to detail I'm just wondering if you've examined it.
One does this in VERY high speed aircraft where flutter is the biggest problem, or sometimes in sailplanes where once again, flutter is the biggest problem. In low speed aircraft this is not a problem. In civilian aircraft with their wings full of fuel, once again, flutter is a big problem and due to $$$ of such aircraft, they can afford to have multiple roll capabilities. In their case, they LOCK OUT aileron movement except at LARGE stick deflections and they still allow down aileron, it is not just UP aileron. Of course swept back wings helps here as well so... This is essentially impossible to do on a mechanical only simple aircraft design. Even the commercial boys have a SMALL flap behind the engines providing roll controll and the main flaps DO NOT move for roll control.
@@w8stralNot sure what flutter has to do with any of this. Nor was I suggesting using the flaps for roll control. I was asking that, if in the event of a linkage failure resulting in an asymmetric flap deployment, was aileron authority sufficient to maintain control.
I'm guessing that wouldn't be a high priority design consideration. I know from my flight training on a C172 to expect that an asymmetrical full flap deployment would too severe to fight with aileron control at all. I doubt many other pilots received training quite as terrifying as mine was but it should be pretty well ingrained that the pilot should undo the last flap adjustment if that failure happens.
I thought that was obvious so answered you in a different way. Ok, here goes, basic algebra time and WHY flaps are NOT considered primary flight control and why aircraft can LOSE a flap and still land with flaps down.
Aileron CL max is? ~2.5 or so(tip stall territory and you die anyways so... not cool), but when problems occur is possible. Percentage of wing ==? Looks roughly 30% Flap Cl goes to max of? 2.3 percentage of wing = ~60%. Wing CLmx ~0.8-->1. Lets call it 0.9. Lever arm length to CG
Moment Flap = 2.3-0.9 = 1.4* center of flap lift @30% or ~0.42.
Moment aileron = 2.5-0.9 = 1.6* center of aileron lift @75% = 1.2
1.2 Aileron >> 0.42 Flap
Losing a flap or one flap stuck down is ANNOYING, no question, and you will have to LAND faster to compensate for loss of lift, but it is not a death inducing event like losing an Aileron. If you lose an aileron: Bail out because if you are in the aircraft when it crashes--> You are dead 100% of time, if you bail you have a 0.00001% chance of living but slightly possible if over water, or fly with a parachute.
@@billstrahan4791
Yup, decreasing the half flaps deployed that are down will decrease your landing speed as one has less downward lift from ailerons on opposite side. @@waywardscythe3358
Krueger flaps. They increase camber too, like all other flaps. They just do it at the leading edge. This is not to be confused with things like Slats and Slots that do not increase camber. There can also be a hybrid Slat/Krueger flap. More types are probably out there that are only found on certain aircraft for unique circumstances or situations like flaperons. Ailerons that also function as flaps.
In applications such as gliders, where drag minimization is most critical, the plain flap can be reflexed, thereby reducing the drag at the best glide speed.
Guys, did you consider placing the torque tube coaxial to the flap pivot? In this case it seem to have more reliable mechanics. At least now if one of the links fail there would be differential lift created, which could be very dangerous obviously
They presumably want more mechanical advantage. In that design, the driving torque tube would rotate very little.
Let's go! I've been refreshing your page everyday for the past week 😂.
Excellent video. I don't quite get to the "biggest myth" part, - I suppose it's the high drag assumption - but I love the factual nature of the presentation.
Aerodynamics for Naval Aviators supports your comments on flap types and their drag and lift charicteristics.
Aerodynamics tells me with the hinge point fixed at the front of the flap, when the flaps come down the trailing edge will effectively come forward thereby decreasing the mean chord. CoP will come forward (relative to CoG) reducing the relative moment arm and inducing a pitch-down tendency requiring nose up trim. That will be interesting to see confirmed during flight testing.
I think it is just super cool that you share this with us all. Thank you.
Nice update gents!
Does the center of lift move back when the split flaps are deployed? (A Mooney characteristic)
If no…. No trim change required with deployment.
If yes…. Trimming while deploying flaps at the same time and rate, is nice…
Safety opportunity…. Nothing worse than flaps accidentally retracting. Fast uncommanded retractions can be extra hazardous, as the stall speed may exceed the current airspeed without warning! (Hand slips off the handle, position lock not engaged)
Split deployment… is there a way that the flaps can accidentally deploy or not retract on one side and not the other?
A few minutes during the transition training should cover how best to use the flaps, trim, and what to avoid during slow flight.
😃
Get that thing flying!!!🆒😎👍!
For fighter aircraft a lot of designs had maneuvering flap position so the split flap would be at low deflection and cause drag. Hurricane and Spitfire only had two flap positions - extended and up and predictably used split flap.
what a brilliant overview of flap types, bravo.
In terms of slipperiness, the closest thing to your design I've flown is the Comanche (not that aerodynamically clean). With the Comanche I'll take all the drag I can get for descents. You are coming towards you destination at cruise altitude, say 12K feet. In the western US the airport is often located on the valley floor and surrounding hills limit your ability to descend early. You start your decent at say 500- 1000 fpm. But your air speed starts to approach VNE limiting your decent rate. You end up having to fly longer patterns aligned with the terrain to loose altitude. That sort of defeats the purpose of flying a fast plane to arrive sooner. Anyway, I wish the Comanche had drag devices I could deploy at higher speeds. The gear helps once you get slowed to a speed you can deploy it. but there you are again fly a fast plane slowly.
Been following for a long time….y’all ever gonna fly this thing?
I have an AMD CH2000 with split flaps. It is not a lift device. It is a drag device. POH calls for zero flaps on short-field. A few times I’ve forgotten to retract flaps after landing and I can feel the drag on takeoff; the controls become very heavy. If you stop by Houston, I’d be happy to let you fly it to see what I mean.
Simplest fowler flap design Ive seen is on the Aviat Husky, which came from the Callair.
Split flaps on the early C-310s.
Fowler flaps are often on Ultralight aircrafts In Europe. For instance in Italy they make the ultrafast two seat aircraft called Risen with fowler flaps.. Please note, with 100hp Rotax they guarantee the top speed at sea level 320km/h (173knots) and with turbocharged Rotax 915 -142hp they guarantee maximum cruising speed at 16 thousands feet 450km/h !!! (243 knots ) !!! Will Dark Aero be able to achieve the same velocity with much stronger engine ??? Risen has got the ultimate aerodinamics IMHO. Extreemly efficient and it is all carbon fiber too. What I like about Risen compare to Dark Aero, that Risen is not using any metal(aluminum) honeycomb, but rather materials which can never ever rust.... On the other hand what I like about Dark Aero is the gear(looks strong) and the 2 baggage compartments.
What CAD are you using? Great explanations. Thanks a lot!
Could you link the video your sampling the airfoil smoke demos? I've seen these stills before but can't find the source video.
Fowler flaps: we have them guite often on ultralight airplanes in Europe, for instance Risen(from Italy) , or Stream(from Czech Republic). In Italy they make the ultrafast two seat aircraft called Risen. Please note, with 100hp Rotax they guarantee the top speed at sea level 320km/h (173knots) and with turbocharged Rotax 915 -142hp they guarantee maximum cruising speed at 16 thousands feet 450km/h !!! (243 knots ) !!! Will Dark Aero be able to achieve the same velocity with much stronger engine ??? Risen has got the ultimate aerodinamics IMHO. Extreemly efficient(crossed Atlantic from Africa to South Anerica using 200l tank only) and it is all carbon fiber too. What I like about Risen compare to Dark Aero, that Risen is not using any metal(aluminum) honeycomb, but rather materials which can never ever rust.... On the other hand what I like about Dark Aero is the gear(looks strong) and the 2 baggage compartments.
Great discussion and Explanation…always thought split flaps were a simpler but cruder solution…and they’re not!
Great overview guys. Class job.
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How much force to deploy landing flaps?
Looks like the individual cranks for the flaps are at the root of the wings. What about locating them at the center of the flaps so there would be less twist force on the flaps (and their hinges) and also have half as much of a longitudinal chord in the flap which may help with flutter from such a long span.
The flaps are stupid lightweight. Probably five pounds, at most. The heaviest parts of the flap mechanism are all internal to the fuselage, so leverage is still as high as possible while minimizing the moment of inertia in the wings themselves.
@@spdcrzy I'm not worried about the weight of the flaps. The aerodynamic force on the flaps is much greater than the weight of the flaps.
@@davidchow9528 that's the question though - will it be, really? Even if it's five hundred newtons per flap, I doubt it would be an issue. And I don't think anybody has ever done a full carbon fiber flap with carbon fiber IN the linkage - it will likely be more than stiff enough to prevent torquing in any way.
@@spdcrzythe concern is not just the force but also flutter. the carbon fiber for sure is stiff enough but what about the hinges and bond points. the greater the chord the higher the likelihood of flutter especially at lower speeds. to me attaching the crank mid cord makes the most sense. But what do I know I didn't do any analysis. Just bringing up an idea for the dark arrow team.
Where is the space for a crank in the wing?
great video, do you have an idea of the forces that the mechanism to lower and lifting the split flaps are experiencing?
Excellent.. By the time you are done, I'll be a fully accredited Internet aeronautical engineer!
Please do a total fancial Cost analysis
Thank you for the excellent synopsis on Flap types. Might you know if split-flap designs might be inherently different at high extension angles to Fowler design as far as L/D? I was reciently chatting online with other pilots about the how the early model Cessna 310s had a pronounced loss of lift (not stall) on landing if throttles were reduce below zero thrust, and the Beech Barons like the B55 model with Fowler flaps much less. Both were similar wing-area, airfoils and weights.
I've been wondering if you have a schedule to complete all outstanding air-frame tasks and get into flight testing.
I know by "deflection" you mean that the flap is angled downwards ...
However, I wish people addressed how it manipulates the airflow:
It must also deflect air as a lift source & can't just be pressure differentials.
Beautiful plane, best wishes to you for success. Just some thoughts. Your video shows a flap actuator attached only at the inboard, with no attachments or push rods along the span of the flap. I suggest looking at significantly beefing up (metal Plate) the flap control surface, especially in the zone where debris could be kicked up from the wheels into the flap control surface. perhaps a torque tube extending the length of the flap with multiple attach points. Also, if the flaps get stuck down, is there sufficient power and control authority to execute a go-around? If one flap control surface broke and retracted with the other extended, is there sufficient control authority to manage?
A question if I may! On the split flaps. Technically you have two cord lines when the flaps are lowered? How is that affecting the flight characteristics.
How about stall speed for each flap design in same wing and AoA? Is there any different. And what DA1 project design landing speed and runway requirement?
wait..... that wasn't very specific about what was nest at the end lol. so what exactly are you going to ground test first? I am very curios and excited for your project!!
It would be greatly helpful if you would specify the maximum split flap deflection for CL max.
Johnson bar for the win!! I strongly prefer manual flaps on a small plane like this.
Interesting that you would look at the reduced drag in a split flap verses the plain flap as a goal, when one of the goals with flaps, I thought was to increase lift and drag? Cheers!
I guess a lower drag to lift flap would be better for takeoff purposes.
@@watashiandroid8314most light aircraft can take off less distance then landing. And in a slippery plane like this one you want to be able to increase drag for landing and easier approach, for example in gliders using airbrakes.
@@electricalmayhem of the 6 light aircraft I have flown enough to be familiar with, maybe one could take off in a shorter distance than it could land. Brakes tend to be far more powerful than the engine in a light aircraft, and from what I recall, most light aircraft can land in a shorter distance than they can take off in.
The 6 aircraft I've flown enough to talk about: Cessna 150M, 152, 172M, Aeronca Champ (O-200), Bellanca Citabria (O-235), Super Decathlon.
The one aircraft which I think can take off in less distance than land is the Super Decathlon.
@@watashiandroid8314 Hmm you are right for GA aircraft, looks like I've been spoiled with microlight/Sports aircraft which are fibreglass with Rotax 912's giving a good power to weight ratio! (WT9 Dynamic, Rans, Vans etc) Been a while since I flew a cessna.
just have a separate air brake that is big and deploys on touch down@@electricalmayhem
If the split flap has both less drag (both in cruise and deflected) and more lift... what's the advantage of the plain flap? It doesn't seem simpler.
What is the area of the flap, and what is the expected torque and force that you have to apply to the flap handle?
They explained the structural advantage of the plain flap for conventional built-up aluminum construction in the video.
Is there eventually going to be a flap indicator for the split flap similar to the spitfire since you cant see the flap position from the cockpit? Incase of malfunctions l.