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Old Feb 22, 2009, 09:37 AM
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Clark YH

The difference between a Clark Y and a ClarkYH is the YH has a reflex trailing edge with helps longitudinal stability


Anybody ever use this airfoil on a glider? I wonder how much efficiency you use? Might be of use for a beginner airplane that is a training aid..
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Old Feb 23, 2009, 11:41 AM
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Hmmm, zero response here which I take is a non interest in the Clark Y airfoil.

I was building up an electric glider for a friend who has an Autistic kid. Based on FF so the kid could fly it with zero input when needed.

The ready builts are heavy , fast and expensive. I had some old speed 400 motors and esc laying around no longer used and even old 72 receivers/transmitter.

So I guess I'll just go with the standard Clary Y. I know this works well.
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Old Feb 23, 2009, 12:18 PM
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Didnt see this.

If you have a tail, the stability comes from that..no need for reflexed TE.

The most stable RC designs are RC adapted FF vintage style models. In quiet air, let go of the sticks and they will land themselves.

See the vintage forum for loads of suitable designs.
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Old Feb 23, 2009, 12:33 PM
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A small amount of reflex can be used to reduce the size of the horizontal stabilizer. This usually isn't really efficient, I don't know of any planes that are rigged like that. However, everything has been tried at least once, so there might be a prototype somewhere that uses a reflexed airfoil in a conventional layout, perhaps some early "quasi tailless" prototype
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Old Feb 23, 2009, 03:28 PM
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Yeah the YH was created to lower the moment of the standard Y. It would have the effect of allowing a smaller horizontal stab to be used but otherewise would have no advantage over the standard 'Y' and the slightly lower Cl max would give a slightly higher stall speed.
Full size airfcraft that used the YH would usually have probably been fitted with flaps so the lower Cl value would have been negated application of a little flap deflection when required.
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Old Feb 23, 2009, 05:17 PM
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The Clark YH was used on the Hawker Hurricane and some Russian Airpalnes like the Mig 3 and Yakolev fighters. to minimize pitching.

Since one trouble with planes is pitching and oscillation by beginners I thought this might be a good idea.

Compufoil has it in the library. But he really has some weird airfoils there that I have no idea what they would be used for.

I'm thinking about the Yogi by Jerry Soloff. Pusher to protect the prop. It has a very short fusage and I thought he might pitch a bit in level flight.

I'm just going ahead with the Clark Y and keep things simple. The plans have an airfoil that looks like a 6409 NACA. That was popular FF airfoil but this plane will be a Electric RC.
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Old Feb 23, 2009, 05:29 PM
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the different profile might help you obtain better elevator effectiveness with a smaller elevator, but won't reduce the period of oscillations on the pitch axis. This I believe is only a function of the distribution of mass. if you find the plane to be too nervous in pitch you can lengthen the tail arm, or concentrate the mass at the extremes of nose and tail.
I think that the Hawker Hurricane used Sidney Camm's own trademark "thick" airfoil, I don't know about the Mig 3 though. Both planes had a relatively small tail, perhaps you are referring to scale RC models? On these it might well be used as a "trick" to keep scale looking tail surfaces, since these are usually enlarged for RC models.
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Old Feb 24, 2009, 12:27 AM
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The Hurricane did use the YH but it was thickenned to 19% at the root: http://www.public.iastate.edu/~akmit...foil_usage.htm
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Old Feb 24, 2009, 11:19 AM
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The famous NACA series 23012 to 23018 come with moment coefficients close to zero and can aswell be considered as reflexed airfoils.
Many powered aircraft designs used and still use these airfoils and benefit from the low negative moment.

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Old Feb 24, 2009, 12:05 PM
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Quote:
Originally Posted by biber
The famous NACA series 23012 to 23018 come with moment coefficients close to zero and can aswell be considered as reflexed airfoils.
Many powered aircraft designs used and still use these airfoils and benefit from the low negative moment.
benefit in what way? Why not just increase elevator size a bit?

Thanks, Hans
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Old Feb 24, 2009, 12:27 PM
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Less trim drag for varying flight regimes comes in handy most of the time.
Enabling a more little elevator saves weight and loads on the fuselage which again saves weight.
The torsional loads on the wing are kept low by it aswell, so there might be lighter wing possible or a more simply built one.

Note that one of the most effective ways to improve a powered aircraft in almost any way (performance: speed, climb rate, fuel efficiency, payload; characteristics: stall speed, min turn radii, all around swift reaction to control inputs, ...) is to decrease its weight!

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Old Feb 24, 2009, 12:27 PM
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Low Cm airfoils can be important for full-size aircraft for structural reasons. They lower torsion on the wing structure, and raise the critical wing flutter speed for high altitude operation. They can also lower the fuselage structural load, because less tail load will be present.

None of these factors are liable to be very important for a RC model.

Kevin
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Old Feb 25, 2009, 12:40 AM
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less tail load is interesting for scale planes with small elevators

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Old Feb 25, 2009, 11:30 PM
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I think the Schweizer 2-32 used one of those NACA foils mentioned above. Not sure why they did it, but as I recall the horizontal stab is very small.
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Old Feb 25, 2009, 11:31 PM
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BTW, I think for a beginner plane, it's nice to have lots of drag when you try to go fast. Consider full flat bottom instead of Clark Y. Aquila or 7055 airfoils, maybe?
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