I think this may be an Avro Avian. Wikipedia has a few different illustrations of this (more on Commons) but several types have the pronounced bump of an intake over the propellor; in particular, this 1933 photo of Hélène Boucher is an almost perfect match (shown below).
Agence de presse Mondial Photo-Presse, Public domain, via Wikimedia Commons
I was able ...
From below, the Y-20 and C-17 are near identical.
Y-20 from https://nationalinterest.org/blog/reboot/chinas-y-20-real-china-military-plane-you-need-fear-185509
C-17 from https://www.aerotime.aero/28603-800-people-board-c-17-flying-out-of-overrun-kabul-airport
Ramstein AB (USAFE) being a short hop from Frankfurt, that would be the logical conclusion.