Thrust and Power

[tgrayson]

You know, I was a bit confused as to why anyone would ever use engine braking if terrible problems were associated with it...seems much cheaper to replace brakes than crankshafts or rings...

When I got my first manual transmission auto, I did some searching around on the internet about using engine braking. I found a lot of references that said "never do this" and others that said it was ok. I don't know the truth.

So it seems that even at high pitch, the parasite drag from the prop (in a low MP high rate of descent scenario) will be less than the reverse thrust you'll get from going high rpm, so if you really need to shoot down, that's your best bet.

Probably so. (Why don't you perform some tests and report back?)

So next question: In a real engine out scenario, would I be better off then to go to a low rpm setting to decrease drag and increase my glide distance (assuming I'm in a single engine with no feathering)?

Almost certainly. I think that Aerodynamics for Naval Aviatiors has a pertinent graph.

 

[Cessnaflyer]

TG another one of your discussions goes into my instructor save file for reference.

Thanks again!

 

[USMCmech]

I don't see anything there that dismisses this issue.

I reread that article, and it seems I misunderstood that paragraph.


That said, I still have never seen or heard about a case of "ring flutter" in any internal combustion engine, even ones that regullary used engine braking. And I have done more than a few.

Deakins points about the unique design of radials make sense that they may be the origin of the "never operate your engine oversquare"

 

[tgrayson]

That said, I still have never seen or heard about a case of "ring flutter" in any internal combustion engine, even ones that regullary used engine braking.

I really can't defend it, other than to say that those more knowledgeable than I say it's an issue, or rather, can be. John Schwaner mentions it in his "Sky Ranch Engineering Manual". Perhaps it requires poor assembly tolerances along with poor operating practices? Dunno.

Like most things we consider "causal", the correlation probably isn't 1.0. Not everyone who smokes gets lung cancer, but we do know that smoking dramatically increases the probability of getting it. Maybe some of these engine operating practices merely apply stress to invisible flaws in the engine, which is why the results appear somewhat random.