From WW II and later, also from its use as rotor tip power in some helicopters, we know Ramjets could have a use in certain applications where fuel economy is not first requirement. German data seized by the UK indicate Lorin Ramjet best arrangement is 10º divergency in the intake/ diffuser section, for a total length of 1559 cm, diffuser would measure 859 cm; burning section 400 cm; convergent-parallel nozzle 300 cm. Ramjet starts producing power at an airspeed around 300 km/ h, while Pulsejets can generate thrust from zero air speed. A PulseJet installed inside a RamJet, with the appropriate diameter, increases in RamJet section, the 'Hot' PulseJet section inside the RamJet burning section. This would add the heat currently wasted, from outer Pulsejet part, to thrust, an additional free air around the Ramjet, acting to cool it, this heated air sent to outlet nozzle section, may add some improvement in overall propulsion efficiency of this 'compound duct.' Thanks. Blessings +