Building VGs
Experimenter: Steve Craigle

Triggered by Richard Martin's VG tests Steve has further experimented with fabrication, application, shape, size and position of the VGs.

The tests are still ongoing. Until completion we'll post some pictures and keep a lose log of the test runs on this page.

The glue is still to be tested properly.

From: Steve Craigle
Date: Sunday July 18th, 2004

Here are the preliminary test results from my VG installation.

My plane is stock except for 3' wingtips (29' total span). It has an O-360 Lycoming with Hartzell C/S prop and and conventional landing gear. The test conditions were with ~2/3 fuel and me as pilot.

I first did a baseline check with only stabilator VGs installed. These are 1.40 " long and 0.30" high with the leading edge cut off at a 45 deg angle. The material is 0.042" thick. They are spaced at 3" intervals on the bottom 5" behind the stabilator LE at a 20 deg incidence angle alternately switching directions. (+20, -20, etc.) They are attached with double sided tape.

The cruise speed at 3400 MSL, 24" MP and 2400 RPM was 152 MPH IAS. Power off stall with full flaps was at 60 with a sharp fall off to the left.

VGs were then applied to the wing. These are 1.50" long, 0.50" high, 0.062" thick and have the leading edge cut off at a 45 deg angle. They are mounted on top of the wing 6" behind the LE at 4" intervals at 20 deg incidence angles varying as per the stabilator VGs. No VGs were applied to the cabin area.

The cruise speed under the same conditions as above was 149 MPH. The power off stall speed could not be reached with full aft stick. The IAS at this condition was 55 MPH and the aircraft turned slowly to the left despite right rudder application. I attempted to accelerate into the stalled condition but couldn't make it fall off as it had without the VGs.

Based on the flight test results I made my approach at 77 MPH vs a normal 85 MPH. The landing was uneventful except for not having to use brakes to make the first taxiway as I normally have to.

I will leave the VGs on pending some further tests. I plan to increase the stabilator travel a bit to see if I can get more of the potential download available and see if it is sufficient to get the wing to stall.



From: Steve Craigle
Date: Monday July 19th, 2004

Another day, another flight test. This time with more heartening results. I moved the wing VGs forward and reduced the incidence angle to 15 deg for this morning's run. Lo and behold, I not only got back the 3MPH I lost in the initial installation, but I gained 2 MPH on top of it. The low speed data remained the same. (55 MPH with stick full aft, no break) I also discovered that the slow left turn I noted in my previous report could be arrested with aileron input. This was amazing, because ailerons were the first control to disappear at the stall previously. Again, I made the approach at 77 MPH IAS and had plenty of time to flare and touch down slightly tailwheel first.

The attachment shows the details of today's flight test config. I'll leave it like this for a while and maybe try adjusting the stabilator stop for more up later on.



From: Steve Craigle
Date: Tuesday July 20th, 2004

I started with yesterday's configuration and added 14 VGs across the bottom of the fuselage just forward of the upward break at the aft end of the side channels. These were the stabilator sized VGs, 0.3" high and at a 20 deg incidence angle. I took off, zipped up to 3400' MSL and carefully set the MP at 24" and the RPM at 2400. I then flew as level as I could for about 3 or 4 min and watched the IAS. Result: No noticable change from yesterday. I then tried a couple of power on stalls at the same throttle setting and RPM. As I suspected, the attitude was awesome. The stall occurred at just under 50 MPH IAS and the break was extemely abrupt. On the second run I tried to reverse the break with ailerons but they were not too effective. I think I may have finally stalled this modified wing!



The paper template was used to position and space each VG.

The left half of the wooden die is cut with an angle smaller 90deg to allow for springback. It also has the curvature of the wing profile. The VG is formed by hammering the sheet against the die with a rubber hammer.

The two nails serve as a stop and control the height of the upright part of the VG.


From: Steve Craigle
Date: Thursday March 3rd., 2005

OK, attached is my sketch of the VG tooling. Another view of the installation of the VGs is on my builder's profile at Click on "Vortex Generators" at the bottom of the pictures then on "The Attachment" in the paragraph next to the botttom one. Some of the pictures on the main page of my profile give an idea of some of what it all looks like going together. The attached drawing leaves out the 3/16 bolts I used to align the blocks; the small pins (nails or whatever) take care of that. To use, slip the pins into the matching holes on the backup block, drop a blank part in between them so it's supported by the 2 pins. Clamp the whole assembly in a vice and use a rubber hammer to bent the gluing flange down into the 33" radius. That's the radius of the wing contour where you will be attaching them later.

Drawing for Tooling
Click on the image for a larger view.

I then clipped off a .25 chamfer on one end of each VG. I could say this was for aerodynamics, but really it keeps the builder safer later on from sharp corners, etc. Then a LOT of filing to eliminate sharp edges & corners, and run them all through an alodine process. I used a cardboard template to draw lines on the wing where they go, and glued them on with DAP tile & tub sealant. They're still on there.

If you cant get to the builder profile above, the VGs on the stabilator go on the underside 5" aft of the leading edge at a spacing of 3" and 20 deg incidence angle. The wing VGs go on top and cover the panel area only, not the cabin area.

Good luck------Steve

From: Steve Craigle
Date: Thursday March 20th, 2005

> Would substitution of 7075 for the flat gussets i8n the aft
> fuselage be satisfactory? This is harder than 2024 but will not require any
> bending or forming. I have been unable to find comparative single shear
> values.

For future reference, 7075-T6 has a shear ultimate/yield (KSI) of 46/38. 2024-T3 values are 40/24. So, not a whole lot of difference in ultimate, but considerable (>50%) in yield.

In this application, either one would be more than adequate for the job, structurally. The downside to 7075 is that it's much more prone to corrosion, so you would want to carefully alodine and prime each gusset. Once you've put the skin on, these things are tough to inspect and even tougher to repair.

FWIW   Steve