Hello,

I'm making a 1/4 scale Extra and looking over many different designs of kits and full scale I noticed there is a difference in airfoils between the model and full scale.

I've noticed the full scale has the thickest part around 18%-20% or so but the models are around 25%. The model I'm making will be for 3-d and slow speed of course but could some one tell me which would perform better.

These images I uploaded are just an example of the differences. One is thicker with thickest part closer to the front and other thinner with thickest part further aft.

I'd use the fatter forward for 3D which requires slow speed stuff.

The full scale extra uses a thinner aerofoilf due to the fact that it relies on speed more than brute horse power of the engine. Most RC models are overpowered and thus can do more aerobatics at a slower speed with the thicker aerofoil, mostly due to the fact that the thrust to weight ratio is so much greater for the models as compared to the full scale type. I would definately use the thicker aerofoil for slower speed!!

Reg

Of the two the first one will tend to delay the stall more. The forward thickness and blunter leading edge are the reasons.

That's almost exactly what I thought also, fatter more forward airfoil for better 3-d.

I also found this one that's from a Cap 21, 15.59%@15.7%

The first one was a 12% Joukowski. All these I found with Profili 2.
So using the fatter more forward theory the cap 21 would be an even better airfoil?
Maybe I should make 2 sets of wings with these 2 airfoils and see which one flies best.


Thanks guy's.

Kelvin.

Yep the last one you posted is pretty much the same as a Wasp wing. You can pretty much draw a 2 1/2 circle and then draw straight lines back to a point for that profile of wing . They fly very well at slow speeds.

Do you mean the sirex wasp? I have one and can vouch for the airfoils slow speed performance, mine is overweight, but you still have to try very hard to stall it.
When it does stall, the only way you can tell is the slight bobbing motion the nose of the plane makes.

That's good news. I'll have to try it and with any luck it might make a good slow speed 3-der.