"P" factor question

[Ralph Jones]

"ground return"

Excellent metaphor!

[Russell Holton]

In flat pitch, the prop's contribution would be the mass being accelerated. With feather pitch, there would be the drag part of it.

Another point of view, once accelerated, and at steady state RPM, a flat pitch prop would have little torque reaction. But a feather pitch prop would have a torque reaction from the drag.

Another point of view - the entire "ground return" of the engine's output goes into the airframe. That is, everything the engine produces that isn't lost in friction torques the aircraft. A high-performance engine mounted on the centerline in a light aircraft - that's going to get ugly.

[Tom Charlton]

Hmm, I will have to think about that a bit.

In flat pitch, the prop's contribution would be the mass being accelerated. With feather pitch, there would be the drag part of it.

Another point of view, once accelerated, and at steady state RPM, a flat pitch prop would have little torque reaction. But a feather pitch prop would have a torque reaction from the drag.

Hi Terry,

Yup that’s what I’m think’n there’s torque from accelerating the inertia of the prop. A separate consideration is steady state RPM wherein torque is just a function of how hard does the power plant need to work to keep’er spinning.

Seems I read something in the past saying with a typical General Aviation aircraft the torque was about equivalent to moving from the right seat to the left seat. In effect . . . inconsequential.

Regards,
Tom Charlton

[Terry Carraway]

Hmm, I will have to think about that a bit.

In flat pitch, the prop's contribution would be the mass being accelerated. With feather pitch, there would be the drag part of it.

Another point of view, once accelerated, and at steady state RPM, a flat pitch prop would have little torque reaction. But a feather pitch prop would have a torque reaction from the drag.

[Ralph Jones]

Terry--
Remember that an instant before the power application, the blade drag is contributing some torque reaction, which is being taken up by aileron trim. When you slam the throttle, the torque the crank delivers to the prop jumps up, and by Newton's 3rd, the same torque increase is delivered to the airframe, and you get roll motion.

As the prop accelerates, the blade drag goes up as the inertia reaction tapers off. Eventually, you reach a steady state where the torque reaction is increased by a comparatively small amount, and you adjust the aileron trim to take it up. The consequence of a prop being in flat pitch is not so much increasing the roll reaction as extending it for a longer time.

[Terry Carraway]

There are actually two reactions.

Torque is free space thing ,based on mass and acceleration.

But in air, with a prop, you have a different, but similar consequencies factor, of the "bite" of the prop.

Two identical engines with flat blade props (no twist, no airfoil). One is set with the blades in full flat pitch, the other with the blades set to full feather pitch.

At idle, slam the throttle forward, which one is going to produce the most amount of rolling motion?

[Randy Sohn]

Not Greek... He speaks GEEK...

Chuckle, nah, I just meant that the advice you'd offered was "Greek to me".

best , randy (who is severely technical/computer challenged, "sorry 'bout that")

[Jeff Hartmann]

Chuckle, you always speak in Greek??????

best, randy

Not Greek... He speaks GEEK...

[Jeff Hartmann]

You can adjust your browser's zoom-level with <CTRL><+> and <CTRL><->. <CTRL><0> takes you back to 100%.

Larry….that was wayyy too easy, Thanks.

[Tom Charlton]

So how does that work if the aircraft is on a treadmill?

Sorry Mase, I beat ya to it in my post# 5 of this thread:<g>
Hidden within the word salad of my post you’ll find:

You could do an experiment with an airplane on a giant treadmill.<GD&R>

But . . . your contributions are always appreciated and looked forward to with great anticipation.

BTW, Got your tickets for Duluth?

Regards,
Tom Charlton (who doesn’t recall ever having been on an actual treadmill<g>)

[Tom Charlton]

Possibly, but an image and sound of a P-51 rolling inverted and crashing directly in front of me at OSH upon jamming on the throttle to do a go-around . . .

Hi Tom T,
Ya-but, but . . . note my “non-accelerating” mention.

non-accelerating, constant RPM

Likely incorporated into my sentence in a confusing manor.

I will have to go think about this some more.

Ha, don’t we all! Sometimes I even think with less than inconsequential inconsistencies! (now what’n the sam-heck does he mean with that) (Hmm . . . nice word salad)

Regards,
Tom Charlton (likely good that he’s confined his self to fly’n a Cub now-a-days)<g>

[Ralph Jones]

Tom, I'd expect the inlines to react worse because they had higher rpm limits than radials: larger change in angular momentum with a sudden application.

[Mase Taylor]

So how does that work if the aircraft is on a treadmill?

[Tom Tyson]

Hi Tom T.
. . . I’d postulate that: The –mass- of the rotating parts, non-accelerating, constant RPM, is irrelevant. The resistance to turning the propeller against air molecules is everything.

Regards,
Tom Charlton

Possibly, but an image and sound of a P-51 rolling inverted and crashing directly in front of me at OSH upon jamming on the throttle to do a go-around after a botched formation landing is indelibly etched in my mind. I was not thinking in a detached manner and had neglected to factor in the weight of the prop.

I will have to go think about this some more.

I must ask those with experience in both types (in-line/"V" vs Radial) if one type or the other has more of a tendency to bite when jamming on the throttle.

- TT

[Randy Sohn]

You can adjust your browser's zoom-level with <CTRL><+> and <CTRL><->. <CTRL><0> takes you back to 100%.

Chuckle, you always speak in Greek??????

best, randy