suitcase

My Feedback: (1)

I don't know if any of you are familiar with the thread that addresses the problem with the Funtana S 40's wing leading edge. There's a thread in the 3D forum, and at the end is some posts about a mod to the leading edge which supposedly fixes the tendency to stall at the worst moment. It involves sanding off the current leading edge and adding new balsa and resanding to a more constant shape the entire length of the wing. I have a new plane unassembled and the leading edge is wierd in that it's thicker and more blunt on the end than the root. Very much so. Those who have done the mod swear by it. I was just wondering if one could fab the end of the wing to look like one of the sticks, i.e. US 120 or the big boy. My Mayhem has that same style of wing tip and the stalls are totally predictable. Would that make the wing better of worse?

dolanosa

suitcase,

Thicker LE's generally will delay the stall so in the case of your Mayhem, the root will tend to stall first, which is a good thing. You can simulate this by adding triangle stock to the root LE's and go about 1/5 - 1/4th out spanwise. (triangle stock used for testing only. I don't recommend leaving them on.) You should notice that the plane will stall a little earlier (very sharp LE of the triangle stock) but straight ahead since the tips are still flying. If you're happy with the performance, you can sand down the root LE ot a sharper profile.

I was trying this out on an old plane, a 60 size stick a few years back. It was already a good flying plane but a little on the boring side so I decided to make that into a test bed for different configurations.

Hope this helps.

suitcase

My Feedback: (1)

If I understand you correctly, the Funtana's wing should work well because the leading edge at the root is thinner than at the tip. Yet many complain about the terrible stall characteristics of the plane and several have done modifications to the wing with, according to them, great results.

rainedave

My Feedback: (1)

suitcase, that does seem a bit strange. I know that old pattern planes from the '60s that had tapered wings often used the root LE radius all the way to the tip. As dolanosa explained, the blunter LE at the tip made the inner wing stall first. The Taurus is a prime example of that.

In your first post you said "more constant shape" LE. That sounds to me like the same thing as saying "constant radius." If the root rib is, say, 3" thick and the tip rib is 1" thick, then the LE radius will get smaller if the rib is simply reduced in size. Sticking the root rib's LE radius on the tip rib will result in a blunter airfoil. Another thing that a lot of designers do is to keep the thickness the same while making the chord shorter on tapered wings. That's sort of like using an NACA 0014 at the root and transitioning to an NACA 0018 at the tip, same effect.

suitcase

My Feedback: (1)

"like using an NACA 0014 at the root and transitioning to an NACA 0018 at the tip, same effect. " Huh??
Look, I'm just a dumb ***** welder. Don't get too tech on me ok. Yeah, I mean the mod was to remove the existing leading edge and install a 5/8" piece of square stock and sand to shape, making the leading edge "sharper"as opposed to "blunter"... all the way to the wing tip. Looking at the H9 Funtana 50, the wing seems to have the exact same shape to me.

dolanosa

If I remember correctly, the wing design of the Funtana 40 is that the thickness of the wing stayed constant. I forgot what the thickness is but let's say it's 1.5". For example, the root chord is 10" and the tip chord is 5", the thickness would stay the same at 1.5" thick. Now I'm just using those numbers as an example. The root is 15% thick but the tip is a whopping 30% thick! Now, even though air tries to stick to the surface to the tip, it's actually pretty difficult since the incoming air is basically hitting a wall, and probably causing separation early instead of sticking to the foil. This is just a theory. As far as the other planes are concerned such as the Mayhem, their LE's might be blunt but they have a pretty big chord at their tips in contrast to the Funtana's puny chord.

I haven't seen the mod yet but I think I'll search for it tonight. I bet that you add some balsa to the leading edge (which is what you said) and shaped it like the LE of the ROOT. Is that right? I can't wait to find out. Anyway, my theory goes: (and this is only a 2D wing section thinking, no spanwise flow or anything like that)
1. The sharper leading edge actually guides the air more efficiently, rather than hitting the leading edge of a balloon and actually stalling out.
2. The additional chord length helps a little as well.
3. Probably even the little bit of added wing area helps.

Anyway, that's my 5 minute thinking about this problem. Wish I still had my Funtana 40. Believe it or not, I lost it while I was moving. I don't get it. How does one lose a huge box with a plane in it while moving?