I have built an M-25, but not run it yet. Within the next few weeks hopefully.
Correct me if I'm wrong, but the idea behind designing a well-running valveless pulsejet is to match the resonant frequencies of the various tubes that make up the unit.
For example the M-25 is 1.036 m long, at a combustion temperature of 954 deg.C gives a resonant frequency of 152 Hz.
Should the inlet tubes be tuned to a harmonic of this fundamental frequency?
For example an inlet tube of length 0.169 m at an air temperature of 25 deg.C gives a resonant frequency of 911 Hz
This 911 Hz is a 6x multiple of 152 Hz.
How many of the various parts of the pulsejet unit need to be 'tuned' to length?