arp67

My Feedback: (55)

I am designing a giant sport scale A-4 skyhawk in pusher config (brushless motor) and need to decide upon an airfoil for the project. A scale wingspan on the model is about 60" and I was planning to stretch this out to 70" or 72". I plan to use a symmetrical airfoil. The few delta wing model plans I own use a symmetrical airfoil with the max chord thickness around the 50% length of the airfoil....so this leads me to believe that delta wing models use their own set of airfoils? Anyone know what airfoil was used on the old Bob Violett A-4, the JHH A-4 or the Yellow Aircraft A-4?

Thanks,
Andrew

funkworks

If it were me, I would start with a symetrical airfoil with a thickness of 12%-14%. Possibly with a max thickness location at about 30% from the leading edge. I'd add in about 2 degrees of washout at the tip too. I would also build it flat upside down and have the tops of the ribs lined up so you end up with a little dihedral in the wing.

arp67

My Feedback: (55)

funworks,

That is exactly what I did on a smaller scale A-4 skyhawk I designed and built a few years ago but have not flown yet....great minds think alike! I guess it should be safe to just upscale what I did on the smaller Skyhawk and see what happens.

Thanks,
Andrew

BMatthews

You'd better crunch the numbers on that. 12 to 14% on that big a chord is going to produce a VERY thick airfoil.

Symetrical is fine but I think you're going to want to use something more like about 5 to 6% to keep the thickness anywhere near scale'ish looking.

funkworks

...fly your small one (if you still have it) to see how it responds before investing into the larger one. I think it will be ok as long as you keep the wingloading reasonable. The A4 has a high tail so be careful when slowing it down b/c the wing might blank out the elevator at higher angles of attack. Thats something you can check out first when the model is nice and high up in the air before making a nose high approach for landing... Keep us posted on your progress!

arp67

My Feedback: (55)

Thanks for the input guys....I will have to dust off my smaller skyhawk and get it ready to fly and see how it performs.

Andrew

BMatthews

I saw a Byron ducted fan A4 fly with a more or less stock thickness airfoil and it was actually pretty darn good. I second the testing at the high altitude but it didn't seem to suffer at all from stabilizer blanking.