On May 16, 12:46*pm, Brian wrote:

Take a glider at approach speed about 5 feet off the runway in steady
state (at least for a glider) level flight with all drag devices
retracted..

If you deploy the spoilers and do not change attitude the glider will
drop onto runway, speed will change very little.

if you deploy airbrakes the glider will slow and settle to the runway.

If you deploy flaps the glider will balloon up.

Maintaining a constant attitude in the test you describe will require
a pitch control input and that input controls what happens to the
glider as the devices are deployed. To put it another way,
maintaining pitch attitude is an arbitrary choice. You could have
specified constant sink rate, constant glide path, constant airspeed,
etc etc. That close to the ground my intent is to control sink rate
and the controls interact to achieve that.

In my experience deploying my top surface devices with stick free
results in nose down pitch, increased sink rate, and airspeed remains
essentially constant. Who can define the name of the device that
causes that?

Andy