Avid MK4 Undercambered Wing
John Miller accidentally installed the 15 VGs at each wingtip at 30mm instead of the recommended 60mm,
and the remainder at 60mm instead of 90mm.
The results are unexpected and truly amazing!
More tests today in 75F OAT.
Idle clean was 47 is 38 mph TAS 19.1%
Idle flaps was 42 is 36 " " 12.1 %
Cruise power clean was 41 is 33 19.5%
Cruise flaps was 34 is 28 17.6 %
All speeds above TAS
Touch dawn was 40 MPH IAS is 35 MPH IAS 12.5 %
Not too shabby.
Avid MK4 under chambered wing.
Jabiru 2200 Engine.
Paul in Victoria, Australia has added VGs to both the tail and the main wing on his Avid.
He reports that he feels much more solid elevator authority from the VGs on the horiz stab.
The VGs on the wing allow him to push the envelope for very slow STOL landings without suddenly dropping on.
I have been doing more testing on my Avid Flyer model B STOL plane using VGs.
Here is what I have found so far:
Stall speeds with the flaperons on have been reduced only 1 or 2 MPH, but stall speed with no flaperons has been reduced 5 MPH so that with and without flaperons stall speed are almost the same at 39 MPH and 41 MPH respectively at idle RPM.
My climb had definitely increased by about 200 FPM. My glide ratio has gotten better, but this is hard to quantify. I have 3970 hours in this plane so I can sense the improvement.
Now here is the big surprise...
When My plane was built back in 1988 the vertical stabilizer was offset to the right (passenger side) to compensate for the P-factor of the 2 stroke Rotax engines that were turning the opposite of normal aircraft.
When I installed the Jabiru 2200 which turns the normal way I really had to hold right rudder on take off and climb out. So I put a trim tab on the rudder bent at a 45 degree angle to relieve the rudder pedal pressure.
I had a brain fart and decided to try putting your VGs on the left side of the vert stab 4 inches in front of the rudder hinge.
Today with I took my feet off the pedals the plane would turn to the RIGHT and now I had to hold LEFT rudder.
So I bent the trim tab straight back so it would have no affect and found that I could fly feet off.
Tomorrow the trim tab comes completely off.
I have to believe that the VGs have less drag than the trim tab at 45 degrees and I will see if I sense a better cruise speed. I suspect it will be too small and increase to notice.