What are the takeoff and landing distances of motor gliders? I'm doing some estimations of weight and thrust loading for a college project, and in the formula below the landing distance is not a variable, but should be estimated using similar aircraft and usual runways. (There is also a formula for landing with the same problem)

The similar aircrafts are 18-21 meter self-launching motor gliders like DG-505MB, DG-1001M or ASG 32 Mi (but with absolutely no data I have now, information about any other gliders would be appreciated as well).
The only thing I've found was that European Regulations CS-22 allow motor gliders a maximum takeoff distance of 500 metres.
Source; T.C.Cork, Design of Aircraft
You may wish to obtain POH data from the 18-21 meter motor gliders you have listed and compare it to your calculated results. Also look into information such as wing loading, aspect ratio, takeoff speed (or stall speed), and airfoil type in addition to power source to include in your report.

Motor gliders, true to their name, should lift off well before 500 meters.  Landing distance would be similar and also available in POH.