KNIFE-EDGE FLIGHT

  Knife-Edge flight is where the planes wings are 90 degrees to the ground and the side of the fuselage is acting as the wing (ie. producing lift). To fly a knife edge, apply full power, roll 90 degrees (so the wings are straight up and down), now apply enough rudder to  keep the nose from dropping (for example, roll 90 degrees to the right and apply nessasary left rudder). Depending on the plane you will more than likely have to correct with the ailerons and the elevator to continue a strait path. Usually the plane will try to roll out when you apply rudder, you correct this with opposite ailerons. When this is nessasray this is called having some "roll-coupling". Also some designs might pitch to the belly or towards the canopy, correct this with elevator. If it does need correction with the elevator this is called having some "pitch-coupling". With todays hybrid radios you can usually "mix" this coupling out, so instead of you correcting them the radio will!

     If you are the designer, type and want to make a plane with out any coupling heres how:

First of make your plane how you like it then go fly it. Roll into a knife-edge and see if it has any roll coupling. If it does heres how to fix it, if it rolls out of the maneuver (ie. with the rudder) than there is excessive dihedral and you need to lower the amout of dihedral in the wing. If it rolls into the maneuver (in the opposite direction than the way the rudder is applied) than there is not enough dihedral in the wing, and some needs to be added.

Now fixing pitch-coupling is abit harder.

Fly a knife edge and observe. If it starts to fly towards the belly (as if you were adding down elevator) than you need to lower the stabilizer or raise the wing or a little of both. For pitch to the canopy do the opposite.

I've found the best Knife-Edge set up is a plane with a wing JUST below the thrust line with NO dihedral, and have a stabilizer right on the thrust line. Also a rudder with little rake in the TE (ie almost the same length top + bottom) helps.

One last thing to improve knife edge flight is to have a tall fuselage profile, so there is lots of side area. Also a big rudder with a strong servo helps.

             -Darrell