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The Complexity of a WW II P-47 Thunderbolt’s Powerplant (2015)
- aphextron 6y agoIn 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?
- jacquesm 6y agoI 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.
- GeorgeKangas 6y agoThe 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. I don't have any dates for these usages. Edit: that p-47 powertrain is an absolute beast!
- diarrhea 6y agoSo when you have such a turbine supercharger driven by the crankshaft, what does the turbine do at all?
- usrusr 6y agoA 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.
- diarrhea 6y agoExactly, but GP's > "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.
- agurk 6y agoWhat 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.
- diarrhea 6y ago> 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.
- agurk 6y agoYou'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] [0] https://www.globalspec.com/learnmore/flow_transfer_control/pumps/turbine_pumps https://www.globalspec.com/learnmore/flow_transfer_control/p... [1] https://en.m.wikipedia.org/wiki/Pump https://en.m.wikipedia.org/wiki/Pump
- sk5t 6y agoI think what you’re getting at is that there is no turbine (only an impeller) in the case of crank/belt driven units.
- Toutouxc 6y agoI don't get the downvotes, you're right. A crankshaft driven supercharger doesn't need a turbine (a device that extracts power from a fluid), only an impeller (the opposite).
- jandrese 6y agoThe 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.
- czch 6y agoBut the P-47 is on fairly high power the whole time it’s running. Most Veyrons will never use 50% of their rated power. That being said, modern metallurgy really revolutionized ICEs. Followed by computerized control.
- Gibbon1 6y agoNot 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.
- lovecg 6y agoCouldn’t you gear down? This whole discussion makes me think what would a modern maxed out aircraft piston engine be like!
- Merad 6y agoIf 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.
- 6y ago
- NathanielK 6y agoSupercharging 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.
- louwrentius 6y agoVery interesting! 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.
- Synaesthesia 6y agoThey say war brings technological advancement, it certainly did. It also brought waste and an acceleration of environmental destruction.
- Steven_Vellon 6y agoA relevant video on the same topic: https://www.youtube.com/watch?v=IwqTN5fhMR8 https://www.youtube.com/watch?v=IwqTN5fhMR8
- olivermarks 6y agoAlmost like a modern turbo drag racing setup! 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.
- jandrese 6y agoI 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.
- olivermarks 6y agomy 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
- hedgehog 6y agoI 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 https://www.youtube.com/watch?v=8_5kSxWO5rg
- jabl 6y agoLiquid 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.
- mentos 6y agoOff 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 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.
- usrusr 6y agoHow 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?
- mentos 6y agoImagination? [0] [0]-https://youtu.be/2vOr_wUChmk?t=37 https://youtu.be/2vOr_wUChmk?t=37
- hypertexthero 6y agoOr 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 https://www.youtube.com/watch?v=J_kAFi9G7-0
- lgats 6y agoWould it be more accurate to refer to this as the Powertrain, not the power plant? I expected this article to be about electricity generation
- p_l 6y agoPower plant is common term in aviation.
- nielsbot 6y agoIt's like the pilot is simply sitting atop a huge engine! But I bet most fighter planes at like that.
- Koshkin 6y agoIndeed, even flying a small plane like a Cessna 172 or a Piper Warrior feels like that.
- hangonhn 6y agoIn 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 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. The channel itself is just amazing.
- asdff 6y agoWhat did they end up doing? Dump in more or less fuel according to the altimeter?
- hangonhn 6y agoIIRC, they used a turbo supercharger system that had multiple stages that can be enabled at different altitudes.
- jabl 6y agoIIRC 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).