Dimensions and Scalable Templates

[larry cottrill]

To start with, here are two scalable templates that you can download and use as cut-and-paste "paper dolls" to design your own Fo Mi Chin style engine. If all you care about are the dimensions, you can use either one; but if you're interested in using them to make your own scale drawings, you need to choose the one that's in the units you like: English or Metric. The two drawings are NOT interchangeable at a single scale; the Metric drawing [Scale: 4 pixels = 1mm] is about 2% larger than the English one [Scale: 100 pixels = 1 inch].

I drew the outline 4 pixels wide, so you should be able to scale it down to 50%, 33%, 25% or even 20% without losing any of the lines. For the same reason, I beefed up the centerline to 3 pixels wide in the middle of the drawing, so again, there should be a centerline left that you can extend, once you scale it down. When re-scaling, you can expect a line here or there to drop down to a single pixel width that you'll need to re-build with Paint or whatever you use. The scales suggested above should be quite adequate for most work.

The can was measured in inches; the mm dimensions are calculated to the nearest whole mm. I just measured in the units I'm used to. The drawings are not perfect, and I only indicate the dimensions I consider critical for pulsejet chamber use. This was a Gilette Foamy(R) can; I found that a Colgate shaving cream can I bought a couple of years ago is absolutely identical - the same can exactly.

Below the templates I show a simple scale drawing of the original Fo Mi Chin in its final running form, made by scaling down the English units version of the template to 20% and restoring most of the resulting linework to 2 pixels wide. Nothing to it.

L Cottrill

[steve]

jeez that tailpipe is long!

perhaps we should start using the phrase "Larry sized tailpipe"

[larry cottrill]

Steve -

Yet, the engine starts and runs beautifully that way, but of course at a rather low frequency. Note where the intake pipe joins the tailpipe - that's the Reynst Point, and the engine had to be lengthened until that hit L/8. Then, voila - a perfect running Reynstodyne engine!

Note also that the intake pipe is nowhere near long enough to get back near the L/3 point on the pipe. Yet, that doesn't seem to bother it at all! So, this engine is really running in violation of the Hinote Criteria, but works when the L/8 Reynst Point is satisfied! All criteria are not created equal.

That actually turned out to be a very interesting project. It was my last engine "design" [just a throw-together, really] before Bill Hinote convinced me that the lengths have to be somewhere near right for an engine to work. The Elektra II was conceptualized earlier, but was re-designed to hit the Hinote Criteria perfectly. Unfortunately, the criteria didn't fit that engine perfectly, for reasons I've already hypothetically explained. Then came the FWE, and as you know, the rest is history ...

Steve [or anybody, for that matter], try cutting and pasting the outline at a reduced scale from the templates with MS Paint or some such. You'll like how easily it works. I plan on providing more templates, with common stuff we use such as a few sizes of conduit, the antenna mast tubing, different size flares, etc., in both English and Metric scales. That should at least allow people to simply and quickly work up drawings of projects and ideas with low hassle value. If you go to my "New - Improved" Fo Mi Chin II intake drawing, you'll find it's at the same scale as the English mode template above - you can cut and past them onto each other with MS Paint at 25% scale or something and extend the tailpipe out to its full scale length with little trouble, and see how a well-proportioned pressure can pulsejet ought to look!

L Cottrill

[Bruno Ogorelec]

Larry, thank you for going to the trouble of drawing this and the other things you plan to offer. You are making people's lives easier.

[larry cottrill]

I didn't say anything about how to print real-size drawings from the templates. So, here's how it's done.

The English and Metric templates are slightly different scales as already mentioned. On the printers I use at work, I get VERY close to perfect true size prints by printing at 97% for the English scale templates and 95% for the Metric scale templates. So, for your first try at printing, use these numbers and see what you get - they may be just right. Measure the longest possible dimension shown to test accuracy; remember, they will not be perfect, but you can get very close with the right percentage. My printer drivers don't let you select fractional percents, and it seems doubtful that many do, so you just have to use the percentage that comes closest.

If the above numbers don't work, print each image at 100 % and measure the longest dimension - let's say that's the 122 mm dimension on the pressure can template, and say your measured value for it turns out to be 147.5 mm as close as you can call it. Divide the intended value as shown on the drawing by the measured value you obtained: 122 / 147.5 = 0.8271186... Round to the nearest hundredth, 0.83, and multiply by 100 for the percentage - you would use 83 % for your next trial print. Re-measure to verify that you don't need to go up or down one percent to get it as close as possible, but this should be as close as you can get.

Again, always use the longest given dimension for the best accuracy in establishing the percentage you need top re-size. You can also re-scale on many office copiers, and in some cases this will turn out to be more accurate. However, you'll almost certainly still be limited to the nearest whole percent.

L Cottrill

[larry cottrill]

Here are scalable templates for the "standard" [i.e. original dimensions] FWE combustion chamber. Again, note the difference in scales.

Note that the original intake shown here will only be exactly correct for the original engine length of 26 inches, end-to-end. It is shown for the convenience of those wanting to build the original FWE engine - it can be omitted easily for other uses of this chamber. The intake pipe is shown in the drawing 'as built' from 3/4-inch EMT [i.e. electrical conduit], as originally designed by me and built by Steve Bukowsky in the first prototype. In my build [second prototype], I used 1/2-inch EMT cut to the same basic lengths and located on the same centerlines, and the engine ran successfully. For maximum power, the 3/4-inch conduit is probably the better choice, however. The size of the intake flare is not considered critical, so no dimension is shown - it was about 1.5 inch across on Steve's build.

L Cottrill

[larry cottrill]

Here's the next installment - one size of tubing, namely 3/4-inch EMT [US common steel electrical conduit]. The template has flares with end views, bends at a few common angles, and junctions of the tubing with other tubes at the same selection of angles.

It is not possible to predict what OTHER size tubing someone might want to bring this tube into with a welded joint, so what I decided to do is provide a few selections and let you use the one that comes closest. They are: the same OD as the tubing in the template; 1.5 x the tubing OD; 2 x the tubing OD; and, 3 x the tubing OD. Hopefully, one of those should be "close enough" to look about right for any junction you want to draw.

Anyway, see what you think. Other tubing sizes will be added, someday.

L Cottrill

[larry cottrill]

[Reserved for future use]