Airfoil for a 20" chord

[eplanedude]

I also asked this qestion in the Scale Modeling forum as I wanted to get more people to look at it. Here (http://www.rcgroups.com/forums/showthread.php?s=&threadid=67976) is the thread there:


This is just a hypothetical question. If you were to scratch build a large Corsair, say 94" WS. What airfoil would you use?


The reason I ask is I have a possibility on getting a large fiberglass fuse with a wing opening of 20". I talked to the maker of the fuse and he says it's the same airfoil as a Ziroli kit. I looked at the Ziroli plans and it's a monster of a big fat 15% thick airfoil. In my opinion, it'll hold back some of the performance. The builder, Ralph Saxton also said that as long as I could get the wheel tucked back into position inside the wing, any airfoil would work. He also mentioned that using a newer, thinner more laminar airfoil would probably increase performance. It would also move the high point back allowing the retracted wheel to more easily hide within a thinner wing.


So, knowing these parameters, what airfoil would you recommend? Would you go with it stock or change the thickness? BTW, the wheel well sits perfectly between 33% and 66% of the chord of the wing. The wheel on the retract is 2.25" thick so the wing at 66% must be at least that thick there! :D

[Sail 'n Soar]

Right off I would play it safe and stick with the Ziroli proven airfoil. 20" is a nice big cord. The other key question is what wing loading are you planning? The higher your wing loading, the faster you will have to fly, the higher the Reynolds number you will have. I assume you will be at greater than 1 pound per sq ft. But at one psf, your stall speed will be around 20 mph, or 30 ft per sec.

As I recall, at sea level Reynolds number = 6378*U*C, where U is the air speed in feet per second, and C is the wing cord in feet. With 30 fps and a 20" cord, your minimum Reynolds number will be greater than 300,000! At 300,000 you are beyond the low speed aerodynamic problems. About any foil you choose should work. Going thinner won't cut your drag that much, but will make the stall characteristics worse. And why would you want to go thicker?

[eplanedude]

This wing has a measured 1550 sq. in. (10.76 sq. ft.) and the plane my buddy has is 33 lbs. with a G-62 gas powerplant. That's a 49 ounce wing loading!!! That doesn't mean it'll land at 60 MPH, does it? He did say that weighing before and after painting showed 6 lbs of paint!! :eek: He also had to add nose weight to get it to balance. I'm hoping to apply a light paint job and NO nose weight. BTW, I weighed the white foam wings in thier cores this afternoon, 2 lbs, 12 ozs.!

I did call the maker of the kit last night and he said that up to 35 lbs., it's a real pussycat to fly. No bad habits such as wingtip stalling and a real low landing speed. At least that is incouraging.

[Dick Huang]

eplanedude,
The full size F4U used the NACA 23015 airfoil at the root and the NACA 23009 airfoil at the tip.
Dick Huang Vought Retiree:)

[Sail 'n Soar]

Without flaps it may not be 60 mph, but your landing speed will probably be somewhere around the mid 30's.