Beginning work on a 55-75 pound thrust valveless pulse jet
(copied from Bruce Simpson design, same one Furze built)
Initial parts list is $340, with main costs being $89 for 4’x4’ 20ga 304 stainless sheet and $79 for the 3" 18ga 304 stainless U bend
Cut the 20ga stainless sheet on the CNC plasma, at 325 inches/minute it cuts all the pieces in about a minute
For my first time ever attempting to use a slip roller it turned out pretty good (realizing later I forgot to adjust distance between infeed rollers for material thickness with the knobs in the front). Learned quickly that it gets exponentially harder the wider the piece is, and cones make it tricky to be sure you are bending radially as larger end needs to feed faster than the smaller end.
Only took about an hour to bend all these, need to order some huge hose clamps to hold them together for welding
Off topic, but is this metal roller something we have at the space?
Yes. @Brandon_Green unpacked it last night and put it on a temp base. There’s a thread about it elsewhere on Talk.
Sweet man, always been interested in Jet propulsion, i have plans for a micro turbine @3-4 pounds of thrust, next project maybe?
You can use wire to achieve the same end. By twisting the ends of the wire together you can control the clamping pressure. This is a common technique in model engineering and jewelry making.
This is nothing short of hella interesting. Am I digging too deep to ask what the application is for this pulse jet?
I note that pulse jet has valve of some sort that brings in fuel/air mix, closes, then ignites. So you get a pulsed effect, hence pulse jet. They say, however that this jet has a low (thrust)/(fuel consumed) ratio as compared to other sorts of jets. Hence, the question about application.
Meanwhile, yours has the word vavleless in the title. How is this possible? Are fuel and air injected instead?
From looking at the design, is this just the piping for the pulsed jet, or is this the whole unit? Where does the valve or valveless injection system reside? How is fuel/air injected? What is used to ignite the mixture? What controls everything and how? Do you have plans for benchmarking the design, or am I off point? Why is it curved? Is all of the length necessary? Why?
This is quite an interesting one to me. And while I have no doubt you could figure ways to do stuff like this, I have an interest in creating a thrust characterization system (vs. any other variable or variables) for a different project. Do you have plans for something like this in the works, or would an early effort on my part to get such operational early be of benefit somehow for your project?
Will likely stick it on something with wheels just because, but it has no practical application. It is obscenely inefficient in turning propane into a propulsive force, but it is the simplest possible jet to construct. It’s just something interesting to build. There are no valves in this design, the air column and unequal lengths of the U shape combine to suck air in on the intake side
http://www.interestingprojects.com/pjbook/pjbookrev2a.pdf
Is the Bruce Simpson book that I am just following for this build
Well that doc is awesome. Or should I say most excellent?
(sound of James saving to his way cool docs archive in the background)
Why does this jet have a curve? Could it have been done without?
What effect does the banana have?
Blue tape, tack the ends, small tacks down the side, remove tape and fill in between the tracks. Being stainless, you’ll need to cap both ends with paper and blue tape, then fill it with argon to prevent sugaring the back side.
Pp. 55, 57 of the document discuss the reasons for the u-bend.
Basically packaging, but also Lockwood claims BOTH ends contribute thrust in this valveless design (some debates ensue re: thirst and actual thrust claims).
What about the “flux paste” discussed in these circles (and “the document”)? Any experience on that? (None here, just reading, and it SOUNDS interesting).
I have heard of flux from technicians in reference to soldering. Don’t know if its the same stuff. But during my limited experience soldering electrical stuff, it was the liquid squirted to that helps solder flow appropriately.
Paste is a gel from of this liquid I think. But again I am conjecturizing.
The correlation between welding flux and solder flux is unclear to me.
In soldering/brazing, it promotes flow of the solder or brass into the appropriate places.
In welding, it promotes flow, but the more important function usually is to keep the fill/weld from oxidizing. In arc welding, the flux is solid and coats the filler rod, melting upon use and “doing its thing”. It ends up a slag on top of the weld. In flux core, the filler wire is hollow, and filled with flux, which works otherwise roughly the same as with stick. With MIG and TIG, there is no flux, usually, so I’m unclear on how the mentioned stuff functions. I assume it works like brazing/solder flux in application, but also works as in stick and/or flux core to keep the molten metal from oxygen for an appropriate period of time…
Never heard of this flux, but I’m still a beginner and have very limited experience with anything other than mild steel. I have done a little stainless square tube, and the back purge with argon worked well.
Got the fuel rail created, it’s 1/2" diameter stainless tubing. It’s mounted with nuts, so to thread it put tube in lathe on slowest possible speed and used tool post to hold die straight as it started.
Drilled some 1.5 and 2 mm holes
Made some flares
And tested propane flow, neglected to weigh bottle to determine how much the 3/8 line with no regulator is flowing
Laser cut some mdf circles to help form the tubes which worked great with the hose clamps, still required a bit of hammering
Bonus feature of using flammable circle templates was that I could weld one into the combustion chamber then just burn it out
…why you didn’t use the slip roller?
He did. The problem is, if you’re new to using rollers, you probably don’t notice the material isn’t “bent” for the first inch or last inch at end of material, so iit s basically flat because the material isn’t pinched enough and engaged between all three rollers.
When the shop I was QA Manager at rolled material we allowed an extra couple of inches and rolled passed the start point so there was overlap of fully engaged roller parts. Then we would saw the seam line. But that was a specialty saw (cut through multiple over lapping layers) which is not (yet) available in Metal shop. Overall, I’m impressed with what he’s producing for a first attempt, especially with Stainless which is uber nasty for work hardening and he MIG’ed it without back purging. Stainless is finicky enough to weld as it is.
