Well, it probably isn't quite as simple as that. I think it's more like only a little of the flow is making it through the flameholder, with most of the air just pressurized in front of it. The air is stalled at the flameholder - that is, you don't get more flow, no matter how much pressure you add beyond that point. Instead, the diffuser just fills to overflowing with turbulent, high-pressure air. Then, the air you're driving into it mixes in with the turbulence just inside the intake, and mostly overflows along with it. The speed of the air inside the diffuser is fairly slow and turbulent, so combustion easily forms there. And, yes, once it gets out, it would feel the influence of the flow stream closer to the blower and be pulled in toward it.Zippiot wrote: a wierd thing that i cant explain is that the closer i bring the shop vac to the opening of the jet, the more the flames curl back towards the shopvac. my only explaintion is that the back of the jet is making high pressure from the heat and the shop vac with its high speed moving air is making low pressure. a vacume making a vacume...
Just what you said, I guess, but in more detail (of a mostly speculative sort ;-)
Good observations on your part, though!
Remember that Maggie has the crude flameholder she does precisely because she's supposed to work at the very lowest range of practical flight speeds. Reasonable efficiency is unattainable, and is considered a non-issue in this design.