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Model Forum / Radio Controlled / Air Models / November 2003Right thrust?
I'm in the process of repairing my electric 3D airplane. When I checked the thrust line, it turned out to be about 3 degrees to the right. I had thought that it should be 2 degrees. My question; Is (Are) 3 degrees too much? While we're at it, doesn't right thrust become left thrust when the plane is inverted? Hmm.... Wan right thrust only matters if the nose is up. Do a full power vertical climb as close to vertical as you can and let go of the sticks and see which way it yaws. If it goes right, it is too much. also check to see if it pitches up or down when you do this. You may even need up or down thrust. Brad > I'm in the process of repairing my electric 3D airplane. When I > checked the thrust line, it turned out to be about 3 degrees to the [quoted text clipped - 6 lines] > > Wan > I'm in the process of repairing my electric 3D airplane. When I > checked the thrust line, it turned out to be about 3 degrees to the [quoted text clipped - 4 lines] > While we're at it, doesn't right thrust become left thrust when the > plane is inverted? Hmm.... Exactly. A plane designed for symmetrical flying should have (i) No thrust offset of any sort (ii) Thrust as near to CG and Cof drag as possible (iii) No dihedral (iv) Fully symmetrical wing section (v) As much fin and rudder below teh cenbter line as above (vi) plenty of fuselage side area for knife edge. and a fair bit in front of the CG as well as aft. (vii) Ailerons in the prop wash. That way it will fly in almost any attitude. Side thrust is normally used with dihedral to counteract torque rolling via yaw. Its a bastrad way to do it. If teh ailerons are in teh wash, just couple a tad of right stick to teh throttle. That should work even in 'hover' > Wan answer to question #1--NO answer to question #2--NO > I'm in the process of repairing my electric 3D airplane. When I > checked the thrust line, it turned out to be about 3 degrees to the [quoted text clipped - 6 lines] > > Wan > I'm in the process of repairing my electric 3D airplane. When I > checked the thrust line, it turned out to be about 3 degrees to the [quoted text clipped - 6 lines] > > Wan Is is correct. There is no magic number for right thrust, but enough to make absolutely sure you don't have left thrust is always helpful. The Right thrust acts in relation to the propeller thrust, regardless of the attitude of the plane. Pete Baylinson > > I'm in the process of repairing my electric 3D airplane. When I > > checked the thrust line, it turned out to be about 3 degrees to the [quoted text clipped - 9 lines] > Is is correct. There is no magic number for right thrust, but enough > to make absolutely sure you don't have left thrust is always helpful. > The Right thrust acts in relation to the propeller thrust, regardless of the > attitude of the plane. That's what I thought! John > Pete Baylinson > > wanjung@toast.net (Wan) wrote in message [quoted text clipped - 12 lines] > > Is is correct. There is no magic number for right thrust, but enough > > to make absolutely sure you don't have left thrust is always helpful. >>The Right thrust acts in relation to the propeller thrust, regardless of >> [quoted text clipped - 3 lines] > > That's what I thought! I didn't, because frankly that statement makes no sense anyway. IF you have dihedral, then anything that introduces a yaw, will end up rolling the model. Right thrust works to counteract power dependent rolloing moments via dihedral. Right thrust works upise down - as does rudder, because when upside dwon teh wings have ANHEDRAL if you like. To get an invrted rudder only model to turn left, you do indeed use LEFT rudder, which doesn't turn the plane INTO the desired bank, it turns it OUT, but the (anhedral) rolls the plane in the OPPOSITE direction to the yaw, and if you then take the rudder off, and apply some 'down' elevator, you can turn your plane to the left...a most unnatural looking manouver to be sure, but thtas how it works.. If you have no dihedral, then right thrust is going to simply make your model yaw, and not actually turn it right. IF you have sweepback, and no dihedral, then the effect is to always roll in the direction of the yaw. So under these circumstances the right thrust will roll the model to the right , right way up, and to the left, when inverted. Its no surprise then that pattern models have no right thrust and slightly sweptback wings, typically. This makes them behave the same way either way up, and any propwash/torque effects are taken care of by aileron trim, and, with teh ailerons inboard near the propwash, the work under low airspeed conditions as well. Sidethrust IMHO is an ugly way to get a scale model or trainer to track straight when you haven't got a computer mixer. On a neutrally stable aerobatoic model it shouldn't be necessary. > >>The Right thrust acts in relation to the propeller thrust, regardless of > >> [quoted text clipped - 21 lines] > If you have no dihedral, then right thrust is going to simply make your > model yaw, and not actually turn it right. Now, there is an aerobatic low-wing homebuilt aircraft known as the Jurca Scirocco that has NO dihedral. The designer felt that dihedral was not always necessary for stability. This airplane will roll in the proper direction when rudder is applied, even without dihedral, partly because the fuselage blanks a bit of the inside wing as a skid begins. Many high-wing airplanes have no dihedral either, and behave perfectly normally, banking when yaw is introduced. The Bede BD-4 is one. All of the Cessna high-wingers have only a degree or so, and still bank with yaw. There are other factors that will make a wingtip rise if the wing is yawed a bit. I believe a minimizing of the tip vortex on the leading tip has something to do with it. Our first RC was a powered two-axis sailplane, with plenty of dihedral. It banked normally using rudder whether right side up or upside down, though it was difficult to keep it inverted. In full-scale training, you will learn that the turn is accomplished using bank angle, to change the lift vector from vertical to toward the centre of the turn. The rudder is used ONLY to eliminate the adverse yaw created in most airplanes as the downgoing aileron on the outside wing creates more drag than the upgoing aileron and pulls the nose a bit away from the desired turn direction. Rudder is a coordinating device, not a turning device. Using rudder to turn creates a skid, which at low speeds can result in an uncoordinated stall and a spin. Dan |
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