Many years ago, I too saw one on a control line aircraft. The noise had to be heard to be believed. Everyone watching had their fingers in their ears. The pilot and pit crew all had earmuffs on. But when this thing got going, it was unbelieveble. And this from a pulsejet that was about 12" long and no more than 1.5" diameter at the widest point.

The model was all engine, with a couple of short stubby wings, no mopre than 14-16" span. The pilot was leaning way way back against the centrigugal force of this little rocketship that was doing circles around him. It went by in a blur. I'm surprised the lines took the load. I noticed afterwards that he had a 3rd line on the handle which I was told was a fuel cutoff in case things got 'out of hand'.

The starting procedure seemed a lot of hassle. These guys had a small cylinder of compressed air that they would squirt into the intake, and what looked like a car ignition coil and battery which they hooked up to a tiny sparkplug on the body of the jet. It took quite a few goes to get it running. It would fire up, go BANG BANG BANG BANG in quick succession then die. The re-prime, repeat process with a few more BANGS added, then die again. Eventually the BANGS became one continuous roar and it was away. By the look of it, it didn't produce much thrust, and took a lap or two to get up to flying speed, but once there, it was was an impressive sight indeed.

I have had an interest in these things ever since. But I doubt I'll ever actually build one, though I have come across a few plans on the net for them. They look very simple, but from what I have heard, for someone building one from scratch, they usually go through several prototypes before arriving at a viable design.