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Newbie Qs on stalls and spins



 
 
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  #71  
Old November 22nd 04, 05:05 AM
Marc J. Zeitlin
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Phil wrote:

Climbing - Lift is Greater than weight
Level - Lift = weight
Descending (including landing) - Lift if less than weight


This is substantially incorrect. As long as there's no acceleration in
the vertical or horizontal direction, lift and weight are essentially
equal, whether climbing, descending, or flying at a level altitude.
F=ma, and all that. If a=1, then L=W. This is a common misconception,
and until the climb or descent angle gets large, so that thrust/drag
become a substantial portion of the vertical component of force, L=W.

You don't climb because you've got excess lift - you climb because you
had excess lift for a short period of time which accelerated you
vertically so that you have a upwardly vertical component of velocity.
Conversely, you descend because you had insufficient lift for a short
period of time which accelerated you vertically so that you have a
downwardly vertical component of velocity. The LW periods were short,
and are NOT the steady state conditions.

The stall is uncontrolled "flying" and the only time this should

happen
whilst "flying" is in stall recovery practice, aerobatics and

sometimes
a second prior to touchdown.


Stalls can be completely "controlled" flying. I fly a COZY canard
aircraft, and I can fly all day with the canard stalled. I've done so
straight and level and in up to 60 degree banked turns. I've flown in
an acquaintance's Glastar (not a canard - looks a lot like a C-150), and
was able to do pretty much the same (although he only demonstrated 30
degree banked turns while stalled). In both aircraft, we maintained
full control at all times.

Just because your C-150, C-172 or Warrior (what I used to fly) can't do
it doesn't mean that that's the be-all and end-all of aerodynamics :-).

--
Marc J. Zeitlin
http://marc.zeitlin.home.comcast.net/
http://www.cozybuilders.org/
Copyright (c) 2004


  #72  
Old November 22nd 04, 05:43 AM
Andrew Sarangan
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At high pitch attitudes, due to the vertical component of thrust, the
lift could actually be LESS than the weight during a climb.


"Marc J. Zeitlin" wrote in news:hAdod.374264
$wV.338235@attbi_s54:

Phil wrote:

Climbing - Lift is Greater than weight
Level - Lift = weight
Descending (including landing) - Lift if less than weight


This is substantially incorrect. As long as there's no acceleration

in
the vertical or horizontal direction, lift and weight are essentially
equal, whether climbing, descending, or flying at a level altitude.
F=ma, and all that. If a=1, then L=W. This is a common

misconception,
and until the climb or descent angle gets large, so that thrust/drag
become a substantial portion of the vertical component of force, L=W.

You don't climb because you've got excess lift - you climb because you
had excess lift for a short period of time which accelerated you
vertically so that you have a upwardly vertical component of velocity.
Conversely, you descend because you had insufficient lift for a short
period of time which accelerated you vertically so that you have a
downwardly vertical component of velocity. The LW periods were

short,
and are NOT the steady state conditions.

The stall is uncontrolled "flying" and the only time this should

happen
whilst "flying" is in stall recovery practice, aerobatics and

sometimes
a second prior to touchdown.


Stalls can be completely "controlled" flying. I fly a COZY canard
aircraft, and I can fly all day with the canard stalled. I've done so
straight and level and in up to 60 degree banked turns. I've flown in
an acquaintance's Glastar (not a canard - looks a lot like a C-150),

and
was able to do pretty much the same (although he only demonstrated 30
degree banked turns while stalled). In both aircraft, we maintained
full control at all times.

Just because your C-150, C-172 or Warrior (what I used to fly) can't

do
it doesn't mean that that's the be-all and end-all of aerodynamics

:-).


  #73  
Old November 23rd 04, 05:05 AM
Greg Esres
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I suppose it is possible that you can reach max elevator
without reaching critical AOA. But I think that is unlikely, because
that would mean you will never be able to perform power-off stalls in
level unaccelerated flight.

The horizontal stabilizer and elevator are sized so that you can reach
max lift coefficient under the most extreme conditions, which will be
forward CG and in ground effect.

Since GE increases the stability of the aircraft, it is possible that
you could stall at altitude, but not close to the ground.
 




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