Unfortunately, it turns out that (for ideal gases, such as our atmosphere) a 'negative shock', i.e. a rarefaction shock, is impossible. It would violate the 2nd law of thermodynamics!
And if you have multiple, subsequent shocks (one at the aircraft tip, another at the engine inlet, another at the wing, etc), the later ones will eventually catch up to the first one, resulting in the N wave we would want to avoid.
And if you have multiple, subsequent shocks (one at the aircraft tip, another at the engine inlet, another at the wing, etc), the later ones will eventually catch up to the first one, resulting in the N wave we would want to avoid.