Bell AH-1W SuperCobra

[Richard]

I will try both yasim and jsbsim huey models and will inform you soon.

I'm looking forwards to your feedback on these models.

[Johan G]

Some more general posts about licenses were split of to the new topic GPL vs. CC licenses for development..

[amue]

In terms of JSBSim helicopters that I know about there is the Alouette-III and bomber's UH1.

I'm not a RL pilot, so maybe what I write is totally wrong, but IMHO bomber's UH1 FDM is not a good example of a JSBSim helicopter FDM.
He implemented his own rotor model instead of using JSBSims internal rotor model. If I understand it correctly he assumes that the rotor is just a simple propeller those attitude can be changed with the cyclic. That results in the (IMHO) wrong behaviour: if the cyclic is moved forward then the propeller (and the helicopter) is pitched nose down. Because of the assumption of a simple propeller he also applies a precession moment that rolls the helicopter to the left. In my opinion that left roll does not happen in RL. The rotor is not a simple propeller but way more complicated. Maybe @bell_pilot can refute or confirm this?
Further I've noticed that if I move the cyclic left or right I couldn't bank the helicopter more than 30 degrees. I think thats also incorrect.

The Alouette-III uses the JSBSim rotor model and it behaves more like I would expect from a helicopter in RL.

[bell_pilot]

I wrote down my opinions about bomber's model to his forum. You may check it there.
@amue is right about banking issue.

[Warty]

. . . The rotor is not a simple propeller but way more complicated. . .

It certainly is. One day I must get round to making an FG version of this

[bell_pilot]

I will use these videos in rotarywing flight courses. Great job!

[amue]

I wrote down my opinions about bomber's model to his forum. You may check it there.
@amue is right about banking issue.

Thank you for the information.
May I ask you about the other issue I mentioned: If I move the cyclic (rather rapidly) forward, the helicopter pitches down (nose down). Thats correct. But simultanously the helicopter also rolls left. Thats in my opinion incorrect. Similar happens when I move the cyclic (rapidly) back. The helicopter pitches up (nose up). Thats correct. But simultanously he also rolls right. Thats in my opinion incorrect.
Does the Huey (or helicopters in general) in RL roll left/right when the cyclic is moved (rapidly) forward/backward?

[bell_pilot]

Helicopter is needed to controlled by 3 controller simultaneously. When you give forward cyclic input, you need to collective up to maintain level flight. When you collective up, torque applied to the body increased, so you give left pedal input and so on... Three controllers are used simultaneously always for flying helicopters.
Tilting rotor changes angle of attack so torque applied is also changed. Rotating direction of the rotor is important. Advancing blade is the source of the torque. To sum up, yes. Those affects you encountered are correct but as i understand they are a little bit more than it must be. They can bu tuned easiliy. I will check

[Gijs]

I think I have a unterstanding problem here.
Assuming the following situation:
I'm in a hover (so all blades are equal advancing) and I push the cyclic forward and I don't touch the collective and pedals, then there shouldn't be any change in applied torque. And even if the applied torque changed, torque changes should only create a yaw tendency not a roll tendency. Where does the roll tendency, I see in the FDM model, should come from?

[Gijs]

No, some moment is produced by tail rotor also. Tail rotor is tending to bank helicopter while tail and main rotor hubs do not lay on the same axis. So, pedal inputs also bank helo, not as much as cyclic input but it does.

[S&J]

[S&J]

Tail rotor is tending to bank helicopter while tail and main rotor hubs do not lay on the same axis.

And that's why helicopters fly on the, roll attitude when flying straight and level.

Does your preferred flight model do that

[amue]

@bell_pilot:
Just to confirm that I understand you correctly. You are saying that in a hover if I push the cyclic straight forward (and while don't changing the other controls: collective or pedals) the helicopter not only tilts nose down but also rolls left. Meaning the helicopter then effectively tilts forward left. And respectively the same happens if I pull the the cyclic straight back: the helicopter tilts nose up and also rolls right? Is this correct? Can you give an estimate of how much the effective tilt direction is displaced to the left (if pushing the cyclic forward) instead of straight forward? E.g. 10, 20, 30, 45 or more degrees?

@S&J:
Nice video, but wrong. Phase lag in a helicopter rotor has nothing todo with gyroscopic precession. I know that gyroscopic precission is tought in a lot of places to describe rotor physics, maybe because the real physics are to complicated. This comment to a blog post that also mentioned wrongly gyroscopic precession in rotor dynamics sums it up nicely:
https://blog.aopa.org/aopa/2012/01/29/gyroscopic-precession/#comment-9722

[S&J]

Watch the series

[S&J]

And whilst you're learning something