I like the idea of the single duct because it works to provide a
solution that provides reduced sound power in all aspects, rather than
only in the plane of the earths surface. I'm not sure what sharing a
duct would do to the resonance, especially being that its firing
opposite to the prefered phase of the resonating system.

Synchronization Problem- Aren't these motors fired with a spark? It
would seem you could force any phase you wanted. Of course the
frequency being dictated by the natural frequency of the pipe.

Smaller vs larger- I'm not talking about a cluster, I'm just talking
about firing 2. I'd be interested to know what the effiecy difference
is between a pair of 400lb thrust pulse jets and a single 800lb jet.

Harmonics, Jim- I think you're right, but most of the noise power
is contained in the fundamental. I'd aim to cancel that. The
remainder might be tollerable.

Try it, Bob K.- Unfortunately I live in an apartment, not a ranch
in Idahoe. I don't think my neighbors would appreciate me firing up a
pair of pulse jets slightly off frequency, beating against each other,
on the balcony at 2am. One of my buddies runs his private machine
shop in his apartment though. Carpet is covered in oil.

Regards

Bruce Simpson wrote in message . ..

That's not going to work.

The best that can be done is to run multiple pulsejets feeding a
single duct and try to keep the engines operating out of phase.

Doing this would result in the the pulses from each engine being
integrated into a wafeform that had a lower amplitude.

However, it si extremely difficult to keep pulsejet engines operating
at a fixed phase differential to each other when they're clustered
like this -- the prefer to synchronize and operate in phase.

The other problem is that smaller pulsejets are less efficient than
larger ones. You'll burn a lot more fuel to get a given amount of
thrust if you cluster several small engines together to do it.