Hey Chuck, have a question about 3 blade gyro

skyguynca

Gold Member
Joined
Sep 23, 2004
Messages
1,162
Location
Acampo, CA
Aircraft
depends on what I have sold recently
Total Flight Time
5000+
Hey Chuck when you built your 3 blade gyro where you use a spider to control cyclic pitch to fly your gyro, what degrees aft did you set the head mast axis?

I am tempted to play with a tractor design using a helicopter style head with swashplate cyclic control.

I am thinking of using a 4130, .090 wall round mast to have a flexible mast to lower 2 rev shake. If I remember I think you had said that a round mast of this dimension would be a good choice.

Please direct me if I am wrong.
David M
San Jose, CA
 

Gyro_Kai

Senior Member
Joined
Nov 29, 2006
Messages
3,228
Location
near Frankfurt, Germany
Aircraft
MT-03, Calidus (rent)
Total Flight Time
about 150
I would throw into the discussion, that the 2/rev vibration only occurs in 2 blade rotors.
3-blades ones need to have lead lag joints, in order to cushion the changing drag per blade, while 2-blades ones do this with the entire mast.

Kai.
 

C. Beaty

Gold Supporter
Joined
Apr 16, 2004
Messages
9,854
Location
Florida
David, the limber mast is a requirement for seesaw rotors. 3 blade drag hinged rotors need a rigid pylon otherwise they can get into an instability called “pylon whirl”; a 3 blade rotor with a blade or two lagged back where the CG is off center produces a stirring motion that can react violently with a limber mast.

The 3-blade rotor that I played with was known as a “floating hub rotor”; a rotor without flap or drag hinges; such a rotor can tolerate a limber mast.

Here’s a discussion about such rotors from a number of years ago:

https://www.rotaryforum.com/threads/3-blade-rotor-system.11965/



The rotorhead axis was tilted back at a 9 degree angle.
 

skyguynca

Gold Member
Joined
Sep 23, 2004
Messages
1,162
Location
Acampo, CA
Aircraft
depends on what I have sold recently
Total Flight Time
5000+
I was thinking of using a 2 blade rotor. Sorry for not clarifying that. The reference to your 3 blade was just to specify that I intended on using a rotor system that used cyclic pitch control via feathering bearings and not the standard gyro teetering head. Also to inquire about the rotohead angle.

That is also why the question about the limber mast.

Sorry for not being clearer

David M
San Jose, CA
 

C. Beaty

Gold Supporter
Joined
Apr 16, 2004
Messages
9,854
Location
Florida
A rotor running at a 9 degree angle is operating at a lift/drag ratio of 6.3:1 (1/tan 9 degrees), typical for an airspeed of 50 mph.
 

skyguynca

Gold Member
Joined
Sep 23, 2004
Messages
1,162
Location
Acampo, CA
Aircraft
depends on what I have sold recently
Total Flight Time
5000+
Thanks for the info Chuck.

What do you think the best mast to use for the project to lower 2 rev?

David M
 

C. Beaty

Gold Supporter
Joined
Apr 16, 2004
Messages
9,854
Location
Florida
For a single place gyro with mast running in ~ the same direction as rotor thrust line, a 2” x 0.065 wall 4130 tube should be fine.
 

skyguynca

Gold Member
Joined
Sep 23, 2004
Messages
1,162
Location
Acampo, CA
Aircraft
depends on what I have sold recently
Total Flight Time
5000+
Thanks Chuck, I will post an idea drawing later today, having to home school the kids during the day because of the covid lockdown
 
Top