On 23/01/2014 22:14, The Natural Philosopher wrote:
On 23/01/14 21:33, Vir Campestris wrote:
On 23/01/2014 13:41, The Natural Philosopher wrote:
(there is a formula to do with drag and power and all sorts of stuff
that more or less says the best speed to fly a plane at is 1.5 - 2.5
times stall speed, so a 747 flying at 500mph has to take off at getting
on to 200mph plus. Even with all the flaps and stuff. A 300mph turboprop
need only take off at 120mph or so. And that means less runway: variable
pitch propellors are also very good at low speed thrust as well, so they
accelerate better from a standing start)

A 747 at cruising is alarmingly close to its stalling speed. The air is
thin up there - and that's why they go up there. Less drag.


It's not flying close top its stalling speed AT GROUND LEVEL where it
does its taking off.

My point being that there's not a simple ratio between ground-level
stalling speed with all flaps and slots set, and high level economical
cruise.

But this is not an area I have enormous knowledge of, I'm only an
interested amateur.

Andy