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My understanding of the effect of dissymmetry of lift was that an imbalance between the advancing and retreating blades, for example as airspeed is increased, results in fore-and-aft tilting of the rotor disc (flap back), which is corrected by forward cyclic. The pilot increases pitch of the retreating blade relative to the advancing blade by applying forward cyclic, not right cyclic -- is that not correct?

 

My understanding of the need for left cyclic when transitioning through ETL is due to an imbalance in lift production between the forward and aft halves of the rotor disc (inflow roll/transverse flow effect), which like the above case causes a response from the rotor disc 90 degrees later.

 

I can't think of an effect that would require right cyclic as speed increases, and even more confusing is that it appears to be required at 90kt but not at 100kt...

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My understanding of the effect of dissymmetry of lift was that an imbalance between the advancing and retreating blades, for example as airspeed is increased, results in fore-and-aft tilting of the rotor disc (flap back), which is corrected by forward cyclic. The pilot increases pitch of the retreating blade relative to the advancing blade by applying forward cyclic, not right cyclic -- is that not correct?

 

My understanding of the need for left cyclic when transitioning through ETL is due to an imbalance in lift production between the forward and aft halves of the rotor disc (inflow roll/transverse flow effect), which like the above case causes a response from the rotor disc 90 degrees later.

 

I can't think of an effect that would require right cyclic as speed increases, and even more confusing is that it appears to be required at 90kt but not at 100kt...

 

You answered your question in your first sentence. Keep in mind these are cyclic trim requirements you probably don't even notice. Most pilots correct subconsciously to these seemingly small needs for trim. If you're an R22 pilot, you have a trim knob for this.

 

That the backward S pattern that's sometimes called the cyclic snake. it's a regular S on helicopters with clockwise turning rotors from above.

 

it's called the snake because the cyclic trim position kind of snakes around the hover position as you push forward and gain airspeed. Also, coning roll increases as more thrust is produced.

 

XyvrxQB.jpg

 

https://youtu.be/_Hrm3DRyKg8

Edited by iChris
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Thanks for taking the time to explain all this repeatedly. After much reading and re-reading here, FM 1-51, and the Wagtendonk I see the light and it seems obvious now that cyclic action is what compensates for (or maybe more accurately prevents) dyssemetry of lift when the cyclic is used to gain airspeed.

 

I wish my flight school would have at least mentioned it. They spent so much time making sure we understood dyssemetry of lift and flapping to equality when airspeed is >0, but didn't touch on cyclic blowback and the ramifications. Again, obvious once you've considered it but the way it was presented was 0 airspeed = no flapping, >0 airspeed = flapping.

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