Elektra I Jet Engine Builders Web Log

This Web log is to encourage building and experimenting with the world's cheapest working pulsejet engine: the Elektra I(TM) - total cost in brand-new materials: Under $10.00 US, not counting the spark plug.

Want to build your own Elektra I pulsejet, with help from designer Larry Cottrill? Then this page is for you!

Wednesday, June 30, 2004

Elektra I Prototype Dimensions

Steve -

As promised, the prototype dimensions, including a couple of recommendations for improvements in the design. This should be readable by simply printing the page, or you can access the original size drawing by clicking here and printing it out.

Elektra I Valveless Pulsejet Prototype Dimensions - drawing Copyright 2004 larry Cottrill

The dimensions on this drawing are shown in the form 'inches [mm]'. Note that NONE of these dimensions are critical in any way; you could be off by several mm anywhere and still have a running engine! Some details of construction are critical, however:

First, as mentioned before, make sure you build up a nice big, smooth intake flare as shown. If you don't want to have the primitive fuel pipe permanently anchored in place as shown here, just form the flare without it and file a slot at the lip to hang the pipe in, similar to the way I did it in the edge of the pipe originally. If you use the fireplace cement as suggested here, let if dry overnight before using tools on it. Ordinary metal working files will smooth it up nicely, as needed. The cement is available at places like Menards or Loewe's, in a big tube you put in a caulking gun. It cleans up from your hands, etc. with water.

I originally cut the bottom end of the intake pipe off at a 60 degree angle, to match the angle of the pipe as it penetrates the chamber. I now think it should be cut off at about 45 degrees, so that the opening is more 'shielded' from the blast gas heading back into the tailpipe, as shown in the new drawing. That should significantly reduce the portion of the blast that gets diverted out through the breathing tube. Try it -- you'll like it!

The transition zone from chamber to tailpipe is crudely formed into a 'smooth nozzle' by making the hole significantly oversize and tacking the pipe on with about a 2mm gap between the face of the chamber and the front end of the pipe. Then, after you establish near-perfect alignment with your tack welds, you bridge the gap with a fillet weld all around to finish it up. Sounds tedious, but it's not very many inches of weld, and it's some of the best practice a weldor can work on!

All right, Steve -- that may be enough to get you started on having an Elektra I ready to run by the Fourth of July! Just post any questions you may have as comments, and I'll try to respond as soon as possible.

Go for it!

Friday, June 25, 2004

Elektra I - the real pulsejet engine anyone can afford to build and run!

'Elektra I' experimental valveless pulsejet in test run - Photo Copyright 2004 Larry Cottrill

Are you able to do simple metalworking and welding? If so, you can build a working pulsejet engine design for less than the cost of dinner for two at a family restaurant!

This Web log is to encourage amateur building and experimenting with my new design for the world’s cheapest working pulsejet engine, the Elektra I(TM) – total cost in brand-new materials: Under $10.00 US, not counting the spark plug. This engine is built somewhat larger than the classic Dynajet model aircraft engine, with the combustion chamber section somewhat clunkier in shape, and total engine weight at least double, because of the materials used. Version I is already being tested right now; if it is successful, I’ll go ahead and build an improved Version II. I’ll provide detailed drawings of Elektra I on this Web log page after initial experimentation, if anyone is genuinely interested in building your own.

The combustion chamber is an ordinary electrical box called an 'octagon box', but is really shaped like a square with heavily rounded corners. These are 1/16-inch mild steel stampings, galvanized. You can buy one brand new anywhere for less than one US dollar, including the flat steel cover plate. The tailpipe and breathing tube are chunks of readily available steel tubing. Since the 'nozzle zone' into the tailpipe is suboptimal, I decided to extend the breathing tube down into the chamber. I planned to start with a tailpipe about 26 inches long, hoping for approximately the same internal volume as the Dynajet tailpipe section, but this had to be lengthened severely to get the prototype to run.

'Elektra I' experimental valveless pulsejet concept drawing - Copyright 2004 Larry Cottrill

The inside edge of the intake tube is cut off so the rearward expanding gas just grazes past it. The hope was that at this point in the chamber, and with this orientation, there is neither static pressure nor velocity head to drive expansion gases up the tube. Thus, we have the basic mechanism of ‘Reynst’ aspiration, but achieved in an unashamedly easy-to-build form. [Note: This did not work as well as hoped for in the original prototype built, so the design in this region will be modified for the Model II engine.]

Advantages of the Elektra I design

My target audience is anyone who sincerely wants a real working pulsejet engine, but has almost no money to spend on materials to build it and has no machine tools or special skills, other than welding. For this person, the advantages of the Elektra I design are many:
- Around $10 total cost if you use a readily available lawnmower sparkplug
- No machining
- Tools required: hack saw, round file, flat file, half-round file, small hand drill [high speed], large hand drill [low speed], good set of twist drills, bench vise, steel tape rule, welding outfit [Optional: Dremel grinder, drill press with vise-type clamp]
- Runs on regulated propane, one of the cheapest and most readily available fuel gases
- Valveless design means absolutely no moving parts and nothing to replace, ever [except perhaps the spark plug, eventually]

Disadvantages of this design

Naturally, there is some downside to this design: There is a lot of hand metal working. There is a lot of careful welding needed, for joining cracks and filling little holes, etc. [because of all the weird punch-outs that electric boxes have], AND, of course, the potential medical hazards in welding coated steel. The main assembly welds have to be painstakingly done so that good alignment will be achieved between the pipes and the box. Because of the gaseous fuel used, you need a high-voltage spark rig of some kind for starting – but this is no different from most homebuilt engines. [Once you have it working, you could experiment with carburetion of liquid fuels, including methanol for glow plug ignition.] Also for starting, you’ll need some high-speed air source such as a leaf blower or workshop vacuum cleaner ("shop vac").

You don't need to be a machinist to build Elektra I!

'Elektra I' experimental valveless pulsejet in test run - Photo Copyright 2004 Larry Cottrill

Version I is incredibly simple in terms of metal work – You only have to drill a big hole [and enlarge it] for the breathing stack and a little hole for the spark plug [you can just use the knockout provided in the box if you use a larger plug, like a lawn mower plug], and enlarge another knockout hole for the tailpipe to join on. There is no smooth 'nozzle' section – you just try to get the smoothest weld you can between the chamber and tailpipe.

Version II will be more difficult in terms of the shop work, because NONE of the needed holes coincide with the standard knockouts in the box! However, performance [and maybe, ease of starting] should be better, because the box shape set up as a ‘diamond’ rather than a ‘square’ gives a lot better nozzle effect leading to the tailpipe and probably better flow from the spout of the intake tube forward. But, as I said, ALL the usable holes need to be custom cut for this one.

I have not shown any engine mounts on the concept drawing; but, these are just simple metal brackets cut from readily available fence hardware.

Curious? Check out the main Elektra I Website

You can check out the entire Elektra I construction page right here: Elektra I Construction Page

What is this engine good for?

These engines, made from the cheap materials shown, will probably never be light enough to power model aircraft. But, they are an excellent way to learn and demonstrate the principles of valveless pulsejet design. They would certainly make good bottom-dollar Science Fair projects, or they could become part of more advanced projects. I think it would be an absolute blast to see a jet-powered hydroplane take out across the water. And, they’d probably make good cheap laboratory heat / noise sources. They’re probably not the smoothest looking pulsejets you’ve ever seen, but the price is right – So, hey, you wanna build jets or not?

'Elektra I' experimental valveless pulsejet prototype, ready for its first test run - Photo Copyright 2004 Larry Cottrill