choosing an airfoil for a scale model

[shaneyee]

I am planning to build a 1/8 scale model of the Messerschmitt BF110 twin engined night fighter. It will have an 80" wingspan and wing area of 880sq in. Root chord is 16" and the tip chord is 6" so there is significant taper. I was worried about tip stall because of the highly tapered wing so I posted a thread about it in the scale section of this forum. I received some good practical advice which I plan to incorporate:-

1. Percentage Wing tip airfoil thickness should be greater than root thickness
2. Washout of 1/4" at the tips
3. Blunter leading edge at the tips than the root.

On the question of airfoil selection, it wasn't so clear.... I was going to the well known Clark Y section but someone suggested the Clark YH instead. Various people thought that the Clark Y had too much camber which could predispose the wing to tip stall....

Since I have Profili, what parameters would I have to study to determine what AoA the airfoil stalls at? What other characteristics should I be looking for? Can I use the popular glider airfoils like the MH32 for good L/D - that cant hurt can it?

Thanks

Shane

[vintage1]

Not sure it will really matter. I have used thin wingtips with sharp LE and not had problems. And a section just eyeballed a bit.

The key is washout and a thin tip.

Any really nasty tendencies can often be tamed by adjusting outboard ailerons a little bit 'up'

[shaneyee]

Actually, I am from the TLAR school and honestly, I dont think it will matter in terms of flying qualities but.... I really want to improve on my design skills and learn a bit more. Reading how Mark Drela designs his sailplanes has been an eye opener... his is a clear headed methodical approach and there's a reason for everything . Of course, there's all that theoretical knowledge behind it and thats what I want to learn.

Shane

[Sparky Paul]

For that size plane, a Clark-Y or NACA 2412 would be perfectly fine.
Washout at the tips, keep the same nose profile for the thinner tip airfoil.

[BMatthews]

The original used an airfoil that was near symetrical. No reason you shouldn't follow that pattern. The end result will be a model that is happier when doing even scale type aerobatics. I'd suggest the NACA 2412. This is a low camber section with a flat lower rear portion so it makes it easier to build and the 12% thickness is close to scale and a good section for carrying a heavy scale model. The other option I'd suggest is the Selig 8035 which is used by Top Flite on some of their scale kits and has a reputation for carrying heavy wing loadings well. It's supposed to have a softer stall with lots of warning.

For the book camber actually raises the stall angle of attack and therefore delays the stall. Using a section with an % or two more camber at the tip in conjunction with some washout will almost guarantee no tip stall.

[shaneyee]

Thanks all for your input.

The NACA 2412 seems to be well regarded for this use. I shall try it out along with the other tips.

1. Percentage tip thickness should be greater than percentage root thickness.
2. Washout will be incorporated
3. The leading edge should have the same radius all the way out to the tips.

Appreciate all your help.

Shane