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Old 18th Jun 2009, 03:23
  #21 (permalink)  
411A
 
Join Date: Mar 2000
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Lets look in the distant past to see some of the other considerations that govern vertical stabilizer size on a swept wing jet transport airplane.

Type, B707 Intercontinental (707-320/436, straight-pipe powered).
There was a definite problem with this airplane regarding the vertical fin size, not driven by the engine out case, but yaw stability.
These aircraft had a parallel type of yaw damper (which needed to be switched OFF for takeoff/landing).
When this airplane was submitted to the British ARB for certification, DP Davies demanded that the rudder power and yaw damper be modified.
The rudder power Q-feel system was re-designed, and the normal 13 inch ventral fin was increased to 39 inches in width, to provide increased yaw stability.
When this series of airplanes were fitted with fan engines later on, Boeing once again redesigned the vertical fin...this time by increasing the height and, a series type full time yaw damper was fitted.
However, in extending the height of the vertical fin, Boeing just barely avoided another problem...IE: too large a vertical fin, and the spiral stability certification standards could not be met.

Aircraft design...a very large compromise, in many areas.
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