On Sunday, July 5, 2015 at 11:50:39 PM UTC-6, wrote:
You've blundered into the white room. You have primitive gyro guidance in the form of a turn rate indicator and so you are keeping the wings level, sort of. You are trimmed for 55 and the airspeed has just risen (alarmingly rapidly) to 85 and then temporaily plateaued there, staying constant for a couple of seconds. Answer quick: what do you do with the stick?

S

Open the spoilers (add drag) and leave the stick alone. A phugoid is damped by drag.

Don't believe it? Put your glider into a stick-free phugoid pitch/airspeed oscillation (roughly 17 seconds peak-to-peak) and then open the spoilers and watch it go away - or at least be significantly reduced.