Helicopter on a turntable

[Hanakuso]

So will it take off if the turn table was spinning at the exact same speed as the blades in the opposite direction?

[monjorrow]

Yes the blades will still be cutting through the air producing lift no matter what the turn table is doing. Same debate as the airplane on a moving runway...

[neutron256]

I assume by oppisite direction you mean that the blades would remain stationary relative to the world and the fuselage would instead spin. In that case there would be no relative movement between the rotor and the surrounding air and no lift.

Of course the tail rotor and drag of the fuselage would probably cause havoc, but not flight.

[Snoopyalien24]

Yes. The movment of the blades is not what causes it to lift, but the actual air it pushes down causing it to lift.

Speaking of lift...

[neutron256]

Originally Posted by monjorrow

Yes the blades will still be cutting through the air producing lift no matter what the turn table is doing. Same debate as the airplane on a moving runway...

Not the same at all. The airplane on a conveyer belt still works because the the airplane is not getting any significant resistance from its wheels on the conveyer belt. The wheels just have to spin faster then normal.

The helicopter's wheels (or skids) are not oriented to move with rotation so the helicopter fuselage will spin with the turntable.


Fun with physics

[b.e]

Blades will be stationary, and the body of the helicopter will rotate rapidly instead.

Secondary question: Will the load on the engine be less than or greater than the load experience in flight?

[JDMenrique]

hmm...

[wbradley]

Originally Posted by b.e

Blades will be stationary, and the body of the helicopter will rotate rapidly instead.

Secondary question: Will the load on the engine be less than or greater than the load experience in flight?

The load is less since there is no wind drag on the rotor which remains stationary relative to the air.

The airplane will not lift if taking off on a conveyor either since the net airspeed is zero hence no laminar flow on the wings to cause lift.

A guy in my office is a former Learjet pilot and I'll throw this at him when he's in. He s not certifiable now due to medical issues related to neurological surgery.

[neutron256]

Originally Posted by b.e

Blades will be stationary, and the body of the helicopter will rotate rapidly instead.

Secondary question: Will the load on the engine be less than or greater than the load experience in flight?

Should be considerably less since there should be no drag from the blades moving through the air. Just any mechanical load from the transmission, and resistance from the tail rotor.

[Dave-ROR]

Originally Posted by wbradley

The load is less since there is no wind drag on the rotor which remains stationary relative to the air.

The airplane will not lift if taking off on a conveyor weither since the net airspeed is zero hence no laminar flow on the wings to cause lift.

A guy in my office is a former Learjet pilot and I throw this at him when he's in. He s not certifiable now due to medical issues related to neurological surgery.

The airplane riddle was that if it were on a belt traveling at the same speed as the airplane in the opposite direction. The plane will absolutely take off. The ONLY thing the belt affects in this case is wheel speed and wheel speed has absolutely nothing to do with whether or not a plane can fly. The planes prop(s) or turbine will still propel the airframe forward to take off speed regardless of how fast the pavement under it is moving.

The helicopter won't take off. Lift is in this case determined by the rotors speed against the air. So if we assume the turntable is spinning at the same 5,000RPM (easy number) as the rotor shaft, in the opposite direction then the rotor would not actually move through the air at all, instead the airframe would. Of course I could be missing the trick with the helocopter.

[wbradley]

Originally Posted by Dave-ROR

The airplane riddle was that if it were on a belt traveling at the same speed as the airplane in the opposite direction. The plane will absolutely take off. The ONLY thing the belt affects in this case is wheel speed and wheel speed has absolutely nothing to do with whether or not a plane can fly. The planes prop(s) or turbine will still propel the airframe forward to take off speed regardless of how fast the pavement under it is moving.

The helicopter won't take off. Lift is in this case determined by the rotors speed against the air. So if we assume the turntable is spinning at the same 5,000RPM (easy number) as the rotor shaft, in the opposite direction then the rotor would not actually move through the air at all, instead the airframe would. Of course I could be missing the trick with the helocopter.

Thanks for explaining the airplane riddle.

No way the airplane can lift.
If the prop is providing thrust for the plane to move forward on a treadmill/conveyer in the exact opposite to the movement of the belt then the net airspeed is still zero. The plane is standing still relatyive to the air/ground. In other words since the plane is not moving forward relative to the ground (or air) then there cannot be sufficient airflow over the wings to generate lift.

Try launching a kite while running on a treadmill.

[Dave-ROR]

Originally Posted by wbradley

Thanks for explaining the airplane riddle.

No way the airplane can lift.
If the prop is providing thrust for the plane to move forward on a treadmill/conveyer in the exact opposite to the movement of the belt then the net airspeed is still zero. The plane is standing still relatyive to the air/ground. In other words since the plane is not moving forward relative to the ground (or air) then there cannot be sufficient airflow over the wings to generate lift.

Try launching a kite while running on a treadmill.

I think you misread it if you were trying to agree.

If you launch a kite while running on a treadmill, you are correct, it won't work. But that's because your legs are your interface generating speed. Instead, strap a jet pack on and try it again, your legs no longer matter, the kite will fly. Of course you'll fly off the treadmill too lol

Think of it this way instead..

A Car running 60MPH on a treadmill traveling 60MPH in the opposite direction has a groundspeed of zero. That's because the WHEELS which are ON the treadmill provide thrust.

An airplane traveling 60MPH on a treadmill traveling 60MPH in the opposite direction has a groundspeed of 60MPH and a (useless to know) wheelspeed of 120MPH. That's because the PROP/TURBINE is providing thrust by moving AIR which is completely unaffected by the treadmill.

[neutron256]

Originally Posted by wbradley

Thanks for explaining the airplane riddle.

No way the airplane can lift.
If the prop is providing thrust for the plane to move forward on a treadmill/conveyer in the exact opposite to the movement of the belt then the net airspeed is still zero. The plane is standing still relatyive to the air/ground. In other words since the plane is not moving forward relative to the ground (or air) then there cannot be sufficient airflow over the wings to generate lift.

Try launching a kite while running on a treadmill.

But the airplane doesn't push against the ground (treadmill) to move itself forward. It is pushing against the air which has no connection to the treadmill. This is the same reason airplanes take off into the wind. A plane generating lift is all about relative airspeed not ground speed.

What I find really funny is many experienced pilots don't understand this, and will insist the plane couldn't take off.

[HunterGreene]

Why has nobody mentioned Mythbusters yet?

(Because I'm a noob and I don't know how to post video)

But Neutron is correct. The drive, or thrust forward is provided by the prop, not the wheels.

/argument