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Old 03-13-2018, 08:45 PM   #11
Chic
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When rolling left while turning, the advancing (right) blade actually sees a relative reduction in lift do to Relative Wind effect on AoA. This induces a nose down attitude of the rotor disc.


No doubt Flamin Squirrel, graspin rotary aerodynamics can make your head hurt.
Furthermore, rotor hub variations and engineered control biases unique to each helo contribute to varied opinions amongst us.
Filtering out these variables and recognizing accepted rotary aerodynamic principles helps to get us on the same page.
I submit that, for the issue we are sorting, a review of Acceleration and Rate Cross-coupling might help.
Good luck with your pursuit. I'm jealous.
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Last edited by Chic; 03-14-2018 at 12:12 AM.
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Old 03-13-2018, 11:51 PM   #12
Gunnars Driver
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Quote:
Originally Posted by Chic View Post
When rolling left while turning, the advancing (right) blade actually sees a relative reduction in lift do to Relative Wind effect on AoA. This induces a nose down attitude of the rotor disc.
Yep.

The gyroscopic precession makes the action from a input 90 degree later in rotation, that might be the confusing thing for people trying to get this?

Rolling left ( cyclic stick perpendicular to the left) will make no change in pitch on blade when straigh to the right and straight to the left. Maximum pitch increase will be when the blade are pointing straight back and maximum decrease in pitch will be when blade is forward.

When rolling left the left blade moving down gets higher AoA relative to air, thus higher lift and gyroscopic precession makes this action come 90 degrees later, increasing lift behind rotor mast= nose down. Right blade going up see decreased AoA = decreased lift and action fomes 90 degrees later, nose down.

All this is a bit theoreticall. IRL you doesnt notice this. Roll rate vs blade speed make the nose up and down so small so you dont notice this fenomen.
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Old 03-14-2018, 04:15 PM   #13
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Quote:
Originally Posted by Chic View Post
When rolling left while turning, the advancing (right) blade actually sees a relative reduction in lift do to Relative Wind effect on AoA.
Not seeing how that would be the case.
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Old 03-14-2018, 04:59 PM   #14
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The advancing blade is on an ascending track due to the roll. This reduces the angle of attack, similar to the effect seen with up Flapping.
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Old 03-14-2018, 05:07 PM   #15
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Ah I see what you mean, yes.

I guess it depends on which ends up being the most dominant effect? That might well depend on the heli, as per your earlier post. I think I need a lie down now!
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