Installing Micro Vortex Generators (VG) on the STOL CH 701 Elevator

Over the past year we have been testing micro vortex generators (VG's) on the bottom of the STOL elevator. We've been using them on our factory demo planes and have sent out samples to experienced STOL pilots, including CH 701 owner and pilot Bob Jones (of Alaska).

We manufactured our own micro vortex generators out of .020 6061-T6 aluminum in our hydraulic press to match the curvature of the elevator, and for maximum durability and ease of installation.

A while back, designer Chris Heintz wrote an article on the use of VG's on the STOL CH 701. He explained how VG's "may improve the stall on small leading edge radius airfoils (so-called laminar airfoils) by “pumping” energy from the free airstream into the boundary layer which will then separate at a higher angle of attack, and the airfoil will have a larger maximum lift coefficient, thus reducing the stall speed. Note also that because of the above-mentioned “energizing” of the boundary layer with the use of VGs, the local stall can be delayed on a large deflection of a control surface, as illustrated below on the STOL elevator:"

We've since tried a number of different VG's on the bottom of the elevator (as shown above) with good results, allowing us to approach and to land the aircraft at even slower speeds. We've been using the micros VG's on all the STOL aircraft, including the new STOL CH 750 model. Some different micro VG types on the market:

In February, Bob Jones installed his VG's and explained: "They went on very fast... the VG turned 180 degrees makes an ideal spacer." Shown below with the STOL CH 701 elevator removed from the aircraft (the VG's are installed on the bottom of the elevator):

"It took 15 per side, the tape edge makes a perfect guide." Note that we made the VG's with pre-drilled pilot holes. Two sided tape (such as carpet tape) can be used instead of rivets (at least until you establish the optimum location).

The installed vortex generators:

Last week, Bob had the chance to fly his 701 with the VG's in place. Bob Jones has been flying his CH701 in Alaska for a number of years, utilizing the STOL characteristics of the design on skis and floats. He reports: "There is a very noticeable change. I was able to fly the length of my runway at a true ground speed of 38mph. as slow as it would go and maintain altitude but not so fast as to climb, I was able to slow my normal approach to 45 mph and have a nice steady descent rate, with a noticeable decrease in rpm needed to keep good elevator control. The transition from no VG effect (no elevator deflection) to vg effect (elevator deflection) is very noticeable - like flipping a switch. You know I push the boundary some and I think the only negative is that without a tail skid you could get into trouble. Testing them has been a rewarding experience that I would definitely recommend!!!"

We plan to keep testing these VG's for optimum location (this doesn't seem to be a real science!) and will make them available to builders and flyers who want maximum short take-off and landing performance with their aircraft.

Retired airline pilot Viktor Strausak has been flying his Zodiac CH 601 HDS for many years now with many VG's in various locations. He has posted some impressive photos! (Follow the link to his webpage for many more photos and info).

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Comment by Sebastien Heintz on March 10, 2009 at 5:00pm
Bob - thanks for testing the VGs and for showing the results on video! I can see why you've warned "Caution - some exteme attitudes." If you haven't seen Bob's video yet, have a look.

Last week we installed our new pressed aluminum VGs on our STOL CH 750 demonstrator:

We've started by installing exactly half the number used by Bob Jones, and the results have been very good so far. During the test phase, we've used (sticky!) two-sided carpet tape. We'll share performance figures once we get the chance to verify them.

Comment by Bob Jones on March 10, 2009 at 2:55pm
Flying with the VG's - See the video:
Comment by Viktor Strausak on March 4, 2009 at 12:07pm
Some more informations:
Comment by Viktor Strausak on March 4, 2009 at 12:04pm
Thanks to make flying safer. As I experienced and reported from the beginning with all my test flights with VGs an my 601HDS: It is the best modification I ever made for a few Dollars.
I will never fl again without VGs. Lift off speed below 40kts, stall full power 35kts IAS, idle power 42kts.
For emergency landing touch down speed is below 40kts.
Comment by Rick Lach on March 4, 2009 at 11:34am

What performance differences, if any, did you see between slats without and slats with vortex generators? I’ve flown pipers with and without VG’s and there is a big difference. But I’m interested to know weather there is any difference in the 701/801 slat configuration with VG’s. Sebastien indicated that they had done some testing with “Interesting Results” and I was hopping for his comments also. Your thoughts would be appreciated too.

Comment by Jerome Shepard on March 3, 2009 at 7:15pm
I have flown my 701 with VG's, with and without slats. Yes you do gain some speed without slats. The down side is that if you are going to push the envelope for STOL preformance landings without the slats, The aircraft (not perfectly coordinated) will break off at stall instead of just mush as it does with the slats installed. It is just not as safe in that situatiion. I noticed this in stall tests without slats. Jerry
Comment by Rick Lach on March 3, 2009 at 12:14pm
Sebastien you pleae elaberate on your "Interesting Results" of using Vortex Generators on the 701 wing with the Slats.


Comment by Sebastien Heintz on March 3, 2009 at 11:26am
We had experimented a while back with VGs on the 701 wing (with the slats) with interesting results...
We do not recommend that the slats be replaced with VGs as the fixed leading edge wing slats are effective short take-off and landing (STOL) devices and are surprisingly not that draggy. Sure, it's a little faster without the slats, but not as "STOL."
See Chris' article on this: Vortex Generators (VG) and Leading Edge Slats.
We are still testing these aluminum micro vortex generators, and we'll offer them with suggested installation instructions.
Comment by John Edwards on March 3, 2009 at 9:36am
Are you going to be using them on the wing also?
Comment by Debra and Patrick Nesbitt on March 2, 2009 at 10:24pm
Sebastien, is Zenith going to be selling VGs and for how much?

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