In article , Peter Kemp
peter_n_kempathotmaildotcom@?.? writes
Hmm. Whittle's first patent was 1930 (after he'd been working on jets
for a while), and the first successful jet aircraft arrived in what
'44? So 14 years, and jets were hardly reliable at that point, and not
for many years afterwards.

If you're starting from scratch, Bell have been trying to get the tilt
rotor to work for 30-40 years with little to show for it.

--
John