"Kevin Brooks" wrote in message
...

"Pooh Bear" wrote in message
Fuel efficiency ( cost per seat-mile ) is what it's about. This factor
is
skewed by amortised cost of old but serviceable a/c - like the 727s I
just
mentioend. Not efficient - but the lease purchase was paid off decades
back.

I tell you what--you want to start up a new low-cost airline here in the
states with 727's, be my guest---but don't be planning on getting many
financial backers.

Question - how efficient is a 727 re-engined with the RR Tay conversion?
These seem popular with the higher end of biz-jet operators.

I think someone on here, though may have been on TV, said that the
difference between cruise speeds on various airliners is to do with the
critical speed of the wing. Above this speed, the thrust required is much
more, so you use much more fuel. The 747 was designed for a faster
speed in this respect so has a higher cruise speed? I think the 727 was
quoted as being quite good at M 0.75 but not at 0.85? Something like
that?

Paul