German Puzzle

I have acquired an aircraft landing flap from Germany.

It is 2.44m long ( at longest part) and 37 cm wide.

It is skinned on one side only.

It has a plate with the number 5351 scored into it.

I was told that it was wartime German.

Post war it is claimed it was used as a sign in Russia. The remains of the sign are still visible on the upper surface.

The scrapman it was acquired from had cut it in to three pieces. There were a pair of these – I have one only.

The puzzle is what is it from ?

The suggestion by the number is a late Emil – but I thought they had fabric covered flaps ?

I appreciate any guidance.

Kind Regards

Brian