1/4 scale T-Craft S.C. 46" Floats incidence setup HELP
07-15-2006, 04:52 PM
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1/4 scale T-Craft S.C. 46" Floats incidence setup HELP
OK, the top of the "round top EDO" Sea Commander Floats 46" are slightly bow/nose down so plane is slightly at a positive angle of attack in the H20. But here is my problem. What is the flying angle of the plane as it flys thru the air? I know with the tail-drager you throttle up, the planes tail rises and eventually lifts of ground. With a nose wheel the opposite happins, the tail lowers and it flys away from the ground. With floats the plane rises on step and flys off H2O. ALL 3 situations the plane flys level when airborn. But the ? is what is the incidence of this level flight? is it + 1 or 2 or is it 0. So when setting up these floats (basicly the N struts) what do i set the plane to? I put a level on the stab, I put an incidence meter on the wing, they are both equal and are level set at zero with the fuse set on shims and spacers.( i wosh i bought the fuse cradel with the float cradel i have) OK... it just doesnt look right, it looks to nose down. The prop shaft angle seems nose down as well as seen from nose to tail. So what do i due/us? or is this just an illusion b/c the fuse tapers so much from cockpit to tail. HELP... Also the CG of plane should be 1" or so ahead of the step, and float tips about 2" ahead of prop. Well for what i have test fit so far, the step is 2" behind the CG and the float bow/tip extend 4-1/2 " infront of prop arc. HOW should i average all that out. Thanks to all very much...
07-16-2006, 12:10 PM
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RE: 1/4 scale T-Craft S.C. 46" Floats incidence setup HELP
If I'm reading your post correctly, the incidence angles are correct. The incidence between the top of the floats and the chord line of the wing should be set at 1.5-2 degrees. In flight you will need a bit of up elevator trim to balance the drag of the floats, so the airplane will fly slightly nose up and the floats will fly slightly nose down.
The step position is the important one. Put the step 1-2" behind the CG. That rule of thumb for nose extention beyond the prop is a minimum.
Jim
The step position is the important one. Put the step 1-2" behind the CG. That rule of thumb for nose extention beyond the prop is a minimum.
Jim
07-16-2006, 03:44 PM
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RE: 1/4 scale T-Craft S.C. 46" Floats incidence setup HELP
Alternately, put the plane and floats on a flat surface and rock it back until it is resting on the step of the float and the stern (of the floats). At that point, your wing should have 7 degrees AoA.
07-16-2006, 10:25 PM
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RE: 1/4 scale T-Craft S.C. 46" Floats incidence setup HELP
Im sorry i mite have been a little unclear, its hard 4 me 2 explain this with text... What im trying 2 find out is at what angle does the plane fly level? Zero or plus 1-2 degrees? At zero on incidence meter, stab is zero, engine around -3 ish. So im assuming the plane flys thru the air level arond 1.5 positive and the engine would then be -1.5 so all equal. It is a semi-sym. wing so im thinking it has to be positive not 0. I could be wrong... What angle does the plane fly??????????????????????
07-17-2006, 01:59 AM
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RE: 1/4 scale T-Craft S.C. 46" Floats incidence setup HELP
I suppose you think there is a simple answer to that question. 
The correct answer is, it varies depending on airspeed. At slow speeds, the wing needs to fly at a high angle of attack (which is not the same as incidence, but we can pretend it is) to make enough lift to keep the airplane up. As speed increases, so does the lift and so the angle of attack necessary to keep the airplane up will decrease. That is why you need to add up-elevator to maintain altitude when you fly slowly.
The simple answer would be that after trimming the elevator for level flight, a conventional monoplane, at cruise speed, flies with the stab at approximately 0 degrees to the airflow. With a semi-symmetrical airfoil, 0 incidence (angle of attack) does not mean 0 lift. At high speed your T-craft will fly with the wing at 0 and the engine at -3. At low speeds the wing may be as much as 2 or 2.5 degrees positive.
Add floats and the wing needs to operate at a higher angle of attack to lift the extra weight. Now the wing will have to cruise at perhaps 1 or 1.5 degrees positive. You accomplish that by adding up-trim to the elevator.
None of that has anything to do with float incidence. The floats have to be set at an angle that will allow the airplane to safely build up speed on the water. The rising angle of the rear of the floats will allow you to add 3 or 4 degrees to the angle of attack of the wing when you add up elevator for take off lift. Setting the float tops 1.5 degrees negative to the wing chord line on your T-craft will give you +1.5 degrees of wing incidence when the floats are level. (Just about matches the high speed requirement.) That should allow you to safely run along the water as you build speed and the floats will allow you to increase that angle of attack to 4 or 5 degrees with up elevator for take-off.
Aerodynamics is a very complex subject. This explanation is oversimplified in order to get the basic point across. I hope you find it helpful.
Jim
The correct answer is, it varies depending on airspeed. At slow speeds, the wing needs to fly at a high angle of attack (which is not the same as incidence, but we can pretend it is) to make enough lift to keep the airplane up. As speed increases, so does the lift and so the angle of attack necessary to keep the airplane up will decrease. That is why you need to add up-elevator to maintain altitude when you fly slowly.
The simple answer would be that after trimming the elevator for level flight, a conventional monoplane, at cruise speed, flies with the stab at approximately 0 degrees to the airflow. With a semi-symmetrical airfoil, 0 incidence (angle of attack) does not mean 0 lift. At high speed your T-craft will fly with the wing at 0 and the engine at -3. At low speeds the wing may be as much as 2 or 2.5 degrees positive.
Add floats and the wing needs to operate at a higher angle of attack to lift the extra weight. Now the wing will have to cruise at perhaps 1 or 1.5 degrees positive. You accomplish that by adding up-trim to the elevator.
None of that has anything to do with float incidence. The floats have to be set at an angle that will allow the airplane to safely build up speed on the water. The rising angle of the rear of the floats will allow you to add 3 or 4 degrees to the angle of attack of the wing when you add up elevator for take off lift. Setting the float tops 1.5 degrees negative to the wing chord line on your T-craft will give you +1.5 degrees of wing incidence when the floats are level. (Just about matches the high speed requirement.) That should allow you to safely run along the water as you build speed and the floats will allow you to increase that angle of attack to 4 or 5 degrees with up elevator for take-off.
Aerodynamics is a very complex subject. This explanation is oversimplified in order to get the basic point across. I hope you find it helpful.
Jim
