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Airfoil considerations....multiple questions...

Old 01-23-2006, 09:19 AM
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r3tic
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Default Airfoil considerations....multiple questions...

I am in the preliminary stages of designing a couple of aircraft, one sport and one scale. For the sport plane I am looking for an airfoil that is fastish and with some aerobatic capabilities. I have Profili 2 for drawing out the plans but I would like to know what would be a good airfoil to go with.


With the scale plane....I haven't picked which one I would like to do first.... I would like to know if there is a database somewhere that has the different airfoils for full scale aircraft.



Also if anyone could point me in the direction of an on-line tutorial for cading plans I would appreciate it.


Thanks for any feedback



Dave
Old 01-23-2006, 01:12 PM
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Pelle Gris
 
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Default RE: Airfoil considerations....multiple questions...

Database of scale airfoils.

http://www.ae.uiuc.edu/m-selig/ads/aircraft.html
Old 01-23-2006, 01:24 PM
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SoCal GliderGuider
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Default RE: Airfoil considerations....multiple questions...

You don't want to use a full scale airfoil for a scale aircraft. The air molecules just don't behave the same over the smaller wings. Several considerations must be taken into account such as is the wing built up or will it be moulded? What is the projected weight/size of the model?
Old 01-23-2006, 03:56 PM
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Default RE: Airfoil considerations....multiple questions...

For the scale model a current hot item is the Selig 7036. It deals with higher wing loadings better than many others. If it's a classic lightplane style of design then just use the good ol' ClarkY.

For the other one any of the symetrical options in the 10 to 13% range will do nicely. Something like the Selig 8020 would do nicely and has a minimal drag over a decently wide range of angle of attack so the speed won't slow much for gentle to medium maneuvers at speed.
Old 01-23-2006, 08:18 PM
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Default RE: Airfoil considerations....multiple questions...


ORIGINAL: BMatthews
For the scale model a current hot item is the Selig 7036.
I think you meant to say S8036 Bruce. If it's a tapered wing, S8036 at the root with the S8037 at the tip with a degree or 2 of washout.
Old 01-23-2006, 10:12 PM
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Default RE: Airfoil considerations....multiple questions...

I have GOT to stop relying on my memory........ Yeah, what Dickeybird said...
Old 01-24-2006, 08:17 PM
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Default RE: Airfoil considerations....multiple questions...

Thing that I have found on reducing scale airfoils, is that they no longer permit retracting landing gear to fit within the confines of the wing. Usually the model tire and retract gear is then just too big to fit. If you are working upon some jet, forget it for most of them are too thin for commercially available retract parts.

Wm.
Old 01-25-2006, 09:40 PM
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e=mc2
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Default RE: Airfoil considerations....multiple questions...

Isn't it true that the Selig 8036 - 37 combination does not work well with flaps over 40°? I think deploying flaps causes an excessive pitch up moment which could raise the pucker factor if the CG was already a little more aft.

I am designing a 1/3rd scale airplane and was considering this airfoil combination, but didn't really want something that could give me a premature heart attack . I am not a very good r/c pilot yet, getting better though [sm=RAINFRO.gif]

Thanks
e=mc2

Old 01-25-2006, 09:58 PM
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Default RE: Airfoil considerations....multiple questions...

Any style of simple flaps will cause a strong pitch if used at speed. Oddly enough I've found with flaps on two gliders that if you let the model slow down to the trim speed with teh flaps down the need for down trim almost completely goes away and the model just floats along. In any event this pitch up is not restricted to the 8036 and '37 by any means. In fact it would be a very rare exception that did not have a strong pitch up effect when flaps are deployed if the flaps are any good as what they are supposed to do.

However if you alter the style of flaps then things change. Split flaps, where the top surface stays consistent and a flat flap comes out of the lower surface, show very little tendency to pitch up. This is because they add far more drag than they do lift in relation to the surface area that moves. Expamples of this style are found on the Spitfire and T6 Texan.

But obviously folks will want to use a flap style that is close to the original in the case of a scale model. Fortunetly with modern Tx's having the ability to mix their hearts out it's easy to mix in some down trim to go with the flaps.
Old 01-29-2006, 09:39 AM
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r3tic
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Default RE: Airfoil considerations....multiple questions...

First of all...Thanks for all of the feedback. As far as what plane I'm looking to build and the techniques I will be using, I think I am pushing towards composite construction. Again I'm not too sure what my sport plane will look like, but it is basically going to be a test platform for my scale project. I'm leaning towards a couple of jets for my scale project. Either the X-29 or possibly the Ares 151.


If anyone knows of any tutorial for going from 3-view to cad drawing I would greatly appreciate links.


Thanks again
Old 01-29-2006, 03:52 PM
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Default RE: Airfoil considerations....multiple questions...


ORIGINAL: r3tic
...If anyone knows of any tutorial for going from 3-view to cad drawing I would greatly appreciate links.
The first part is simple. Jus import the 3 view image and trace lines over top of the image. If it was a small image you'll have trouble centering the CAD lines over the image but just fake it. Ideally you get yourself a really nice fine lined full page 3View and scan that in first. working off the usual small files is a pain and results in only a "sorta scale" final product. It's the old Garbage In, Garbage Out scenario. Your final CAD 3vew is only as good as the quality of the image file.

From there things get complicated in a hurry. You need to have an understanding of the appropriate structural needs to arrive at a strong but light design. Light where possible and strong where needed and a good way to transition the loads from the strong points to the light ones without creating stress concentrations.

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