Formation of the bow wave in the first instance cannot happen unless air is travelling (relative to the a/c) at at least M1 and then meets air being slowed by the presence of the aircraft structure.
If the aircraft continues to accelerate, the size of the region of slower air (by slower I mean <M1) infront of the stagnation point, is reduced. Everything else is determined by the shape and size of the leading edge of the structure. Small sharp structure leading edges will cause the bow wave to be initially weak, forming relatively close to the LE, and attaching quickly beyond M1 (maybe at M1.1 for example), and quickly become oblique. Large blunt LEs will cause the bow wave to be bow wave to form relatively further from the LE, a stronger shock wave, possibly never attaching (below maximum speeds for the a/c of course, the bow wave will allways eventually attach), and part of the wave will remain oblique (again dependant on structural speed limits).
For the JAA, as with the AoA that are taught as representative angles (-4, 0, 4 and 16), an attachement number of around 1.3 is suitable for most med to large jet transport a/c.
Final point on attachment Mach No.. This is the same as detachment Mach No. in magnitude, but each is used respectively for accelerating through the transonic range, to describe the M when the bow wave attaches, and decceleration for the detachment of the wave. The JAA have asked questions talking about accelerating up through the transonic range wrt detachement. This is because it is the same number in the end, and because (as far as they seem concerned) anything that disorientates the students must be a good thing!
Please email me for anything else
Mik Moore
Oxford
[email protected]
