Block Jet, The start of something new?

[Mark van Werven]

I had some quite strange thoughts about a block-jet, a weldless, metal- less, but heavy pulsejet...


What is it?
A pulseBlock, made of solid.... Gypsum!!! 8)

How do you make it?
By cutting a styrofoam mold in the shape of a FWE Pulsejet, i used the 2.25 lbs version, and making another mold that connects to the PJ mold inlet.
When the molds are done, find a container, which will have both molds inside.
Fill the whole molds with heat resistand gypsum, and let it dry.
When the gypsum is dry, cut off the other mold, and then use a propane torch to burn out the styrofoam Pulsejet mold, inside the block.
Drill a hole for the sparkplug or light at the end, using propane thru a stinger, it worked for me, by just lighting the end.

Day is at its end for me, i must rest now, and type again later...

Mark van Werven

Picture (paint) included...

[larry cottrill]

Mark -

I like the basic idea very much. I have always wanted to try ceramic ducts, my favorite being the glass/ceramic bright white stuff that Corning makes Corelle Ware(TM) dishes out of.

I'm afraid that one problem you'll have is cracking due to the uneven expansion between the vastly different thicknesses. But, I hope I'm just wrong. It is CERTAINLY worth making the attampt!

L Cottrill

[Irvine.J]

I would be concerned about the blast effect if it failed, especially with ceramics and glass, you'd have effectively a bomb with thousands of pieces of razor sharp glass/ ceramics if you DID have a failure. On the aardvark site good old Brucey shows a "fail-safe" technique to direct the force of an explosion during failer, I think its an excellent idea. (Though i'm supremely confident in your abilities- Prove me wrong!)
The jetblock would definantly be worth trying, and I would be very interested to see the results. Good luck!

[El-Kablooey]

I like the ceramics idea too.

Don't pay attention to Bruce's "fail safe" thing LOL. That is the only time I've ever read anything about a PJ popping open. IF it even happened it was because of a really terrible welding job. When PJ's fail structurally, they kind of implode, flattening a spot on the engine.

[Anders Troberg]

Don't pay attention to Bruce's "fail safe" thing LOL. That is the only time I've ever read anything about a PJ popping open. IF it even happened it was because of a really terrible welding job. When PJ's fail structurally, they kind of implode, flattening a spot on the engine.

If I remember correctly, it happened while he was trying to start it and the tail pipe was full of fuel/air mixture and made a bang.

That said, I still got the feeling that the "fail safe" thingy was invented after the fact.

[El-Kablooey]

How many of us have made big bangs with our engines though? I know when I was first learning to start my lockwood I made some bangs that scared the crap out of me. A couple that made me think twice about trying again. I haven't been in this hobby a super long time, and by no means know as much as alot of you guys, but that is the only place I've ever heard of an engine exploding.

[Mark van Werven]

:oops: it broke apart at the exhaust pipe...
i think the walls where too thin...

[Irvine.J]

Well, thats bad luck mate, its time to whip out the gaffa, try wrapping a few layers of it around it, might just help hold the thing together. :D Goodluck! Gaffa solves everything!
As for the failsafe, if its happened once, it would suggest it WILL happen again, -somewhere-, -somehow-. I think i'll still incorperate some of those principles into my future pulsejets, better to be safe then nicknamed "stubs". Too bad a lot of saftey measures are sometimes only incorperated, "After the fact."
Peace.

[larry cottrill]

Mark -

Try adding some kind of fiber to your gypsum mix. In the old days, when real plaster was used on walls, they used to mix hair clippings into it. Believe it or not, something like that increases the structural strength significantly. When plaster is prepared today, perlite is often added as an aggregate to strengthen it.

In the architect's office where I used to work (a very old office building), the non-load-bearing partitions were not wood framed as they would be today, but were built up from "gyp block" - hollow-core gypsum blocks laid up like brick (but about two or three times as long) and finally plastered over. Those were almost perfectly "sound proof" partitions, and when they had to tear one out for remodeling, it was tough going - that was one strong wall! I doubt that you can even find such blocks today, but they were ready-made gypsum tailpipe material! I have no idea what was used to mortar them together, but it must have been something like regular gypsum plaster.

Incidentally, one other interesting detail: Unlike concrete, gypsum is not destroyed by contact with bare aluminum! I used to do plaster sculptures, using a combination of iron and aluminum wire for the armatures, and never a trace of spalling out, even over an extended time after curing.

L Cottrill

[Mark]

Another route that might be productive is to buy a cheap roll of steel shim stock and build a structure/glove around that. You could use some really thin shim or thicker than foil. It's fun to imagine making a pulsejet as a piece of art, like a potter makes clay pots.
Some creativity required.
Mark
http://tinyurl.com/fzfpk
http://tinyurl.com/je4cc
http://tinyurl.com/elrs3

[larry cottrill]

If you want to make a fairly big gypsum or concrete (or whatever) FWE chamber, you could used a welded wire tomato cage as the supporting structure. They look like very nearly the right conical taper. You'd want to build up your "ceramic" material thickness both inside and out, of course. The ones I've seen seem to be built up out of about 3/32-inch galvanized wire. You could use a waxed wood or waxed cardboard conical form for the inside surface.

L Cottrill

[Mark]

With that .001ths steel shim you could easily form a pulsejet just as you were working with aluminum foil. To attach a valve, you might have a groove in the valve edges that you could hold it in place like a caveman would lash an stone arrowhead to a spear; instead of rope or sinew use some steel wire.
And then if you were really good, you could make a valveless too, maybe even incorporate a small fuel tank in the body somewhere. ha
I suppose you would need a way to prevent collapsing, perhaps design some ribs in your pulsejet.

The "Wickwire 101" pulsejet coming soon to a theater near you.
Mark

[Irvine.J]

Mate just checking if you ever got this idea to work properly, it was very interesting.
Also, can someone tell me what the critical temperature of plaster of paris is? If you were to have a plaster mould, and then pour molten metal into it for instance. I melted a bunch of aluminium cans and some tent pole cutoffs in my cast iron brazier today, had to just dump it all in a bucket of water. I made some nifty sliding pilons out of aluminum and would be really helpful if I could use the cutoffs for something else. Would plaster be up for this kind of thing, or would it just be destroyed? I have 5 kgs of plaster, gotta find a use for it somehow.
I read somewhere it can survive 1300F in a kiln, but am not sure if that is entirely accurate.

[Irvine.J]

Excellent info thanks very much ben, I've been waiting to throw my aluminium into something so I'll whip up a plaster mould and get my little brazier furnace cooking this week...have to think of a shape to pour now...

[larry cottrill]

Excellent info thanks very much ben, I've been waiting to throw my aluminium into something so I'll whip up a plaster mould and get my little brazier furnace cooking this week...have to think of a shape to pour now...

If you can make a reasonably accurate wax mold, there's no reason you couldn't cast a nice Dynajet scale, or even larger, valve head. Investment casting is so accurate that about all you'd have to do is hand lap the rear surface with a few grades of abrasive against a piece of plate glass to get it perfectly flat. Success would depend mostly on how accurately you can make the wax pattern (and how good you are at the actual casting, of course).

L Cottrill