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Is 140 degrees too much for a V Tail Glider?

Old 10-12-2006, 07:56 PM
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flyranger
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Default Is 140 degrees too much for a V Tail Glider?

I'm rusty at math, but looking at building a 1.75 meter electric glider with a V tail instead of a conventional tail. The area of the fin and rudder is 22.5 sq in. The area of the stab and elevator is 61.3 sq in. 22.5/61.3 times arctan gives 20 degrees from horiz. Multiply 20 degrees x 2 and the angle inside the V is 140 degrees! My only other experience with V tail gliders is my nanoplane falcon which has an inside angle of 110 degrees. I went to the DJ Aerotech site and studied their materials to come up with the above "constant control authority" method of calculation. Each of the resulting panels should have an area of 41.9 in sq per their calcs. Those of you that have v tail sailplanes - what is your inside angle? 140 degrees seems high (flat) to me.
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Old 10-12-2006, 09:42 PM
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I designed and built a couple of sailplanes last winter. One just about the size your working on and the other slightly smaller. The smaller glider I made the tail 110 degrees and after further study made the second glider 120 degrees.

They both flew fine. Actually, the 120 degree appealed to my sense of design more than the steeper angle. I read what others do but generally I trust my instincs. For example, I know how you came up with the v-tail size however when I tried to match what I thought a conventional fin and stab combo should be the v-tail looked too big to me and I rebuilt it probably 15-20% smaller. Then it seemed to fit the overall design much better than the bigger tail. As I say, it flies just fine...they both do.

I'm sure you've read the longer the tail moment the smaller the tail has to be. I would say my plane resembled the format of 2-meter kits or arfs available. They are both electric powered by the way...not that matters particularly toward your concern.

Good luck,

Weller

P.S. 140 degree seems flat to me as well, but again I have read where that angle is sucessful on some v-tail gliders.
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Old 10-13-2006, 01:00 AM
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Thanks, Weller.
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Old 12-03-2006, 03:22 AM
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Sparky Paul
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The shallower the angle on a vee-tail, the less effective the rudder function becomes.
For an aileron equipped plane it's not that big a deal, but for rudder-vator control, closer to 110-120 degrees works best.
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