Clipping wing

[edragon]

The wing on my 40 size sport plane (similar to a Sig 4*40) has a 60-inch wingspan, 13-inch constant chord and fair amount of dihedral. I've put the CG at about 50% chord, but the plane still won't do flat spin at all or lomcevek consistently. I'm afraid to move the CG any further back. What effect would clipping the wing tip (like 3 inches off both sides) have on making the plane more aerobatic?

[phlpsfrnk]

Clipping the wings should make the roll rate faster. It will also increase the wing loading due to less wing area so your landing speed will increase. I don't think the dihedral will allow very good flat spins. For the kinds of maneuvers’ you are trying, get an acrobatic plane or at the least an aileron trainer with little or no dihedral.

Regards
Frank

Takeoffs are optional, landings are mandatory.

[edragon]

I guess I could saw the wing in half and then reglue it back together without dihedral. It's probably a lot cheaper than buying a whole new plane.

[Brandano]

Why don't you just build a new wing instead? You could just keep a short constant chord central section and two tapered outer panels so that it will fit properly with the fuselage, and if it doesn't work you can still go back to the older wing.

[lincoln]

It will make the low speed handling tricky, but I understand that aerobatic planes sometimes use stall strips far out on the wings so that the stall just starts out there. Basically, they are just a bit of material added to make the leading edge sharp. But if you get nice snap rolls when you want, you might also get snap rolls when you don't want them!

[vintage1]

Flat spin probably needs less fin area..but that compromises knife edge.

[BMatthews]

A good snap and lomcevak comes from mostly a marginal design that is close to "disaster" at the best of times in terms of snap rolling. If this is a 3D model with the typical generaous horizontal and vertical tail surfaces then it's no wonder you're having troubles. As vintage pointed out the side area and fin area is a key item. Too much of both is great for knife edge looping but that much provides far too much spin damping and it'll be hard or impossible to achieve a true flat spin. It's sort of like your model comes complete with built in anti spin fin strakes. But if you reduce these to achieve a flat spin then you will find you can't knife edge as well.

Life is about compromises.....

[edragon]

I crashed the plane this week. I put the CG too far back. After flying for 20 minutes, lack of fuel caused the engine to quit. The plane was quit high; so I made a series of zig-zag over the runway. I overdid it. The plane stalled and dropped a wing, at about 6 feet off the ground. Right wing tip hit the asphalt not too hard, but then the plane cart-wheeled. The wing is built like a tank; it survived with a scratch or two. However, the fuselage is built like cheap korean car; it snapped clean in half. Lesson learned: don't move the CG too far back.

[Brandano]

Shame, but if the snap is clean it ought to be fixable.

[Texas Buzzard]

Flat Spin : No dihedral, minimum fin and large rudder + CG moved aft as far as posible.

In some 40 years of flying I have seen just one RC actually do a true flat spin and that bird was difficult to fly.

[StevenatorLTFO]

I had an old Midwest fun scale 109 that would flat spin really nicely, sometimes on purpose, and other times with little or no warning (snap, spin, and not come out). I flew it into the dirt two times, when I got it flat, and it would not come out for anything. To spin it flat, I would get it in a rudder/elevator only spin, then when rotation was firmly established, cross over the ailerons.

It was built per the plans, except I ditched the last wing bay on each side, and very small amount of dihedral. It was fun to fly, but would bite back without alot of warning.

(and yes, the CG was way back, pretty close to 50 percent MAC)

Steve

[MCarlton]

Just back from an RC hiatus...

Are what 3D pilots call "flat spins" actually "spins" as in the aircraft is stalled? Or are they just high AOA descents with a high yaw rate due to the large rudder/propwash?

It seems to me that most "flat spins" I have seen involve the throttle being pretty much fully open and the spin being maintained by the propwash over large surfaces with big throws?

Matt