www.pulse-jets.com

iv'e heard of attempts to make ram/scram jet engines that continue using same operation forces and involve minor changes in mechanics but could a jet have PDE to obtain ram jet minimal cruise speed and then affectively change using bilayered metals in which diffences in expansion due to heat changes...

Why not get easier compresson to the engine by using the difference in pressure caused by the air moving over the plane/missle in question. this would save engery and space.