Originally posted by Hal deBolt
Dear Stick.
Are you trying to pull someone's leg? Forward sweep plus anhedral yet ! Believe you are serious?
I doubt if this combo has ever been tried. Forward sweep yes,
Anhedral yes but in combo ???
I have no way of knowing if you understand what you are going
to use or not. So will summarize briefly>
Wing sweep: it detracts a bit from lift. it reacts a bit like hedral,
tending to right a craft upright or inverted.
Sweep back is primarily used to delay compressability when approaching Mach 1.
Many years agoit was used on rubber powered models supposedly so less dihedral would be required
Sweep forward reacts similiar and it is said to be more efficent.
Dihedral and anhedral react in a similiar fashion. When the craft
turns laterally on the longitudinal axsis one wing panel effectively
becomes longer and closer to horizontal while the other panel
effectively becomes shorter with an increase in hedral.
The longer panel has a lift increase tending to right the craft.
When a dihedraled craft flys inverted it has anhedral. So when a
anhedraled craft flys inverted it has dihedral.
There could be different control reactions between the concepts
but that is beyond the scope of this message
Hope this helps, good luck!
Hal [email protected]
hmmm... the dihedral explanation given above is commonly quoted, but it's not entirely correct. if the aircraft is flying at zero sideslip, dihedral will have no effect. The reason that dihedral tends to right an aircraft is because when the airplane is banked over, it tends to "slip" downhill in the direction of the bank. This results in a sideslip angle which has a component in the y direction (y is the axis that runs out the right wing). This component creates a net upforce on the low wing, since the sideward component is hitting it from the bottom. The high wing, on the other hand, sees the crossflow hitting it from the top (since the dihedral angle is in the opposite direction on that side), and therfore is pushed down. This results in a moment (torque) that tends to right the airplane. It should be noted that the above argument neglects the fuselage's influence. In the case of a high wing airplane, due to the flow around the fuselage in a sideslip condition, a wing with zero geometric dihedral actually demonstrates positive effective dihedral. Likewise, a low wing aircraft with some positive dihedral can have no effective dihedral (witness the CAP 232).
If anyone is incredibly confused by this explanation and its lack of clarifying illustrations, let me know... I'll draw some pictures that should help. I know I had a hard time with it in Flight 2.
On the anhedral forward swept thingy... why? I don't see any reason to pursue such a design - other than that it would look cool, which is reason enough, I suppose. But in order to have something that behaves well, you'll probably want to sling the fuselage under the wing to counter some of the negative dihedral with the fuselage flow, and make sure to put a nice big vertical fin on it. (see below)
Starfire's design rule number 3: If you think the fin might be a little to big, make it bigger. Too much fin is a little extra weight and maybe spiral divergence, which won't hurt you in an R/C, but too little fin, and it'll do the "bonanza boogie". Poorly damped dutch roll is no fun.