news8.htm Tri-Mode ARLA

Amateur Rocket Launch Assist (ARLA)

Newsletters and Random Thoughts

This page will include progress reports, notes, random brain farts, and other ramblings.


April 1, 2001

Testing Resumed

I'm currently testing a series of 2.6 inch diameter combustion chambers based on my February 18 concept.

My setup includes a work bench with fuel, air, and mounting frame. The fuel tank is the one I described on December 4, 2000. The 5 psi pressure is from a portable compressed air tank. The air is a shop-vac. The mounting frame is a rectangle of stainless steel with a 1 inch outlet, a spark plug (nearly flush mounted), a fuel line, and a 4 inch diameter glass tube that provides an air ducting that I can see through.

The combustion chambers are mushroom cans with smooth sides, 2.6 inch diameter and about 2.5 inch long. I prepare them by stripping off the paper, cutting out one end with a can opener, and cleaning them out. The first one I put in two opposing holes halfway up the sides. The results were less than stellar. The last one today had six slits near the bottom and six small holes midway. I was still not getting flame holding. I finally modified the mounting so that there is a standpipe mounted over the outlet hole to within 3/4 inch of the top. This makes it a reverse flow combustion chamber. It looked like it wanted to start but couldn't.

Then I switched to gasoline and it lit off like a charm. The downside was that as soon as the flaming fuel exited the mount there was no longer any air velocity to keep it going down. The result was the flame came back up under the mount. That's were I stopped for the day.

I think I'm on the right track with the reverse flow idea. Now I need to work on optimizing the hole pattern and standpipe length. These should allow me to get back to mineral spirits for the fuel. I also need to modify the mount to ensure that the flame exits properly.

The New Shop

Still working on financing.


April 22, 2001

More Testing

I'm been testing a number of minor variations of pilot cans. My goal is to achieve a robust pilot can followed by good ignition and short-length mixing in the main combustion chamber. These will allow a reliable, short, light-weight ramjet, with deep throttling. I believe I'm getting close to these.

The results of an earlier test. The exhaust tube turned out to be low-cost (I found it in the desert) but not robust. It melted or burned. I assumed it was steel because a magnet would stick to it. The replacement uses one-inch steel conduit which held up much better.

This is the combustor can. A 2.6x2.5 inch mushroom can. With the slits it held the flame fairly well. By adding more round holes above these (similar to conventional reverse-flow cans on jet engines) it did better. Later I will try a few variations to see if I can do better. The small holes at the top end were to provide active cooling of the top of the can, which worked fairly well.

The assembly was mounted on a hinged table so that the exhaust could be safely dumped outside where unburned fuel would not be a problem. A spark plug is part of the test setup but eventually I want to be able to eliminate this and have a flare-type igniter.

This was with just the pilot operating. The image was taken after a high fuel-flow run which left burning fuel (gasoline) on the deflection plate.

This picture shows running the pilot with excess fuel that is burning outside the exhaust tube.

This picture was taken after adding a main fuel injector inside the exhaust tube. In this shot the pilot is burning but no main fuel is being injected.

This picture shows the pilot burning and igniting some main fuel.

This picture shows a large amount of fuel injected through the pilot exhaust tube.

This graphic shows the possible construction of the final design as well as the theory of operation.

The pilot can has both slits and holes, which seem to work well. At the end of the pilot exhaust tube, which has holes in the side, is a domed plate. There is also a conical shroud from the pilot assembly to domed plate to help expand, and slow, the main air into the ramjet main combustion chamber.

About 10 percent of the air flows into the pilot can and the rest through the ramjet main intake. The air in the pilot can mixes with fuel and mostly burns before exiting through the exhaust tube. Flame holding is maintained inside the pilot can. Additional fuel is added to the airflow inside the exhaust tube. As the fuel-rich mixture travels down the exhaust tube the fuel is heated and partially vaporized. As the mixture reaches the end of the exhaust tube it is diverted sideways to mix with the rest of the air inside the ramjet main combustion chamber. Because the fuel is already hot and burning it should mix well with the air and complete combustion in a short distance.

My testing to date has demonstrated fairly deep throttling of pilot can as well as full throttling of the main fuel. Future testing should refine the pilot can hole pattern and move on to testing various designs of the downstream components and finally the complete ramjet.


June 14, 2001

Back to Thinking

I didn't see much need for additional testing until I had a specific design to test. That design will depend heavily on how I launch it because of g-loads and such. I was in touch with a rocketeer but the last words I got were not encouraging. As in, I may need an advanced license (which takes months), and possibly some very expensive equipment. I was hoping for a rocket ride to quickly test a ramjet by the end of the summer but that doesn't look likely.

So, I went back to the drawing board on tube launch. I talked to a couple of ham radio folks about a tower (to support the launch tube) but I need 80-120 ft and those are very expensive. Over the last few days I've come up with a lightweight framework design that can be built for a couple hundred dollars and transported/erected at remote sites in a few hours. It won't handle strong winds but should get my ramjet to 500 fps with a peak of less than 100 Gs. I'll try to get a drawing together sometime soon. Now I'm working on ideas for building a low-cost gas generator. My current thinking is propane for the gas. Standard day vapor pressure is about 140 psi (before expansion) and easily transported, though safety procedures will have to be in place. I can build and test the tube at home but will have to go elsewhere for the powered flight tests.

I can now start on the design for the ramjet to be flown. I don't anticipate any construction work to begin before late August. I've made arrangements for a new 30x50 shop to be built and expect it to be completed about the end of July. It will take me a couple of weeks to move my tools and materials in and get set up. The finances are still being worked so I won't know how much I can spend on project materials until about mid-July. The uncertainty is about $3K either way so I don't know if I'll be rich or broke.

Solid Fueled Amateur Ramjet Tested in 1980

I received the following message. The author has given me permission to post the information here and agreed to provide me with a couple of pictures at a later date.

"Just found your web site on ramjets and found it very interesting. More than 20 years ago I joined with two rocket friends in building three rocket ramjet vehicles which we launched. These were solid fuel ramjets burning a low oxidizer solid propellant loaded with magnesium in a separate combustion chamber. The hydrocarbon rich exhaust products were injected into the ramjet combustion chamber.

"Two of the three vehicles were test vehicles to study launch characteristics and contained no ramjet fuel. The only fueled ramjet, vehicle #2, performed very well reaching a height between 8,000 - 10,000 ft (calculated on the time of flight and previous test flight tracking). It was too small to optically track past 2,000 ft, 1.5" diameter 14" long. Vehicle #3 used a 3" diameter combustion chamber and was 28" long. I was very disappointed that the others lost interest in the project before we could launch the 3" fueled. The smaller vehicles were boosted with "G" motors and the 3" was boosted with an "I" motor. All three were recovered with minimal damage."


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This Page created April 1, 2001

Last Updated June 14, 2001