(Is this a private food fight, or can anybody join in?)
Well, this has certainly got the brain cells working overtime.
I might as well put in my 2 cents for what (very little) it's
worth.
I got to thinking about a simplified car. Front wheels, rear
wheels, a big bowling ball (representing the Center of Gravity)
in the middle, and me, sitting in the back trying to steer.
Thinking about rear wheel steer. Here I am going down the
track. For whatever reason, the front gets a little to the
left, and I need to straighten it out. Even though the front
is going left, I need to steer to the left, to get the back
wheels behind the front wheels.
Also, as the front end goes left, that big bowling ball wants
to keep going straight down the track (inertia) which creates
some centrifugal force that I have to overcome. Seems like the
rear steering tires have to do double work, move the back end of
the car back into line and overcome the centrifugal force.
It also seems like I am chasing the front end, trying to keep the
back end in line behind it. Since the centrifugal force will build
with speed (it's probably a square, a cube, a root or something,
Mayf will know) the rear wheels will have more and more to overcome.
I recall that when the back end of a front wheel car spins out,
even though the back tires are pointed like 90 degrees to
the direction of travel, they seem to have lost most
of their 'steering ability'.
With front wheel steer, it seems like all I have to do is
to move the front wheels back in front of the bowling ball.
I seem to be working 'with' the bowling ball's desire
(inertia) to continue down the track.
Front wheel steer seems like pulling a string.
Rear wheel steer seems like pushing a string.
In a tricycle landing gear airplane, the main weight supporting
wheels are behind the CG, and the nose wheel steers.
In conventional gear (tail dragger) airplanes, the main
weight supporting wheels are ahead of the CG and the tail
wheel steers.
You can ground loop (spin) a tail dragger easily. Indeed in
some cases, you start a turn and then apply full opposite control
to prevent this from happening. In the air - no difference. On
the ground, pretty much everyone agrees tail draggers are harder
to drive.
Tricycle gear airplanes don't have this problem.
It seems to me it has to be something to do with the location
of the CG in relation to the directional control location.
Someone may be able to do a vector drawing that show the forces
involved. Or, maybe, I'm not fast enough to keep up with the
minute perturbations (but you may be).
Jim W.
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