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Blade drag/lag properly modeled?


sinelnic

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Hi ED,

 

I´ve been reading about rotor design in the hope to understand a certain flight behavior that was finally related to my poor joystick´s design :music_whistling: (found Pilotasso´s thread about modding his X52 very useful for solving the problem in my X45).

 

Nevertheless, I found an interesting feature called blade drag/lag, where in a fully articulated rotor individual blades can have independent movement along the mast axis. Now, I was very surprised when I closely examined my parked Shark and found a slight rotation of individual blades along this axis... could you please confirm if blade drag/lag is currently implemented, and if it´s actually fully modelled in the rotor simulation?

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"Engineering is the art of modelling materials we do not wholly understand, into shapes we cannot precisely analyse so as to withstand forces we cannot properly assess, in such a way that the public has no reason to suspect the extent of our ignorance." (Dr. A. R. Dykes - British Institution of Structural Engineers, 1976)

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Which kind of rotation do you mean? BS does modell different parameters on single blades, as it also reacts to wind, weight, etc.

 

If you mean rotation around the rotor-axis, I don't think that should be too much, just enough to not break the rotor during accelleration or applying rotorbrake.

 

If you mean vertical movement, yes of course. The blade moves up and down due to different parameters like wind and drag. This also causes the dangerous closure of the counter-rotating rotors of the BlackShark.

 

If you mean rotation around the length-axis, that happens, too, of course, as this is influenced directly by the swash-plate, either by activating the collective or more obviously independently with the cyclic controls.

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Which kind of rotation do you mean? BS does modell different parameters on single blades, as it also reacts to wind, weight, etc.

 

If you mean rotation around the rotor-axis, I don't think that should be too much, just enough to not break the rotor during accelleration or applying rotorbrake.

 

If you mean vertical movement, yes of course. The blade moves up and down due to different parameters like wind and drag. This also causes the dangerous closure of the counter-rotating rotors of the BlackShark.

 

If you mean rotation around the length-axis, that happens, too, of course, as this is influenced directly by the swash-plate, either by activating the collective or more obviously independently with the cyclic controls.

 

Thanks for your response, I´m referring to the first case, rotation along the mast axis. I´m well aware of the other two, they must be there in order to simulate realistic conditions such as blade collision or, of course, just controlling the aircraft. But the first one is AFAIK related to structural tension management and as such not immediately mandatory to actually simulate in BS, hence my curiosity on if it´s indeed fully modelled.

 

Reading further, there´s something called ground resonance which can destroy your chopper if you land hard on a single gear, which happens because an individual blade gets out of "sync" with the others. I´ve not yet tried to reproduce this effect in BS, but if it behaves as I describe, then blade lead/lag is properly implemented...

Westinghouse W-600 refrigerator - Corona six-pack - Marlboro reds - Patience by Girlfriend

 

"Engineering is the art of modelling materials we do not wholly understand, into shapes we cannot precisely analyse so as to withstand forces we cannot properly assess, in such a way that the public has no reason to suspect the extent of our ignorance." (Dr. A. R. Dykes - British Institution of Structural Engineers, 1976)

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Yes, the blades in BS lead/lag and flap. Lead and lag is also commonly referred to as "hunting" or "dragging". The hinge is usually referred to as the drag hinge.

 

I've never encountered ground resonance in BS, but that may be because I have not run into the proper conditions for it. I think that the Ka-50, due to it's coax rotor, is less susceptible to ground resonance that your typical single-rotor helicopter, although it is more of a problem for rotor systems with three blades than any other type.

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Yes, the blades in BS lead/lag and flap. Lead and lag is also commonly referred to as "hunting" or "dragging". The hinge is usually referred to as the drag hinge.

 

I've never encountered ground resonance in BS, but that may be because I have not run into the proper conditions for it. I think that the Ka-50, due to it's coax rotor, is less susceptible to ground resonance that your typical single-rotor helicopter, although it is more of a problem for rotor systems with three blades than any other type.

 

I think Yo-Yo said it can happen, although the dampeners in the gear seem to do very well in countering ground resonance.

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Yes, the blades in BS lead/lag and flap. Lead and lag is also commonly referred to as "hunting" or "dragging". The hinge is usually referred to as the drag hinge.

 

I've never encountered ground resonance in BS, but that may be because I have not run into the proper conditions for it. I think that the Ka-50, due to it's coax rotor, is less susceptible to ground resonance that your typical single-rotor helicopter, although it is more of a problem for rotor systems with three blades than any other type.

 

 

Thanks for your response Alpha. One more time, impressive job!

 

AFAIK ground resonance requires shock waves to be modelled propagating from the landing gear to the rotor. That would be too much to ask, I can assure you I won´t ask for my money back if it´s not there :D

Westinghouse W-600 refrigerator - Corona six-pack - Marlboro reds - Patience by Girlfriend

 

"Engineering is the art of modelling materials we do not wholly understand, into shapes we cannot precisely analyse so as to withstand forces we cannot properly assess, in such a way that the public has no reason to suspect the extent of our ignorance." (Dr. A. R. Dykes - British Institution of Structural Engineers, 1976)

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  • ED Team
Thanks for your response Alpha. One more time, impressive job!

 

AFAIK ground resonance requires shock waves to be modelled propagating from the landing gear to the rotor. That would be too much to ask, I can assure you I won´t ask for my money back if it´s not there :D

 

 

 

No shock waves. Any acceleration of the body along horizontal axes leads to the hunting movement of the blades moving their CG from the rotor axis. So the unbalanced rotor move the body. If this mechanical feedback is sufficient enough the magnitude will rise.

The best way to initiate this effect is to collide with something low... to avoid blades damage.

Sometimes light vibrations from hunting one can feel during abrupt maneuvers. It is so called "in-flight resonance". We did encounter it when damping was insufficient. By the way one of the first Kamov's helo suffered of it. The cure is to use dampeners in vertical hinges that is additional factor to avoid GR.

 

Another good way to examine ED rotor is to run on the ground with rotor spooling down. If the rotor rpm is low it is easy to observe how ground humps affect blade movement.

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Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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