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From: x13245i2@usma6.usma.edu (Obrien Patrick CDT)
Newsgroups: sci.military
Subject: RE: Autorotation of Harriers
Message-ID: <1990Dec6.021723.18639@cbnews.att.com>
Date: 6 Dec 90 02:17:23 GMT
Sender: military@cbnews.att.com (William B. Thacker)
Organization: AT&T Bell Laboratories
Lines: 41
Approved: military@att.att.com



From: x13245i2@usma6.usma.edu (Obrien Patrick CDT)
     I was confused by the question but I think I may have the answer.

     Autorotation - this is a state in rotary wing aircraft where the blade is
producing lift due to the remaining rotation of the blades.  I did autorotos at
Hunter AAF this summer and it was fun.  I learned why it worked when I got back
to academics this year.  Helicopters are designed so that when the collective
is bottomed out, part of the blade is acting as a pinwheel (called the driven
portion) and some acts as a fan (in the "windmill prop state")  The outer
portion provides lift and the inner portion is driving.  The two forces come to
equilibrium and the helo settles into a steady descent rate.  At the end near
the ground, the pilot pulls up the collective and turns the whole blade into
the thrusting portion allowing kinetic energy of the blades to be converted to
lift.  Of course, you can only do this once, for when the kinetic energy is
gone... no lift, so you had better be on the ground by the time you run out.

Harriers use pure thrust of mass amounts of air moving at high velocities to
hover.  Thrust in Newtons = (mass flow (kg/sec) of air) x (velocity of air
(meters/sec)) x (area (square meters))  If that turbine engine shuts off, the
flow stops immediately.  No mass flow, no thrust.  So if that harrier is not
moving forward when the engine quits, look out below.

Autorotation, therefore, does not apply to Harriers.  It is quite unique to 
helicopters and even then, it is a designed condition. (believe me - I know)

Everyone watch on 8 Dec as ARMY Kills navy in football.  Also learn how we
stole their goat. HA!  Beat Navy!

I hope this is not too technical and feel free to write me if you have any
questions on what I've written.  I'll use a small sig file as Mr. Thacker
yelled at me last time I tried to be motivated about my branch. :-)

[mod.note:  I remember that one... esprit d'coredump.  8-)  - Bill ]


1                     /   /                     Patrick C. O'Brien
2    /\              /   /                      Cadet USMA
3   |  \/______-----/   /----\_|                x13245i2@usma6.usma.edu
4   |/ /-----------/   /-----/~|                (914) 938-5466


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