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Paul Aldridge
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 Posted: Mon May 21, 2007 6:10 am Post subject: Helicopter Aerodynamics |
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Can somebody please explain or point me to a reference as to how a
helicopter can fly with its rotor (as in rotating wing) at 90 degrees to the
earth. i.e. with the nose pointing down and the tail rotor upwards or vice
versa. Military helicopters can seem to do this. My basic knowledge of
physics tells me that the main rotor would be driving the helicopter
forwards or backwards, generally parallel to the ground, but what is
negating the force of gravity when a helicopter is in this aspect? |
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veritas
Guest
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| Posted: Mon May 21, 2007 5:17 pm Post subject: Re: Helicopter Aerodynamics |
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Paul Aldridge wrote:
| Quote: | Can somebody please explain or point me to a reference as to how a
helicopter can fly with its rotor (as in rotating wing) at 90 degrees to the
earth. i.e. with the nose pointing down and the tail rotor upwards or vice
versa. Military helicopters can seem to do this. My basic knowledge of
physics tells me that the main rotor would be driving the helicopter
forwards or backwards, generally parallel to the ground, but what is
negating the force of gravity when a helicopter is in this aspect?
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Think of the rotors as a solid DISC that is hinged from its centre and
simply does not care what direction the machine travels - it just does
what it is told by the pilot's cyclic control. The position or attitude
of the fuselage is not really all that important. Helo's have a
horizontal tailplane that assists in eventually levelling the fuse in
forward flight.
What is usually witnessed when moving from hover to forward flight is a
forward disc angle causing helo acceleration (forward) with the
airframe literally being dragged along behind. The greater the forward
tilt of the disc angle - the treater acceleration - and the greater the
'nose down' fuselage attitude - until sufficient forward airspeed allows
the tailplane to correct the situation. Unlike the tail rotor control -
the main rotor control does not directly influence the airframe behaviour.
No smoke or mirrors :)
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veritas
Guest
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| Posted: Mon May 21, 2007 5:18 pm Post subject: Re: Helicopter Aerodynamics |
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cp wrote:
| Quote: | Paul Aldridge wrote:
Can somebody please explain or point me to a reference as to how a
helicopter can fly with its rotor (as in rotating wing) at 90 degrees
to the earth. i.e. with the nose pointing down and the tail rotor
upwards or vice versa. Military helicopters can seem to do this. My
basic knowledge of physics tells me that the main rotor would be
driving the helicopter forwards or backwards, generally parallel to
the ground, but what is negating the force of gravity when a
helicopter is in this aspect?
Aboslutely nothing will be negating the force of gravity. It will be
falling like a rock.
What the pilot will do however, is eventually pull back on the stick
which will raise the nose, and the downward speed will be converted to
forward speed as the main rotor starts generating lift again.
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HUH? |
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Stealth Pilot
Guest
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| Posted: Mon May 21, 2007 5:58 pm Post subject: Re: Helicopter Aerodynamics |
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On Mon, 21 May 2007 15:50:01 +0930, cp <cfparson (AT) gmail (DOT) com> wrote:
| Quote: | Paul Aldridge wrote:
Can somebody please explain or point me to a reference as to how a
helicopter can fly with its rotor (as in rotating wing) at 90 degrees to the
earth. i.e. with the nose pointing down and the tail rotor upwards or vice
versa. Military helicopters can seem to do this. My basic knowledge of
physics tells me that the main rotor would be driving the helicopter
forwards or backwards, generally parallel to the ground, but what is
negating the force of gravity when a helicopter is in this aspect?
Aboslutely nothing will be negating the force of gravity. It will be
falling like a rock.
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wrong.
the pilot would be using the aircraft's inertia and the manouver
couldnt last long.
Stealth Pilot |
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Coop
Guest
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| Posted: Mon May 21, 2007 7:09 pm Post subject: Re: Helicopter Aerodynamics |
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On Mon, 21 May 2007 15:02:50 +1000, "Paul Aldridge"
<paulaldridge (AT) hotmail (DOT) com> wrote:
| Quote: | Can somebody please explain or point me to a reference as to how a
helicopter can fly with its rotor (as in rotating wing) at 90 degrees to the
earth. i.e. with the nose pointing down and the tail rotor upwards or vice
versa. Military helicopters can seem to do this. My basic knowledge of
physics tells me that the main rotor would be driving the helicopter
forwards or backwards, generally parallel to the ground, but what is
negating the force of gravity when a helicopter is in this aspect?
Nothing, I figure. That's why it can't stay in that attitude for very |
long.
The same applies to a fixed-wing machine. With few exceptions, if the
wings are vertical to the ground, the machine will lose altitude.
Exception 1: Some aircraft have such powerful engines and/or so much
side fuselage area (or both, as in the GBII) that they can maintain
flight with the wings vertical. Some aerobatic machines can do this,
and essentially the thrust from the prop is what is holding them up
(plus the lift from the side of the fuselage).
Exception 2: Aircraft flown through a manoeuver that takes them to
wings vertical can continue along their flight path briefly purely as
a ballistic effect. The wings may provide the force that pulls them
around a curved path, but their path relative to the vertical is
essentially that of an artillery shell.
Coop |
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cp
Guest
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| Posted: Tue May 22, 2007 6:10 am Post subject: Re: Helicopter Aerodynamics |
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Stealth Pilot wrote:
| Quote: | Aboslutely nothing will be negating the force of gravity. It will be
falling like a rock.
wrong.
the pilot would be using the aircraft's inertia and the manouver
couldnt last long.
Stealth Pilot
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Ok. I will rephrase my answer to be more technically correct.
While the craft is at 90° to the earth (ie pointed nose up or nose down)
it will be accellerating towards the earth at exactly 9.81 metres per
second per second. If the aircraft has positive inertia, this will be
negated from the aircrafts inertia until it actually starts falling. |
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