ive just made a quick cardboard model of the swallow, same size. no engine though just to test the glide

i balanced it where the instructions say, and it seemed tail heavy, moved the C of G back an inch and it glided good,

makes it more puzzling because when it takes off with the help of a bit of up elevator, as soon as you relax the elevator it dives into the ground.
which to me would indicate the nose is too heavy

so im wondering if the elevators need to have a bit of up trim