VGs

7 posts in this topic

Posted

I put this up over at Rotax, but that site seem pretty dead now...

Has anyone ever put VGs on their flapperons?  This would be in an attempt to minimize the inversion issue when the flap function is extended. 

If I understand correctly, the inversion situation happens when the further deflected flapperon stalls, loosing it's lift and allowing the opposite flapperon to roll the aircraft in the "wrong" direction.

Just a thought from the nooby.  :nobashing:

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Posted

Or.......would the vg's on the flaperons make things worse?  The reason I'm wondering this is because of the following, and perhaps wrong thoughts.

1. When the flaperons are deflected too far, have they gone from providing extra lift, to providing mucho drag?

2. As the stick is pushed, say to the left, the left flaperon raises, and then goes from causing drag to once again causing the left wing to have more lift.  The vg's at this point are providing additional lift, and the left wing, because of this, raises even more.                    3. Meanwhile the right wing's flaperon is deflected even further down.  This causes more drag and would cause the aircraft to yaw to the right.  Reversed control, right?

4. So, did the reverse control happen because the flaperons were deflected too far down, or because the flaperon on the side in the direction of the desired turn, started providing lift causing the wing to rise, while the other wing had increasing drag which caused yaw in that direction?

I wonder what is the cause for the control reversal, this or some other aerodynamic mystery?

My head hurts.

Jack       

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Posted

So... I'm betting that the vg's would increase the range of increased lift that the flaperons provide, but would or could increase the lift a lot when transitioning from their drag range into the lift range.  This along with the increased drag on the other side, the control reversal could be dramatic. Probably the only way to really get a good answer would be to do inflight tests with little streamers attached to the flaperons and see what the differences are with and without the vg's installed.  I don't know of anyone who has done this.

One question leads to more, eh?  I wonder if anyone from the original Avid design crew is following this thread?  Or maybe the test pilot.

Jack

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Posted

I put this up over at Rotax, but that site seem pretty dead now...

Has anyone ever put VGs on their flapperons?  This would be in an attempt to minimize the inversion issue when the flap function is extended. 

If I understand correctly, the inversion situation happens when the further deflected flapperon stalls, loosing it's lift and allowing the opposite flapperon to roll the aircraft in the "wrong" direction.

Just a thought from the nooby.  :nobashing:

The "inversion" is caused by flaperons deployed too steeply (more than 15 degrees. The reversal is cause when the wing actually begins to twist from the excessive flaperon deflection. Besides weight reduction the B52 G and H models removed ailerons and use spoilers instead. The B52 wings are very flexible and can twist with ailerons.

I have my flaperons (trimerons) limited to 10 degrees deflection and reversed the bellcrank to the micer to give much more aileron/flaperon deflection at slow speeds.

Avid B STOL 3850 hours

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Posted

On my mkiv, I allowed my flaperons to drop 40 degrees and used it that way for 75+ hrs. I never experienced control reversal. I did quit using 40 degrees based only my speculation that it might be too much airload on the wings/flaperons/hangars. Bryce

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Posted

I increased my flaperon "flap" travel to 26 degrees after I originally set mine up with 13 degrees or so. I used 26 degrees because I could still get full aeleron deflection (at full stick travel right and left) without binding the flaperons. With flaps full on and stick at full deflection the down flaperon is around 40 degrees and the up one is about 0. I have not experienced any control reversal at this setting but I have not tried a full deflection bank with flaps full on.

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Posted

I'm also at about 25 degrees flap travel. Since my original post on this thread I have put several hundred hours on the plane and use full flapperon often without inversion or any other issues.

I still don't understand the fear of flap use with these planes... ?

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