B-17 Bomber's Engines and Propellers Explained
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- เผยแพร่เมื่อ 29 ก.ย. 2024
- The intent of this video is to provide an introduction to the WWII B-17 bomber's Engines and Propellers.
Topics include:
1. B-17 Bomber Wright Cyclone R-1820-97 engine factoids
2. B-17 bomber Hamilton Standard propeller
3. B-17 bombers propeller feathering capability
4. B-17 bombers propeller anti-icing system
5. B-17 bomber engine turbocharger, supercharger and inter-cooler functions
Just a terminology note: The propellers were not just variable pitch, they were constant speed. The normal mode of control was not that the pilot varied the pitch, but that he set the desired rpm with the propeller control lever. The system automatically and continuously varied the blade pitch to keep the engine at the set RPM despite changes in airspeed and throttle setting.
Thanks for that great description.
It might be a good idea to do a piece explaining the difference between a supercharger, and a turbosupercharger, and why the engines had both.
Greg's Airplanes and....
@@lamwen03 Exactly.
I read not long ago that when the FW190 whose single stage supercharger started loosing power at 15,000 ft was in pursuit of a B17 at 25,000 ft it's performance was down so low at that altitude that once it was in range of the B17's .50 cal tail guns it took around 2 minutes for it to close enough to where it would be in range to use it's 20mm guns, and any type of evasive maneuvering would cause it to lose ground, so if they tried approaching from the rear they had to sit in .50 cal fire for about 2 minutes before returning fire would have effect, how'd you like to sit in .50 cal fire for 2 minutes before you could shoot back?
The article claimed that it was the real reason that they adopted the head on attack, not because of the B17's lack of chin guns on the early model, that was simply an added bonus.
But the head on attack had it's own disadvantages the two biggest being that between the closing speed of the two aircraft being around 600 MPH you only had a couple of seconds to get shots off and only the best pilots at gunnery even stood a chance at getting hits and you only had one chance for a head on attack, the only reason they could do it in the first place is because they had adopted early warning radar which enabled them to already be at altitude and ahead of them, they only had one shot at it because once they made a head on attack and went through the formation they'd never get turned around and get back out in front of them again with their performance being so low at that altitude, especially considering that they'd have to arc around them at a safe enough distance that the B17's formations defensive guns couldn't effectively fire on them.
Supposedly the ME109's supercharger had better performance at that altitude than the FW190's did, so if they had a mixed force they'd use the ME109's to attack the bombers and meanwhile down below the FW190's would attack any stragglers or escort fighter's that got pulled down to that altitude engaging fighter's attacking the bombers.
@@dukecraig2402 The superchargers could be tuned for the altitudes they were going to be fighting at. But they had to be tuned on the ground. So if they suddenly had to fight at a different altitude, they were pocked.
@@lamwen03
Yea, but only certain types, the Allison's had different gear ratios, those could be changed on the ground or tuned so to speak.
Rolls-Royce chose to use different impeller sizes, those really can't be "tuned", in the case of those you need to change entire supercharger assemblies which, in my book anyways, doesn't fall into the category of tuning.
Now the hydro coupled superchargers like what was on the ME109 could just have the pilot move a boost lever to fine tune the boost for the engine's requirements at varying altitudes which is why they ran a little better at higher altitudes than the FW190 with it's supercharger that was mechanically driven and was optimized for medium altitude, the hydro coupled type however does have it's own drawbacks, primary is that it has more parasitic power loss, so a mechanically driven one will run better at the altitude it's optimized for but as you pointed out it's locked in to run best at that altitude, like anything else they've all got their in's and out's.
Whoa, you've put together a lot of episodes in just four months. Great work, very good presentations, decent detail and I really like your source supporting documentation and images.
That is an incredible amount of information. Great job.
On this type of propeller if the engine seizes or if the oil pressure drops off to zero the propellers could not be feathered, these were the hydraulic type of variable pitch propellers, and in all actuality they're not "variable pitch" propellers, they're actually "constant speed" propellers.
Engine oil and it's pressure is what controls the pitch, if an engine seizes or if it's oil pressure drops to zero the pitch cannot be changed.
During the war some aircraft like the P47 switched to electric propellers meaning it was an electric motor that varied the pitch, that way if something happened to the engine's oil pressure then the pitch can still be controlled and the props could be feathered, if a prop starts to windmill from the aircraft's forward motion it'll tear the engine apart because the engine's were balanced to drive the prop not the other way around.
And the way a constant speed propeller works is within parameters when the pilot would push forward on the throttle engine speed would not increase because as the throttle was being pushed forward and the engine attempted to increase it's RPM a governor in the prop assembly would automatically increase the prop pitch so it'd be biting more air and therfore put a heavier load on the engine, and the opposite would happen when decreasing the throttle, similar to when you go uphill in a car and you push the gas pedal down further but the engine RPM doesn't increase, or when you start downhill and take your foot off the gas and engine RPM stays the same (although with a car on a steep enough hill it also takes the brakes to maintain engine RPM's).
The pilot could change the parameters of the system allowing the engine RPM's to increase by decreasing prop pitch but after that any throttle changes would automatically change the prop pitch and result in the engine staying at the same RPM.
There's many good TH-cam videos that cover how constant speed propellers work, the difference between them and variable pitch propellers and the difference between hydraulic propellers and electric propellers, including one from Greg's Airplane's and Automobiles, his is an excellent video explaining everything about how they operate.
On the B-17 the oil for the engine come from a tank equipped with a stand pipe so that if an engine oil leak started pumping oil overboard there would still be oil in the tank to feather the propeller. There was an electrical pump that supplied oil to the feather mechanism in the prop that would twist the blades to the feather position. The drill to feather the prop was to push in the feather button switch. A solenoid would keep the switch engaged until the blades reached full feather and then the solenoid would release and the button would pop out and the pump would be deenergized. To unfeather the blades the same switch was pressed and manually held until the blades were unfeathered.
7 years working on B-17 Texas Raiders.
@@tfogelson3139
What about if the tank was shot full of holes or whatever and lost all the oil?
There's a video here on TH-cam that's an interview with a B17 pilot or copilot where he talks about their aircraft being damaged from a fighter attack and due to the loss of oil or oil pressure they couldn't feather the prop and it windmilled causing the engine to shake so violently the entire engine departed from the wing.
And did fighter's with the hydraulic pitch controls like some variant's of the P47 have that same system with the stand pipe?
@@dukecraig2402 If you lost all the oil in the tank, then you were SOL. You would not be able to feather. The tank is not armored and sits behind the engine. I don't know about the P47 as I never worked on them.
@@tfogelson3139
I get what you're saying about the stand pipe, I've always heard them referred to as a stand off pipe but I knew immediately what you were referring to, and I'll assume that the pick up for the emergency system with the electric pump draws from the very bottom of the tank.
The oil tanks on Harley's are the same way, the feed line for the oil pump comes off the bottom of the tank but if you have one off and clean it out and look down inside where the feed line hooks up on the outside on the inside there's a short pipe that sticks up about an inch, the purpose being so you're not drawing oil from the very bottom of the tank where metal shavings and any other type of contaminates settle to the bottom and build up, that was probably also why they did it on the oil tanks for the B17, having the oil from the top of the stand off pipe to the bottom of the tank acting as a reservoir for emergency use was an added bonus, that stand off design was especially important on those old Harley's back when oil filters were an option on them, hard to believe that there was a time when oil filters on an engine were considered to be a luxury or at least not a necessity.
Mad Max Road warrior taught a generations of kids like myself that you can turn off a kick ass supercharger when the fuel gets low.
Where can I find the airflow diagram? Great video byw, thanks.
Quick question? What kind of gear reduction did the engines use? do you have a diagram? Thanks for sharing.
How can the pistons be directly connected to the crank? They probably use connecting rods.
Nice videos good content thanks :-) (The Wright R-1820 was 1823 cu.in. or 29.88 litres).
Thanks, I always wondered why these engines has a turbo and a supercharger. One little suggestion: I wonder what the actual pressures and temperatures are at each stage on the air intake and exhaust process? How much does the inter-cooler actually cool the air? How hot is the exhaust?
th-cam.com/video/ULLsIo1VzTw/w-d-xo.html
How hot is the exhaust?
Well you wouldn't want to stick your finger in there.
PDH!!!
No, seriously, the temperature after the turbo depends entirely on how fast the turbo is spinning, at lower altitudes generally the turbo isn't even being driven by the exhaust, instead the exhaust is being routed out of the wastegate dump valve's, at the lower altitudes the engine's single stage supercharger can provide all the boost the engine can handle, as a matter of fact at sea level the throttles can't be opened up all the way or the supercharger will overboost the engine, around 7,000 ft or so is about the altitude that the superchargers were optimized for, in other words the throttles could be fully opened without the engine being overboosted, around 10,000 ft or so is where boost will start to drop, at this point the wastegate dump valve's will start to close diverting exhaust to the turbos spinning them up so they can start to feed the same air pressure to the supercharger that it had around 7,000 ft where it's optimized for, then as it continues to climb the wastegate valve's close more and more to divert more exhaust to the turbo spinning it faster to keep the inlet pressure at the supercharger at that sweet spot that it's optimized for.
The supercharger/turbo configuration that the US Army preferred on it's aircraft (B17, B24, B29, P38, P47 and some others) was a result of NACA tests in the mid 30's to determine what supercharger configuration produced the most HP at all altitudes.
The US Navy for it's own reasons selected the 2 stage 2 speed supercharger for it's aircraft, that type of supercharger doesn't produce maximum HP at the highest altitudes and also has a horsepower drop at medium altitude when it's shifted into it's high range because at that point it wants to overboost the engine requiring the throttle to be reduced, then as the aircraft climbs it hits a sweet spot where the throttles can be opened all the way producing maximum HP just the same as when it was in it's low range and climbing after take off it'll hit the sweet spot at a certain altitude, above that when power falls to a certain point at medium altitude it shifts into it's high range as previously described, but even a 2 stage supercharger in its high range still hits an altitude where it's power starts dropping off, with the turbo as a 2nd stage that altitude is much higher because of how fast a turbo can be spun.
Another bonus of the supercharger/turbo configuration is that each stage of a supercharger drags around 150 HP off of the motor, so when a 2 stage 2 speed supercharger shifts into it's high range it's losing another 150 HP driving the 2nd stage but since a turbo is a waste energy recovery system the engine isn't drug down another 150 HP to make enough boost for high altitude, with that system you only lose the initial 150 HP because of it's single stage supercharger.
The downsides are the turbo system costs more, is bulkier between the turbo and the ductwork needed for it and aircraft with that system have longer development times.
A classic example of that is the P39 and P40 fighter's, they were both supposed to have the supercharger/turbo system but everyone and his brother were screaming for aircraft so the turbos were dropped from them to speed up development time and get them into production.
As far as your initial question as you can tell everything happens at such varying altitudes and with temperatures that drop as low as -50° F at the highest altitudes that the temperatures after the turbo and how much the inner-cooler cools things would require charts to show those figures at say 1,000 ft intervals, both temperatures would be very different at relative sea level compared to 30,000 ft.
Hope all this helps and doesn't just confuse you.
Footnote; The B17's you see fly in airshow's don't even have working turbos on them, since there's no oxygen system for people in the plane and the engine's supercharger can provide all the boost the engine's can handle up to 10,000 ft there's no need for them to even have the turbos hooked up and have the expense of maintaining them, years back I was talking to a B17 pilot at an airshow and he told me they have the wastegate dumps locked open, as he pointed out they can't go above 10,000 ft without an oxygen system anyways and even if they had one for all the passengers nobody would be dressed for altitude.
@@dukecraig2402 Thanks for the in-depth explanation. I always wondered why some planes like the Spitfire had two stage supercharging while others like the Jug had the supercharger/turbocharger setup.
The pattern seemed to be that in-line engines tended to have the two stage supercharger while radial engines tended to have the supercharger/turbo, but not in all cases (the Lightning being one of these exceptions). I knew there had to be a reason for this, but I just didn't know what it was.
You've answered another question that I was always wondering about as well. Greg's planes channel did an in-depth dive into the turbo system of the P47, and I was amazed at the amount and weight of all the duct-work needed to get the turbo to work. It seemed to me that a two-stage supercharger would have been a much simple solution. Now that you've explained, and knowing that the P47 was specifically designed as a high altitude fighter, it makes perfect sense that they would use the solution that gave the best performance at extreme altitude. Thanks for all the info!
Excellent! Excellent! Excellent! Very good in-depth explanation!
Very good explanation. I learned a lot. Thanks.
Glad it was helpful!
Number one blasts away.
A check of all engines prior to takeoff to confirm oil pressure and magnetos with cowl flaps open to prevent overheating conditions.
Numbered from left to right from pilot seat number one the left most engine and last to start.
Number three the first to start as only one with hydraulic power for ship.
Inboard engines first as well for fire crews not having to walk through propeller arc of starting engines.
On the G model hyd power was provided not by #3 engine, but by the the hyd panel. An electric driven pump that was located on the stbd side of the cabin, the hyd accumulater and reservoir were on the aft bulkhead of the cabin. Hydraulic power was only used for the cowl flaps and the brakes. Brake lines ran thru a debooster that lowered the pressure for the expander tubes that pressed against the brake pucks that then rubbed against the brake drum.
Your Videos are very understandable even for those with little technical knowledge. Pretty tricky for a European to deal with inches and pounds though, but one gets used to it.
Can you make a video on the start-up procedure of the aircraft?
great video except for the dancing arrow, suggestion in my opinion ,
would be park the arrow in the area where you are talking about
instead of zooming it around....I spent too many years in corporations
doing audio visual shows with presenters doing the same thing with
laser pointers, the audience always gets confused....best wishes,
a subscriber and fan.....Paul
Thanks for the suggestion. I have greatly modified my TH-cam presentations. The engine video was one of my early pitches. Now I add a lot more graphics to isolate the talking point, no pointers, and I script the annotations. Lessons learned. I may go back and redo my earlier unpolished videos.
@@WWIIUSBombers well done.....and best wishes......Paul
Great vid, I’m putting a B17F model together from wingtip to wingtip little over 3ft long. Thanks to your vid it helps me understand under the engines an exposed exhaust pipe that leads to turbine but what I got from your vid they close the exhaust exit for they can recycle it. So my question is the only place I see to get rid of the left over exhaust is to exit out of the vents on topside of the wings because when I look at old photos it’s easy to see oil and exhaust stains on both sides of the wings 🤷
You pretty much covered everything I'm about to say, but just to be clear-
The Wright Cyclone R1820-97 Has a internal gear driven, single-speed centrifugal supercharger that produces above ambient manifold pressure, during all engine operating parameters. Its primary function is to increase engine performance regardless of altitude.
The turbocharger is a bucket turbine & compressor type. It's output is regulated through an exhaust bypass wastegate. It's primary function is to maintain manifold pressure based on altitude, allowing the engine to operate at peak performance, regardless of altitude. It typically isn't used on sea level take-offs.
In addition to a fully feathering prop and variable pitch blades, the engine also use a propeller governor. It's purpose is to automatically alter the blade pitch in order to maintain a specific engine rpm.
Engine Compression ration was 6.45:1
Bore & Stroke: 6.25" x 6"
Thanks for the video!
The radial, air-cooled could absorb tremendous amounts of damage compared to the very finicky inline-liquid cooled Merlin for example. One P-47 pilot landed his plane and his crew chief informed him battle damage had completely blown off two cylinder heads. The pilot said he didn't even notice.
How were the engines numbered on the B17?
Really good stuff here. Thanks sir
Love your videos.Great work and home work.
Very interesting, thanks!
Fascinating. Thanks
Why the high octane fuel when compression ratio was below 7:1 ?
you are sending compressed air into the cylinders raising the ratio.
The pistons are connected directly to the crankshaft by way of a rod, the same as any other piston engine.
Only one piston is connected to the crankshaft directly by a ‘master’ connecting rod, the other eight ‘articulating’ con rods connect via ‘wrist pins’ to this master con rod. This is to prevent independent con rod wrist pin ends from rotating with a floating crankshaft bearing and crashing against each other, the master con rod houses the main rod to crankshaft bearing and maintains the alignment of all the con rods with their cylinders.