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What to expect when you thin down an airfoil

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What to expect when you thin down an airfoil

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Old 03-05-2002, 02:49 AM
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mglavin
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Default What to expect when you thin down an airfoil

I have a model that was modified by another. The intenetion was to go fast and turn left. It's a Mustang with what was originally a symmetrical wing much like the Great Planes 40 Mustang, only this one is smaller. The wing has been thinnned down on the bottom side. I would say it has nearly no arc "NOW". It seems to me that this should work, but I have never went this route. I have always used the apropriate air foil.

Any ideas out there? How about some one with first hand experience with said modifications?
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Old 03-05-2002, 06:06 PM
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ChuckN
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Default Sounds like a Clark Y

You now have a wing section that has more in common with a Clark Y than the symmetrical wing profile you had before. It will create more lift at lower airspeeds and will require some negative angle of attack at high speed in order to remain in level flight. It will also have more induced drag and a higher pitching moment due to the higher lift coefficient. You basically have an airplane that is slower now than before it was modified.
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Old 03-06-2002, 03:51 AM
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Phil Heller
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Default What to expect when you thin down an airfoil

Hi Michael -

What chuckn says is not necessarily true. A symmetrical airfoil has to maintain a positive angle of attack in order to generate lift. True, some thicker symmetrical airfoils will take advantage of the the differentiation between the air pressure above and the higher density pressure below to achieve some lift, but basically at 0 angle it is just a directional vane. By eliminating the lower curve ChuckN is right, you have a flat bottomed foil similar to a Clark Y - BUT - it is a much thinner airfoil with about 1/2 the frontal area! It should create enough lift at speed to cancel any positive angle and the aircraft should fly faster. It will also probably land faster and stall at a higher speed. In many, many years past when I was flying Controline speed, my favorite and fastest wings started at the root as a Clark Y and gradually transformed to a symmetrical tip. Might be an interesting experiment for a pylon racer wing.

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Old 03-06-2002, 09:38 AM
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Ollie
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Default Airfoil Modification

Reducing the arc on the bottom of a symmetrical airfoil (no mean line camber) changes it to an airfoil with mean line camber. The devil is in the details. If too much of the bottom arc is taken off, the drag will increase in high speed flight. The thinning of the airfoil will reduce its minimum drag but it will occur at a lower speed. The increase in mean line camber will allow more lift in high speed turns and allow quicker, sharper turns. The balance between speed lost or gained in the straightaway and quicker turns will determine if lap times improve and by how much.

Why not go to an airfoil specifically designed for pylon racing like the S8052?
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Old 03-06-2002, 10:59 PM
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mglavin
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Default What to expect when you thin down an airfoil

Chuck, Phil and Ollie

Thanks for the input. I would have chose an airfoil like the S6061 or S6062 if I had built the wing myself. I have had good luck with these in the past. As I mentioned this was a modified wing form an existing model. The bottom of the wing has some arc and is not flat. I'll just have to give it a ride and find out what happens.

If the wing was not such a piece of work I'd propbably pitch it and start over. The wing has tip ailerons and servos with veneer installed to close the air gap, retracts installed and is sheeted. Its of reasosnable weight and what the heck worst case I can bolt on a stock wing or build another.

Thanks again for your help guys.
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