Q-500 Racing Discuss AMA 428, AMA 424, and any other variants of Quickie 500 racing

Q500 Racers!

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Old 04-18-2008, 09:35 PM
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Backplate
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Default Q500 Racers!

Hi there guys,
Just want to know from some of you, your thoughts on a v-tail versers a standard tail.
I know there has been a thread on this before, but I'm just thinking about what to do for my next plane! Is a v-tail faster than a standard tail because of less drag? 0r do you guys think there is no difference. 0r I suppose it depends on how good the flyer is thst is racing the model? Your thoughts thanks.
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Old 04-18-2008, 09:56 PM
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Default RE: Q500 Racers!

Dave, the V tail in theory should be quicker as you have one less junction at the fuselage, and is never totally blanked out by any wing wash. Place the vee tail on the top of the fuselage and not part way down.

Some years ago I read an article on the design angle for the Vee tail- it went something like this Sin2+Cos2=1............design for a vertical equivalent of 1/3 of the horizontal area, and solving the equation you find the ideal angle to be 120 degrees. Use a 30-60-90 triangle and it will be easy to set the dihedral. Use the 30 degree angle to set the dihedral per side ie 30+30+120=180.

Its based solely on less drag- less tailplane surface area, no vertical fin area, and less frontal area
regards big T
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Old 04-18-2008, 11:35 PM
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Default RE: Q500 Racers!

Yeah, I've posted that formula before. Tractor conventional airplanes (prop on the front, tail in the back) are destablized by the prop. The bigger the prop diameter, the larger a rudder is required. Racing models have quite small props, so the vertical area need is pretty low. I have flown quickies with the V-tail at 130 degrees, and it was perfectly stable in flight. But with the limited surface area and throw, I had almost no steering on the ground when landing. So I decreased the angle to 120 degrees.

But you say, so many the designs are set at 110 degrees and work fine. True, but this angle was copied from gliders which need massive vertical area and little horizontal due to the long wings high inertia and limited pitching moment due to the narrow chords. The flatter V-tail have less drag, so those are the trade-offs.

If you get real clever with your fuselage design, you can arrange the slope of the top of the fuselage so the tail comes out at the corner. It takes a couple of measurements and a bit of trig.

First, measure the width of the fuselage where the leading edge and trailing edge of the V-tail meets the fuselage. Subtract the TE width from the LE width and divide by two. I try to measure this to a 1/32" accuracy. Take the Tangent of the angle to horizontal (180 – {V-tail angle})/2. For example on a 120 degree V-tail, it’s 30 degrees. So working out the trailing edge position is : [(LE width– TE width)/2] x tan (30). This distance is the amount that the TE of the V-Tail is lower on the side of the fuselage than the LE for zero incidence. Place the fuselage with the wing mounted so that the leading and trailing edges are blocked up an equal amount (zero-zero) on the obligatory flat surface.
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Old 04-18-2008, 11:48 PM
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Default RE: Q500 Racers!

High Plains ,
Its obvious you and I went to ,or studied under the same maths/ trigonometery lecturer. Dave lives just up the road so Dave, if you want me to explain all this to you then give me a call- its not difficult but you need to have a good indepth knowledge of those mathematicals/ trig subjects. Dave, all you really need know is the answer!.............but we are available to help. trevor h
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Old 04-18-2008, 11:59 PM
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Default RE: Q500 Racers!

Actually, I never took trig. But 16 hours of Calculus, series and differential equations made me pick it up.
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Old 04-19-2008, 12:54 AM
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Default RE: Q500 Racers!

you have a good grasp of the problem all the same, trevor h
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Old 04-19-2008, 01:33 AM
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Default RE: Q500 Racers!

Hi guys,
Thanks for all the imformation on the V-tails verse standard tails.
Just wondered if a standard tail would be as fast as a V-tail, but it seems not.
So I will make it a V-tail.
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Old 04-19-2008, 01:38 AM
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Default RE: Q500 Racers!

Backplate, I have raced both conventional and v-tail Q500 models. There is not much in it for speed but the V-tail handles alot better, mainly though the turn. And they tend to fly straighter without the wanding. I would go V-tail but either way you should manage a 1:30 in Q500 sport. Anthony
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Old 04-20-2008, 04:24 AM
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Default RE: Q500 Racers!

Thanks wildstyle it seems the V-tail is the perfered airfoil.
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Old 04-20-2008, 06:13 AM
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Default RE: Q500 Racers!

I would not even dream of disputing High Plains Trigonometry and Calculus. I set my "Vee" at 120deg simply because it it easy to measure with standard plastic set squares (Triangles in the US).

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