[question] Two bladed rotor system
Thread Starter
Joined: Aug 2004
Posts: 68
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From: NE
[question] Two bladed rotor system
Hello
in a hangar talk discussion, this come an argument:
"...in a two bladed rotor system, the blades can change from the 180º position (lead lag)... to equalize the forces in each blade during forward flight ... this is accomplished by the hub itself ... "
using, as example, the rotor head of the R22, and what is written in the POH - "main rotor articulation : free to teeter and cone, rigid inplane",
i always have the idea, that 180º is always maintained and the forces are resisted by the hub itself, that "fights" to maintain it (resistance of the materials)
comments?
thanks
regards
in a hangar talk discussion, this come an argument:
"...in a two bladed rotor system, the blades can change from the 180º position (lead lag)... to equalize the forces in each blade during forward flight ... this is accomplished by the hub itself ... "
using, as example, the rotor head of the R22, and what is written in the POH - "main rotor articulation : free to teeter and cone, rigid inplane",
i always have the idea, that 180º is always maintained and the forces are resisted by the hub itself, that "fights" to maintain it (resistance of the materials)
comments?
thanks
regards
Joined: Nov 2004
Posts: 1,334
Likes: 0
From: Cambridgeshire, UK
CS-Hover,
I would have a look at the various types of rotorhead that exist:
Aircraft in Detail - Helicopter Rotorhead Gallery Index
You could also lookup "effective hinge offset" in Prouty.
2 bladed rotors "teeter" about a bush on the hub to keep the machine weight (and cost) down. The blades actually cone slightly above the plane so that centrifugal forces carry the weight of the heli.
I would have a look at the various types of rotorhead that exist:
Aircraft in Detail - Helicopter Rotorhead Gallery Index
You could also lookup "effective hinge offset" in Prouty.
2 bladed rotors "teeter" about a bush on the hub to keep the machine weight (and cost) down. The blades actually cone slightly above the plane so that centrifugal forces carry the weight of the heli.
Joined: Dec 2001
Posts: 1,835
Likes: 3
From: Philadelphia PA
The lead and lag forces are absorbed by the hub, but as these forces change due to rotation, they are taken up by the mast.
The mast actually has a slight twisting and untwisting as the blades go around.
If that helps confuse the situation.
The mast actually has a slight twisting and untwisting as the blades go around.
If that helps confuse the situation.
Joined: Apr 2003
Posts: 1,635
Likes: 1
From: Vancouver, BC, Canada
Shawn has given the answer that you are looking for. Undersling reduces these unbalanced in-plane forces.
The following sketch is of a Kaman intermeshing twin-rotor. It requires another means of handling the lead-lag, because the two rotors are mechanically interlocked. You can see that Kaman uses lag hinges and a friction damper.
Dave
The following sketch is of a Kaman intermeshing twin-rotor. It requires another means of handling the lead-lag, because the two rotors are mechanically interlocked. You can see that Kaman uses lag hinges and a friction damper.
Dave
Joined: May 2001
Posts: 563
Likes: 1
From: queensland australia
the underslinging of the yoke, holding the blades on to the gymbal with pillow blocks, allows the yoke to rock under the head and this small action absorbs all the hunting stresses bought about by acceleration and deceleration of the blades. very simple and very effective.
