ORIGINAL: Sport_Pilot
Hmm.. I disagree that car engines run hotter and faster.... Let's compare a 160 HP airplane with a similar car on a cross-country trip....
Normal cruise power in light airplanes is 65-75% of rated HP - Take Flyfalcon's sample 160 HP Cessna 172 - that equates to 120 HP at 75%. The airplane will probably cruise at around 130 mph true airspeed. The block hour fuel consumption will be around 10 gph...
In my 160 HP Honda, I get around 25 mpg, using probably 40 hp and cruising at 65 mph for a block hour fuel consumption of 2.6 GPH
Poor comparison. First you are using rated horsepower not size. The aircraft engine is probably 2 1/2 times larger, and is rated at a much lower horsepower than its capablilities. Aircraft engines running gen sets run at higher speeds, same engine but maybe one less plug per cylinder and it is running a constant 3600 rpm for about half the TBO or 1000 to 1200 hours. (some actually do better because of the cooling fans, no hot running waiting to be cleared for takeoff). Why GA doesn't put powerd fans for cooling during taxi is beyond me. Your Honda is loafing, but similar engines run at or near full power in Germany on the autobaun and get the same or better TBO. Why? Because running at speed is actually less wear and tear than many starts, and stop and go driving. The aircraft engines run at much less than their capabilites and do not have to contend with short runs with lots of stop and go running, and do not have as many starts during their life. Consider that the caussut racers ran their C O-200's with smaller props than the C 150 and turned them at up to 4,000 RPM with few problems. Though I doubt they ran 100 LL thus suffering stuck valves every 10th flight or so.
Thanks for proving my point... the airplane engine is designed for its operating environment - long duration at constant RPM, the auto engine for its ever changing speed, start and stop... Similar things that do different jobs... sorta like a plow horse and a quarter horse... both are horses, but I wouldn't expect a quarter horse to pull my plow for long...
