When Slingbys tried to produce the HP14 for the British market they ran into
trouble with the use of flaps only for cloud flying. At that time to get an
airworthiness certification the glider had to have speed limiting devices
for cloud flying. It had been proved in test flying that the flaps
certainly limited the airspeed to "rough air max." but the test pilot ( John
Williamson) reported if the airspeed was already high and rising, the effort
required to lower the flaps down to 90 degrees was just too much.

If the sailplane was genuinely going out of control in cloud the flaps would
be useless. Various methods were tried to overcome this including a high
pressure air bottle to actuate pneumatic jacks- unfortunately at high speeds
forcing the flaps down in this manner caused problems with the supporting
secondary spar structure requiring yet further modifications.

DB