collective / torque change?

Is it just me? I'm running the UH-1 UN campaign at the moment, and for the mission Teachers, there's a long stretch at the beginning of constant speed formation flight.

As I have been running it, I have noticed that substantial collective changes, like 25% or more, aren't requiring any rudder inputs, it's like there's no torque effect. Is that the way it's supposed to be when cruising at speed, and I just never noticed? It also strikes me as odd that when I do any turns, I am having to always input reverse rudder, right rudder for a left turn, to keep the slip ball centered. Again, maybe I just never noticed before?

Either scenario is reasonable given the right conditions.

Huh, just seemed like it might be different from before, but maybe my flying is just maturing. I could have sworn immediate rudder inputs were required to adjust for any changes in the collective, more like the Hip. As for the turns, maybe I'm just paying more attention to the slip ball instead of flying by feel, but I still think it's odd for a helo to need reverse rudder in a steep banked turn, unless it is somehow seriously front-end heavy. *shrug*

A helicopter will experience wind-cocking in forward flight (or any direction) and that coupled with the horizontal and vertical stabilisers mean that the tail rotor has very little authority in forward flight. This means that collective changes in forward flight will not need large t/r input (should still require some).

As for turns, I'd say that possibly you're not compensating for nose up/down in the turn? Turning to the right you need to raise the nose slightly to remain in-plane with a lower collective setting and right pedal, opposite for the left. Not sure why it's happening the other way around.

Turning to the right you need to raise the nose slightly to remain in-plane with a lower collective setting and right pedal, opposite for the left. Not sure why it's happening the other way around.

In the Huey, with counter clockwise main rotor, the nose has a tendency to come UP when banking to the Right.

In the Huey, with counter clockwise main rotor, the nose has a tendency to come UP when banking to the Right.

Nope, Chargeo is correct, a left turn causes the nose to rise.

Nope, Chargeo is correct, a left turn causes the nose to rise.

Yah, I knew this was coming. Attached is Prouty's take on R-P Cross-Coupling. See the section on Rolling Velocity.

I am not expert on subject and welcome any interpretation.

Crosscoupling effect on helicopter flight.pdf

Well the helicopter I fly is also anti-clockwise rotation, and the instruction mnemonic is "right raise, left lower" for a s&l turn.

I'd think the reason for this is that when rolling right, the blades with the most lift (on the right-side of the disc) are tilting their contribution to total reaction away from axis of rotation, meaning less lift and requiring a raise of the nose to maintain level flight. Opposite for a left turn, the rotor thrust from the right side of the disc is now tilting closer to total reaction and inducing a climb for the same power setting and attitude.

I understand what the reference is saying about the rotor flapping more and increasing aoa in a left turn but a rotor with enough flap travel should find the aoa difference negligible.. maybe it is more present in rigid rotor heads?

Well the helicopter I fly is also anti-clockwise rotation, and the instruction mnemonic is "right raise, left lower" for a s&l turn.

Thanks for following up Chargeo. Might the mnemonic be describing what the nose is doing as opposed to what the pilots response should be?

I think the aerodynamic arguments of Roll Rate & Acceleration Cross-coupling would support the former.

Thanks for following up Chargeo. Might the mnemonic be describing what the nose is doing as opposed to what the pilots response should be?

I don't think so. I'm only a student helo pilot and have only flown the R22 so I'm no expert, but the following is my understanding:

With the advancing blade on the right, a left turn will lead to an effective increase in lift on said right hand advancing blade. This additional lift will cause the disc to precess 90 degrees later, lifting the disc at the front, causing a nose up effect.

Principles of helicopter flight are complex though, so there could be more to this that I'm missing; and I have to confess I've not read through your post as thoroughly as I'd have liked yet.

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.

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.

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.

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.

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!