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Old Jan 21, 2005, 02:53 AM
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best wing shape

hi

i saw some of wing shapes for models but i am confused now
because i dont know what kind is better for an indoor model

does anyone haveany idea about this?

thanks for any input.
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Old Jan 21, 2005, 09:35 AM
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Frederick Maryland USA
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There was an article a few months back in RCflyer (I think, but am not certain) that presented a wing that had a maximum cross section of 4% of the chord with this maximum thickness located 40% of the way back from the leading edge as an optimal wing section for slow flyers. I cut the article out for my files which are at home. I can check on the details for you if no one else has anything else to offer.
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Old Jan 21, 2005, 01:51 PM
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Design to the lift and Cl distribution over a wing. Design to combinations of AR, sweep, taper and twist. Design for the angles of attack range you want with in working airfoil range of angle attacks. Play around the program.
http://aero.stanford.edu/WingCalc.html
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Last edited by Ollie; Jan 21, 2005 at 01:58 PM.
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Old Jan 21, 2005, 03:40 PM
B for Bruce
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The 'Wack, BC, Canada
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Indoor models often just use a simple arc shaped airfoils with only the top side covered. For very low airspeeds thin is best and single sided is as thin as you can get. The height of the arc should be between 3 and 5% of the chord of the wing.
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Old Jan 22, 2005, 08:10 AM
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thanks all friends for your inputs

"The height of the arc should be between 3 and 5% of the chord of the wing" what this means(3 and 5% of the chord of the wing!?)

but about this arc you was mentioned i saw some of models that leading edge of the wing is covered to downside but tailing edge is not covered to much
such as i know with this setup the plane will do flight with difference of pressure between top wing and down this setup make the plane to go forward with more speed (because of less friction betwin the wing and the air)but what i dont know is with this setup my wing needs for tail shaping or no and is this setup suficent for model flight or i need for any else shape for it??
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Old Jan 22, 2005, 01:14 PM
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my mean is in this case it seems the model dont need for a angle of attack!?
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Old Jan 22, 2005, 03:08 PM
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The term 3% refers to the wing chord x 3/100. The wing chord is the distance from leading edge to trailing edge. So a 10 inch wing chord would have an airfoil with a 0.3 inch arch for the airfoil.

Actually now that I think of it 3% is too small. 5 to 8% sounds much more like what the real indoor rubber models use for the airfoil. So a 7 inch chord wing with an 8% arc aifoil would have an arc shaped airfoil that is 7 inches long and 0.56 inches high at the highest point in the middle of the arc. An arc is just part of a circle

That help?

All airfoils even with the arc (also called camber) must fly with some angle of attack. For free flight indoor models that angle is up somewhere close to 5 or 6 degrees because we set the model to fly very slowly and just a little bit faster than the stalling speed for best flight times. Radio control models change the angle of attack all the when you use the elevator control and change the speed with the throttle. When going fast they have a small angle of attack and when going slow the angle is higher.

Quote:
but about this arc you was mentioned i saw some of models that leading edge of the wing is covered to downside but tailing edge is not covered to much
If I'm reading your english right I think you are trying to describe how some wings use balsa sheeting from the front of the wing ( the leading edge) back to the spar and just have open ribs from the spar back to the trailing edge. Is that right? If so then the function of the balsa sheeting is to add some extra stiffness to the wing and to prevent the covering from sagging between the ribs where the curve is the tightest. If the sheeting on the top of the wing is match by sheeting on the bottom with a full spar at the thickest part of the wing then we call that type of construction a "D" tube wing because the spar, top and bottom sheeting all form a D shape. The D tube style is very stiff and warp resistant.
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Old Jan 22, 2005, 05:54 PM
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thanks alot BMatthews for your attention
see these pics,they show what i was saying
my mean was i saw some of wings such as what you see at 2 first pics with no any angle of attack that and what is making the lift is wing shape
how? such as i heard This wings have airfoil shaped profiles that create a pressure difference
between upper and lower wing surfaces, with a high pressure region
underneath and a low pressure region on top that makes the lift
if it is correct so plane can go forward with more speed because the wing has a very very small friction between the air (because we have a very very little angle of attack) and in this case we need for less power for push the plane

i wanted to know is this correct,am i wrong

why at third pic designer used from that setup for the wing see near the top of the wings?

thanks
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Old Jan 22, 2005, 06:47 PM
B for Bruce
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The arched shape of the last model with just the simple single side covering is what I've been talking about so far. It sounded like that was what you wanted.

Aifoils like you show do have lift with a zero degree angle of attack and they even have lift with a negative angle for a small range. the arch or camber of the airfoil does this. But even these airfoils will operate at higher angles of attack depending on how slow you are trying to fly. At high speeds the angle for level flight may be negative if the model is light enough. At just before the stall the angle will be highly positive. In between it depends on how fast you fly and how heavy the model is. In other words it's constantly changing. Especially with a radio control model where you use the elevator a lot. Every time the elevator moves it changes the wing's angle of attack.

You can play with this idea online at http://www.grc.nasa.gov/WWW/K-12/airplane/foil2.html . Its best if you use the DOWNLOAD APPLET and install it in your own computer. You'll also need Java installed. But once working you can play with the camber and angle of attack and see the lift changing in real time. Very educational.
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Old Jan 22, 2005, 06:56 PM
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Quote:
Originally Posted by BMatthews
All airfoils even with the arc (also called camber) must fly with some angle of attack.
Not neccessarily....

--Alex
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Old Jan 22, 2005, 09:06 PM
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Alex, read my last post just above your's where I clear up what you saw and confirm the idea of low and even negative angles. But yeah, you're right, I goofed that one.

All airfoils have what is called an Angle for Zero Lift. For a symetrical airfoil that angle is 0 degrees and for cambered airfoils that angle is a negative angle.

OK?
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Old Jan 22, 2005, 09:53 PM
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o, okay. didn't see the post.
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