On Thu, 5 May 2005 16:36:44 -0400, "Morgans"
wrote:

Can you describe the design and placement of these bob weights, and how they
added to stability?

Here's an explanation of a bob weight from a website on supplemental
flight controls:
http://142.26.194.131/aerodynamics1/controls/Page3.html

"Bob weights are sometimes known as counter weights. Their purpose is
to change the amount of control force required to deflect the control
column under different g-loadings.

Normally the amount of force the pilot must apply to the control
column, assuming reversible controls, varies with airspeed only.
However, by installing a bob weight the aeronautical engineer can make
it more difficult to pull on the control column as g-force increases.

The purpose of the bob weight is to reduce the likely hood the pilot
will overstress the aircraft."

I should mention that this explanation comes from a website describing
light airplanes, not fighters. If bob weights can be used to increase
the force necessary to move the elevator as G force increases, they
can also be used to lighten the elevator as G force increases. This
appears to be the intent when used in the P-47 to assist it from
pulling out of high speed dives where the elevator was locked. I
don't think this would be very effective though as the elevator was
locked by the onset of compressibility and the pilot literally could
not move the stick back at all at that point, at least not at high
altitude. Since the nose would not come up, there would be no G force
to work on the bob weight. And yes, this was for sure a problem in
combat. Several times the Thunderbolts dived down on unsuspecting
German fighters from high altitude only to find themselves unable to
pull out of the dive and rocketed by the very startled Germans. At
lower altitude because the speed of sound was faster than a high
altitude, the effects of compressibility lessened and the pilots could
pull out, albeit slowly. The P-38 which also was affected by high
speed elevator locking was actually plackarded against exceeding a
certain speed. Unfortunately that meant that they really couldn't
dive much from high altitude. I've read that the Germans figured this
out and exploited the situation against P-38's but this seems pretty
unlikely to me.

It would appear that bob weights work only with the elevator.

So having a counterweighted control stick (bob weights) could add
pressure to the control stick making it require more force to pull it
back. This is a stabilizing effect and would counter over controling
when the Mustang's rear 75 gallon fuel tank was filled.

Corky Scott