Joseph G. Foa is a researcher on pulsejets without valves, with direct frontal air intake.

"Simple pulsejet schematics, cut nozzle"

-A front and annular cover -with air intake through the center- has a shape that makes gases from the explosion return backwards, favoring the flying direction.

"Gas return effect"

-The majority of the gases from the explosion leave through the nozzle (truncated in the scheme) and depending on the length thereof it produces the explosion cycles per seconds. It is a matter of trials and balances.