One doesn't fly a typical g/a plane at pitch-angles above 20 degrees - so the point is mute. For example, the operational pitch-range of a typical light-aircraft constant-speed prop is only 10.5 degrees to 22 degrees for fixed-gear & 11 degrees to 26 degrees for retracts. And you never cruise at max pitch unless you're turbocharged & flying in really thin air, up near the plane's service-ceiling. That's why I stressed REAL-WORLD flight-conditions.

Joel

Originally Posted by turboparker

One doesn't fly a typical g/a plane at pitch-angles above 20 degrees - so the point is mute.......... And you never cruise at max pitch unless you're turbocharged & flying in really thin air, up near the plane's service-ceiling. That's why I stressed REAL-WORLD flight-conditions.

Uh, excuse me........This isn't about "typical" flying and cruising merrily along.

It's about stopped prop vs. windmill situations. (That was framed by you.) Engine-out. Dead-sticking. Etc., etc.

Unfortunately, those are real-world, too!

Situations where the book tells you to trim (including prop pitch) for max glide.

The diagrams clearly show that for most of the pitch range on the way to feathering (and, also, including at full-feather!) a stopped prop will not have less drag than one that's windmilling.

Q.E.D.

objection your honor: umx planes don't have variable pitch

Originally Posted by pugsam

Uh, excuse me........This isn't about "typical" flying and cruising merrily along.

It's about stopped prop vs. windmill situations. (That was framed by you.) Engine-out. Dead-sticking. Etc., etc.

Unfortunately, those are real-world, too!

Situations where the book tells you to trim (including prop pitch) for max glide.

The diagrams clearly show that for most of the pitch range on the way to feathering (and, also, including at full-feather!) a stopped prop will not have less drag than one that's windmilling.

Q.E.D.

Wrong. Real-world pitch conditions with props that are connected to real inoperative engines with real compression loads are all that matters. Besides - you've changed your stance so many times it's nuts. You originally stated that intuition says a stopped prop should have more drag than a windmilling prop, with no reference to any other conditions. Totally wrong.

You also stated your intuition says that pilots feather the prop on a dead engine to reduce the drag of the stopped blades, and that stopping rotation was just a byproduct. Also totally wrong. As the graph clearly shows, there's very little difference between the drag of a stopped prop that's @ 90 degrees & one that's at 0 degrees. The big exponential increase in drag happens when the prop is windmilling at practical pitch-angles that sustain rotation at the airspeeds typically encountered during an engine-out situation.

Therefore, the primary reason for feathering the prop on a dead engine is to get rid of the exponential increase in drag caused by windmilling that's equivalent to the drag of a solid disk the same size as the prop - NOT to reduce the drag of an already stopped prop.

Joel

Originally Posted by falcongsr

objection your honor: umx planes don't have variable pitch

Correct. And at the pitch-angles we use at typical RC airplane RPMs & airspeeds, a stopped prop ALWAYS has a lot less drag than a windmilling prop. No question about it!

Joel

Originally Posted by falcongsr

objection your honor: umx planes don't have variable pitch

True, but don't rope-a-dope me with that!

I started-off with that university study involving fixed-pitch RC props. (It supported the questions I asked.)

But, immediately, I was pummeled with the objection that it was unrealistic, and wasn't done by experienced pilots of real-world, full-scale aircraft.

So the discussion shifted to the big-boy domain, particularly the FAA/Navy findings.



In both domains, however, the answers seem to be pretty much the same: drag is critically affected by pitch angle. And there's a crossover point, meaning that at some pitches a stopped prop -- whether RC or full-scale -- is not "cleaner" than a windmilling prop.

Even more so, in the full-scale world of variable pitch props and life-or-death forced landings: Over most of the pitch range a stopped prop is not cleaner than a windmilling prop. (The cleanest state is feathered.)

well that's why i fly umx. nothing's life or death with a foamie. and yeah, no feathering, so...

oh hey i guess we can use folding props!

Joel, I'm cracking-up with delight, as you wriggle and slide!

I thought you were pinned-down when you introduced that awesome FAA/Navy diagram. (Which seemed to neatly validate my questions.) But now you're relentlessly bad-mouthing it!

So I can read those tea leaves. Your superior authority leaves me defeated.

You win!

_______________
My ignore list just grew by one

Pity the guy in the second picture---so much DRAG beating up and down.......... didn't someone tell him if the stick were stationary there will be a lot less DRAG....... My!

Loving the humor from the sidelines!

Very interesting stuff. So a stationary prop can produce more drag than a windmilling one at high angles of pitch. Though not a lot more, but nonetheless, more. (Assuming the whole graph is even true? Proof for the graph plz?).

Maybe that's not so important in the real world, but that does not make it useless.

it's a shame Joel never flew a real plane and can only guess at stuff like that... . .

I fly jets, nice not to mess with props anymore. For the job that is.