With no PoDs prior to 1904,* what is the earliest that an aircraft could break the sound barrier? What is the earliest that ramjet technology could be developed? And this being done, how early could TTL see the first serious** designs for a scramjet plane?
*or 1895 at the earliest, if you want to utilize earlier rocketry a la Pedro Paule
**I'm not saying "functional" here, since OTL still doesn't have a working plane capable of reaching LEO (to my knowledge)