Please put your "I am new and need help" question here.

[JustinG]

Hey! I'm new and I need help.

I'm making a Lockwood pulsejet as my high school senior project and I need specific guidance. The actual design of the jet isn't the problem --I plan on using the Lockwood Patent design-- but I need help learning how to assemble it and where and how to buy/make all the parts.

For the actual jet I think I understand what to do for everything except the fuel injector, I've read up on the rosscojector but I'm not sure where I should put it.

Any suggestions?

[metiz]

Hey! I'm new and I need help.

I'm making a Lockwood pulsejet as my high school senior project and I need specific guidance. The actual design of the jet isn't the problem --I plan on using the Lockwood Patent design-- but I need help learning how to assemble it and where and how to buy/make all the parts.

For the actual jet I think I understand what to do for everything except the fuel injector, I've read up on the rosscojector but I'm not sure where I should put it.

Any suggestions?

Sorry for the late reply, place is a graveyard these days

You can go to the scrapyard to find sheet metal (stainless preferably). To make cylindrical parts, either find tubing in the right size or make a layout (inside diameter times pi for width and the length for, well, length.) cut out the parts using a metal sheer or an angle grinder. Either use a sheet roller to get the parts round or clamp a pipe in a vise and hammer your sheet around it. Weld using mig or tig. For mig I find it easiest to "zap" the edge repeatedly and to slightly overlay the beads. If you go in a straight continuous line, you run the risk of blowing through the metal, especially with stainless steel.

For coned tubes, use this program (or any other CAD program will do) https://www.conelayout.com/ just punch in the inside dimensions and it will spit out a layout for you to print and trace.

For bend parts, either make them yourself in sections, 22.5 degrees (or less) each (use cone layout for patterns), or google for car exhaust parts, steel shops, etc. You can also have them made, here for example https://hs-umformtechnik.de/en/stainles ... ipe-bends/

Make sure to flare the intake, very important.

If you use a Rosscojector, place it somewhere close to the intake opening, in the center, pointing straight back. You should be able to start the motor without air if you use a Rosscojector, so you could make a 90 degree bend in the tube and extend it ~75cm so you can hold it in your hand and play with the right distance (make sure your back is in the wind if you do this outside!). When you find a good distance you can fix the injector to the intake.

And finally, don't use a restriction on the gas bottle (no it won't explode)

[ScrapQueen]

Hey folks, long time dreamed of a pulse jet, first time builder. I threw this together in my welding class on my 3rd day of TIG welding so shes kinda a mess. Im also A HUGE IDIOT and didn't notice the intake was the wrong way when I stuck it to the cone. Will it work with an intake like that? I could always miter saw it off and put a flipped around one.

Next question is, how the heck do I fuel it. I got ahead of myself building it with some vague notion of "attach tubing to propane tank." What kind of fittings do I need? The idea was id bend some 1/4 inch refrigerator tubing into the intake but I don't know how to pipe it to the tank.

The main chamber is a 5 inch pipe tapered to a 3 inch pipe with a 1.5 inch wide intake, if that helps. Measuring? Ratios? Who?

Cheers!

[metiz]

Hello ScrapQueen, welcome to the forum. For a first build, those welds don't look half bad. My first thermojet looked horrendous. To business: I doubt your engine is going to run. Your exhaust pipe looks to be too fat and too short. Your intake is way too long. Having the intake in the wrong direction (nice job jackass ) isn't necessarily a huge issue I think but it isn't going to help things either. If you have the chance, I would strongly suggest starting over. It's probably less work than trying to fix the issues with your current build. If you want something simple that is going to run, check out Pyrojoe's recipe for beginners.

For fuel, get something like a propane cylinder adapter. Stick a propane hose to that, and your 1/4" tube in the other end. Secure both ends with a hose clamp. bend your tube into a U shape and use some bigger hose clamps to clamp it to your intake. A simple engine like described above will run with just a straight tube pointing in the intake. If you want to start it a bit easier, make a Rosscojector (scroll down for pics). It's a tube cut off with a pair of cutters. This will crush the tube before cutting. Slightly squeeze the resulting slit to open up the tube about 1mm. Place close to the opening of the intake.

Couple more things: don't put a flow restriction on your propane tank. No, it won't explode. Flare your intake. This is very important for breathing. Good luck!

[ScrapQueen]

Thanks for the info! I eyeballed it and went "yep I'm pretty sure this is what they look like" after thinking about it so long you'd think I'd actually have plans drawn out. I built it *then* found this forum. I'll give that design a try between my projects at school this next week.

[ScrapQueen]

Here's my next attempt. 4x8 inch combustion chamber, 1.5x5.5 inch intake, 2x40 inch exhaust. I believe I've followed the caliber guide?



Fingers crossed then!

[ScrapQueen]

I need to make a mount for my engine. Something like straps nailed to a board with a metal sheet in between should be sufficient? I'd hate for my shiny new engine to escape. I'm not trying to measure thrust right now, just to keep it in place.

[metiz]

Sounds good. Just make sure you don't mechanically constrain the front AND the back of the engine. When it gets hot it will expand a bit and if it can't move, something's gonna buckle. If your engine is red-hot and soft, guess what'll happen.

[ScrapQueen]

Good to know! I wasn't sure if I'm overthinking it and trying to put it on raised brackets and what kind of tie downs. Thanks! We'll see if it runs tomorrow!

[Dallara]

Hi All,

I have questions, some of which I am aware of answers to, but I would value experience over all else in the answers I seek, so I will do more searching of the forums to make sure it hasnt been answered satisfactorily already before I post them here.

A little bit about myself, I'm a mechanical engineer with broad experience, I have built a turbocharger gas turbine before as well as tesla turbines, 4 stroke engines, all manufactured from scratch and designed by me. I am always hesitant to adopt anothers design without verifying it for myself first, but with the black art that is pulsejets it looks like I will have to try everything and anything on this forum to find what works best for me.

One observation from hours on this site already, a lot of the links no longer work, I would say half or more, and that's a terrible thing to lose that knowledge. Maybe something can be done about this going forward.

My 40" sheet roller arrives saturday morning and I'm itching to get going, I hope to speak to you all in future.

Regards,
Dallara

[Mike Everman]

Welcome! Please let me know what links no longer work. The site was just updated last month for that very reason and they should all be working now.

[Dallara]

Hi all,

Some questions:

1. Does the mean diameter for calcs include the exhaust nozzle large diameter (at the wide end)
2. Does effective length include the length of the exhaust nozzle?
3. I am looking to build the original Lockwood hillier design, but where the hell can I get stainless pipe 76.2mm or 3” in internal diameter to have bent?
4. Has anybody thought of making a Lockwood style pulsejet using dairy pipe? A lot of sizes align nicely with certain requirements
5. What has to be preserved, in order of importance, and a brief description of the definition of that property if not obvious to all, in order to scale the Lockwood type design found on this forum?

Thanks in advance!

[metiz]

I can answer questions 3 to 5, to a degree. I don't really understand what you are getting at with the first 2.

3: You can get 3" pipe from exhaust manufacturers. Although having a smooth 180 degree bend is ideal, you can definitely get away with cutting straight pipe up into six 30 degree segments and welding them together.

4: If you can weld the pipes, go for it.

5: Scaling a pulse-jet isn't as easy as simply multiplying all dimension by a factor x. Read through Pyrojoe's recipe for beginners' caliber approach. You can design a Lockwood-like engine as big or small as you want (within reason)

If this is your first engine I suggest starting smaller than a Lockwood. The "free plans" section of this forum has a bunch of smaller engine designs you can try first. Good fist engines are the fwe or the small 3 pound thermojet.

[Dallara]

@matiz thanks for your prompt and informative response. "Effective length" and "mean diameter" are terms I saw for working out thrust estimations, I was simply exploring that calc for what it is, a very rough estimation with a great degree of error. I was wondering does the mean of all diameters include the exhaust nozzle large diameter or does one only consider the diameters of the engine proper, same with effective length does this include the exhaust nozzle length or just the engine proper. Same with the inlet pipe for both terms.

As for 3" exhaust pipe, that would be rarer as scrap where I am as we are cursed with outrageously expensive road tax, based upon cc of engine or emissions, so unfortunately we are not blessed with stonking v8s and 6s. I researched the ID of 3" exhaust and it wont do for the lockwood, as the dims are internal? Unless you tell me different, of course

Now to the matter at hand:

I saw some good info via the search regarding which material 316 or 304 to use where, but as it relates to pulsejets, am I better off buying a sheet of 316 or 304 to construct the entire thing? 316 I can only get in 1.5mm thickness, whereas 304 I can get 0.9mm or 1.2mm.
Having never welded stainless before but some ok experience welding 1mm mild steel, the 316 option looks nice and safe for me to experiment with, but I know too once I get used to it welding 0.9mm wont bother me, but I've a long way to go till then.
Which is better of the 3 options for the entire task? I live in a small cottage on my landladys property, so buying 2 sheets or even storing 1 is impossible, my idea was to get several engines cut from sheet metal in 1 go, and use up the whole sheet so I can store just the cut patterns in my sitting room or something. I intend to cut the lockwood, a big chinese style, and a couple of thermojets/linear pulsejets, and plenty of material strips to practice my welding on. For info, its a gas mig I have, which was recently rebuilt with new gun, wire feed tube etc. and I believe I have to use argon and 308 wire, is this correct?

Thanks in advance!

[metiz]

I think your best bet is to get some scrap sheet steel from the scrapyard. It's where I get all my stainless. You can roll of hammer it into the pipes you need. 304 works fine for pulse-jets and is much cheaper too. Go for the 0.9mm stuff as it is easier to work with (and cheaper). In my experience, welding 304 is about the same as mild steel. Maybe even a bit easier for sheet steel, as 304 is less thermally conductive so you won't blow through the metal as easily. I use 316LSI welding wire, but i suppose 308 work ok too. unless you're welding gas pipes that need to pass rigorous inspections, you'll be fine either way. I use 90/10 argon co2 shielding gas. When welding thin metal with a cheap mig welder with limited settings, try either welding small overlapping beads of weld about 0.5" bottom to top, stop, move down 1" and start another bead bottom to top to meet with your first bead and repeat. This prevents blow through. Do you have a link to those thrust calculations?