posted on Jun, 21 2007 @ 12:15 PM
Figher Master FIN
Here is a link to a reasonable explanation of what Critical Mach Number means...
As the air passes over the wing it is accelerated due to the airfoil shape, so on any wing shock waves begin to form at the point where the air is
moving fastest when the air speed at that point reaches Mach 1 (slightly below Mach 1 actually as the air compresses), so that speed is less than the
speed of the aircraft as a whole. The actual speed difference is determined by the airfoil shape - generally speaking the thickness of the wing -
actually the ratio of thickness to chord. That's why different aircraft may have a different critical mach number.
Therefore, to delay the drag rise and the onset of shock waves, one must reduce the thickness to chord ratio - that means making the wing thinner.
Obviously there are problems with that because it is structurally more difficult to make a thinner wing as strong as it need to be, and a thinner wing
makes for less space to accommodate undercarriage, fuel tanks or weapons within it.
The swept wing concept is simply this. By turning a thicker wing to an angle to the airflow, the air has to travel further over the wing surface (in
the direction of flight) presenting an apparent lower thickness to chord ratio to the airflow, even though structurally the t/c ratio hasn't changed.
Of itself it doesn't solve the problem of transonic drag rise or loss of control effectiveness, but it does increase the speed at which these
However, this also induces part of the airflow to travel spanwise to the tip (or to the fuselage with a forward swept wing) which creates handling
problems, especially at low speed and high G (called tip stalling).
The early answers to the spanwise flow problem included wing fences, leading edge cuts, and sawtooth leading edges (the latter two creating vortices
to help keep the airflow in line with the direction of flight).
The Delta wing solves the structural problem because of the very long root chord, allowing a wing with a low thickness to chord ratio to be quite
thick at the root.
I hope that helps.
The Winged Wombat
[edit on 21/6/07 by The Winged Wombat]