Today,
I designed and made my diy plane but problem is of wings. Wings are soft instead of hard. Dihedral is changed after flight as plane reach ground and wings hit ground then there is some changes  in dihedral.
that is why i get 2-4 seconds of flight time.
Please tell me if you know solution for thermocol.
Note: I made plane thermocol piece which is from thermocol plate.

Design own plane is difficult task.
If you have some design for HLG then please provide design and give website link if possible.
Thanks.

You can make a solution of water and fevicol(50-50%) and stick pieces of tissue paper or newspapers on your wing (like a coating) with this fevicol solution. It will provide your wing a good strength.

But the problem is that it will make the wing heavier which you don't need for a glider

Using clear tape on the thermocole increases its rigidity.