Posted: 2/6/2009 10:48:22 AM EDT
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I'm by no means an aviation expert nor do I play one on TV. But I am a hardcore gear head who thinks anything that uses pistons is cool in the extreme
, I'm curious about the last generation of liquid cooled inline piston aero engines from Late wwII, and more specifically were the Jet not invented just how far would large displacment piston engine development have come along were todays automotive technologies employed. How much power would a 30 litre v12 produce if it were a ground up modern design? Employing technologies such as turbocharging, coil on plug ignition, variable valve timing and modern EFI systems. Merlin II 66.6 h.p. per litre honda F20C inline 4 cylinder 120 h.p. per litre |
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There is an awful lot to this subject.
I'll start with number one. A practical airplane needs long range. A fuel efficient engine is necessary. The old engineers knew this very well. Pratt + Whitney developed what turned out to be the first "modern" aircraft engine. It was reliable, powerful, light weight and economical. How'd they do it? Large pistons travelling slowly, this reduces piston ring swept area, which a MAJOR factor in fuel consumption. 2 large valves per cylinder with sufficient exhaust valve heat transfer. Quality materials that hold up under heavy loads for long periods of time and an overall attention to quality design. (there is much more, for sure). The fact is that low RPM aircraft engines have very high pressures (BMEP) and operate with these pressures for extended periods of time. Much more so than modern high RPM engines. Consider this: Rather than use HP/L or some other formula, use BMEP as a comparison. Then, use average BMEP in cruise configuration. You will quickly see that aircraft engines do quite well in many areas. Even the lowly Lycoming! For instance a Lyc IO-360 makes 200HP at 2700RPM. Can your Chevy 350 do that? Can it do it for 2000 hours? In other words, if the Lyc could turn 5400 RPM, it would make 400HP (with a flat torque curve). It's not really doing all that badly. Even more importantly, Can an automotive engine be competitive with power to weight and fuel burn? The answer may surprise you, as it's no! The cruise BSFC of a modern Lycoming air cooled (so called dynosaur) is 0.38 pounds of fuel per HP per hour. That's better than the MOST EFFICIENT gasoline automotive engines made today (such as the Toyota Prius engine). That Lycoming also weighs in at about 1.5 pounds per HP, fully equipped. It's very, very difficult to achieve good power to weight, BSFC (fuel consumption) and reliable long term operation. Orenda tried it and failed. So did Toyota. Franklin |
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Quoted:
Merlin II 66.6 h.p. per litre honda F20C inline 4 cylinder 120 h.p. per litre Slow that little Honda down so your "cruise flight" RPM is not in the 7500 RPM range (obviously absurd) (yes, I know redline is 9K), I just backed it down for argument's sake. Let's say cruise RPM is limited in that Honda to 4500, a number that that engine might be able to stand. Your max cruise HP is now limited to about 100. Not so good. Add HP loss at altitude and 80HP in cruise seems about right. With a prop reduction drive, radiator and accessories and...... My best guess is that recip engine design would have evolved into something we don't recognize today. Turbo compound, multi valve, lightweight monsters that have excellent high altitude performance. With the emphasis on power to weight, range and reliabilty. Outright HP, or HP per Liter really don't matter much when all the other factors are considered. Franklin |
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Quoted:
How much power would a 30 litre v12 produce if it were a ground up modern design? Employing technologies such as turbocharging, coil on plug ignition, variable valve timing and modern EFI systems. A little more, maybe 10%. But, I would expect far better high altitude performance. Adding more RPM would not be very likely. Nor would I expect significantly higher cylinder pressures. Franklin |