Off topic but given that I'll probably never have the time/money/experience to fly a real P-47 the next best thing I imagine is an RC FPV: https://www.youtube.com/watch?v=a6i0qVHiL8c
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.
Or fly it in IL-2 Sturmovik or DCS flight simulators!
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
How could an fpving an RC model that surely doesn't have the tiniest similarity in terms of performance and operation come even close to what the combat flight sim market/community is offering?
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.
A P-47's engine was fairly resistant to battle damage. My dad was a P-47 driver. One time it swallowed a valve, and the engine kept running, just a bit of vibration.
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.
Though I'm not too familiar with P-51 internals Walter's comment reminded me of this spectacular P-51 engine failure followed by a successful crash-landing (this clip includes pilot commentary explaining key moments): https://www.youtube.com/watch?v=jnODYKx5ics
The US Navy mandated air cooled radial engines due to their robustness. The US Army Air Force adopted water cooled V type engines for performance. An air cooled radial can suffer damage such as "dropping" a valve because each cylinder and cylinder head is largely independent. There is no shared water jacket, for instance.
If your dad should still be alive you should ask him how he managed to get his P51 shot directly above a friendly airfield. I have a hunch, there's a story behind that.
Swallowing a valve is a common engine failure for high performance engines. The valve breaks off at the stem and falls into the combustion chamber. The piston comes up, jams against the valve, and the engine basically comes apart.
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.
Another of his engine failure stories. He was tootling along in an F-86 over Arizona, and the engine failed. The tower ordered him to bail out (pilots are worth more than the jets). But being the math nerd he was, he calculated a parabolic trajectory that would just bring him to the runway. (Knowing the sink rate, winds, distance, altitude.)
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.
P.S. you might wonder how he went from B-17 navigator to P-51 pilot. After WW2, he rejoined the AF in order to be a fighter pilot. Wound up flying quite a diverse collection of machines.
"Charles D. Bright has flown the F-47, F-51, F-84, F-86, B-17, B-25, B-26, C-46, C-47, and T-33, and has been a member of fighter, fighter-bomber, fighter-interceptor, heavy bombardment, light bombardment, and troop carrier units. He served as a lieutenant colonel in the U.S. Air Force; in World War II he was a navigator in B-17s and in the Korean War he was a fighter-bomber pilot. He has also been an instructor pilot in fighter weaponry, and has taught aerospace studies."
Lucky man, flew both the P-51 and F-86, the most beautiful machines of their eras. The only thing left for him was to switch sides and fly the Su-27 :) (yep I know that one is a little younger)
While the time of direct control over engines is over now in this FADEC era...
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.
By swallowing a valve, he means one of the valves that lets air into the cylinder, or exhaust out, snapped off. So you no longer have that cylinder working, plus you have the valve rattling around against the piston that's still moving up and down. Not good.
The good news is that losing intercooler or turbo would just be a fractional performance reduction, not a countdown to an engine loss that an oil cooler hit would be.
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.
IIRC there were some late WW1, or early interwar period, liquid cooled planes that did use skin coolers. As engines got bigger, they became impractically large (covering a significant fraction of the fuselage), complicated with lots of pipes all over the place, and heavy. Don't see why the tradeoff would be that different for an intercooler vs. the main engine cooler.
I was wondering the same thing. What would a few bullets through that huge air tube do to your power?
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.
my thoughts exactly - the engine is relying heavily on forced air induction - must have had a 'limp home' mode built in, hard to tell carbs to do different things though, no ecm controlled fuel injection
The P-47 (like all American warplanes of this era) gave pilots a lot of control over engine performance. The P-47 pilot could adjust throttle, RPM (controlled by a governor that adjusts prop pitch), fuel-air mixture, turbocharger speed (controlled by opening exhaust wastegates), as well as control of the cowl flaps and intercooler shutters for cooling, as needed.
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.
I don't know about the air ducts but loss of coolant pressure was a big deal, here's a video I saw a while back where one of the designers talks about the P-51's radiator: https://www.youtube.com/watch?v=8_5kSxWO5rg
Liquid cooled WWII aero engines generally used pressurized cooling systems, as this allowed running the coolant (usually a 70/30 glycol/water mix) past the atmospheric pressure boiling point. This, in turn, allowed smaller radiators, reducing drag.
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.
I'd guess in a very different way to circuit racing's requirements for zero turbo lag though? They'd be "I need enough boost while staged on the line that I've always got traction-breaking torque available when and for as long after I launch as possible", rather than "I need to be able to smoothly get from off throttle to 30% throttle as I pass the apex, then from 30 up to 100% as I exit turn 4"...
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.
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.
In case anyone is a budding airplane nerd, Greg’s Automobiles and Airplanes did an 8 parts series on the P-47: https://youtu.be/mzQuq2FHdeE
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.
IIRC the allies generally used multistage superchargers. AFAIU they were automatically engaged, presumably by some valve that was activated due to the drop in boost pressure as the plane climbed, or such.
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).
In the first diagram, how is that considered a supercharger if there's no use of mechanical energy from the engine to drive the turbine? Isn't that technically just a turbocharger?
The word "turbocharger" was introduced to shorten the phrase "turbine supercharger", whether driven by the crankshaft or by the exhaust. Later, it came to mean "exhaust driven turbine supercharger" pretty much exclusively.
The crazy part is that by modern standards they aren't really developing that much power. Sure this thing puts out 2,100 HP (using 130 octane gas), but it needs a whopping 46 liters of displacement to get that.
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.
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.
Not my field but the other difference is 1500 hp at 2,400 rpm. The low max rpm is because it needs to match the propeller design speed and needs to be efficient at near full power.
These engines were, in fact, geared down, as was common (if not ubiquitous) in large piston aero engines. This video shows an epicyclic reduction gear inside the bell-like case on the front.
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.
If you're really interested in the topic look up the YouTube channel Greg's Planes and Automobiles. In addition to a deep dive series on the P-47 just a few weeks ago he made a video about late WW2 "super prop" fighters. They were the pinnacle of piston engine fighter performance, but they were all canceled because they weren't needed to win the war and everyone could see that jets were the future. We'd probably struggle to beat them even with modern technology TBH.
Yeah it’s cool to think about how some technology might have developed if the economics didn’t make the evolutionary branch obsolete. I think that’s the appeal of steampunk fiction etc.
Gearing adds a lot of weight, and soaks up some power. Additionally, that weight tends to be at the front of the engine, so it can mess with the CG. You ideally want an engine that produces good power at rotational speeds that keep the propeller tips moving sub-sonic.
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.
Gearing adds weight and complexity, and complexity brings unreliability. Best avoided where possible.
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 maxed out, neither in terms of size nor in terms of wartime-only tradeoffs along the lines of "it's ok when two engines blow up due to low error margins if the performance gains they enable allow four boys more to return", but the RED A3 hn-famous from driving the Otto Celera is a modern aircraft piston engine. Apparently the only one, if you ignore the occasional automotive adaption.
The 130 octane gas you refer to is actually 100/130 lean/rich avgas. Quite similar to the 100LL still used today.
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.
A crankshaft driven charger would haven been called just a supercharger, exactly like we do today. But we don't call turbine driven chargers "turbine supercharger" anymore, we call that a turbocharger.
What we call a turbocharger today has two turbines in it - one that is spun by the exhaust gasses and a second one that compresses the incoming air. These two turbines are directly connected.
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.
> What we call a turbocharger today has two turbines in it - one that is spun by the exhaust gasses and a second one that compresses the incoming air. These two turbines are directly connected.
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.
Well, you can find the term "bike pump" even on newyorktimes.com and that's not about hydraulic brake levers, so there might be some difference between technical language and common usage even in English.
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.
A pump moves a fluid and a compressor reduces the volume of a fluid. If your fluid is compressible, such as air, then moving it will entail some compression. This was the GP's point about a fan.
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.
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).
You're right I did misspeak about the definition of a impeller/turbine.
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]
I think back in the day the terminology may have been used interchangeably, clearly that diagram is pretty old. The article uses the term turbocharger consistently.
Supercharging refers too any way you increase intake charge (air going into the cylinder) above what naturally happens with atmospheric pressure. Using a big turbine to power it used to be called turbo-supercharging, but now we shorten it to turbocharging.
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.