jm-urbani
Junior Member
- Joined
- Dec 21, 2010
- Messages
- 67
- Location
- French Riviera
- Aircraft
- home built mono seat
- Total Flight Time
- 300ish
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Doug it was a while back but I do seem to remember when setting up the cheek plates that we arranged a keel angle of minus 11 degrees when hanging from the teeter bolt. This seemed to give us a pretty level flight attitude. Was this a correct way of doing things? I also can’t remember if we did this pilot in seat or not?The rotor's thrust force pulls upward-and-back on the teeter bolt at an angle of 10-12 degrees aft of vertical (relative to the horizon) in cruise.
In flight the rotor is lifting so it’s weight is separated from the fuselage. If this logic is correct, the the weight of the rotor system from the point at which the rotor lift is applied, in relation to the weight of the fuselage, is zero. Why, then, must the rotor be installed during the second part of the hang test?For the second angle, wheel balancing, the rotor must be installed.
Another way of obtaining the second angle is to make up a harness of rope with one end attached to the rotorhead and the other end attacked to the most forward end of the keel with the hang line attached to the center of the harness. Then draw a straight line from the hang line.
The pilot must be seated on the gyro for all of the hang tests.
It’s easy if you have a laser level to project the continuation of the hang line.
In my opinion the rotor is a part of the mass of the aircraft and affects the center of gravity.In flight the rotor is lifting so it’s weight is separated from the fuselage. If this logic is correct, the the weight of the rotor system from the point at which the rotor lift is applied, in relation to the weight of the fuselage, is zero. Why, then, must the rotor be installed during the second part of the hang test?
I have to disagree. If you were car engine to find the cg and the only way to do that was to suspend it by a chain hoist from two different points, you would not include the weight of the chain during one measure and not in the other. Another example would be,as in a post several years ago, about the thrust angle. This post gave the example of hanging the fuselage from a tall bridge. Again you would not use the weight of the chain/rope to determine the cg.In my opinion the rotor is a part of the mass of the aircraft and affects the center of gravity.
I have to disagree. If you were car engine to find the cg and the only way to do that was to suspend it by a chain hoist from two different points, you would not include the weight of the chain during one measure and not in the other. Another example would be,as in a post several years ago, about the thrust angle. This post gave the example of hanging the fuselage from a tall bridge. Again you would not use the weight of the chain/rope to determine the cg.
One person said one of the reasons we do determine the cg is to center the stick. Now having said that, it does seem to be very important to find the cg to be above or there about the thrust line.
Lets chat about another subject which seems to be sort of ignored and its about the total mass, and specifically parasitic drag. The parasitic drag and the induced drag of the rotor systems seems to be very variable until you get the bird in the air and at its cruising speed and beyond. At that point the battle seems to be at a stalemate.
Common thought says the induced drag will diminish and the parasitic drag will increase with speed. The rotor system will gain efficiency and the fuselage will gain resistance to the wind.
All of these forces are balance around the CG? Or the thrust line. Seems to me the battle of the resistance game travels up and down the mast or fuselage as speed increases or decreases.
All of this play havoc with the stick pressures and trim. Not to mention when the thrust line ceases to be or the influence of the rotor lift/thrust line varies itself in turbulence.
So what really counts? Finding the CG vs thrust line on the ground?
You are correct and it is a part of the mass of the aircraft. If you want to find the cg of the entire aircraft, the leave the rotor on during both phases of the hang test.
In the air, the rotors are flying on their own with a burden of the fuselage independently dangling below. Maybe if it were a rigid rotor system and the rocking of the fuselage affected the rotor or vice versa in some major way might I consider the rotor to be a factor in determining the cg of the fuselage in the air.
I must say I do love our conversations.
Of course not. The fuselage is not independent of any motion from that of the wing. Forget the weightless rotor cause they fly discussion. My real question about this was the statement that the hang test from the rotor mast was done with the mast off. Then the test while balancing on the mains was done with the rotor on. It didn’t make much sense if one wanted an accurate reading. This rotor off rotor on didn’t come from me. This came from on of our long standing members. In my case, I have 29’ Skywheels on a 9’ mast and that’s a major moment arm and in my thinking a source of error.