Engine longevity

Challenged

Challenged

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Challenged
Imagine that we have two identical general aviation, piston engines running side by side, one is running at 100% power, the other is running at 75% power. Will the engine running at 100% power fail before the other? I've often read that our engines are rated to run at 100% power until TBO, why then do the POH's have tables for 75, 65 and 55% power settings? Why not just run the engine at 100% power all the time if they're designed to handle it?
 
The POHes include the lower % power tables because a normally aspirated engine cannot produce 100% power above sea level on a standard day. The tables are to let the Pilot know what performance to expect at his selected cruising altitude while flying
WOT.
 
I do live at sea level, so if there's no wind, I should be able to get to my destination faster by just flying at 90% power at 1,000 ft or 2,000 ft with no harm to the engine?
 
Your true airspeed may be higher at altitude. Now you have to factor the speed you can make during climb and during descent. And are the winds also nil at altitude? What direction are they going? And don't forget that convective turbulence is frequently worse low down. Don't beat yourself (and the plane) by flying the bumpy road!

Also be prepared for a significantly higher fuel bill. To keep your engine cool you will be flying full rich. That will give you high 20's GPH if I remember correctly.

But to answer your questions directly, Provided your POH does not have a power or rpm limitation, go for it.

-Skip
 
Things like TBO and "ratings" are numbers in a book.

The actual time that any particular engine may last is unknown - some will fail well before TBO, some will run much longer - even if the engines are run under identical conditions. And, when you look at the general aviation fleet, operating conditions and flight frequency are so varied that anyone who makes a hard prediction about the life of an engine just pulled that number out of a warm dark place.

In general, though, for a particular engine, running at higher power puts more load on bearings and rings, valves run hotter, etc. These sorts of things would tend to make an engine wear out faster. So, you are more likely to be spending more money sooner rather than later.

https://en.wikipedia.org/wiki/Weibull_distribution
 
I'm sure conti or lycoming has a nice set of statistics somewhere with a nice bell curve graph that has 2000 hours somewheres on it.

I'd imagine 90-95% of all engines should make it to 2000 hours, ok not sure their and the FAA's threshold.
 
Heat and friction are what wear engines out. When you run at high rpm you have more friction. When you run at high power settings that burn a lot of fuel, you have more heat damage. However, cold starts and short trips cause a lot of wear also. I'm pretty sure an engine run continuously at 40% power would outlast an engine run continuously at 75% power. Most normally aspirated first run (new) engines will run well past TBO.

Bottom line, you can run it fairly hard, but if you pull the power back it will probably extend the life a bit.
 
If an engine running at 75% power is sufficiently lubricated and cooled there's no reason why that should have worst wear than the one running at 45. It's a fallacy that the engine only has a fixed number of revolutions in it. What kills most engines before TBO is either excessive heat (as the FAA has determined eats cylinders) or corrosion and other problems from disuse.

Skyhawks run at full rental power in a training situation tend to blow right through TBO limits.
 
It depends on the engine, the cooling, all sorts of factors.

A Lycoming O-360 in a Skyhawk will basically be indestructible regardless of the power setting it's flown at. The 414 would not be happy flying at full power all the time, especially given the fact that the cooling is sub-optimal. I have been tending to do full power climbs in it as I think the time in climb being lower ends up being easier on the engine.

Basically, if you have an engine with a relatively low power rating and high cylinder strength with reasonable cooling, full power won't hurt anything. If you have a high power engine with tight cowling and weaker cylinders, full power will shorten the life.
 
Lets see what Lycoming says:
"For maximum service life, maintain the following recommended limits for continuous cruise operation:

a. engine power setting – 65% of rated or less.
b. Cylinder head temperatures – 400 ̊ F. or below. c. oil temperature – 165 ̊ F. – 220 ̊ F. "
 
Would it be better then for the engine to take off @65% power instead of full power?
 
for the engine YES...but not for the rest of the plane and its cargo, including you.
;)
 
Used to rent a 79 "'N" Skyhawk at KCCB and it was my favorite......ran like a top.......found out somehow it had 3,100 hours on the engine......had the whip put to it every day, it was always in the air.....didn't seem to hurt it a bit
 
Challenged said:
Would it be better then for the engine to take off @65% power instead of full power?
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That one got a chuckle out of me. 65% power on a nice hot summer day should get you into the weeds pretty quick :)
 
flyingron said:
If an engine running at 75% power is sufficiently lubricated and cooled there's no reason why that should have worst wear than the one running at 45. It's a fallacy that the engine only has a fixed number of revolutions in it. What kills most engines before TBO is either excessive heat (as the FAA has determined eats cylinders) or corrosion.
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Agreed.

In a properly designed and lubricated engine, there is virtually no metal-to-metal contact of any important component. Rings and bearings are literally floating on a thin film of oil. If that film goes away, the engine will self-destruct in very short order.

As long as the engine is operated within limits, there's no fundamental reason running at higher rpm increases wear or decreases longevity, and little if any evidence from the field of the either.
 
Vf6cruiser said:
Used to rent a 79 "'N" Skyhawk at KCCB and it was my favorite......ran like a top.......found out somehow it had 3,100 hours on the engine......had the whip put to it every day, it was always in the air.....didn't seem to hurt it a bit
Click to expand...

Mike Busch has a twin with about 3000 on the 6 cylinder engines. Has replaced 3 cylinders. Still running strong. He has a LOT to say about this. Funny some guys think he's a quack....probably wish they had his money!
Good chart here on cylinder longevity and temperature: http://us5.campaign-archive2.com/?u=dfd69bf8f8fec1b9da00eedbd&id=607891e493
 
We had a rental Skyhawk (ol' 73FR now flying traffic reporting around the DC area) that was an ex-ER plane and it was doing well at like 2800 SMOH on the second overhaul when finally the owner gave up listening to the club president carping about how much time there was on the engine and took it in.
 
Challenged said:
Would it be better then for the engine to take off @65% power instead of full power?
Click to expand...

A sustained climb at low power settings will probably heat up your CHTs more than a higher, normal climb power setting, so to answer your question, no.
 
James331 said:
A sustained climb at low power settings will probably heat up your CHTs more than a higher, normal climb power setting, so to answer your question, no.
Click to expand...

What would cause that? Assuming you maintain the same airspeed the "coolant," air, should be cooling the same. Wouldn't less pressure in the cylinder on the power stroke tend to make things cooler?
 
luvflyin said:
What would cause that? Assuming you maintain the same airspeed the "coolant," air, should be cooling the same. Wouldn't less pressure in the cylinder on the power stroke tend to make things cooler?
Click to expand...

In most planes pitching for 100% VY vs 65% VY, you're probably going to just end up riding ground effect, if you even get that far, till you nail the first obstruction.

For a any real climb you're going to have to fight the thing to get it in the air, and I'd wager you'll but more heat on the engine doing that, till the stall, impact and sudden stoppage, which,
I guess would in fact end in very low CHTs...

Not many GA planes have the power to successfully and sustainably take off at 65% power.
 
Challenged said:
... why then do the POH's have tables for 75, 65 and 55% power settings? Why not just run the engine at 100% power all the time if they're designed to handle it?
Click to expand...
Also, in many aircraft, 100% power is really designed to be used for T/O acceleration and climb. It really doesn't get you much extra speed when you pitch over in cruise, it just burns much more fuel and IMO shortens engine life. A Super Cub on floats is going about the same speed at 65% or 100% power.
 
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