[elippse]

Recently an article in a well known aviation magazine stated that the air swirling around the fuselage from the propeller "pushes" the Vstab to the side. I pointed out that the air does not have sufficient sideways magnitude to generate the force normal to its flow. I said that if you are flying along at 300 fps, approximately 200 mph, with a CL of 0.2, and you encountered a region of air that is rising at 300 fpm, 5 fps, that the sudden upward jolt is not due to the upward pressure of the air pushing on the bottom of the wing, but is instead due to the transient increase of 1 degree in the angle of the airflow that the wing sees. This momentarily causes the apparent CL to increase from 0.2 to 0.3, giving a 50% lift increase, or a 0.5G jolt. An upward velocity of 5 fps would give an upward force of 0.024 lb at 8000', which would give a 2.38 pound upward force on a wing with 100 sq. ft.! Can you feel that?
I wrote that the same applies to the swirling airflow around the back of the fuselage, that, with a conventional tractor propeller rotation, at least from the American point of view, corkscrews around from left to right, increasing the positive angle of attack on the left Hstab and the Vstab, and a negative AOA on the right Hstab, giving both a left yaw and right roll. He had someone write back that due to Bernoulli the air pushes the Vstab to the side and that's all that needs to be said!

 

[SHIPCHIEF]

I'm with you on this one..plus the inner wing panels and gear legs that fall within the streamtube of the prop discharge airflow.
I just always wondered how much?
I don't have any problem understanding concepts, the question for me is always Magnetude and Scale.

 

[L.Adamson]

I don't understand everything written here...........but decades ago, Duke Fox, who owned a model airplane engine business........went to the trouble of checking out the forces of the prop blast on the tail.

He added a downward vertical stab to models, in addition to the regular vert. stab. By doing this, the plane went straight down the runway, as well as initial climb. It wasn't practical for full size aircraft. To long of landing gear, and tail strike problems.

If this applies to different principles, the so be it. In the meantime, I'll go with the helical propwash theory.

L.Adamson --- RV6A

 

[elippse]

I don't understand everything written here...........but decades ago, Duke Fox, who owned a model airplane engine business........went to the trouble of checking out the forces of the prop blast on the tail.

He added a downward vertical stab to models, in addition to the regular vert. stab. By doing this, the plane went straight down the runway, as well as initial climb. It wasn't practical for full size aircraft. To long of landing gear, and tail strike problems.
L.Adamson --- RV6A

Good old Fox .59, which had more power than the McCoy, which until that time was the engine of choice in control-line speed.

By adding the lower Vstab it counteracted the yaw force but added to the roll force.
I was standing behind "Son of Galloping Goat" (which has had Goat changed to Ghost this year) when Leah Sommer was doing a ground run up with the Phantom's first 3-blade prop. I pointed out to the crew that the tube of air coming back from the prop had its left edge about 1' to the left of the Vstab and the right edge was about 3' to the right of the Vstab. 'Took us all by surprise!

 

[N999BT]

I don't know for sure...

But the P-51 vertical fin is offset something like 2 degrees at the front for helical prop flow. In my RV with the tail on pretty close to straight, I notice that at low speed I am stepping on the right rudder, and on the left at really high speed to get the ball centered. I finally concluded after much head scratching and adjustments that it was the propwash causing most of the problem.

There is also gyroscopic precession (sp?) that happens when you raise the tail, start a loop, etc. that requires rudder to keep the ball centered. This is a transient issue

 

[airguy]

But the P-51 vertical fin is offset something like 2 degrees at the front for helical prop flow. In my RV with the tail on pretty close to straight, I notice that at low speed I am stepping on the right rudder, and on the left at really high speed to get the ball centered. I finally concluded after much head scratching and adjustments that it was the propwash causing most of the problem.

Not so sure that's right - I experience the same thing in my C-172 at high airspeeds, even at low/no power where propwash is basically absent.

 

[Mike S]

NO!!!

I will not be sucked into another counter rotational inverted helical vortex of theoretical bantering.

Magic, it is all magic

Must resist................................