Dumb questoin re autorotation on electric helis

[Ewan]

Been pondering autorotations, familiar with the pricincipal from study flight as a kid.

My question is how does this work on an electric heli.

On nitro there is a clutch which I assume disengages from the drive train to the prop if you hit throttle hold or the motor konks for some reason.

Surely with an electric heli the motor is engaged all the time or is there some additional link that simulates disengaging the clutch in a nitro bird.

Reason I am asking is I am still only up to flying an MSR at the moment but have a blade stored away for when I am feeling brave and wondered if this can autorotate?

[tiddler]

Yup, there is a one way bearing in the main gear which allows the rotors to spin ahead of the motor.

[coptermanic]

Most copters around 450 size and up have a one-way bearing in the main drive for exactly that reason - if the motor quits, the blades and tail blades still turn. If you have a motor powering the tail, there is generally no OWB, so autos are usually, depending on the circumstances of the failure, not possible.

Bigger helis will auto better than the smaller ones due largely to the greater inertia in the blades. I had my 450 blades really tight in their holders so that I could do autos, rather than having them loose, and suffering from potential blade stop!!

[unwind-protect]

Tiddler is spot on.

The purpose of the clutch is not to allow freewheeling of the rotor, but to allow you to start the engine. If it wasn't for the clutch you'd need very long arms

[p4ddy]

The thro hold is set to have no throttle at all just as if you are ready to take off the motor is dormant untill you start giving throttle.

[jamesb72]

Also you need negative blade pitch to auto, which is why fixed pitch heli's like your MSR don't have or need a oneway bearing - if the motor stops your toast anyway ;-)
Pretty much all the CP heli's will have a one way, even the tiddlers like Trex 250 although to be honest the chances of auto'ing them successfully in case of a failure is pretty small, as the blades are so small and light there is very little stored energy for anything less than a perfect descent and flair.
The bigger the heli the heavier blades give more energy, so when you get up to 500 upwards heli's you have a lot more leeway attempting an auto to get things not quite perfect and have two stabs at a flair without leaving a heli shaped hole in the field.

[Ewan]

Most helpful, thanks all makes a lot of sense.

Soo - guessing that my blade 400 will be able to autorotate.

Just out of interest, taking the point about helis with tail motorsdoes this mean that you could not auto the new SR?

I am also guessing that if there is a main motor/drive train failure in a heli with a tail motor that when it hits the deck it will be spinning due to the tail motor still going and any crash could be pretty damaging?

[Ewan]

The thro hold is set to have no throttle at all just as if you are ready to take off the motor is dormant untill you start giving throttle.

Goes to show what 'book learning' can do, I had thought that Thro hold was primarily an emergency measure to stop the heli beating itself to bits in a crash.

Thanks, I have a hell of a lot to learn.

[Boggy]

Most helpful, thanks all makes a lot of sense.

Soo - guessing that my blade 400 will be able to autorotate.

Just out of interest, taking the point about helis with tail motorsdoes this mean that you could not auto the new SR?

I am also guessing that if there is a main motor/drive train failure in a heli with a tail motor that when it hits the deck it will be spinning due to the tail motor still going and any crash could be pretty damaging?

yes but not something you want to be trying unless its needed.with a 400 you get one shot at getting it right or its lunch time im afraid

[jamesb72]

UPDATED - oops, I thought SR was FP it is CP as others have said !!

A tail motor CP heli theoretically could auto (if it has a one way bearing) as the tail will not turn at zero throttle, and you would use throttle hold for auto, so tail would not spin but would 'weather vane' as you are in forward flight during the auto - HOWEVER these heli's are generally much too small to be able to auto effectively with their very small light blades so I would only try this for a bet, OR if there was a tail problem (ie tail ESC pops and tail stopped in flight).

[Ewan]

You cannot auto the SR as its a fixed pitch heli - the youtube video is of a Blade CP or CPP2 I think.

You CANNOT do flips/rolls/invert with a Blade SR or any other fixed pitch heli without hitting the ground ;-)

A tail motor heli theoretically could auto (if it has a one way bearing) as the tail will not turn at zero throttle, and you would use throttle hold for auto, so tail would not spin but would 'weather vane' as you are in forward flight during the auto - HOWEVER these heli's are generally much too small to be able to auto effectively with their very small light blades so I would only try this for a bet, OR if there was a tail problem (ie tail ESC pops and tail stopped in flight).

Whilst the MSR is fixed pitch the SR is I believe collective pitch.

[jamesb72]

Oops - sorry yes the SR is CP - doh !