Along the way, we got some good experience on how to shape the pulsejets, so that they would ignite and burn reliably.
Overall dimensions and shape
We have tried many different shapes, but these dimensions and shapes worked well for us.
The sizes are relative, so we keep the same relationships between dimensions when we scale the pulsejets for different tones.
Propane inlet angled 45 degrees
Turned out to be absolutely crucial to the operation, to have the inlet of propane in the right position and angle. After lots of experiments, we found out, that about a 45 degree angle like this worked really well.
Pre-mixing air and propane
To avoid the usual way of starting pulsejets, using a leaf blower or compressor, we made a setup to allow us to use a mix of air and propane in the fuel inlet.
Having a constant pressure regulator on both the propane bottle and the compressed air outlet, made it easy to get the right mix using the needle valves every time.