Spiralling Slipstream

Sidious

Sidious

Well-Known Member
Does anyone have a video in a wind tunnel with smoke or some other physical picture of propeller spiralling slipstream? I have someone who just does not believe in it.

Thanks
 
we had a notice come down at my former school to not teach Spiraling Slipstream because it "has not been proven" and "was removed from the PTS." this was from single, and multi.

to each their own!:D
 
jeepthrills said:
we had a notice come down at my former school to not teach Spiraling Slipstream because it "has not been proven" and "was removed from the PTS." this was from single, and multi.

to each their own!:D
Click to expand...

What!!!?

NASA disagrees with your former flight school:

"A tractor propeller of a typical airplane is a destabilizing influence on the directional stability, and it also imparts a rotational velocity to the slipstream."

Source: http://history.nasa.gov/SP-367/chapt9.htm


Slide 27 from aerodynamics at brown university: http://www.brown.edu/Students/Brown_Flying_Club/aerodynamics2.ppt


Could have sworn I had a slide presentation from MIT on aerodynamics with this too. However, I cannot locate it. I don't see how one can claim a lack of existence though. It is clearly visible on any underwater propeller.

Take a propeller on a small fan (the battery ones they sell at the dollar store), stick it in a bucket and watch it make the water spin.
 
I am not saying I dont see the theory, We were just told not to teach it. I didnt write the rules, I was just a mushroom!!! kept in the dark and fed ! Thats what they wanted :dunno:
 
jeepthrills said:
I am not saying I dont see the theory, We were just told not to teach it. I didnt write the rules, I was just a mushroom!!! kept in the dark and fed ! Thats what they wanted :dunno:
Click to expand...

Just seems silly to not teach this very important part of aerodynamics to me. I am not saying you don't know or don't agree, nor am I attempting to argue with you. I am simply trying to give you the ammunition you need to discuss this with them. It isn't a theory, it is known to exist.

Consider this: An aircraft in a torque roll.

First, for some background information: torque is a rolling, not a yawing tendency. Hence the torque roll.

P-factor is not an issue since there is no AOA associated with a torque roll. The relative wind hits the prop perfectly straight on so both the up-going and down-going blades are at the same angle.

Gyro precession has never been a left yawing tendency. It can be a pitching or yawing tendency, in either direction, depending on the application of force.

All that is left is spiraling slipstream. The slower your aircraft is moving through the air the larger this effect is on the aircrafts tail. A torque roll has zero forward speed and hence the greatest effect from spiraling slipstream.

For proof, click this torque roll video and go to about 42 seconds in. In the initial entry, a perfect torque roll. Notice the repeat taps of right rudder being used. The pilot does this to counter spiraling slipstream. At about 52/53 seconds he overdoes it and has to use some left rudder, but the initial is still visible.

I don't know if we have any aero pilots that actually perform this trolling these forums. If we do they can attest to the constant right rudder needed in this maneuver. I never had the pleasure of flying an aircraft capable of this, I learned about it through my RC flying.


----Break----

If you need more information, here:

Aerodynamics for Naval Aviators page 294:

"Slipstream Rotation. A critical directional control requirement may exist when the propeller powered airplane is at a high power and low airspeed. .... the single engine rotation propeller induces a slipstream swirl..."

----Break----

Flight Theory for Pilots page 250:

"Slipstream Rotation. This effect is predominant in single engined propeller aircraft. It may be critical at high power and low airspeed combinations, thus it is important during takeoff and landing operations. The slipstream from the propeller rotates about the fuselage..."

----Break----

Emergency Maneuver Training page 28:

"Spiral Slipstream. A spiral slipstream of air rotates clockwise behind the turning prop. ... Propeller slipstream can contribute significant left yaw, especially during slow flight at high power settings."

----Break----


Hope this can help you convince them of it's existence. I am digging through a more advanced aero book. But due to my lack of recent work with calculus I am having issues understanding the information to present it. However, for the time being this might get you started. Along with the NASA confirmation I don't see how your chief instructor can possibly tell you it doesn't exist and not to teach it.

I would appreciate any feedback from his concerns if you do discuss it with him/her.
 
shdw said:
First, for some background information: torque is a rolling, not a yawing tendency. Hence the torque roll.
Click to expand...

You're talking about the maneuver whereby an airplane hangs by the prop and *rolls* around the longitudinal axis? How can a yawing tendency produce this effect?
 
tgrayson said:
You're talking about the maneuver whereby an airplane hangs by the prop and *rolls* around the longitudinal axis? How can a yawing tendency produce this effect?
Click to expand...

Yes, that is why I said "torque is rolling tendency, *not* a yawing tendency. The engine torque produces the roll in the maneuver. The spiral slipstream induces a left yaw that needs to be countered when performing a torque roll.

Does that clear up your question? Sorry I am unsure how what you quoted was unclear.


Edit: I commented on torque only because I hear many instructors present it as a left yawing tendency, which it isn't.
 
There were several of us who lobbied to keep it, and we were shot down. ( this was a larger school whos' management was quite set in their ways). I am no longer there, so I leave them to their own demise!:insane:
 
jeepthrills said:
There were several of us who lobbied to keep it, and we were shot down. ( this was a larger school whos' management was quite set in their ways). I am no longer there, so I leave them to their own demise!:insane:
Click to expand...

I wish this was allowed on JC, I would love to know who they are. I would write them a letter.



Tgray: Ahh now I see what you mean, thanks.
 
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