Irvine.J wrote:Larry I think we are in the ballpark here, the bangs shoved the test stand foward was just a indication of the power we might see, now its recipricating nicely I think its going to go GREAT.
Yes, I think so!
You get a really good air pressure control if you clamp down your airgun and simply work the regulator valve. I simply silver soldered one of the attachments from the end of the airgun onto the tube as you can see in the photo.
Sounds like a good method. With your arrangement, it probably WILL be a lot less pressure than what I use - because you don't have the big pressure drop through a tiny nozzle. Anyway, whatever works, that's what you do.
Larry, I think I may be able to work the airflow slowly down to nothing, and I think it all rested on that flare. So what does this mean?
Many seem very sure that you have to "ease off" the air to get a good start, but I have never found that tp be the case, once I got the right values of air and fuel flow. Of course, all my previous successes have been with straight tailpipe engines, which are probably more forgiving of vatiations. What typically happens, on an engine where I already know what air level to set, is this:
I start the spark running, then trigger the air and hold it on. I run up the fuel flow until the engine is cycling well, then add just a bit more, then kill the air. The power immediately drops slightly, but now can be throttled up a little before killing the spark. That's all there is to it, really.
The problem with starting is that you can't instantly change the fuel flow when you cut the starting air. So, what you have to establish is an air flow, including entrained air, that is VERY close to what the engine is able to pull by itself at the very same fuel level. Of course, this assumes that the engine is correctly tuned to run. But thinking about this, I think you can see what a delicate balance this is. The air you're forcing in has to be instantly replaced by the right amount of free-flowing air. Of course, it can be off slightly - but it has to be right within a very narrow range. There will always be some change in the balance of fuel and air when you cut the forced air off, and for me this seems to play out as a drop in power at that moment.
This is why the big mistake is overwhelming the engine with air. It causes you to supply a level of fuel that can't possibly be right for the first cycle of the engine suddenly pulling on its own. Of course, with an experimental design you have another problem, too: The engine may be out of tune enough that it REQUIRES some ram air to run! That's why you still end up playing with the lengths of things, even though the non-sustaining operation might sound awfully good.
The most likely error in this design would be the length of the tail cone, simply because I don't have the kind of experience that tells me what the real gas temps should look like. The reason I asked about the pulsing operation "fading" after quickly cutting the air is that I have seen rapid fading away in the case of an engine being a little too long. In my experience, a too short engine won't do this. If the body is just a little too long, a slight lengthening of the intake should bring it in. Lengthening the intake should be done very gradually - one mm longer there is equivalent to about 3 mm shorter at the tail end!
(Sermon follows) James, "honor your father and mother" (I know it can be hard to do!), and be of good cheer - I have never yet met anyone (face to face, I mean) who isn't doing this who really understands why anyone would ever want to do it! My dad was just about gone before I understood how much I had learned from him and how much his life had benefitted me and how much he had to do with me being what I am. (End of sermon.)
Good luck! It will work if you work at it, mate!
L Cottrill
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