M/R Pitch Change Horn

[blkhawk16]

I was wandering why there is a difference between helicopters in the placement of the pitch horn on main rotor blades. I know for the R-22 it is 78 degrees. Gyroscopic precession takes place 90 degrees later, so why are pitch horns not placed at 90 dgrees from the blade. Does it have to do with the number of blades? Maybe control input response time?

 

Any input would be appreciated

 

Thank-you,

blkhawk16

[joker]

blkhawk16,

 

Good observation. The 90-degrees we are taught is a theoretical value for gyroscopic precession.

 

In reality, due to those things you mentioned the 'phase angle' adjustment (Gamma) means that for different helicopters the pitch horns will be offset from 90-degrees. Yes, the R22 is 78; the S76 its 57 I believe.

 

Other factors which will vary this value must be then RPM, blade chord, aircraft speed etc..etc..\

 

Joker

[FauxZ]

The frequency of the blades flapping also plays a role, correct? As in, we have to allow time for the blade to fly to it's new position.

 

Now we know the offset for rotation is 78°, but what is the delta 3 angle for the MR on the R22?

[joker]

18 degrees isn't it?

[FauxZ]

18 degrees isn't it?

 

That sounds right, but I don't have the reference with me.