Notar helicopters and autorotation?
 

Can anyone tell me whether or not the Notar can autorotate? I am unfamiliar with this type of machine but my understanding is that the tail function functions when it gets power from the down draft draft from the main rotors under power. Are there issues with regards to auto's when power is off or reduced? If the question sounds silly then my apologies, I know little about notars or their operation.

If the internal fan is engine driven, and if it stops when the engine stops, then auto is still possible by weather cocking the fusalage on the way down. However if the fan is gearbox driven it should continue to supply low pressure air flow to the slots and auto normally.:ok:

the fan is gearbox driven
in auto it turns with the main blades not the engine

A Notar helicopter uses the Coandă effect to counter torque effect of the main rotor, which does utilise down-wash from the rotors.

The low-pressure air through the slots and for the directional control 'bucket' is, however, produced by a main transmission driven fan.....so still works during autos. I don't know if the anti-torque effects of the notar system are reduced during autos, but there will still be directional control.

no drama A Notar helicopter uses the Coandă effect to counter torque

you wouldnt get coanda effect without the fan

I know...I was just comfirming the point in the original question that downwash from the main rotor does play it's part in how the notar works.

As I understand it, the downwash and coanda effect on the boom is mainly effective in the hover and low speed flight, hence the large angled fins for cruise flight. In autorotation, the airflow over the boom is the wrong way round and presumably yaw control is from the can at the back and the fins. I can remember the yaw effects on entering auto in the 520N feeling a bit strange at first.

Is anti torque required in autorotation?

Wikipedia is your friend -Notar How it works

It should really be called No Visible Tail Rotor. Contrary to popular belief there is still a tail rotor and tail rotor gearbox and driveshaft etc. and in addition a composite tailboom with slots in it and a controllable thruster and controllable vertical fins and control cables and bellcranks and sector gears and bearings and.....................................................blah blah blah.

In autorotation the "autorotative driving section" of the disk which is making the blades rotate is in the inner part of the disk. The section of the disk that is providing "lift" (although not enough to sustain level flight but more than no lift at all i.e. glide) is in the outer part. Therefore the inner and outer part of the blade being connected there are no forces going through the transmission so there is very little torque reaction. The torque reaction that remains is in the opposite direction to powered flight as it is required to overcome friction in the main and tail rotor transmission, freewheel drag, swashplate bearing, mast bearing, still rotating fan etc etc. These items are all still using energy which is now only available from the main rotor.

A little quirk of the Notar is when you increase collective pitch on touchdown during autoration you will get antitorque from the Coanda effect when you don't really need it. This is a little different from "conventional" helicopters.

just had a look.............found a 'driveshaft' and a 'tail rotor' but couldn't find a 'tail rotor gearbox'.

I hope you are all joking. Is there no torque to counteract in auturotation? Thats why you autorotate with a tail rotor failure. Thought it was April 1st for a moment.........

except that for a "notar fan drive failure":

BT,

500N5400 NOTAR FAN GEARBOX

900D1400522-101 NOTAR FAN DRIVE ASSY

Conveniently missing from the marketing blurb.

To be clear, there IS torque reaction during autorotation.

My spies tell me that while there is no problem with controlling yaw in autorotation, in the part between powered level flight and autorotation, i.e. a low power descent, yaw control is less than sparkling - some even report difficulty in turning right. Anyone confirm this?

RVDT: Can't find a 'NOTAR FAN DRIVE ASSY' on mine, just a 'Fan Assembly, NOTAR' ! No gearbox there.

Shawn..what sort of airspeed , when you say 'low power descent'?

Shawn
Think your spies are wrong. Take a 520 put it in the hover with ysas turned on. You can then fly a circuit with feet off the pedals as long as you do a low powered descent and a gentle pull in power at the bottom
Interesting to watch non 520 pilots faces when you do it though. I cant say I have ever experienced yaw problems, dont know about 600 or 902 perhaps they are different

Could someone explain ?

sorry chop,

jayteetoo said; Thats why you autorotate with a tail rotor failure.

I, next post, said; except that for a "notar fan drive failure":

what i meant to say was; except you don't autorotate for a notar fan drive failure

I followed it with the RFM warning given for notar fan drive failure;

CAUTION: Do not attempt an autorotation from forward flight unless an actual double engine failure occurs.

I hope that is a bit clearer!

hughes 500

600 is the same [as long as it has ysas on ysas was a extra on the 600 ]

Well it's a little clearer, but I still do not understand why you should not autorotate after a fan failure and why you can not auto rotate unless you have a double engine failure?