VG's on underside of HH wing

[SuberAvid 617]

My flight to Denali last weekend was the first since I put the VG's on the underside of my wings.  I had previously installed them on the underside of the tips at about mid chord and found no noticeable change.  I then installed them along the underside of the wing leading spar right about at the point where the ribs contact the spar.  You can see them in the attached picture.  I flew 4.4 hours that day and this is what I could observe:

 

There seemed to be a little lessening of the roll stability.  It wasn't huge or spooky and I am not sure if it was just the wind conditions but some times it would oscillate with a slight dutch roll at a slowly alternating rate.  I could easily counter it with aeleron input but it happened a few times during the flight.  I did tight turns up to about 60 degree banks and it handled fine, smooth in and out of the turns with no tendency to overbank.

 

They seem to make the wing a little more efficient.  I was able to cruise at 90 mph using between 3.9 to 4.1 gph and 95 mph using 4.2 to 4.4 gph.  I was using around 4.2 to 4.4 gph at 90 mph and 4.6 to 4.8 at around 95 gph before.  Takeoff and landing speeds and handling seem to be unaffected.

 

If anyone else has tried them on the underside (or top side if you have not chimmed in before) please post your observations.

[EDMO 1078]

Randy,

       I guess with the IFA, you didn't chart differences in rpms and airspeeds - just tweaked pitch?

But, by fuel burns, it sounds like you probably gained some AS at same rpm?

EDMo

Edited 2 Apr 2014 by Ed In Missouri

[saskavid 47]

Randy:

Always been meaning to try this but haven't done it to date.My thinking was to put them on the underside of the wing right at a hoiziontal tangent on the pipe/spar and only on the outside half of the wing from the lift strut attachment to the tip;the area most effected by the 2in. wing washout.It would be interesting to tuft the underside of the wing at mid point to see how much separation you are getting in cruise out at the last half of the wing now with the vg's installed. 

  Mike

[SuberAvid 617]

Ed,  You're right, with the IFA I can fly at 90mph at 4000 rpm or 3600 rpm.  The boost/vacuume gage I put on is really worthless, just not acurate or fine enough to be of use, so the best way I have found to judge the load on the engine is with the fuel flow gage.

 

Mike, I think your right, just installing them on the outboard half of the wing would probably accomplish almost the same thing since that is where the most drag would be and it might lessen the slight loss of roll authority.  I might do that on my next set of wings.

[lostman 198]

Randy,

 

How did you attach your current VG's? I take it you used something a little more than temporary? I have my methods but I'm wondering what you did.

 

I got all my VG's installed on top of my wing yesterday but we've had terrible weather the past two days. It should be good tomorrow for testing though.

[SuberAvid 617]

Hi Kenneth,

 

The first set of VG's I installed on the top of my wings I used a glue like superglu but I think it was made by Locktite.  It is definately permanent.  This set came with  precut cards that you peeled the top paper off, stuck the VG onto the exposed glue and they peeled off the bottom paper to it left a thin surface of rubbery glue on the VG.  They are definately not as permanent and I think you could just peel them off the wing if you  wanted to.