The plane: Aces 1 Edge 540 profile

The question: To sand or not to sand the leading edge round from the 90 degree angle?

Pros and cons of sharp leading edge, or will it make a difference on this D tube wing.

Thanks,

Jess

I believe a more blunt leading edge gives gentler stalls. Definitely all funfly planes that i've seen have very very blunt LE's.

Sand it round for absolute sure. Angled leading edge stalls at higher speed compared to rounded. I have seen a discussion of the idea of leaving the 90 degree angled le in the root, and gradually rounding as you go out to the tip, on the theory that this will guarantee root will stall first, not the tip. But my guess is with this model a rounded leading edge all along the span will be a gentle staller with no tip stall problems. If I'm wrong, you can put an angled stall strip along 20% of the root span and fix the problem. Out of fifty sport/scale kits or more I've built, I've never seen plans calling for anything but rounded leading edge. Maybe some jets like a sharp le, but I don't do jets. (Not smart enough or brave enough or rich enough.)

The flow around an airfoil has a stagnation point where the flow seperates to go over and under the airfoil. As the angle of attack increases the stagnation point moves down and aft from the leading edge a little. With a sharp leading edge, the flow over the top of the wing must first negotiate the sharp leading edge. The sharp leading edge causes turbulence and with increasing angle of attack, seperation of the flow resulting in premature stall. As angles of attack increase, a rounded leading edge allows the flow over the top of the wing to stay attached longer delaying the stall.

More rounded LE goes to a higher angle of attack, but it is an abrupt stall. More pointy LE stalls at a lesser angle but it is a softer stall.

Hmmmm.... :surprised

Some airfoils with round leading edges stall abruptly, some sustain lift for several degrees increase in angle of attack while the drag increases a lot before loosing lift and some airfoils with rounded leading edges don't recover lift after a deep stall untill the angle of attack is reduced well below the stall angle of attack (hysterisis).

Any airfoil which has had the leading edge only modified from round to sharp will stall at a lower angle of attack than its prototype.

I can verify this with the story of my Ace Seamaster.

Many years ago, I built one after seeing what a nice seaplane it was. I didn't like the cardboard tube they used as a leading edge, so I cut a foam wing and "just for looks", gave it a sharper leading edge than the original.

After two seasons of adjusting weights and balances to try to get the thing to land properly, I heard about the "sharp vs. blunt" leading edge thing. I then cut off the sharp leading edge, and added a rounded one, and the plane has been flying great ever since!

I have a Stinger 120 with the wing built according to plans. That is, the leading edge has a radius of maybe 1/8" - 3/16". That's pretty small next to a 18" chord and a thicknes that is over 2".

Flies great, lands slow. Thing is, I want to be able to have better control over the stall as I transition to hovering and hopefully other things (harrier, etc) down the road. Right now, as it gets the nose up, I get wing rock. A rounder LE might help, but inducing separation near the mid-span with stall strips might work as well. I've heard some say that sharper LE is the key and some say that blunter, and some say that a tapered radius works. Without really knowing how the wing stall progresses on this wing, it's hard to tell which approach is right for the Stinger.

I'll probably start experimenting with stall strips soon, by taping 1/4 balsa tri to a small section of the LE.

Comments..?

Another alternative would be to have a more blunt LE at the root and thinner at the tip. You would have to do one wing first, then make cardboard profiles say,every 6 ins apart to get the same profile on the other wing. Also make sure it's not dutch roll causing the wings to rock in which case you would have to add rudder area or add a dorsal fin

Absolutely you must round this LE on the Edge 540 Profile. That is a key design parameter and directly affects the transition stability between high alpha 3d flying. Thanks to the above posts for great answers to why this is important. It's interesting to note that pattern guys invented the shapr LE at the tip (not the root) many years ago to aid in predictable snap roll initiation and termination. During snap rolls the wing tips are stalled!

i HAVE A COMPOSITE YAK THAT WING ROCKS BAD IN A HARRIER.
WHAT DO WING STALL STRIPS LOOK LIKE?
DO THEY POINT UP OR DOWN
THANKS

They point forward. They look like a piece of angle iron glued to the LE