A simple (or simplistic?) view of rotor behavior

[Jean Claude]

Q1, Q2: It is the speed difference (left / right) which produced the flapping angle. Not the position of the stick. The position of the stick lift rates by the average angle (i.e the axial component of Vo through the rotor)
Q3 Q4: The flapping angle is stabilized automatically: If> then the balance of lift decreases the angle. If <, then the balance of lift increases the angle. The flapping angle depends axial component of Vo, and RPM) . No possibility to hit the stops flapping, unless the retreating blade stalles (RPM too low and axial component of Vo too great

Q6 : fig 4 Yes , fig 5 No.
Jean Claude

 

[Resasi]

Sorry guys got fed up with flipping over the page, and to try to follow both the questions and answers. (A presumption and will delete if requested)

MARK: 1. This 'control input point' is where JC's calculated retreating and advancing AOA come in to play? (To equalize the lift... an angle of attack of 1.6 ° for fast stretch, 4.4 ° for the other. This occurs when the flapping of the blades is 1.4 ° ). Would the actual flapping angle therefore be greater overall? (probably relates to Q 4 also)

2. So is it therefore the pilot adjusting the blade pitch at this point and therefore the pitch AOA? ... or is the pitch of the blade that is tilting the teeter bolt rotational plane?

JC: Q1, Q2: It is the speed difference (left / right) which produced the flapping angle. Not the position of the stick. The position of the stick lift rates by the average angle (i.e the axial component of Vo through the rotor)



MARK: 3. If left to it's own devices, would the rotor keep attempting to adjust for the dissymmetry of lift until it hit the stops? The teeter bolt rotational plane has to be held to that position, or the rotor disc will keep pulling it back? (by trim spring or pilot?

fig 2 (front and side view of dic and teeter bolt rotational plane)

Below in Fig 3 is the 'teeter bolt rotational plane' defined, and also showing the different pitch at point A and C (ie 12 and 9 oclock)

(fig 3)

Fig 4 shows CB's cylinder with the blade tip path traced on it ... and 180* of the path (from 12 to 6) if we lay the pipe out flat**:

Q 4. I always find it easiest to think of the blades flying to a lower or higher point ... but do they simply follow a precise path, being pitched as required around that path, therefore creating differing amounts of lift/force? ie - so the teetering angle would not vary with different maneuvers... I find that difficult to imagine?

fig 4

JC: Q3 Q4: The flapping angle is stabilized automatically: If> then the balance of lift decreases the angle. If <, then the balance of lift increases the angle. The flapping angle depends axial component of Vo, and RPM) . No possibility to hit the stops flapping, unless the retreating blade stalles (RPM too low and axial component of Vo too great




Q6. Or do they fly a sigmoid path as in Fig 5? (badly drawn ...)

fig 5

JC: Q6 : fig 4 Yes , fig 5 No.

 

[C. Beaty]

Here’s a plot of JC’s sketch #46 unrolled. There’s nothing mysterious about the path followed by a rotor.

The view from the rotorhead axis is simply that of the blades moving in a simple sine* curve, to a first approximation.

Viewed from the real axis of rotation, the blades don’t do anything except feather periodically.

The most confusing thing is that clocks, usually, run one way and rotors, usually, run the other way.

*What’s a sine curve? Stick your finger in the light bulb socket and you can feel one.

 

[Resasi]

Thanks CB.

Again, clear and illustrative.

* Very droll.

 

[Mark E]

Thanks JC for the answers to my questions,

and thanks Leigh for presenting that on one page ...

and thank CB for the excellent diagrams -

 

[Mark E]

....................The view from the rotorhead axis is simply ................

Viewed from the real axis of rotation, ......


*What’s a sine curve? Stick your finger in the light bulb socket and you can feel one.

I admire your ability to visualize these things Mr Beaty, the only view that works for me is an outside view looking in ...ie an orbiting camera on the plane the teeter bolt rotates on, looking inwards past the blade...

Tried your sine curve visualization ...thought I saw the light for a moment, but ....