Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

X-speed own design, airfoil selection

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Old 09-09-2005, 03:35 PM
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Default X-speed own design, airfoil selection

Hi Folks,

I've been CAD-ing up ideas for a scratch built go-faster, and was looking to the pylon and general go-fast types for airfoil advice.

I am talking about a ~ 44-46" span model designed around a .50 or 60LX, i.e. .46 case size motor, designed to do pretty much what Magnums and the like do.

I have looked at MH43, RG14, thinned RG14 and the like, ignored basic NACA sections for now, and am thinking there must be some preferences based on other's trials and tribulations with pylon model design etc. I can build a stiff enough wing with the thinner sections, materials issues don't scare me. I've designed quite a few successful sport aerobatic models and other this and thats, and can handle basic aero design, but a pure speed model capable of turning around and heading back towards the field before it is out of sight is new for me...

Any thoughts/suggestions? p.s. I have Compufoil.

Mike D.
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Old 09-09-2005, 03:44 PM
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Default RE: X-speed own design, airfoil selection

I built a speed plane using this one, low renolds number, its a selig 6063. It was suggested to me in the aerodynamics forum.

Edit, Sorry the attached gif was too big to attach.
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Old 09-09-2005, 03:49 PM
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Default RE: X-speed own design, airfoil selection

Here is a real good airfoil / pylon site with lots of ideas, check it out:

http://www.mh-aerotools.de/airfoils/
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Old 09-09-2005, 04:01 PM
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Default RE: X-speed own design, airfoil selection

Excellent site, thank you. Plus the bonus Cox section.

Mike D.
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Old 09-12-2005, 09:34 AM
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Default RE: X-speed own design, airfoil selection

Some things to keep in mind - decide up front if you want this to be a pylon type model, or a pure speed model.

Although there are similarities for both, pylon models are designed (if done properly) optimized for turning performance with a good balance of straight line speed. Most of the faster ones use composite wings, and airfoils that can only (for the most part) be molded from tooling and still build strong and stiff enough.

If this is a pure speed machine, straight line speed is what you are after - turn performance is for manuvering and control only. You can select lower lift and more 'unloaded' wing sections that are very quick, but terrible at high alpha.

And as noted a bit above, consider how you are going to build the wing. If its going to be foam/wood built by hand, you will have to be able to actually fabricate the airfoil you select. (I spent two weeks last winter trying to build a 'wood' reflexed airfoil. I had to basically carve the last 20% of the chord and sand it to death using some templates)

Bob
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Old 09-12-2005, 04:34 PM
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Default RE: X-speed own design, airfoil selection

Understood. I realize there is a tradeoff between ultimate top speed and performance at higher loadings/alpha. I would be tempted to start with a pylon-oriented airfoil, nothing says I can't build a second wing to experiment. Well, nothing except dorking the aircraft that is..

No reflex, this is not a flying wing. Some of the more critical airfoil sections I realize will not be much use if not reproduced accurately. I plan to build a capped spar to inset between the front and rear core halves, plus lay up a composite D-box under the balsa sheeting. This would be assembled and sheeted in the female foam shells as per standard foam wing practice. Have already made some very strong, stiff and light wings that way. Not as good as a CNC-cut billet mold but I ain't going that route!

Mike D.

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