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Re: Bell UH-1
Posted: Tue Jan 05, 2021 6:54 pm
by bomber
Cheers, happy new year to you too
Re: Bell UH-1
Posted: Tue Feb 09, 2021 11:15 am
by bomber
amue wrote over on FG forum
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.
Re: Bell UH-1
Posted: Tue Feb 09, 2021 11:19 am
by bomber
I've never flown a helicopter in my life, as such one of the problems I'm faced with is I don't know how 'sensitive' the cyclic is.
All the other stuff, I think you're wrong.... and nice of you to pop in here and have a chat about it before posting
I do suspect it might have a narrower flight envelope than the real thing, so something to work on.
Re: Bell UH-1
Posted: Tue Feb 09, 2021 11:28 am
by bomber
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.
I don't apply procession, jsbsim internal code does, I do nothing.
But I do think gyroscopic effects happen in Real Life
Re: Bell UH-1
Posted: Tue Feb 09, 2021 1:31 pm
by bomber
The Alouette-III uses the JSBSim rotor model and it behaves more like I would expect from a helicopter in RL.
I've just downloaded it.
Please someone tell me this is not how a real helicopter should fly, it's like all over the sky.
Re: Bell UH-1
Posted: Tue Feb 09, 2021 4:30 pm
by IAHM-COL
bomber wrote:Please someone tell me this is not how a real helicopter should fly, it's like all over the sky.
I can t confirm or deny cause I never piloted an helicoper.
But as a passenger, they feel more like your versions of JSBsim.
They are indeed unstable not flying machines, but surprisingly able to hold flight rather stably.
They dont go all-over-the-skies.
Re: Bell UH-1
Posted: Tue Feb 09, 2021 9:19 pm
by bell_pilot
Hi guys, as i am RL pilot of UH-1H, i would like to share my opinions about this model.
It flies well but trimming with side slip indicator unstabilize helicopter. The ball must be in the mid in trimmed flight but it doesnt. If you give pedal input needed as the indicator show, trim is lost.
Another situtation is that aerodynamic forces is not acting as it is.
If you give +collective input, the produced torque must be trimmed with anti-torque to stop turning around. For CCW turning rotors, left pedal input is needed and vice versa. Also nose will pitch up so you need to give fwd cyclic input. Those are not occurs in this sim. You pull the collective and it take off. It is not so easy as in this sim.
Also there is a weird situation with the model. I couldnt bank helicopter above ~30°.
Rpm fluctuates a lot. If you drop rpm below 294 (91%) it is over, you are dead.
In normal flight conditions, governor controls rpm very well with around %1-2 over-under shoot. But this model does not correctly control the rpm.
Another thing with the rpm is at when autorotating.
When i cutted the engine off and downed collective immediately, i lost my rpm to around %70. I tried with starting fully downed collective, same.
Rpm drops so fast. Actually you have around 2-3 secs to gain your rpm when you lost engine in level flight. Also flairing speeds up the rpm in real but not in the model.
I know, It cant be the perfectly accurate but i have to share my opinions with you.
Thanks for this enormous work.
Re: Bell UH-1
Posted: Tue Feb 09, 2021 10:06 pm
by bomber
Thanks for the input.... I can work with this
that said I'm going to have to go through sentence by sentence and get more information/detail out of you.
Re: Bell UH-1
Posted: Tue Feb 09, 2021 10:14 pm
by bomber
And the 30 degs banking is a flight control system issue and not a flight dynamics problem... I didn't know know much damping to add so I aired on the cautious side, so I can easily change this.
I simply don't know what the electronics do with regards taking the workload off the pilot, so I took a flyer.
Re: Bell UH-1
Posted: Tue Feb 09, 2021 10:40 pm
by bell_pilot
bomber wrote:And the 30 degs banking is a flight control system issue and not a flight dynamics problem... I didn't know know much damping to add so I aired on the cautious side, so I can easily change this.
I simply don't know what the electronics do with regards taking the workload off the pilot, so I took a flyer.
There isnt any electronic flight controller, SAS,CAS or SCAS whatever you called it for UH-1 series, except Y models.(i am not sure but B-D-H dont have.)
There is only one stabilizer in UH-1, it is stabilizer bar.
Check the pic:
This stabilize rotor disturbance inputs a little bit, which only augment pitch and roll control. So there is no yaw control augmentation. But, for simply overriding modelling error, you may keep yaw augmentation but present some controlling challenges to the operators