What Myth would you want to see busted?

Good god! Some people REALLY need to learn how a helicopters rotor, main gearbox and engines actually work.

Trust me, as someone who used to work on the bloody things, NO it could not obtain lift and take off.

A choppers rotors run at one constant RPM controlled by the gearbox, the engines will increase/decrease torque when drag is applied to the rotor head and therefore the blades as the blade pitch changes during flight, but the system remains and a constant RPM. Over torque the system and bad things happen.

The engines, gearbox and rotors are physically fixed to the body (actually the other way around but the result is the same). The only clutch in the system is to allow the engines to run up to operating RPM before engaging the rotors (and not all helicopters have one).

As all the RPM sensors are measuring rotor RPM relative to the aircraft (as they are in the aircraft it's the only way they can measure it) it doesn't matter if the aircraft fuselage is rotating at 0 RPM or 1,000,000,000 RPM, the rotors will only spin at their design RPM relative to the aircraft body and the drive train contained therein.

As it's the speed of the blades through the air that produces lift (no different to a fixed wing aircraft) if the blades are not moving relative to the air at the correct RPM the aircraft cannot fly.

Piston engine powered toy helicopter or turboshaft powered merlin, it doesn't matter. The best analogy is the electric motor one mentioned above, think of the motors drive spindle as the rotor head and everything below that point as the rest of the drivetrain & power plants.

Any force imparted on to the fuselage of the aircraft is also imparted on to the rotors in reality, as the system cannot spin up to an infinite RPM. IF we were in a theoretical world were they could, then yes the aircraft could take off, but as we live in this world it couldn't.

This is very much NOT the same as a plane on a conveyor belt. It is in fact the opposite.
 
The way I see it is...

If you turn a clock anti-clockwise at the same speed as the second hand rotates clockwise then the second hand will remain stationary in relation to the ground/you.

It's easy as you can test it yourself - most clocks don't move their hands smoothly so you can easily physically try it yourself without getting confused or mis-judging the speed or amount you have to move.

It's nothing to do with how any mechanical part of the helicopter works - a small electric fan (something on the end of a motor basically) would have the same result!

Same as a helicopter on a turntable - no it would not take off! :)




As for the aircraft on a conveyor... yes it will take off as the thrust acts on the aircraft not the wheels so the wheels would just spin faster but the aircraft would move as normal. If it was a car (ie the wheels are directly driven) it would remain stationary.
 
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Eddie182 said:
As all the RPM sensors are measuring rotor RPM relative to the aircraft (as they are in the aircraft it's the only way they can measure it) it doesn't matter if the aircraft fuselage is rotating at 0 RPM or 1,000,000,000 RPM, the rotors will only spin at their design RPM relative to the aircraft body and the drive train contained therein.
Click to expand...

You sure? That's pretty fast :D
 
Glaucus said:
On to helicopter. Turntable is linked to helicopter boady. Engine internals can still operate and connected to blades. No dirt link between forces. Blades can still spin.
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yea they will be spinning in relation to the copter body/engine but relative to the air that they need to create lift they wont be rotating because the turntable is cancelling it with the opposite spin


edit - the example with a clock above is perfect and easy to see. the clocks mechanism is still rotating but the seconds hand (rotor) isnt going anywhere in relativity to the outside world (air)
 
"andy" said:
QUOTE=Glaucus;21281905]
On to helicopter. Turntable is linked to helicopter boady. Engine internals can still operate and connected to blades. No dirt link between forces. Blades can still spin.
Click to expand...

yea they will be spinning in relation to the copter body/engine but relative to the air that they need to create lift they wont be rotating because the turntable is cancelling it with the opposite spin[/QUOTE]

Glaucus said:
Fine, i'll bow out and apologise with tail between legs.

If anyone finds a nice cut though video showing it, I would like to see it though.
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if you had 2 blades of the quadcopter spinning in the opposite direction (chinook style) and they where correctly placed (symetrically would do) it would actually fly ! the 2 rotors spinning one direction would be cancelled by the turntable but the other 2 rotors would now be spinning double in relativity to the air !
 
"andy" said:
if you had 2 blades of the quadcopter spinning in the opposite direction and they where correctly placed it would actually fly ! the 2 rotors spinning one direction would be cancelled by the turntable but the other 2 rotors would now be spinning double in relativity to the air !
Click to expand...

But you can't rotate about the axis of more than one of the rotors anyway. So I think it's a little more complicated than that, but yeh it'll fly I think.
 
RomanNose said:
Let me extend this a few more pages.
Quadcopter on a turntable.
Click to expand...

As two sets of rotors would be spinning in each direction, you would be able to obtain lift. Although some serious maths would be needed to work out if you could obtain enough lift for flight, and it would be unlikely to be stable anyway. Same would apply for a chopper with two counter rotating main rotor heads like the chinook. The only type of chopper that might be able to fly is one with a coaxial twin rotor design such as the Russian Kamovs.
 
would a chinook not just nosedive everyone to their death ? dont know a lot about them mind , im just assuming the end rotating the same direction as the turntable would be making it want to tilt that way
 
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