x13245i2@usma6.usma.edu (Obrien Patrick CDT) (12/06/90)
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) 938-5466msmith@mrc-crc.ac.uk (Mike Smith x3297) (12/11/90)
From: Mike Smith x3297 <msmith@mrc-crc.ac.uk> Do any of you Harrier experts know if the AV8B/GR5 has a system where the vectored thrust nozzles automatically rotate downwards as airspeed decreases? This would reduce pilot workload and could be termed 'autorotation' although its meaning is completely unrelated to helicopter autorotations. -- Mike Smith Computing Services Janet: m.smith@uk.ac.crc Clinical Research Centre, Usenet: m.smith@mrccrc.uucp Watford Rd, HARROW, Middx, HA1 3UJ or ...!mcsun!ukc!mrccrc!m.smith Tel 081-869 3297 Internet: m.smith%uk.ac.crc@nsfnet-relay.ac.uk
roeber@cithe3.cithep.caltech.edu (Frederick Roeber) (12/11/90)
From: roeber@cithe3.cithep.caltech.edu (Frederick Roeber) In article <1990Dec6.021723.18639@cbnews.att.com>, x13245i2@usma6.usma.edu (Obrien Patrick CDT) writes: > ... 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. > ... What is the rotational inertia of the blades of the standard helicopters? Just trying to work out some numbers, and I don't recall seeing these figures.. -- | Frederick G. M. Roeber | e-mail: roeber@caltech.edu or roeber@vxcern.cern.ch | | r-mail: CERN/SL-CO, 1211 Geneva 23, Switzerland | telephone: +41 22 767 5373 | | "Why don't we nuke Iran, too, and say it was just a typographical error?" |
henry@zoo.toronto.edu (Henry Spencer) (12/12/90)
From: henry@zoo.toronto.edu (Henry Spencer) >From: Mike Smith x3297 <msmith@mrc-crc.ac.uk> >Do any of you Harrier experts know if the AV8B/GR5 has a system where the >vectored thrust nozzles automatically rotate downwards as airspeed decreases? I'm not aware of one, and am skeptical; at the very least, there would have to be a manual override, or things like ski-jump takeoffs would not be possible. (Ski-jump technique is full thrust *forward* until you hit the jump, at which point the nozzles are moved to a compromise angle that continues forward acceleration but provides some lift as well. I think.) Takeoffs in general, in fact, wouldn't be practical without an override, since Harriers very rarely make true vertical takeoffs -- even a very short takeoff roll greatly increases payload. -- "The average pointer, statistically, |Henry Spencer at U of Toronto Zoology points somewhere in X." -Hugh Redelmeier| henry@zoo.toronto.edu utzoo!henry
leif@sugar.hackercorp.com (Lee King) (12/15/90)
From: leif@sugar.hackercorp.com (Lee King) Henry Spencer (henry@zoo.toronto.edu) wrote: >I'm not aware of one, and am skeptical; at the very least, there >would have to be a manual override, or things like ski-jump >takeoffs would not be possible. (Ski-jump technique is full >thrust *forward* until you hit the jump, at which point the >nozzles are moved to a compromise angle that continues forward >acceleration but provides some lift as well. I think.) Takeoffs >in general, in fact, wouldn't be practical without an override, >since Harriers very rarely make true vertical takeoffs -- even a >very short takeoff roll greatly increases payload. Well, I only know what I see on _Wings_ (on the Discovery Channel) and their show on the Harrier leads me to believe that there is no such automatic doohicky(tm), at least not on Brit Harriers. The attitude control is a lever located next to the throttle (on the pilot's left). It moves over approximately 100 degrees of arc (from all the way forward to slightly past vertical, thrusting BACKWARDS!). When making an assisted short takeoff, the pilot sets a simple slide catch on the lever to limit its travel to somewhere between level and vertical, the amount depending on how he wants to do the takeoff. Then he puts it in the forward thrusting position and starts his roll. When he reachs the desired speed he pulls it sharply back (to the stop) and takes off with the engines vectored to the preset position. Does that make sense? -- Andre Marrou for President in '92! Kick the bums out! Vote Libertarian! Curious about the Libertarian Party? Call LP National HQ at 1-800-682-1776, or send your USPS address to 76177.2310@COMPUSERVE.COM, attn. Marc Montoni