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View Full Version : Riddle me this Batman!


bigbob
23rd Aug 2002, 11:48
Upon reading "The Bible" ie Handling the big jets, D.P Davies frequently refers to 'Mach number effect' If anyone could expand on this I would be most grateful.

Cheers.

niallcooney
23rd Aug 2002, 13:16
BB,

Three things that he could be talking about:

1. Mach tuck

2. Mach number variation with change in tempature, with can induce Mach tuck as well.

3. Transonic drag rise (also known as shockwaves) as the Mach number tends towards @ .90 (this can vary with the airfoil's critical Mach number)

Just a guess, but if Davies just says 'Mach number effect' he's being pretty vague!


Nial

Dick Whittingham
24th Aug 2002, 22:24
Just checked in to "Handling the Big Jets" index, and found a list of references to Mach effects. On looking up a selection I find that they cover all the various things that happen as you move higher up the transonic range. These are:

Increasing drag.

Variations in lift, whch produce -

Lateral instability and roll control problems.

The rearward shift of the centre of pressure in the high transonic range, which produces -

A nose down change of trim and -

An increase in longitudinal stability.

Transport aircraft, except Concorde, are not designed for supersonic flight, but are designed to get as high up the transonic range before these effects begin to kick in. The first uk jet I flew would not go over .78, even straight down, but most modern transports fly quite comfortably in the .9s.

Dick W