On 12 Mar 2004 09:21:58 -0800, (Jay) wrote:

In an earlier post I read somewhere that the pulse jet is a device
that converts fuel into noise. Someone else had suggested firing 2
engines 180 degrees out of phase with each other to cancel the sound.
If the 2 engines were stacked one over the other, then you might
actually be able to cancel a lot of the sound at least in a circle
around the aircraft in the plane of the earths surface. Below the
aircraft it would be just as loud but twice the frequency, but
standing on the ramp 50 yards from the aircraft, it might actually be
made to cancel somewhat. What do you guys think?

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.

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