Can a helicopter hover upside down?

By: low'n'slow - 12th December 2008 at 16:25 Permalink - Edited 1st January 1970 at 01:00

Looks like some r/c modellers have beaten him to it!! ;)

http://www.rcmovie.de/video/1d39ff18134e51fe7db8/Manuel-laesst-mich-seinen-Nippel-rumreissen

By: Possel - 12th December 2008 at 21:13 Permalink - Edited 1st January 1970 at 01:00

Yes, briefly!

Have you seen that old "flight safety" film of a "flying banana" in the US which got upside down? It didn't last long.

By: WP840 - 14th December 2008 at 15:35 Permalink - Edited 1st January 1970 at 01:00

Can a Lynx?

I know it is one of few helicopters that can do a full loop but can it also hover upside down too?

By: Scouse - 14th December 2008 at 22:49 Permalink - Edited 1st January 1970 at 01:00

Low'n'slow would you care to jot that down as a sequence of Aresti diagrams?

Blooming impressive, isn't it.

By: Merlin3945 - 15th December 2008 at 02:42 Permalink - Edited 1st January 1970 at 01:00

I dont know if it applies to full sized helis but models hover upside down because of the negative pitch applied while inverted. A bit like a pilot putting in down while inverted with his plane to hold a level flight. Must be possible to do this in full sized but the models do have gyros to correct some of the balance issues and heading hold gyros also.

By: rich_hodgetts - 18th December 2008 at 12:37 Permalink - Edited 1st January 1970 at 01:00

In theory this is probably possibe but I bet the practical limiting factor will be blade flex. Upside down the blades will cone towards the tailboom of the helicopter and almost certainly give insufficient clearance.

Model helicopters clearly can hover inverted and do so very well but they have very high headspeeds and very stiff blades.

Just my thoughts,

Rich

By: hunterxf382 - 18th December 2008 at 14:09 Permalink - Edited 1st January 1970 at 01:00

Helicopter blades are minature aerofoil sections, so I'm wondering how the hover would be maintained with no lift from an inverted set of aerofoils????

The pitch on a real helicopter surely cannot rotate 180 deg? Even then - it would mean each aerofoil is facing backwards..... so you would have to reverse the rotor direction....

Nah - I'm stumped.

By: WP840 - 18th December 2008 at 16:46 Permalink - Edited 1st January 1970 at 01:00

Helicopter blades are minature aerofoil sections, so I'm wondering how the hover would be maintained with no lift from an inverted set of aerofoils????

The pitch on a real helicopter surely cannot rotate 180 deg? Even then - it would mean each aerofoil is facing backwards..... so you would have to reverse the rotor direction....

Nah - I'm stumped.

But surely that would also mean an aircraft wouldn't be able to fly inverted? :confused:

By: sycamore - 18th December 2008 at 19:46 Permalink - Edited 1st January 1970 at 01:00

There are many reasons why a helicopter cannot hover upside down even though models can;
1 it serves no practical purpose.
2 a model rotor can be made extremely stiff,and rigid, both mechanically,and aerodynamically,due to the centrifugal/centripetal forces from it`s high rpm.
3 a real rotor would be impracticable if scaled-up relatively,both in terms of mechanical and aerodymics to accept the scaled forces.
4 gearboxes/engines in real helicopters have oil systems that have sumps/filters/pumps that are designed for `normal` gravity,and whilst you can have special systems for unlimited aerobatic aircraft/combat aircraft,for the limited time that a helicopter `could` hover upside down,it would be totally unnecessary,and expensive,heavy,and impracticable.
5 the rotor-head would further be complicated by having to have almost double the collective pitch range,likewise the controls would also.
6 in inverted flight/hover the rotor would `cone` down,relative to the fuselage,and this would bring the blades closer to the airframe- not a good thing !
7 there are a couple of helicopters that use a `slightly` negative pitch, the LYNX,and the Wasp,but this can only be utilised on the ground/ship,as a means of `loading` the helicopter against sea motion,and assist handling.
So,whilst it may be a fun `what-if`,the negative practicalities far outweigh any supposed benefits. You will see some helos perhaps appear to sustain inverted flight,but it won`t be for more than a couple of seconds...Syc...

By: Merlin3945 - 18th December 2008 at 20:19 Permalink - Edited 1st January 1970 at 01:00

What he said :)

Very well put syc.

Helis really arent my thing and as such I had forgotten how flexable full sized blades are and how stiff the model blades are.

Still in theory it still may be possible even although there is no call for it.