Designs

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blue cobra
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Re: Designs

Postby blue cobra » February 20th, 2010, 8:39 am

If I'm going to offset my stab, in which direction should it be offset?
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Re: Designs

Postby jander14indoor » February 20th, 2010, 7:17 pm

Tail offset. Think of it this way. Look at a long train from the top as it goes around the curve. The engine in front makes an angle to the caboose in the back. Thighter turn, more angle. It has to do this or you get increased drag.

This is what your plane is doing, think of the wing as the engine, the tail as the caboose. For minimum drag, each flying surface should be aligned along a radius of the circle the diameter your plane is flying. For typical circles inside a gym, the tail will be offset about a quarter or half an inch from along the line of the motor stick. Since these planes turn left best, the tail boom, and tail, should be offset to the left as you look at the plane from the top. Looking from front that will be to the right, from the rear, the left of course.

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Re: Designs

Postby blue cobra » February 20th, 2010, 9:38 pm

I'm sorry, when I said offset I meant moving it along a line parallel to the wingspan. In other words, mounting the posts on the stab a bit off center. I haven't seen this on any plans though, so maybe it's not a great idea. I would think though that like wing offset you'd want the inside side longer.

I was thinking about making a new fuse and boom glued at an angle like you said. I'm currently using 1/4x1/8 for my fuse and 1/8x1/8 for my boom. Would that offer enough surface area for a strong joint?
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Re: Designs

Postby YadoMestor » March 21st, 2010, 5:47 pm

I have a new query:

I am considering moving my fin forward on the fuselage, so it sits directly in front of the stab.
Would this introduce any problems?

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Re: Designs

Postby jander14indoor » March 21st, 2010, 7:32 pm

Assuming you have a fairly long plane, shouldn't be a problem. Pretty common solution on really light planes.

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Re: Designs

Postby YadoMestor » March 21st, 2010, 7:53 pm

Thanks!
I also have one additional question, but I'm not too sure if it fits in this topic:
Whenever I create wash-in, the leading edge forms a very shallow V, instead of one side being horizontal and the other being titled up.

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Re: Designs

Postby NJman-77 » April 5th, 2010, 7:25 pm

how long should [one] the moter stick be? after that how long for the tail boom



ive heard the longer the better.

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Re: Designs

Postby jander14indoor » April 6th, 2010, 5:39 am

Motor stick should be long enough to prevent knots from bunching as the motor unwinds. Ten to twelve inches is good, shorter is better because it can be lighter and stiffer.

The tail boom, on the other hand, depends on other aspects of the design. Large wing/large tail desings fly best with a long distance between wing and tail. Small tails should be a little closer in. That said, the usual range that works well is sixteen to twenty inches seperation. Shorter for smaller tails, longer for big ones.

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Re: Designs

Postby NJman-77 » April 6th, 2010, 7:51 am

thanks :)

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Re: Designs

Postby Taran » April 20th, 2010, 2:10 pm

I just read a book about flight and it said that a good geometric angle of attack is around 13 degrees, but seeing all the planes people have built, they are nowhere near 13 degrees. May be only for heavy aircraft?

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Re: Designs

Postby jander14indoor » April 20th, 2010, 5:21 pm

Not sure what you mean by "geometric" angle of attack, but the ideal angle of attack for any flying surface depends on many things and there is no one ideal angle. For this event you want your surfaces to be flying at the best lift over drag point for the speed they fly in mid-flight. This tends to be very near stall on these planes.

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Re: Designs

Postby Taran » April 24th, 2010, 9:57 am

And also, Is it necessary to have stab tips, or should you just use a single rudder?

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Re: Designs

Postby jcollier » April 24th, 2010, 8:53 pm

Either design will work. Ziegler Freedom Flights kit have a single rudder. Cezar Banks Leading Edge uses tip plates. Both can fly well enough to win just about any competition if they are trimmed well and you have good flight data.

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Re: Designs

Postby calgoddard » April 25th, 2010, 10:26 am

"I just read a book about flight and it said that a good geometric angle of attack is around 13 degrees, but seeing all the planes people have built, they are nowhere near 13 degrees. May be only for heavy aircraft?"

This will follow up Jeff Anderson's answer to the above question.

Some experts are of the opinion that indoor duration rubber powered airplanes should not have any downthrust, i.e. the axis of the propeller shaft should be parallel to the longitudinal axis of the motor stick and the rubber motor.

Then the airplane needs decalage, a fancy French word for saying that the stab should have a negative incidence of about one degree and the main wing should have a positive incidence of about one to two degrees, and maybe three degrees at most.

Typically one fixes the incidence of the stab for simplicity and the raises and lowers the leading edge of the main wing by sliding the forward main wing post up and down.

Keep raising the leading edge of the main wing until you detect a slight stall, i.e. an up and down pitching of the front end of the airplane. Then lower the leading edge until the stall just disappears.

Warning: with the very large chord of the main wing of the 2010 WS airplanes that do not seek the bonus it is much harder to detect a stall than with narrower main wing chords.

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Help!!!

Postby emd19 » April 27th, 2010, 10:09 am

We have two days before states and we need a good quality plane design that can be built quickly. It doesn't have to be insane, as long as it flies more than 45 seconds.
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