There is no serious evidence, photographic or otherwise,
that Whitehead ever managed to fly his aircraft. The best
that can be produced is a claim by Whitehead himself, and
the man seems to have been more than a little prone to
exaggeration.

Contemporary newspaper articles, one of which is from the local paper
and describes the flight constitute serious evidence, albeit not
proof. In addition, at least two alleged eye-witnesses later signed
sworn affidavits.

They have built a "replica" of the No.21
(despite the complete lack of plans), equipped it with a modern
engine, and managed to get it briefly into the air.

The Flugpionier-Gustav-Weißkopf-Museum photos depict what certainly
looks like more than "briefly" being in the air (remember, the Wright
Bros.' craft was catapulted and didn't go very far either).