perhaps Jim59 would tell us which airplane these interesting instructions apply to!
Schempp-Hirth Discus-2cT - which is still in production. It has a 2-cylinder 2-stroke Solo 2350 engine with a 5-bladed folding propeller. With a full tank of 13 litres of AVGAS / 2-stroke oil mix it has, in still air, a range of up to 200 nm without reserve.
The same glider is also available with a 'FES' Front - Electric - Sustainer motor. They have become popular because with the electric motor and prop in the nose it is a single lever operation for instant power - the drawback is battery capacity. Experience shows that trying to climb away gives very limited range - but may get you to another thermal - alternatively cruising at low level will get you further - but the range is probably in the order of 40 nm. There have been a few battery fires - with EASA banning there use in some gliders for a while - but I believe that the cause was identified and all restrictions now removed.
A small number of gliders have a gas turbine motor - these jet engines are small and lightweight, erect quickly, and the starting is pretty well full automated. Run on Avtur - but fuel consumption is high so range probable around 100 nm. But they do cruise under power at a good speed! You can hear them coming.
Right now petrol engines have greatest range - but most complex management. Improvements are being made to the petrol engine control systems to automate as much as possible and electric starters are now starting to be offered.