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Aerodynamics question



 
 
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  #1  
Old March 10th, 2004, 08:19 AM
Jim Anderson
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Default Aerodynamics question

What's the ratio of the thrust generated by a hi-bypass turbofan between
what goes out the back and the "propeller" effect of the main fan?

The main fans rotate in the same direction. How much torque (P-factor from
my flying days in a C-152) do they create?

Jim

ps - hmmm... do they rotate in the opposite direction south of the
equator... grin


  #2  
Old March 10th, 2004, 12:00 PM
Miss L. Toe
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Default Aerodynamics question


ps - hmmm... do they rotate in the opposite direction south of the
equator... grin


No, the planes just flip over and fly upside down.


  #3  
Old March 10th, 2004, 07:37 PM
me
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Default Aerodynamics question

"Jim Anderson" wrote in message ...
What's the ratio of the thrust generated by a hi-bypass turbofan between
what goes out the back and the "propeller" effect of the main fan?


Depends heavily upon which engine your are considering. However,
the trend for a long time was towards ever higher ratios. Truely
high bypass engines produce anywhere's from 65% - 85% of their
thrust from the fans.


The main fans rotate in the same direction.


Yes.


How much torque (P-factor from
my flying days in a C-152) do they create?



Can't say for sure. I'd suspect very little.
  #4  
Old March 11th, 2004, 02:04 AM
DALing
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Default Aerodynamics question

p factor is a resultant of the change of apparent pitch during rotate. When
the rotate occurs, the apparent angle of incidence of the prop blade
increases and takes a bigger "bite" out of the air thus producing a net
torque. This site give a better explanation
http://home.earthlink.net/~x-plane/F...y-PFactor.html

or this one which is essentially identical

http://www.madsci.org/posts/archives...3940.Ph.q.html

"me" wrote in message
om...
"Jim Anderson" wrote in message

...
What's the ratio of the thrust generated by a hi-bypass turbofan between
what goes out the back and the "propeller" effect of the main fan?


Depends heavily upon which engine your are considering. However,
the trend for a long time was towards ever higher ratios. Truely
high bypass engines produce anywhere's from 65% - 85% of their
thrust from the fans.


The main fans rotate in the same direction.


Yes.


How much torque (P-factor from
my flying days in a C-152) do they create?



Can't say for sure. I'd suspect very little.


  #5  
Old March 11th, 2004, 03:39 AM
Steve
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Default Aerodynamics question

Torque isn't the issure with jet engines....the main issue is gyroscopic
effect. Jet angines turn VERY fast (15,000 - 65,000 RPM) This high RPM
causes the rotating mass to try and stay stationary inflight, meaning it
inhibits changes in pitch and yaw (not roll because roll is about the same
axis as the rotating mass)

"Jim Anderson" wrote in message
...
What's the ratio of the thrust generated by a hi-bypass turbofan between
what goes out the back and the "propeller" effect of the main fan?

The main fans rotate in the same direction. How much torque (P-factor

from
my flying days in a C-152) do they create?

Jim

ps - hmmm... do they rotate in the opposite direction south of the
equator... grin




  #6  
Old March 11th, 2004, 03:48 AM
Jim Anderson
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Posts: n/a
Default Aerodynamics question

Thanks Steve and DA...

Kinda nice to get back to some relevant subject matter.

J

"Steve" wrote in message
. ..
Torque isn't the issure with jet engines....the main issue is gyroscopic
effect. Jet angines turn VERY fast (15,000 - 65,000 RPM) This high RPM
causes the rotating mass to try and stay stationary inflight, meaning it
inhibits changes in pitch and yaw (not roll because roll is about the same
axis as the rotating mass)

"Jim Anderson" wrote in message
...
What's the ratio of the thrust generated by a hi-bypass turbofan between
what goes out the back and the "propeller" effect of the main fan?

The main fans rotate in the same direction. How much torque (P-factor

from
my flying days in a C-152) do they create?

Jim

ps - hmmm... do they rotate in the opposite direction south of the
equator... grin






  #7  
Old March 11th, 2004, 09:26 AM
Simon Elliott
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Posts: n/a
Default Aerodynamics question

Steve writes
Torque isn't the issure with jet engines....the main issue is gyroscopic
effect. Jet angines turn VERY fast (15,000 - 65,000 RPM) This high RPM
causes the rotating mass to try and stay stationary inflight, meaning it
inhibits changes in pitch and yaw (not roll because roll is about the same
axis as the rotating mass)


Interesting. Would forces due to precession be at all significant?

--
Simon Elliott
http://www.ctsn.co.uk/






 




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