Dehidral

[strouse]

What would be a good amount of dehidral for a small low wing model with throttle, elevator and, aileron control. The plane will be about 7oz. and 130"^2. I'm looking for somewhat aerobatic, but still pleasant to fly. Thanks.

[Tony Oliver]

Size of the model isn't important, so 7 degrees each side for very stable flight - self righting almost - and half that for easy roll but some self righting capability. None for a neutral flightpath - requiring opposite aileron to stop the roll and/or return to level wings.

With a low wing model the dihedral requirement is slightly larger than for high wing, but it often looks wrong if you have too much.

It also depends a lot on other things - fin area and placement, and side area and its distribution in the fuselage.

Tony

[vintage1]

For rudder only operation, 3 -4 degrees for parasol wtng, 5 degrees for cabin style high wing, and 7 degrees for low wing.

For aileron operation, its pretty much 0 degrees for high wing, and 3-4 degrees for low wing, if you don't want too much 'self righting' in a bank. Zero dihedral on a low wing will tighten in the turns by itself, so some is in order.

Lets say enough dihedral to put the center of the wings level with the center of gravity of the model when looked at from the front. So if the fueslage has the CG more or less along the center line, and the wing is on the bottom, the tips should be level with the top more or less.

Needless to say every model is different, so this is a very rough guide only.

[Ollie]

If you mean by pleasant to fly, that the plane is somewhat stable in all axes, then that is at odds with the aerobatic ideal of neutral stability on all axes. Where the balance falls between these conflicting ideals is a matter of personal taste. The advice you have gotten from Vintage 1 seems a good compromise to me. The yaw to roll coupling caused by dihedral makes axial rolls much more difficult.

[strouse]

Thanks for the help. The model is the most aggressive I've built yet. The layout is "normal", ie- fuse 70% of wingspan, wing at 30% of chord 1/4 back on fuse, and stab area around 20-25% of wing area. The power to weight is around 1.2:1. The bottom line is I'm afraid its beyond , my abilities. By pleasant to fly I want I want a plane that rolls well, but doesn't require 100% input to come out of a bank. I've flown mid wing aileron model of similar class OK(Split 280). Rolls are the most important manuver to me, and its a flat bottom airfloil. I guess its a toss up between zero to three degrees of dehidral. Thanks again. WStouse.

[Ollie]

Flat bottomed airfoils require a lot of down elevator while the plane is inverted during the roll in order to try to keep keep the roll axial. Little or no dihedral requires up elevator for level turns. The amount of up elevator required is minimized by an aft CG that gives close to neutral pitch stability.

New planes usually require a lot of adjustment to get them to fly close to the way you want. Also new planes require quite a bit of stick time before the pilot is comfortable with the way they handle and can get the most out of the plane.