Progress

To begin I realized that I would need to find some piece to scale the whole project to. The most logical piece to have as a base for scale was the elbows in the "U" bend. I chose it because it was the only piece I could not manufacture on my own, the only elbows I could produce would have a large crimp on inside of the bends, which would severely impede the flow of gasses critical to function.

I ended up choosing a 6 in long radius elbow, because of its scalability, proportions, and ability to be welded.

The next step was to use the 6in elbow to scale the rest of the design. The design shown in the Concept Tab was scaled to the following design

Now I needed to think about how exactly I would manufacture the assembly. I figured out that the easiest way manufacture the assembly would be to make an "unwrapped" view of the cone/ cylinders in a CAD program (Using This cone generator) , and used those CAD files and turned them into tool Paths for a plasma table.

Then, with the sheet metal cutouts I got to work using a slip roller and some hammering I managed to roll all of the cutouts as close to perfect as possible (Although some of the cutouts were too big so they had to be cut in half, and because of their odd shape they were not cut accurately, but with good labeling I could rectify the problem). After that I welded the cut outs together to form many smaller cones and cylinders.

Note: somebody cut a section of a cutout for scrap metal, but with help from my friend Jack Roche we were able to patch the cut out.

After all of the cut outs were welded into cones and cylinders, I started welding the major sections together.

It was a challenge to align the pieces together, because small inaccuracy in the earlier manufacturing process started compounding into gaps along the seams that needed to be welded together. With care and a system to align the pieces using vice clamps, mallets, and magnets I was able to keep everything relatively flush together, and rectify earlier manufacturing errors.

After some of the major parts were welded together I decided to lay everything out to get a sense of scale.

The build was almost ready for final assembly, but before I weld everything together I needed to make the Propane assembly. Through previous research I had a general idea that it would consist of a thin pipe with holes drilled though it, but the layout and hole size were still a mystery to me.

Now I had to focus on the hole size. I already had a high pressure propane regulator available, so I only needed to worry about the size of the holes on the propane pipe. While looking around at designs, Colin Fruze's pulse jet had measurements for the holes he made. At first I emailed Colin to see if there was a formula or method behind his hole sizes, but he said that there was no specific method or reason, and that a "guess and check" method would work. I didn't feel comfortable guessing the hole size for propane, so I decided to make them somewhat proportional to the Jet he made. His design had 3, 3 mm holes for a pipe that was 15 mm. My design has a larger combustion chamber (Approx. 13.25 in) , and 2 pipes instead of 1. So I decided to make 3, 3/32 in holes in each pipe for a total of 6 holes, that way I had a larger flow rate to compensate for the larger combustion chamber it had to fill.

After I drew up a full design, and an expensive homedepot run, I was able to assemble to propane system.

I drilled holes in the side of thee combustion chamber and assembled the whole thing as it appears in the sketch. I did not weld the pipes into place so we could test to see if we were getting the proper amount of propane flow.

Now it was time to test the propane system to see if enough propane was ignited inside the combustion chamber.

To test It we ran the chamber at around 10 PSI, but it can go up to 30 PSI.

The amount of propane seemed adequate when comparing to pulse jets of the same design, so I welded the propane system permanently in place.

Now that all of the major sections of the Jet were completed, I decided to set everything out to see how it was gonna be before it was welded together.

Since the project was worked on inside of a shop in my high school, and it is temporarily closed because of the corona virus, I moved all of the parts to my home where I will be able to continue working.

Over the course of a week I continued to weld all of the segments together with a flux cored welder and car jacks

After a quick test to see if It would run without an intake flare, I noticed that some of the rubber hoses were getting soft because of the heat, so I extended some of the hoses farther away from the jet, and I used some scrap metal to make some heat shields

Along with the new hose set up, I manufactured an intake flare by cutting a cylinder into a cone by taking out 8 triangles along its circumference

Now that everything was good to go, we tried to run it, but sadly it didn't start. We did get some very loud explosions once the propane bottle iced up, and the jet was hot.

While thinking about why it didn't work, we compared the layout and function of this jet, to other jets people have made.

The main issue is with the fuel system.

To rectify these problems, I came up with a system that:

Now with the new system in place it was time to try starting it again. We were low on propane, and we only ran it off of one bottle so it barely started on just gas, but as soon as we fed it liquid propane it roared to life.

Now that we know it runs, I need to make some improvements to the stand so it doesn't shake as much, and find a place to run it for a long time on account for.

Heres what was was found about the jet.

1. Different factors affect the jets performance such as, wind speed, operating temperature, and temperature of the fuel lines.

2. On more favorable runs we were getting 70 lbs of thrust according to the scale (Peaks of 100 lbs, and lows of 50 lbs per pulse approx)

3. The only run we were able to get a good recording of the scale is the video shown above, and it looks to be running at 45 lbs approx (the viewing angle makes it look a little bit low because the needle is raised high vs the background)

4. 1 minute after a run the temperature reads 692 Deg F and was rising more than that during a run (I did a test without recording, didnt record because of safety)

5. The fuel system still doesn't deliver enough fuel for a maximum thrust run, because we could never give it enough fuel to kill the engine, and most of the pulse was still contained within the Jet

My thoughts on improvements, and methods.

• The scale we used was a bathroom scale, which is adequate for more constant stable force, but for an quickly oscillating force inadequate.

  • since it works though opposing springs, constant push- back of the springs likely dampened the average force of the Jet.

  • An electronic scale would have been much better because the data would be presented much more neatly.,and you could properly make readings.

• Adding a second, parallel fuel system may be able to run the jet at full power.

• we never removed the old fuel systems pipes because we lack the manufacturing capabilities to do so, but it would be interesting to see if they reduced the efficiency.

• A better testing location is still needed on account for the multiple Facebook complaints

• Adding a socket for an air-compressor to start the jet from behind would be very big improvement. starting a jet from behind with a leaf blower is easily the scariest thing I've done (nevertheless exciting)