In article , Julian
Scarfe writes
I'm not sure that's the case, David.

The problem with a decelerating taildragger is that the inertial force at
the CG associated with the deceleration occurs behind the retarding force of
the mainwheels on the runway. This is unstable. If the two forces get out
of line, the couple tends to increase. By contrast, having the retarding
force on the main wheels behind the CG is stable.

Thanks for the comments Julian. My first thought about your suggestions
is that as long as the braking force is directly in the line of
deceleration then there is not a problem but as soon as a yaw develops
then side forces immediately come into play, if they didn't then the
aircraft would not start to turn. It must be very similar to the
oversteer/understeer problem of cars.

In a car if you brake hard and the front wheels lock then the car tends
to go straight on because the yaw stability is still provided by the
rear tyres. If the rear wheels lock up then you will have great
difficulty in stopping a spin. This corresponds to the lack of 'lift'
developed by the tail wheel (particularly if it castors) meaning there
is insufficient yaw stability.

The couple that you mentioned that depends on the retarding force of the
front wheels only produces an effect if a yaw develops. The correction
of the yaw has to be provided by an inbuilt stability or by the rapid
response of the pilot trying, with a big rudder, to introduce
'artificial' stability into the loop.

It has some small similarities to the concept that a high wing aircraft
is more stable because the cg is below the wing. It is more stable but
not due to 'pendulum' stability but due to the way the air flows during
a yaw.
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