Low G pushover recovery
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vorticey
What do you mean by bumping ? In what context, or part of flight ?
Using max-controls can also introduce vibrations.
d3
Using max-controls can also introduce vibrations.
d3
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while on the ground at flight rpm and you push the cyclic full (or close to) forward or taking of from a slope with full cyclic. is this bumping on the bump stops or just vibration from the hooks/ universal joint in the head??
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Nick, I just want to be sure I'm understanding you right, so let me rephrase: pushing the nose over rapidly can/will induce low-G, lowering the collective as you do this can exacerbate it.
However, if you're going 80 KT, and you maintain an 80-KT attitude as you rapidly lower the collective (which would mean coming aft with the cyclic to keep the advancing blade from flapping down), your butt may go low-G in the seat, but there would be no appreciable low-G condition between the airframe and the rotor. The weight of the airframe is in this case pulling the rotor down, so a couple remains between the airframe and the rotor (this assuming the rotor system is not capable of less-than-zero pitch).
However, if you're going 80 KT, and you maintain an 80-KT attitude as you rapidly lower the collective (which would mean coming aft with the cyclic to keep the advancing blade from flapping down), your butt may go low-G in the seat, but there would be no appreciable low-G condition between the airframe and the rotor. The weight of the airframe is in this case pulling the rotor down, so a couple remains between the airframe and the rotor (this assuming the rotor system is not capable of less-than-zero pitch).
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Guys bascically to recover from a low g situation where the heli has rolled right eg : R22, R44.
Either aft cylic to reload the disc or the best way is to lower the collective.
The only reason why the heli is rolling is because the main rotor has become unloaded and for the given power setting the tail rotor thrust causes a the heli to roll.
The easiest way to understand this is enter a autorotation quite quickly and you will get weightless eg: low g. The heli will not roll as there is no torque being produced so the tail rotor will not roll the heli.
All the way in a auto and in the R22 below 18" you can and push and pull the cylic and the heli will not roll because the tail rotor is not producing enough thrust to roll the heli.
I find teaching lowering the collective the easiest way to advoid mast bumpig to a student. As in the mountains approaching a pass simulating bad weather you usually have alot of power in use and if they bring their speed back to 20-30kts this is not enough airspeed to relaod the disc if they nose the heli over adburtly so lowering the colective is the safest.
Either aft cylic to reload the disc or the best way is to lower the collective.
The only reason why the heli is rolling is because the main rotor has become unloaded and for the given power setting the tail rotor thrust causes a the heli to roll.
The easiest way to understand this is enter a autorotation quite quickly and you will get weightless eg: low g. The heli will not roll as there is no torque being produced so the tail rotor will not roll the heli.
All the way in a auto and in the R22 below 18" you can and push and pull the cylic and the heli will not roll because the tail rotor is not producing enough thrust to roll the heli.
I find teaching lowering the collective the easiest way to advoid mast bumpig to a student. As in the mountains approaching a pass simulating bad weather you usually have alot of power in use and if they bring their speed back to 20-30kts this is not enough airspeed to relaod the disc if they nose the heli over adburtly so lowering the colective is the safest.
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Gav500D
Lowering the collective
I would agree that this can be a preventive measure, nl do some kind of flaring to get the heli to descend.
It is not a corrective action for low G !
Once a low G is provoqued, with the associated rolling, lowering the collective is not going to be very helpfull in loading the disk, I would say quite the contrary.
First action should be to gently reload the disk by moving cyclic backwards.
d3
Flingwing207
To put it in your wording : G\'s are measured at "your butt ", assuming it is still sitting where it should be, using your seat belts.
As long as the rotor is attached to the heli :
G-pilot=G-heli=G-rotor.
(angular accelerations may be neglected in this case).
So if you lower the collective first/faster than pulling back the cyclic, so that you feel low-G, then the heli and the rotor are feeling the same.
d3
I would agree that this can be a preventive measure, nl do some kind of flaring to get the heli to descend.
It is not a corrective action for low G !
Once a low G is provoqued, with the associated rolling, lowering the collective is not going to be very helpfull in loading the disk, I would say quite the contrary.
First action should be to gently reload the disk by moving cyclic backwards.
d3
Flingwing207
To put it in your wording : G\'s are measured at "your butt ", assuming it is still sitting where it should be, using your seat belts.
As long as the rotor is attached to the heli :
G-pilot=G-heli=G-rotor.
(angular accelerations may be neglected in this case).
So if you lower the collective first/faster than pulling back the cyclic, so that you feel low-G, then the heli and the rotor are feeling the same.
d3
Last edited by delta3; 21st Nov 2005 at 12:16.
No offence to you personally, Gav, but I find it concerning that you would be teaching people that lowering the collective further is the way to go in a low-g situation.
Removing torque won't necessarily fix the rolling situation in itself; it's pedal position, C of G and tail rotor RPM that determine the side force and therefore rolling moment produced by the tail rotor.
Your main priority is to load up the rotor again to avoid mast bumping, so raising collective and flaring if possible are going to do that.
I'd say that in the low-g, banked situation, my response would be to freeze the cyclic, pull collective as much as I felt I could without pulling it over on its back and maybe use some pedal to help get the nose down to build up airspeed and give me some flaring potential.
Removing torque won't necessarily fix the rolling situation in itself; it's pedal position, C of G and tail rotor RPM that determine the side force and therefore rolling moment produced by the tail rotor.
Your main priority is to load up the rotor again to avoid mast bumping, so raising collective and flaring if possible are going to do that.
I'd say that in the low-g, banked situation, my response would be to freeze the cyclic, pull collective as much as I felt I could without pulling it over on its back and maybe use some pedal to help get the nose down to build up airspeed and give me some flaring potential.
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Flingwing207,
If you lower the collective fast enough, you can reach zero g, and it might be possible to create a problem even if you do not make much pitch down, too, but it would take one hell of a down collective motion.
I don't want to rule out a "collective only" zero g event, although it is far less likely than an event that includes significant nose down motion, as well. Remember, if you down collective and do not use enough aft cyclic, you get both, which is the place you want to avoid.
I also think that the roll contributes to the mast bumping problem, but once at zero g, the mast bumping can occur for other reasons. Significant sideslip (badly coordinated pedal) can also make the flapping go toward limits in the 204, 205 and 206, so I imagine it can in a Robbie as well. Thus, extreme dumping of the collective might get you to a mast bumping, as well, especially since it involves a chance to mess up the pedals while getting to zero g.
If you lower the collective fast enough, you can reach zero g, and it might be possible to create a problem even if you do not make much pitch down, too, but it would take one hell of a down collective motion.
I don't want to rule out a "collective only" zero g event, although it is far less likely than an event that includes significant nose down motion, as well. Remember, if you down collective and do not use enough aft cyclic, you get both, which is the place you want to avoid.
I also think that the roll contributes to the mast bumping problem, but once at zero g, the mast bumping can occur for other reasons. Significant sideslip (badly coordinated pedal) can also make the flapping go toward limits in the 204, 205 and 206, so I imagine it can in a Robbie as well. Thus, extreme dumping of the collective might get you to a mast bumping, as well, especially since it involves a chance to mess up the pedals while getting to zero g.
