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Q-talk 137 - Vortex Generator Experiments

I flew my Q-2 for the first 5 years without the vortex generators and had no major issues with that. After painting my Q I planned on installing them which I did. Around this time another Q-2 pilot reported installing the VG's well forward on the canard with seven inch spacing and also on the wing close to the leading edge with the same spacing. He reported a much reduce landing speed with the setup with little or no decrease in speed (the something for nothing rule should have tipped me off). I installed the Jabiru at this time also. The results were not good with the generators on the wing. I found that they did increase the lift of the main wing but the VG's on the canard did not thus causing the original landing problem that the reflexor was not able to over come. The

VG's were removed from the main wing in pairs with flight testing until they were all removed. With that, the reflexor was able to do its job once again. The generators on the canard handled the rain and bug problem, so I never did get back to moving the generators to the QAC recommended location just behind the 50% cord line.

Fast forward to August of this year (2009) seven years later, I read an old article by an Eze pilot about sanding the canard cord wise and getting better results than with the VG's (one data point without any follow-up). A new paint job is planned for the future so I decide to give that a try. If I had dug into the Q-List archives, I would have found poor results from the process reported by others on the list. So, I was able to confirm those findings. The wing was polished out again and the generators were installed behind the 50% cord line, but using Keith Welsh's spacing, basically omitting every other pair.

I flew the plane once in windy and gusty conditions before FOD and headed out to some virga but gave up and returned to the airport due to some bad gusting, turbulent conditions. My next flight was my trip to Beatrice for the fly-in with even worse condition there. My first landing attempt I set the reflexor to my normal landing position and ended up tail low (to much lift killed in the main wing). After reducing the reflex to neutral I was able to land the plane OK. The conditions were much nicer on Saturday when I returned home but flying at low levels the bugs were as bad as I have ever experienced. With that in mind I check my landing attitude at elevation before letting down for fuel in Torrington, WY on the way home. The surprise was to find that even with the wings and canard contaminated more than ever before the reflexor was right around neutral.

The light came on so to speak, and the bottom line is that VG's placed forward of the 50% cord line kills lift on the canard. This explains a great deal and in my mind proves that VG's will not increase lift on a GU canard and thereby cannot reduce the stall speed.

To close, if there is anyone still out there building with the GU canard, I recommend installing the VG's where QAC suggested, but the wider spacing works just fine.

You can order a printed copy of Q-talk #137 by using the Q-talk Back Issue Order Page.