When is it OK to ignore the "Squares" (MP/RPM)

[snippyfsxer]

Yes, these are fascinating discussions!

Here is another link I found about this:

http://calclassic.proboards.com/index.cgi?board=fsaviator&action=display&thread=51

I agree that this discussion about windmilling stress would make sense if we are talking about the crankshaft and the gear box, but not the bearings, but then I don't know engines.

[DaveSims]

A pilot has to play mechanically stupid, and just follow published numbers. Problem is.. I can't DO that..lol

That makes you more than just a pilot, a good pilot.  Any monkey can follow procedures, but by having that understanding of the mechanics and physics of flight, you will be more able to handle abnormal situations.  As I've always heard, and said, a pilot's license is only a license to learn. 

Now back to the original post.  I also don't see why negative torque would be any more harmful to the engine than the same amount of positive torque.  Those engines are putting out over 1000 horsepower to the props, and should be able to handle at least some of that coming back, much like semi trucks using the engine brake.  But I do admit, my knowledge of those large, high power radials is slim.  I do know a couple of warbird pilots around here, perhaps next time I see them I will pose the question.

[specter177]

Well, I know that in my 185, I cruise at 23 squared and climb at 25 squared. I don't know about other aircraft, as that is the only constant speed prop that I've flown enough.

[Brett_Henderson]

Well, I know that in my 185, I cruise at 23 squared and climb at 25 squared. I don't know about other aircraft, as that is the only constant speed prop that I've flown enough.

That's the other discussion..  do you keep it squared as you climb ? What's your cruise setting for something like 8,000msl  (and your climb setting(s) getting there) ? How soon after takeoff do you go to 25/25 ?

[specter177]

I keep it squared all the way, or full power and 2500 RPM for climb. Our 185 as the IO-550, which is rated for continuous full power operation, so at altitude it's full power and 2300 RPM at cruise. Climb power is set when the flaps come up and I'm above obstacles. I usually take off a little under full RPM, just for noise reasons (185s are loud).

[Brett_Henderson]

Full power is relative..    ..  You lose an inch or so of MP  per  1000 ft, anyway. .. so if you plan on cruising much above 5000msl, you'll firewall the power for takeoff, and just leave it there.

I was just wondering if you continuousy lowered RMP as MP went down.. but is sounds like you do it similar to the way I do.. relatively high RPM, even as MP drops, for a climb.

At altitude is where a constant-speed prop starts earing it's keep. You're already dealing with lowered MP .. and with a fixed-pitch prop, you have to reduce MP even further, to keep the RPMs low.. whereas the constant-speed prop allows wide open throttle, with economical RPMs  8-)

[snippyfsxer]

I thought I would revive this old thread briefly, for those that are interested in this sort of thing, because I've come across a very good article that answers some of the technical questions raised in this thread so long ago.

http://www.sandersaircraft.com/library/general/Warbird_Notes-R4.pdf

My interest revived recently because I've been on a Vintage Prop kick, and returned to the Accusim stuff after an extended absence.

[Ivan]

One other reason why there are limitations in how fast you can change throttle on turbocharged engines is that most aircraft engines do NOT have water cooled turbos. You kill the engine oil and destroy oil flow when the turbo cools down too fast. The same reason why most tuned Imprezas have turbo timers, that will pump oil and water for a few minutes after shutdown to keep the turbo bearings in good condition.

What also makes these things a bit complicated I think is that most American and European GA pilots don't fly radials that much. For Russian GA pilots these are the only thing they see when getting airborne, so it is quite possible that the whole handling thing is not in the basic 'how to fly' lists for European and US pilots anymore