Re: Langley_wind_tunnel_on_Q.pdf


Jay Scheevel
 

Hi Imraan,

 

Good questions. The plot I put in there is datummed to the pivot axis of the main gear. So all of the other items change the relative vertical projection with respect to the main gear during rotation about that axis. My use of alpha is probably not appropriate in this circumstance, my bad.  My use of FS is probably incorrect also, since it is only valid when the plane is at 0 degrees deck angle. The FS axis only serves as a reference to the projection of the labeled items onto the horizontal plane (the runway).

 

The CG is forward of the mains and located vertically near the midpoint of the fuselage, so as you pitch the airplane on the mains, the CG gets closer to going over-center on the mains. Prop effects and ground effect are not factored in, however tuft testing on Reg Clarke’s plane shows that the prop does not significantly impact the airflow over the fuselage and wing in any phase of flight. Other’s results may vary. My projection of the separation bubble is a bit of artistic license, but lack of data never stopped my arm waving in the past.

 

Maybe Gary McCurdy could comment, since he is the only one I know of that admits to having experienced what he described as a deep stall in a Q2. Gary?

 

Cheers,

Jay

 

From: Q-LIST@...
Sent: Wednesday, May 23, 2018 6:34 AM
To: Q-LIST@...
Subject: Re: [Q-LIST] Langley_wind_tunnel_on_Q.pdf

 

 

Jay,

I am missing the details (I knew I was missing good material at spring fling!) and may not have the full picture. I enjoy your usual aerodynamic analysis.

What is causing the cg position change with alpha? Alpha is an aerodynamic term and we do not normally see changes in cg position due to aerodynamic terms.
I'm also curious about the separation bubble extending as far beyond the canard as you've labeled it. Most of us have props that are have a decent diameter (60in for me) and both blown wing effects and ground effect have created enough difference in feel that I do not expect they are negligible.

I fully appreciate your caution against over rotation and would agree with that. All sorts of bad things there.

Best,
IF

--------------------------------------------
On Tue, 5/22/18, 'Jay Scheevel SGT' jay@... [Q-LIST] <Q-LIST@...> wrote:

Subject: [Q-LIST] Langley_wind_tunnel_on_Q.pdf [1 Attachment]
To: Q-LIST@...
Date: Tuesday, May 22, 2018, 6:23 PM


 









Talked to a few people at
Kevin’s spring fling about this, but a few pictures are
better than a lot of talk. I superimposed some Langley Wind
tunnel pics on top of the Q canard so you can see where the
turbulent air mass caused by the stall ends up. Obviously
over-rotation is not a good thing. This could happen in an
accelerated maneuver or on the runway in a Tri-Q. If it
happens on the runway (only possible in a Tri-Q), the CG
rotates aftward very close to, or perhaps even behind, the
main gear axis and there is no recovery except to apply
brakes and get the nose back down. PDF attached for your
consideration.
 Cheers,Jay









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