What is "power"?

Ron Levy said:
But it was true in the 66 VW in which I learned to drive. :wink2:
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You too? :)

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Mine even got hit by an airplane. It was parked at our tiedown at FUL, while I was flying our C-150, when a newly-licensed PPL lost control on landing. He hit my car (in the photo), went through the fence into the street, and hit another car. Had I not been flying, our airplane would have been hit. The VW was repaired and soldiered on.

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One third of rated RPM does not equal one third of rated horsepower.

Horsepower is a function of torque times RPM. Unless the torque is the same at redline and at one-third of redline, you won't get one-third HP at one-third redline. You would have to have a heavy load at the lower RPM that demands the same torque as at full-throttle redline, and an engine capable of delivering that torque, to get the linear relationship. Not likely at all.

We can cruise comfortably at 2400 RPM, say. At 800 RPM, one third, the airplane will barely taxi.


Dan
 
Sac Arrow said:
The only way to directly measure power is to have a torque meter on the propeller shaft, as power is the product of torque and RPM. Since most GA airplanes don't have one, we have to estimate power based on power fuel and manifold pressure settings, and performance charts.
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Nailed it !

Full power is what the manufacturer says it is.
 
Regarding cars, you will notice that at lower elevations higher octane ratings are offered. Transitioning to higher elevations the octane ratings at the fuel stops are less. Sort of like leaning for cruise I guess.
 
woodchucker said:
Regarding cars, you will notice that at lower elevations higher octane ratings are offered. Transitioning to higher elevations the octane ratings at the fuel stops are less. Sort of like leaning for cruise I guess.
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Reduced manifold pressure results in lower pressure in the cylinder so lower octane fuel is fine.
 
Clark1961 said:
Reduced manifold pressure results in lower pressure in the cylinder so lower octane fuel is fine.
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Well that and electronic ignition and knock sensors.

I doubt if I towed any of the cars from here to sea level and then burnt the 85 at sea level that the thing would detonate.
 
denverpilot said:
Well that and electronic ignition and knock sensors.

I doubt if I towed any of the cars from here to sea level and then burnt the 85 at sea level that the thing would detonate.
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not to be contradictory or anything but they were selling lower octane fuel up here long before knock sensors...of course on most low compression engines it really didn't matter
 
Clark1961 said:
not to be contradictory or anything but they were selling lower octane fuel up here long before knock sensors...of course on most low compression engines it really didn't matter
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True. Just thinking about that there's surely plenty of folk who've taken vehicles from here to lower altitudes via methods that didn't burn all the fuel, and the vehicles didn't blow engines. Well, that we know of anyway. ;)
 
denverpilot said:
True. Just thinking about that there's surely plenty of folk who've taken vehicles from here to lower altitudes via methods that didn't burn all the fuel, and the vehicles didn't blow engines. Well, that we know of anyway. ;)
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And most auto engines rarely see WOT much less operate at max power. Of course a lot of folks did lug 'em around and that is a poor condition. For the most part they just rattled and didn't blow...
 
Clark1961 said:
And most auto engines rarely see WOT much less operate at max power. Of course a lot of folks did lug 'em around and that is a poor condition. For the most part they just rattled and didn't blow...
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T'is twue, t'is twue!
 
Yeah, so Sea Level is not exactly accurate for when the peak(usually that's the case or close to it) and/or rated(almost never the case) power is produced.

The engine is designed to produce the "Rated" power at 29.92 and 15C, but that does not have to mean the Sea Level(usually never is). If you are flying in high pressure system, the 15C/29.92 conditions may exist at 3000ft. Or, if you are flying in the winter, when it's -20C, you do not need 29.92 to get your rated power.

Similarly, you may produce more power than the engine is rated for(on the ground or in the air) if you are flying high pressure, low temperature environment.
 
And for the humor-impaired, that last post was humor...
 
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