Originally Posted by
Ascend Charlie
Robbiee, you must have learned somewhere other than the Hew Hess Hay - someplace where instructors have over 100 hours more than their students, and where the horsefeathers aren't passed from one under-informed pilot to the next. Well done!
Some people still think that "flapping to equality" is happening in forward flight, and that even though the disk is tilted down at the front, "the advancing blade is still flapping up."
Hmmm.
We may be speaking different dialects of English, but here is the equation of motion of flapping in forward flight, [eq:6.130 of reference]
The aerodynamic coefficients are the flap moments due to angle-of-attack changes produced by the blade pitch, twist, inflow, flapping velocity, and flapping displacements, respectively. A flapping velocity produces an angle-of-attack perturbation that changes the blade lift to oppose the motion; hence the blade has aerodynamic damping given by the coefficient MBetadot.
Johnson, Wayne. Rotorcraft Aeromechanics (Cambridge Aerospace Series, 36) . Cambridge University Press.
Now, remove flapping to equality and you need a ton of cyclic input to achieve a zero roll moment other than your desired roll command. Helo aerodynamics and the laws of motion, control derivatives etc are fun; there is a lot going on and most of it is non linear, but it has algebraic solutions to give an understanding of what is actually going on. For transition from steady state hover, there is a characteristic cyclic position to achieve a flight path, and that is able to be determined using all of the effects that occur in the process, and right in the middle of that all is the harmonic of flapping motion.
In what context are we telling people that "flapping to equality" (a passable descriptive term of harmonic flapping) doesn't occur in forward flight?
Beta is flapping
Theta is blade pitch
Zeta is lead/lag...
Psi is the azimuth position that is being considered.
And here is the Fourier series of the harmonic motion of a rotor, and that gives the flappy bit above which is occurring in forward flight.
These harmonics don't suddenly stop as the rotor shaft, skids, fuel, engine, and bio mass starts to move forward, they explain the motion that results at all times.
Your comment confuses me, I can only refer to the equations of motion in our universe.
