The Complexity of a WW II P-47 Thunderbolt’s Powerplant (2015)
lynceans.org
lynceans.org
I'm hoping the DJI FPV goggles may come down in price over the next few years I hear the video quality and transmissible distance is incredible.
It feels like a big, heavy, complex machine compared to other WW2 fighters.
Here is a practice run using Track IR head-tracking showing the engine management simulation, including a mid-flight engine failure due to my ineptitude: https://www.youtube.com/watch?v=J_kAFi9G7-0
I always wondered with all that duct work running the length of the fuselage sending intake air back to the turbocharger, which then fed cooled air back to carburetors serving 18 cylinders, what enemy fire damage would do to this complex setup. Presumably this doesn't have single points of failure in a sealed compressed air system but it almost feels like race car level tuning for optimal performance, let alone for limping home with fuselage damage.
I recently had a pressure leak on my turbocharged car on the air intake between the turbo and the block. It seriously wrecked the performance. The engine was close to stalling and my gas mileage dropped by half. These big radials aren't quite as picky, but I bet you'd still feel the difference.
The downside was that even a small rifle caliber hit to the cooling system caused the coolant to flash to steam and rapidly escape through the hole, giving the pilot only minutes until the engine seized.
Conversely, the German fighters of this era were much more heavily automated. A Bf 109 pilot had a throttle lever: RPM, mixture, and radiators were controlled automatically (with manual overrides available).
If you ever look closely at the P-47's throttle quadrant, you'll notice one small feature that's pretty interesting. There is a one-way gate on the throttle lever that catches the RPM lever as it's advanced, precisely because without it, it was too easy for a pilot to (in the heat of combat) shove the throttle forward without adjusting RPM and blow the engine apart.
For contrast, one time he was in a P-51 that swallowed a valve, and he said he was lucky he was over the airfield, as that airplane was going down promptly. The P-51 had a much more fragile engine, I wouldn't want to fly one over water.
He was forced to land immediately.
The story was more about the P-47. He was nearing the airfield (again!) when the valve broke loose. He was asked by the tower if he could do another lap of the airfield and give someone else priority in landing. The vibration wasn't so bad, so he said "sure".
After landing, the chief mechanic called him over and chewed him out for doing the extra lap. The mechanic showed him the engine, which was just turning rubble.
He was a B-17 navigator during WW2. On one mission, one of the four engines was hit by flak and stopped. The pilot talked to the crew, saying they had a choice. Three engines meant the B-17 couldn't keep up with the formation, and would get picked off by the trailing Me-109s, so they would preemptively bail out over Germany. Or, they could drive the 3 engines way past their rated power, and pray they kept turning for the many hours of the return flight. They risked crashing into the Channel.
They chose the latter, the engines held, and they landed back at base (the engines were scrapped).
I have my dad's "Lucky Bastard" certificate, he earned it :-) He passed away a few years ago, I doubt there are more than a handful of WW2 aviators left.
http://generalatomic.com/jetmakers/introduction.html
So, yes!
He really liked the F-86 Sabre.
You're right, my dad had a great life. When people would ask him "how are you?" he'd reply "shot at and missed!"
In the olden tymes, ordinary lusers were able to turn the machine's dial past 10..., knowing that their account might be terminated.
Now all that's left is excel.
The FADECs have a control panel, where universally there's a button for "screw the engines, give me power". Required for things like losing one of two engines immediately during takeoff, or having to do go-around on one.
Dead stick touched down on the runway.
Got chewed out for saving the airplane instead of his ass.
He admitted to me decades later that he should have bailed out, but had never done so and was afraid of doing it.
I’m guessing neither of those applications care too much about turbo lag or throttle response.
Back in the 90s (and maybe still, I've lost touch) rally cars used to do off throttle "anti-lag" by using the direct fuel injection to pump fuel into the cylinders during the exhaust stroke, so it'd burn in the exhaust manifold and keep the turbine spinning to make boost without needing the engine to be creating torque by burning the fuel in the ignition strokes... They had less hard requirements for gradual application of torque than circuit race cars though, they mostly wanted to be able to get back on the throttle exiting a corner and immediately start spinning all 4 wheels again.
This ties in with a question I was asking myself after seeing this impressive setup: did anyone build a skin surface intercooler? I seem to remember reading about at least one plane that had its oil cooler in the skin early in development until they accepted that the added vulnerability was worse than the drag from a conventional box radiator and abandoned the idea. But with the intercooler the tradeoffs might be very different. You could even add a bypass mechanism for when the skin/cooler has become so leaky that the engine has effectively become naturally aspirated and turbo without intercooler would be an improvement.
Off-topic: Although I’m very into green energy, I have a love for these extremely large displacement engines and their insane power output. You can go nuts on YouTube with this.
- large radial engines like this one
- large train engines going north of 5000 - 10000 horsepower
Love the engineering, the size and sturdiness, the sound. Amazing technology.
He really nerds out on the engineering and flight details and pulls out NACA charts to illustrate. The complexity of getting good performance out of WWII airplanes was immense because the air pressure changed with attitude.
The channel itself is just amazing.
The DB 60X engines that powered the German Bf 109 had an ingenious system with an oil filled clutch, where depending on the oil level there was a differing amount of slip. So they got an optimal level of boost pressure at any altitude (up to the limit where the supercharger was full on, of course).
I don't have any dates for these usages.
Edit: that p-47 powertrain is an absolute beast!
> "turbine supercharger", whether driven by the crankshaft or by the exhaust.
made it sound like there's "crankshaft-driven turbine superchargers", which I stumbled over.
If you look at super chargers they're all some kind of pump driven by the mechanical energy directly from the crank. If this pump was a turbine, then you'd have a crankshaft driven turbine super charger.
So this is half of a modern turbocharger (the compressor) being driven by the crank rather than the exhaust gasses.
That's incorrect, a turbocharger has one turbine, and its driving counterpart is the impeller. That impeller/compressor is never referred to as a turbine. Turbines can only ever extract work from a fluid.
Superchargers as well as turbochargers also don't have pumps, those are machines for which the working medium is incompressible (water, ...; density is not a function of pressure, in "engineering precision"). If it is compressible, it's a compressor: it affects not only an increase in pressure but also in density.
A fan also works on compressible media but is only supposed to impose some velocity. For this, it necessarily also increases the medium's pressure, but to a low degree, such that (IIRC) changes in density are negligible.
Never is a strong word though and there are such things as turbine pumps which are not true turbines[0]. As far as I can tell they've never been used for engine applications.
Regarding pumps they operate on a fluid, of which air is definitely classed as. [1]
[0] https://www.globalspec.com/learnmore/flow_transfer_control/p...
But I'm posting this to say thank you, I was completely unaware of this detail. In my mind, and likely in GP's mind, the term pump was characterized by the piston principle, not by the medium. And I realize now that the "pumps for air" incorrectness is much less common in English than in German (my home language).
Apparently in engineering German the distinction is exactly the same as in English, but it's completely absent from common usage. German never even adopted a verb for high pressure inflation that is not derived from pump. Other than that, the terms pump and Pumpe are extremely similar in English and in German, which is unlikely due to common Germanic roots but because of something much more recent. I suspect nautical terminology which must have been a strong language unifier before navies became a key element of national separation.
This means there are not two distinct binary categories of pump or compressor that these things can be neatly classified as. This is compounded a little as fluids are often erroneously thought of as only incompressible fluids like water without realising it's a much bigger category.
Due to my brainfart regarding turbines, I assumed the GP had misunderstood the mechanism of action so I used the simpler word pump to explain. It is not incorrect to describe the action of a turbocharger as pumping more air into the cylinder, especially in my native dialect of English.
Agurk has a point as well.
All I know and was saying that in my field (engineering thermodynamics... in some sense the field on this topic), people feel very strongly about "compressor -> compressible fluid" and "pump -> incompressible fluid" (and the "fan" stuff).
A crankshaft driven supercharger doesn't need a turbine (a device that extracts power from a fluid), only an impeller (the opposite).
A Veyron engine puts out about half the HP using 17% of the displacement on worse gas. You can't even buy 130 octane gas anymore. The Veyron is a notorious fuel hog, but it has nothing on a twin Wasp radial.
That being said, modern metallurgy really revolutionized ICEs. Followed by computerized control.
This whole discussion makes me think what would a modern maxed out aircraft piston engine be like!
At least, that's what I found in brief investigations long ago when I was interested in the idea of a wankel rotary powered plane.
https://youtu.be/EyPvpdy4dgg?t=117
IIRC, piston speed was an issue in how fast these engines could run, as, for given RPM, the piston speed is proportional to the stroke. And, for reliability and the corresponding safety reasons, aero engines are more conservatively designed than most car engines.
Putting car engines into recreational aircraft has been popular over the years, but never really 'took off', with high failure rates from being run at consistent power levels way past their design goals. The best conversions are high displacement naturally aspirated engines that end up looking remarkably like the existing Lycoming/Continental aviation engine installations.
Not at 45,000’ altitude it doesn’t.
And that Veyron engine won’t be too happy running at 80+% of its rated power level for more than a few minutes at a time.
This is the part that a lot of people are unware of when it comes to engine power ratings --- aviation engines are designed to run at their rated power continuously, while most passenger car engines aren't. Even comparing a truck engine with the latter has people confused at why the power numbers seem so small both absolutely and relative to displacement. A 9L engine in a truck used for pulling semitrailers may make "only" 330HP, but it can do that continuously, and indeed will spend the majority of its life at or close to full throttle.
Towards the end of the war the Allies were using 115/145 in fighters for even more oomph.
As for fuel consumption, those WWII piston engines actually were quite efficient, look up BSFC numbers if interested. Fuel load and range were critical issues. It took many decades, energy crises and computer control for car engines to catch up.
I expected this article to be about electricity generation