Vortex Generators

[Madhatter]

I am using vg's on wings and stabilator and there has been no change in cruise speed with any configuration. Any increase in drag from the vg's is countered by the decrease in drag due to the smoother flow created by them which is typical on most aircraft. No change in 310 either, but reduction in vmc is tremendous and that's what kills most people. As for the j3, it's  a cub, goes nowhere fast anyway but reduces stall from 39 to 23 mph, a high drag but high lift Clark Y airfoil. I put 100 hp on the cub so no reason to even try to analyze speed difference. 

[Mike Koerner]

Hatter,

Thanks for doing this work. I think you’re performing a significant service for the CT community.

What is different about the most recent configuration as compared to what you had tested prior to August 27 when you reported no reduction in stall speed in any configuration?

Mike Koerner

[Madhatter]

8% is not a huge amount so determining exactly where stall is, requires consistent accuracy. After a great many stall sequences you get better at consistency. According to Micro AeroDynamics 8 to 10% is an average reduction for most aircraft. The behavior of the aircraft under different configurations is the real goal. This turned out to be more involved than I realized in the beginning. I am trying to finish this before any large fall temperature changes occur so that the flight variables don't change .

[Madhatter]

Final thoughts on vg's after 3 weeks of testing(and $500)

In the last 3 weeks I have tried the vg's from Micro AeroDynamics at 6, 4, and 2% of chord on both the wings and stabilator and at each time flown the CT in all different configurations. Power off stalls, min airspeed level flight, deep stalls until falling out, all at different flap settings. Also flaring high to see if the bottom drops out. The last test was yesterday after installing Stolspeed vg's on the stabilator at 2% chord which are twice as tall as Micro AeroDynamics vg's to make sure I had full boundary layer penetration. Within an hour after that last flight is the most important test, removal of all vg's and fly without them doing the previous flight tests.

There was no significant change with the Stolspeed vg's over the Micro AeroDynamics vg's. The reduction in power off stalls was minimal, maybe 1 or 2 knots, all the other stall configurations were similar. As far a dropping out on landing they helped a little. The problem with that is as you do many high flare tests , you get better at managing them and they are all done in smooth air with no gusting to be consistent so it's difficult to compare. 

The changes for the better are :

min airspeed level flight 20 kts indicated vs 25,    more stability in stalls with better aileron control,  deep stalls handle better,    maybe some better landing.

In my opinion vg's don't warrant the cost and installation time. The CT is very efficient  aerodynamically,  kind of like some of the high performance sailplanes I have flown. I have always considered the CT to be a poor primary student trainer. The stall characteristics are so good that the student who learns in a CT then buys a Cessna 150 and does a full power stall------- welcome to the world, and if the ball isn't centered------welcome to aerobatics. 

I have to thank Anni Brogan, owner and test pilot for Micro AeroDynamics for all the help in the vg test process.

 

 

 

 

[Jim Meade]

Did you test stalls such as 30° bank with 40° flaps, power off?  How did vg perform in max slips (rudder to the stop)?  How about in accelerated stalls?  The reason I ask is that while we seldom intend to fly in these configurations, events can overtake us to where we find ourselves in them and we would prefer to know the plane's performance.

[Madhatter]

Those configurations are not valid for the vg analysis because of too many variables involved. Power on stalls, accelerated or straight have too many variables, pilot skill, propeller pitch, engine power, aoa, etc. Slips would be even worse. The key to vg performance is at what point the boundary layer separates from the wing. Power on stalls would only be done to verify no unanticipated issues if indeed the vg's were to be installed permanently. Even trying to analyze landing performance is difficult to get repetitive data due to so many variables. Power off stalls and a few others will have no variables if temp and altitude remain close for all tests. This project was far more involved than I anticipated. 

[Jim Meade]

I understand.  Interesting restrictions on flight parameters.

[sandpiper]

MH

Thank you for doing these tests and reporting the outcome. 

[Mike Koerner]

I agree with John.

Thanks!

Mike Koerner

[AGLyme]

Saw this example at the Midwest airshow... the concept is worth pursuing from a safety perspective driving down stall speeds.  A no brainer given the accident metrics on slow flight and pattern calamities.  Thanks for leading this MH.

[Clay Johnson]

Madhatter,

Did you find VGs at 2% of chord, on both the wings and stabilator, to be the best location or was there no difference  2% vs 6%?

 

[Madhatter]

There was no significant difference that I could tell. 

[Philip Welsch]

Did you notice if the vg's allowed the nose (prop) to be lifted away from the runway at a lower speed than without. Would they be useful reducing prop damage on unimproved runway?

[Madhatter]

If it was it would have been almost not possible to be accurately measured. My minimum speed to maintain level was 20 knots indicated  with vg's and 25 knots indicated without vg's all at approx 3600 rpm. This was done at 2000 ft at about 85 °F.