flying up side down?????

[dandeman]

How does a helicopter fly up side down?
Tahnks,
Dan

[David Drew]

When it's flying the right way up the blades have positive pitch - that is - they attack the air forcing it down and the heli up. Just like a plane wing

When upside down, the heli has negative pitch (which if the heli was the correct way up would drive it down) so the blades work in the same way as normal. As they spin round they attack the air in a positive way. - negative but upside down = positive)

To make it fly the blades have to point slightly up (away from the ground) whichever way up the heli is.

Hope that helps.

David

[163phil]

How does a helicopter fly up side down?

Very badly, and for only a couple of seconds before hitting the deck in my case

[heliTV]

Only on the way to the scene of the accident with me at the moment...

For a serious answer, read David's post!

[Adrian]

if i fly upside down.... im doomed!

[jboweruk]

I'm a long way off trying that yet....

[Balders]

also, just to point out, heli blades differ from plane wings, in that they do not generate lift without positive pitch, ie the curvature of a wing creates low pressure on top, high pressure underneath thereby creating lift.

A heli wing is "flat" by comparison and "bites" into the air to create it's lift. Hope this explains things a little better.

[trebor27]

Model heli blades tend to be fully-symmetrical. In that they curve over the top of the blade is the same as over the bottom. As a result lift can ONLY be generated by angling the blade in relation to the air it's moving through to "blow" air downwards... Now if you angle them the other way it blows air upwards, this is how it flies upside down....

Some plane wings are fully symmetrical like heli blades too, and they fly the right way up and up-side down equally well.

Some heli blades are semi-symmetrical. In this instance the curve over the top is greater than over the bottom. These blades then don't fly very/as well upside down....

The alternative answer is:
They fly upside down just as well, if not slightly better, then the right way up!
(Usually a heli can climb faster/better upside down as when the heli is inverted there isn't a body in the way of the air-flow down towards to the earth, so you get more lift!)

lol

Cheers
Rob

[heliTV]

I'm a long way off trying that yet....

Me too mate - if it happens, its not by design that's for sure!!

[jboweruk]

[163phil]

Model heli blades tend to be fully-symmetrical. In that they curve over the top of the blade is the same as over the bottom. As a result lift can ONLY be generated by angling the blade in relation to the air it's moving through to "blow" air downwards... Now if you angle them the other way it blows air upwards, this is how it flies upside down....

Some plane wings are fully symmetrical like heli blades too, and they fly the right way up and up-side down equally well.

Some heli blades are semi-symmetrical. In this instance the curve over the top is greater than over the bottom. These blades then don't fly very/as well upside down....

The alternative answer is:
They fly upside down just as well, if not slightly better, then the right way up!
(Usually a heli can climb faster/better upside down as when the heli is inverted there isn't a body in the way of the air-flow down towards to the earth, so you get more lift!)

lol

Cheers
Rob

A good description there Rob, but just to add a little:

A heli blade works exactly like a fixed wing in that it produces about two thirds of its lift from the reduction in pressure over the top surface, and only one third by pushing down on the air it's moving through (so it actually "sucks" itself upwards!). The greater the angle of attack, the more lift it will produce (until it stalls).

The characteristics of the lift produced is dependent on the wing section, so a symmetrical blade section will work just as efficiently upside down as the right way up so long as it has a positive angle of attack. When inverted the angle of attack is negative in relation to the heli, but positive in relation to the ground (the heli doesn't know which way up it is) and so the lift is produced downwards in relation to the ground (and to the observer (the pilot)), and the heli keeps flying.

A non-symmetrical blade will still work upside down, but will require a greater angle of attack to produce the required amount of lift (the weight of the heli if in a hover), and may never get there as it may stall first. Of course it would also require more power from the motor to be pushed through the air at that higher angle of attack, and so more torque would have to be counteracted by the tail rotors (which are producing their own lift in exactly the same way, but sideways in relation to the observer).

So for an aerobatic heli, symmetrical blades would be the blade of choice.

When inverted, the body of the heli is not in the way of the displaced air, and so there is less drag (the lift produced by the blades is actually the same). (A pusher prop on a fixed wing will do its job (of pushing) better because there is not a fuselage in the way of its displaced air. The downside (and there always is one) is that there is no propwash over the control surfaces so they will be less effective at low airspeeds)

Must go and lie down now