mustang65 wrote:It seems that the YF-12 was the only plane to have the rear facing periscopes but it would make more sense even on the Sr-71 for them to be facing forward instead.
The Blackbird had decent enough forward vision to fly by - the periscope was installed to permit the crew to check out some areas of the aircraft that were otherwise out of sight. From my memories of SR71- Myths and Legends, which I don't have to hand, I believe this was after an early loss or near loss due to some control surfaces being damaged and the crew being unaware of this fact.
Fitting periscopes to aircraft for this reason isn't uncommon and I believe the Victor, Vulcan and also the Valkyrie were similarly equipped.
The only proposals for aircraft to have forward facing periscopes that I recall were the Thunderwarrior and the British fast bomber proposal - the AVRO 730 in the 1950's - both for similar reasons - the intended cruise speed was too fast for any existing transparent material to survive in flight.
Ian