Tin Can jets

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j.m.
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Tin Can jets

Post by j.m. » Fri Nov 21, 2008 2:23 am

Hey guys. I'm new here.

I've built a jet before, one from a jam jar. I followed a guide in Make Magazine they had a few years back.

Saw some videos like this:
http://www.youtube.com/watch?v=j9y0gN8cOCo

And thought they could really use a thrust augmentor. Does anyone know of a good shape for one on this type of jet?

Could I use a straight tube?

larry cottrill
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Re: Tin Can jets

Post by larry cottrill » Fri Nov 21, 2008 12:41 pm

j.m. -

Welcome!

Keep in mind that even a "perfect" augmentor (whatever that might be) is only going to improve thrust by some reasonable fraction. A straight tube is not going to do as well as something with an inlet flare. Please look for the augmentor paper by Bruno Ogorelec, in the FAQ section at the top of the fora directory.

What you could try next that might be a real improvement, and is only slightly more complex than the original "plain" jam jar would be this design by Hank Whittle, from an article I published a few years ago in jetZILLA:

http://www.jetzilla.com/Vol01Num06/jetZ ... #Article_2

This one almost crosses over the line from jam jar to pulsejet (but not quite, because is still relies on a liquid pool for fueling).

Again, welcome aboard! Have fun!

L Cottrill

Mark
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Re: Tin Can jets

Post by Mark » Fri Nov 21, 2008 1:51 pm

I've held various lengths of tubing over the top of running jam jars and while they increase the amplitude and pep up the combustion it never seemed to increase apparent thrust by a large amount. It does make them louder.
One thing I happened upon was to directly attach a snorkel to the "jar", something like a Helmholtz resonator pictured in Tharratt's article. My snorkeler breathes ever so slightly around the threading because the plumbing pipe bell connector isn't a perfect match to the threads on the soap dispenser I bought. The stainless steel soap dispenser holds about a pint of air. ha
The combustion is such that it won't tolerate much of a pool of methanol in the bottom, as some jam jars would. The most I have been able to run it is 8 or 10 seconds at best. Any more of a puddle of methanol in the bottom and it will only rev up and flame out suddenly, the combustion too violent. What I remember when I first ran this configuration was how loud it was. It starts to hurt your ears, I'm sure this level of sound isn't good for them.
There is that flare, the bell connector that helps transition/funnel the flow from the snorkel to the jar, that helps to pick up the pace.
This intermediate between pulsejet and jam jar would make a good pinewood racer I think. It just needs a little tweaking to run longer. It's a quick starter too, just mist the snorkel with a prime from a spray bottle and put about a tablespoon of methanol in the canister and mist the canister too. Then light the tip of the snorkel and she's off and running full grease before you have time to think. Instant on!
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Snorkeler.jpg
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PyroJoe
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Re: Tin Can jets

Post by PyroJoe » Fri Nov 21, 2008 2:54 pm

Welcome! I have tested several augmentors using Bruno's dimensions. These where not found effective on jars/cans in my opinion. What did work well, was to use a augmentor approx 1/2 the diameter of the jar (even just a straight tube did reasonably well). An example would be, if your jar is 2" in diameter, then use a 1" diameter augmentor. The ones built here ended up at about the same length as the jar or shorter. The weight is a considerable penalty.
I would recommend jars that are 3" diameter x 6"height with a 7/16" opening as a good beginners jar.
Joe

j.m.
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Re: Tin Can jets

Post by j.m. » Sat Nov 22, 2008 12:08 am

What I really meant by "increasing thrust" was increasing performance, reliability, noise...

It would only be running on my driveway, pointed towards the ground. Not really looking for more thrust, wouldn't do any good...

I do have some 7/16" brass tubing that I was thinking I could use as an exhaust port in the center, and then put 4 or 5 1/8" or 3/16" holes in the top of the can.

I know those dimensions are all small, but if the jet could run for 5 minutes, that would be much better to me than 10 seconds.

I tried just the basic Cambell's soup can tonight with a 1/4" hole in the top, and it seemed to flame out after the initial ignition. I am using denatured alcohol for fuel.

Because of this, I am thinking that small holes might be better for this small can.

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Re: Tin Can jets

Post by Mark » Sat Nov 22, 2008 1:25 am

This canister is 3 inches in diameter and 6 inches tall, and the 1/2 plumbing pipe snorkel is also 6 inches long. Then there is the 1 X 1/2 inch bell reducer. If anyone were to replicate this shape, they might, if not initiated, be quite surprised by the volume of sound it puts out. You really get a much more energetic engine than one might expect. It impressed me. When you think about it, a jam jar is extremely draggy the way the air has to flow in and out an abrupt aperture. This snorkeler kind of takes on the shape of a really stubby pulsejet with exaggerated proportions, but as such allows for this peculiar inbetween world. There is a certain zest that is inspiring and for so little effort.
I suppose if you were only going to run it for a minute or so, an aluminum model of very light weight would hold up. And too, such a design would surely, with a little work, have just enough thrust for that special fun factor, that when you lit the tip of the snorkel and had worked out a good fueling system, it could not only push a car, but lift itself straight up into the air like a slow moving Saturn Five for a 10 second burn or so and that would be a laugh. Oh!
I really love this little toy, yet I haven't done anything with it in years except fire it up now and then for inspiration. I didn't have to make any of the parts and the spark plug I installed was just something that isn't needed, but can be used to start it from a distance with wires and a simple piezo ignition.
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j.m.
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Re: Tin Can jets

Post by j.m. » Sat Nov 22, 2008 2:59 am

Well, It seems that the can I have had a little tiny peep hole in the bottom that was leaking on on of the cycles, and causing the can to flame out.

Now that this has happened, I will try to start on my new project.

Thread will be posted shortly.

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Re: Tin Can jets

Post by Mark » Sun Nov 23, 2008 12:26 am

I thought I would throw this 2 cents in. It's about twice the size of my previous snorkeler yet will rev up and run fine using the same snorkel as the pint canister. Both have that 1 inch thread that the bell will screw into. I just now fired it up the garage and held my hand about a foot above the snorkel. It really does throw some air.
Another thing is that I tapped out the bell so that the pipe nipple will screw in from the inside of the bell all the way up until it is flush with the lip of the half inch end. In this way it becomes a fire ring launcher just by putting a tablespoon or so of methanol in a canister and misting it with methanol for a prime. When you light the bell fitting, the flame travels down the internal pipe hitting the large volume of the fuel/air mixture and fires it back up the pipe, the fire ring grows/appears in size from a foot at first to at least 6 to 8 feet as it flies up in the air but is very short lived. At night it is really quite fun with a little boric acid added to color up the vortex. I showed some friends and they really liked it. It's just a single shot deal though and you have to air it out each time.
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Snorkelers with Fire Ring Thrower Configuration.jpg
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Re: Tin Can jets

Post by Mark » Sun Nov 23, 2008 12:43 am

Tangent/tidbit
In this configuration with the snorkel hidden inside, I had this sitting on the concrete floor of my garage with just a little methanol in the bottom of the canister. I lit it to see if it would rev up or backfire or what. I had some concern that there might be too much confinement. But it just went off like a mortar, making a kind of a thump sound and then I noticed my ceiling was on fire. That was a long time ago, when I first discoverd the effect, quite by accident. Old story/yawn.
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PyroJoe
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Re: Tin Can jets

Post by PyroJoe » Sun Nov 23, 2008 1:17 am

Here is a augmented jar. The J style draft engine is also alot of fun for off the shelf pipework. viewtopic.php?f=7&t=4682&st=0&sk=t&sd=a

The big scorpion draft engines can be heard clearly at one mile.
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Mark
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Re: Tin Can jets

Post by Mark » Sun Nov 23, 2008 8:08 pm

That jam jar with the large augmenter seems like an interesting design. I never tried any augmenters quite so wide in diameter as compared to the jam jar lid hole. I shouldn't have said that I never noticed a large increase in thrust from holding little pipes over my jam jars, it's just that jam jars really don't make that much thrust in the first place. Certainly an augmenter helps. As for added weight, I recall the Lockwood packet I bought with the big twin engine unit, he used fiberglass reinforced plastic for augmenters because the exhaust heat was low enough to get away with a plastic I guess. Lockwood says the unit produced 300 pounds of thrust, each engine have a 10 to 1 thrust to weight ratio. His augmenters are very short, the unit looking about a foot high with four holes in the molded(?) square shaped augmenter cluster. There's a picture of a man in a suit with a bow tie holding an engine that quilified for a fifty hour preliminary flight rating test for the U.S. Bureau of Weapons, the caption says.
I never really thought about it, but I wonder with your very light aluminum jam jars, what might be the thrust to weight ratio? I've always wanted to make something pleasantly quiet enough, yet strong enough to lift itself off the ground. The other day Don Laird called me, and I asked him if he had done anything new with pulsejets or had any news. He said no, that world doesn't need another pulsejet. ha
He's still interested in getting that Russian pulsejet book translated though. On the subject of Dynajets he recounted how he made this thin, steel valve plate that fit over the Dynajet port face, so that if you had a damaged reed, you could affix this plate under the valve retainer and run your jet on 9 petals. He said you lost about 10% power but that he used to fly jets all day, using other people's broken reeds that he salvaged in this way. He couldn't get the Dynajet to start with two ports covered. I guess it might have been interesting to fly an eight port Dynajet, but who knows, maybe if you played around with the idea it could work, if for some reason you wanted to see just how low you could go.

But surely the world needs a simple jam jar or snorkeler that could lift itself off the ground. Could be "the best new toy of the year."
And too, I don't see why a jam jar car couldn't be as popular as a putt-putt boat.
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Re: Tin Can jets

Post by Mark » Sun Nov 23, 2008 9:33 pm

Another fun toy would be to use a jam jar can to propel a feather light plane, perhaps naming it the "Gossamer Candor".
(forgive me)
http://en.wikipedia.org/wiki/Gossamer_Condor
Last edited by Mark on Mon Nov 24, 2008 5:52 am, edited 1 time in total.
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j.m.
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Re: Tin Can jets

Post by j.m. » Sun Nov 23, 2008 9:49 pm

I don't know about feather light, but there are a few rc planes out there that weigh less than .5 grams. My lightest is 1 gram.

I really don't see the point in using a pulse jet for an rc plane with other power equipment being so much cheaper, lighter, more powerful, and less hot. Unless you are making a plane and substituting a pulse jet for a turbine, but I don't think they would produce nearly the same thrust.

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Re: Tin Can jets

Post by Ghrey » Mon Nov 24, 2008 7:43 am

Mark: I should give you a 21 pun salute for that one, ... But I have been sick, and having just recovered I am in not dodging well :)

Why use a valveless pulse jet? One word. Endurance. It is the one engine type* that will run as long as it has air and fuel.




* I do seem to remember a pressure jet that also had these attributes, but my memory is foggy ...


Besides; They are fun and ( comparatively ) easy to fabricate.



.:.
In the process of moving, from the glorified phone booth we had to the house we have.

No real time to work on jets, more space, no time.

Life still complicated.

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Re: Tin Can jets

Post by larry cottrill » Mon Nov 24, 2008 1:32 pm

Mark wrote:I never really thought about it, but I wonder with your very light aluminum jam jars, what might be the thrust to weight ratio? I've always wanted to make something pleasantly quiet enough, yet strong enough to lift itself off the ground.
. . .
But surely the world needs a simple jam jar or snorkeler that could lift itself off the ground. Could be "the best new toy of the year."
And too, I don't see why a jam jar car couldn't be as popular as a putt-putt boat.
Mark -

Remember the days when 35mm film came in little aluminum alloy cans with a tiny layer of rubber gasket in the domed screw-on lid? Man, those would be beautiful for tiny jam jars, and it wouldn't take too much effort to rig one to lift itself -- I'll bet you could do it with one of those, by rigging a "snorkel" tube up through a centered hole in the bottom (secured with J-B Weld, naturally). The rubber gasket would probably be the basic weakness. I used to have a small box full of those little cans, but I couldn't put my hand on one now to save my life. Maybe on eBay ... ha.

L Cottrill

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