Getting a grip on gyroscopic precession?

[weedy]

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The notion that one can push or pull on the disc at all is incorrect. Consider the situation when the rotor blade is fore and aft. When you pull back on the stick, you can have no effect on the rotor because the teeter bearing will simply allow the rotor to swivel about the axis that you re trying to manipulate it on.

But, a control input onto the Rotor Head is directly changing the rotational axis of the disk. It is this that forces the change in the AoA of the blades relative to the previous "disk plane"

[Magnifan]

Yes you are correct, as the rotor turns around this new axis the AoA of the blades changes, which rsults in a precession of the disc. Actually my brain is getting tired of trying to visualise this!

[Wargames]

Positional Statement;

1. Gyroscopic precession (torque-induced precession) explains the activity inside the flapping/teetering hinges.
2. Aerodynamic precession, including non-gyroscopic dynamics, explains the activity outside the flapping/teetering hinges.
3. An exception to 2. is the rigid rotor where, because of the flapping stiffness, some of the blade that is out is of the virtual hinge will partially contribute to the gyroscopic precession.

Therefor;

* Gyroscopic precession has nothing to do with teetering rotors.
* Gyroscopic precession has very little to do with all other rotors.

As per Kosies links. This is for helicopters, and they have established that precession is actually not having much of an impact on rotor craft. A Gyro's rotor is much simpler and do not have teetering rotors.

Why do you guys discuss this topic as if your Gyro's have teetering rotors??

[Condor]

I am so glad there are clever guys that can write a doctorate on why gyro's fly.

I can then sit back and enjoy my plane and worry as to do I have enough fuel left (as this is far easier to understand)

[Magnifan]

Our gyros do have teetering rotors.

I read the thread quite carefully last night. The positional statement is, from what I could research, his personal opinion, but the only debate as far as I could see, was whether we are dealing with gyroscopic precession or aerodynamic precession whch both act in the same manner, as a result of the change of AoA of the rotor blade at some position on its path around its axis of rotation, and always at a point in advance of where the final effect will occur.

[Gyronaut]

A Gyro's rotor is much simpler and do not have teetering rotors.

Why do you guys discuss this topic as if your Gyro's have teetering rotors??

Is this wordplay on the plural Dirk? Rotor/Rotors?

A gyro HAS a teetering rotor system. Fact. The rotors do not teeter individually no. Technically a semi-rigid rotor system.
The rotor system is semi-rigid in-plane, because the blades are not free to lead and lag, but they are not rigid in the flapping plane (through the use of a teeter hinge). Therefore the rotor is not rigid, but not fully articulated either, so we call it semi-rigid due to the teetering between the two rotor blades... or am I repeating myself...

Lekka topic

[Wargames]

Understand that. Sounds better to the ear though.

Next question:

Please explain that in relation with the following quote you gave in a previous post. I read it as opposites, but maybe I'm wrong.

This is the function of the blades flying to position. The blade's pitch change precedes the resultant flap or teeter.

[johnht]

What a most interesting topic! I'm coming in a bit late, but I really wnat to raise a point (hopefully this has not already been discussed somewhere already!)

Is the rotor of the Gyro really a gyroscope at all, and thus posess/exhibit gyroscopic properties? At the risk of being shot down in flames, I suggest not! Here's why:

The Gyro's rotor consists of two blades fixed to a central (teetering) hub, which when spinning, appears as a rigid disc - not a real disc. If one looks at a bicycle wheel (a good example of a gyroscope), it is a ring with spokes of equal length connecting it to a central hub about which the it rotates (could equally well be a flat disc with an axle through its centre). It is a real ring. Our rotor is nothing like this. If I look at my Gyro's rotor hub, the only little piece that could be construed to be gyroscopic is the pre-rotation gear - hardly able to have any gyroscopic influence. It is my conclusion that the rigid virtual disc moves in the direction we want is simply the result of our applying the appropriate force in the desired direction. I don't see anything supporting the idea of the effect of gyroscopic precession. I do agree that if one was to apply a very sudden force to the stick, depending on the position of the advancing blade one could experience some undesireable movement, but then with the rotor spinning quite fast, the movement on the stick would have to be very abrupt and forceful.

Hopefully what I've said makes sense - and even more hopefully it's correct! But I'm prepared to bow to someone else's superior knowledge!

Regards
John

ZU-REB

[Gyronaut]

Wargames, I quoted that from Kosie's link-article to illustrate prevalence of aerodynamic precession rather than gyroscopic precession. More accurately perhaps pitch should read AOA "this is the function of the blades flying to position. The blade's pitch/AOA change precedes the resultant flap or teeter" since technically our gyro's have fixed pitch blades.

[lion]

"School of Mechanical Engineering" 44 page PDF

http://www.google.co.za/url?sa=t&source ... LtSc5dmCXg

[Magnifan]

Thanks lion, it looks like a very interesting and comprehensive document.