Yellow triangle on airspeed indicator.

Hi,

Please...anyone point me to the source document on the yellow triangle on most new sailplanes?

It seems to be best glide for our ASK-21 for 'solo' flight, however our New LET L-23 the triangle is at the 'dual' gross weight best glide. (As it happens the triangle is at 49kts on both gliders!)

My understanding is the triangle is best glide without ballast. Seems Schelicher has determined that the second pilot is 'ballast' and Blanik may figure ya can't dump the second person.

I suspect there is probably a 'JAR 22' certification description!?!?

Thanks

Jeff Banks