Question about teetering rotors

[zeja]

Hello everyone,

I am a young research who is doing some numerical simulation of helicopter rotor blades.
Nowadays, I am computing the two blades AH-1G. It is a teetering rotor.
I need for my simulations to know the flapping mode of the helicopter for given flow conditions:
betha=betha0+A*cos(azi)+B*sin(azi)
I have the values of the A and B from the experiments of the helicopter but there is no data of betha0 (cone angle).
I may be wrong, but since it is a teetering rotor, is this betha0 (cone angle) the same as pre-cone angle?

Hope somebody can help me. Thanks in advance :D

[Ascend Charlie]

Send a PM to Nick Lappos or Shawn Coyle, both experienced test pilots.

The average pilot hasn't got a schmick about his cos lettuce, sin contracts and tan booth values.

[Shawn Coyle]

Way past my knowledge, I hate to say. Nick???

[ShyTorque]

Zeja,

Most of us here are pilots. We fly helicopters, not design them.
Your question is a mathematical one, as far as I can understand it.

[Otterotor]

Zeja,

Precone angle (permanently designed into the rotor hub) is arrived at using the calculated centrifugal force for a blade and the design lift the blade is intended to generate. The Arc Sin of thrust / C.F. produces P.C. angle, generally around 2.5 degrees. So for one thrust condition (100% design thrust) and one RPM (100% Nr, and assuming the C.F. is calculated correctly) the coning angle = Pre Cone Angle. This angle relieves the steady stress in the main rotor hub generated by Beam Moment or Mb and thus the peak stress levels which are the sum of the steady and max positive oscillatory beam moments.:ok:

[John R81]

That's easy for you to say !

[Dave_Jackson]

betha=betha0+A*cos(azi)+B*sin(azi)
I have the values of the A and B from the experiments of the helicopter but there is no data of betha0 (cone angle).
I may be wrong, but since it is a teetering rotor, is this betha0 (cone angle) the same as pre-cone angle?

Different rotary aerodynamicist will sometimes use different symbols.
Wayne Johnson and Gordon Leishman uses the following. Gareth Padfield is more detailed but appears to be in agreement with the following;
Beta ~ blade flap angle (positive upward).
Betap ~ precone angle.
Betao ~ coning angle.
Beta1c ~ longitudinal tip-path-plane tilt angle (positive forward)
Beta1s ~ lateral tip-path-plane tilt angle (positive toward retreating side)

I assume that (azi) stands for 'azimuth'.

Hope that this helps.


Dave