Lu
The results of gyroscopic precession and aerodynamic precession are the same, but the result of gyroscopic precession is easier to see. It therefore is a quick way to explain precession to mechanics and pilots who have to work with it but do not necessarily have to know its 'innards'. If a pilot or mechanic want to fully understand precession then to continue to explain it in terms of gyroscope precession becomes a problem.
I am not saying "
that gyroscopic precession has nothing to do with helicopter rotors". It plays a role, but its
direct roll is a very small one and its
indirect role is exactly that ~ 'indirect'.
A gyroscope (gyroscopic precession) functions because of high mass and high rpm. Aerodynamic plays no significant role.
A rotor (aerodynamic precession) functions because of aerodynamic forces. Mass and high rpm play no significant role
Direct role:
I believe the magnitude of gyroscopic precession's direct role in aircraft is dependent upon the rigidity, mass and speed of the device. A propeller will have a reasonable amount of gyroscopic precession, whereas a teetering rotor will have very little.
Indirect role:
Nick mentioned "
The wheel is rigid, of course, so each part of it cannot move relative to any other.". What he is saying [I think
]is that a force at one location on the
rigid wheel is creating forces at all locations on the
rigid wheel. If a force at 90-degrees azimuth results in an upward force of 5 lbs at that location then there will be a force of -5 lbs at 270-degrees. There will be a sine(45) * 5-lb force at 45 and 135-degrees. There will be a 0-lb force at 0 and 180-degrees, etc,etc. The culmination of all the upward forces is at 180-degrees, and this is the high point. . The culmination of all the downward forces is at 0-degrees, and this is the low point.
Nick is talking about a singular force being distributed around the circumference due to the rigidity of the circumference. As he said, he is describing gyroscopic precession.
The helicopter rotor does not have this rigid ring at its circumference. It also does not have a singular force at one location. The pitch of its blades is providing a force
directly to all the locations.
For these reasons, I believe that aerodynamic precession is a cleaner description.
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In addition
Gyroscopic precession and aerodynamic precession only give the same results because the swashplate and gyroscopic precession produces a sinusoidal curve. When the swashplate (pure sinusoidal curve) is replaced, gyroscopic precession must fly out the window. This is because the new pitch controllers will be able to put into the blade any pitch at any azimuth they want to. I.e. no longer pure sinusoidal.
In the case of an intermeshing or coaxial helicopter, it may be possible to add a little additional short-term pitch to the lower blade as it passes through the downwash of the upper blade.
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Phase lag, Gamma, offset and delta-3 are subjects for other future threads.