The new engine

OK, this update will be a big one. Yes, I know it has been too long since the last update. Yes, I know there are a lot of questions as to what is going to happen with this part or that part, and how will that go together. Hopefully this update will answer a lot of questions that you have been wondering about, and then some.

To start off with, the combustor parts we were waiting for the arrival of, never showed up. All of the water jet cut parts are still nowhere to be found. This is due to a manufacturing issue in which our water jet sponsor received a very big production run of parts which of course takes precedence over freebie sponsored parts any day. Apparently with all of the confusion in the sponsors shop, the parts of ours that were already cut were misplaced. Hopefully we will get the original order sometime soon and be able to use those parts as well.

To fix our predicament, I called in a friend to help get the parts cut. Chris Krug of KRUGtech laser services stepped in to help me get all of the parts laser cut to the same specs as the no show order. You may remember Chris Krug from the episode of Junk Yard Wars where the two teams built jet engines in 10 hours. I would like to thank Chris publicly for coming through for us when we really needed it. Thanks a Million Chris!!!

If you are on a dial-up internet connection, this update may take a while to load. At least I warned you about it!

3D modeled combustor

Well, I guess the cat is out of the bag about the first combustor. Yes I was trying to make a very small combustor for use with the bike so that I could keep everything inside of the plastic body panels, or "fairings". I know that it was a bit ambitious to try to make the combustion chamber so small, but I had to try. It certainly made for a more interesting build as well.

It isn't that the small combustor didn't work, the video shows that it did obviously. It is just that the small combustor didn't work well. The limited volume of the combustion chamber combined with the small plumbing would mean problems which I wasn't willing to deal with. In a project like this, some sacrifices have to be made occasionally, just not on the issue of thrust. As I went to design the new engine, I decided to go back to a design method I often use which is 3D CAD or "Computer Aided Drafting and Design". The image above is the basic combustor housing which I will be using for the bike and some future projects.

Combustor heat shield

I just love going the route of 3D CAD work, as it lets me be precise in the parts I create. I have expounded before about Solid Works, and I will say again that it is top notch for this kind of work. It is a simple matter to draw even the most complex parts. The intricate cuts in the heat shield are a breeze to lay out in 3D, and the laser can follow the pattern with no problem. It would be almost impossible to create this part with any other tool such as a mill. (try getting square insde corners even with a CNC mill!)

Exhaust bend added to combustor

Since I had already made the exhaust piece with the bend to route the hot gasses from the combustor to the turbine, I only had to add it to the Solid Works drawing to get it in the picture.

Combustor expanded drawing

Since all of the parts in a Solid Works assembly are individual entities, I can do a break-apart diagram as is shown above. This is especially helpful when sending work out to be cut as in the laser cutting that I had done. The cutting service can see each part and how it goes together in relation so that tolerances and fit can be checked easily.

Combustor exit funnel

This piece was modeled in Solid Works to act as an exhaust funnel, which will allow the hot gasses to escape the flame tube more easily. The complex rolled and formed funnel can be drawn and then flattened to make a sheet metal piece that can be cut from flat sheet steel. The other nice thing is that the parts can now be made modular. If the bike has good performance without this piece, I may not use it due to the limited space in the bike. If it is necessary though, I can always bolt it into place quickly.

Solid Works design of the engine

With all of the parts now firmly in the 3D realm, I can check for fit and alignment of everything before I actually create the engine. I was fortunate enough to have "TS" from the Yahoo DIY Gas Turbines user group provide me with a copy of a VT-50 turbo. Using the entire combustor and turbo assembly, I can lay out for my oil tank which will snuggle right under the front of the turbo.

Combustor drawing

Every part of the combustor assembly is in the model. The fit of every part can be checked for clearance and other issues. The length of the combustor can also be shortened very easily. By using one "dimension" property, I made the combustor 10 inches long to fit into the small bike frame.

Complete engine

The final step in the modeling was to due some mass equations, flow modeling, and stress testing. The weight seemed to be in line with what I was thinking it would be. The flow testing showed there should be adequate flow for the hot gasses, and the stress this design can take is quite amazing. Overall, I was very happy and decided to send the parts for production. Of course you know what happened to the first set of parts, so when the new set arrived I was thrilled. The laser cutting process does not leave as clean of an edge as water jet cutting does. Water jet cutting seems to bevel the edges of parts slightly however, so I guess it is a trade off. There was very little cleanup of the laser cut parts though, and I am extremely happy with the results. These were my first set of parts to ever have laser cut.

Combustor end cap for injector side

I have to say that when the new parts arrived I was so happy that I couldn't resist bolting a few of them together to "test for fit". That is a really snazzy way of saying I wanted to play with my new toys! The main parts are mild steel 1/4 inch plate, but the snazzy "heat shield" is cut from 1/8th inch stainless. It will polish up nicely eventually, and look really good against the engine when it is in black.

Afterburner flame holder pieces

I know it is a jump, but I have to get things done as I have the time. I wanted to build a flame holder for my afterburner, so I figured out in Solid Works what I needed to do and got started. I decided to use steel angle to make the flame holder, but it needed to end up roughly round when done. I considered having the angle rolled to a round shape, but settled on trying an approach to cut and weld it together.

Afterburner flame holder pieces

I cut 8 small pieces of the steel angle with the ends mitered to 22.5 degrees so they would all fit up to each other. I used the chop saw to do this. The hard part is keeping the same angle for each cut. The parts must be cut with the wide side down in the vise, then flipped so that the edge is at the bottom in the vise to make the next cut. I used a small v-jaw piece from my vise to be able to hold the steel with the edge down so that it would be steady during the cut.

Flame holder parts all cut and assembled

With all of the cuts made, I assembled the pieces and they fit together nicely. I am not happy with the hole in the center as I believe that it needs to be bigger. This is due to the fact that I had steel angle with 3/4 inch sides instead of the half inch sides I had spec'd in Solid Works. I have two choices to fix this. I can either buy more angle and recreate the cuts, or I can grind the edges down all the way around to make it the equivalent of 1/2 inch angle. I think I will try the grinding first, and if that doesn't work I will make the trip to the metal store. Well, I figured that was enough afterburner fabrication for the day. It was time to make use of the new laser cut parts!

Laser cut parts all wrapped up

Chris did a good job of packing all the pieces up for shipment and they all arrived without any damage. Once they were here I separated all the parts into different "kits" so that I could grab what I needed and go to work at a moments notice.

Exhaust funnel "kit"

This kit is for the exhaust funnel. It would simply bolt in between the exhaust cap and the combustor if needed. The "C" shaped part is the funnel. It is rolled and bent into the funnel which is a circular opening on one side and a rectangular opening on the other. The entire part would be 1 inch thick when welded together. The plates weld to the funnel piece after it is formed. Spacers or a thin section of combustor pipe can be used to provide stiffness around the perimeter of the rings, otherwise the whole unit could crush when the bolts that pass through into the combustor housing were tightened.

Exhaust cap welded

The next part to create was not the exhaust funnel, but I will get around to that eventually. I just don't want to use the time to build the funnel right now, unless I know for a fact that I will have to have it.

Using the exhaust bend created previously, I would weld the exhaust manifold. The manifold for the bike had to make the right angle bend to get into the turbine section of the turbo. Once again, I would have rather had a straight in shot to the turbine, but I am at the mercy of the bike frame and the constraints of the tiny space I am allowed to work in. Even though the exhaust bend was fabricated from thin steel sheet, it has a lot of strength to it. Once welded to the end cap and the turbine flange, it would not budge at all and can actually support the weight of the turbo it will be attached to.

Afterburner cone assembly

All right, in my ever growing quest to confuse you beyond belief, I am jumping back to the afterburner again. Actually, this is just the way things happened in the shop here. Now, take note at this point that I am cutting the pieces for the afterburner by hand. I am sure that you are asking yourself why I didn't just have these pieces cut via the laser as well. That's a good question, and I am asking the same one myself! Truth is, I just didn't think about it before I sent the order. The parts are so easy to fabricate anyway, that it really isn't a big deal. I think it took me about 15 minutes to get them cut to match the pattern seen above.

Rough cut afterburner cone parts

Using the same method that I used to make the exhaust bend, I first rough cut the parts after tracing them onto the sheet steel. All I need is enough steel removed to make the grinding process easier.

Grinding the parts to shape

OK, here's my trick for making parts really quickly. I take the rough cut parts and place them together with the template in the jaws of my portable vise table. With everything lined up pretty good I take out the angle grinder with a flap disc on it and start grinding. If you are new to this, it will be much easier if you use a piece of double stick tape to hold the parts from moving when you change positions in the vise. Just a small bit of tape will do, otherwise it will be really hard to pull them apart. A piece of tape about 1 inch by 3 inches would do fine here. The template can be held on with a loop of masking tape or some spray adhesive like is used for photo mounting.

Finished afterburner cone parts

With just a few minutes of grinding, you can get some nice quality parts really quickly. I usually leave about a hairs width of metal around the pattern, which will get ground away when I clean up the edges of the parts and bevel them for welding. As a note, be careful with inside corners and inside radius parts so that you do not cut too deep into the metal.

With the parts cut and checked for accuracy to a master template, I hand formed the cone parts by pressing them over a pipe section similar to the way I made the radius parts of the exhaust bend. This is just a trial and error thing that you have to get a knack for. Just don't bend to far, and you will be able to correct mistakes.

Completed and welded afterburner cone

After forming the cone halves I fit them to the pipe which will be used as the afterburner. A little fine tuning at the edges of the parts to compensate for the thickness of the metal used was all it took to make it fit together. Patience is the real key here. A rushed job will stick out like a sore thumb. The end result for me was a nicely formed cone with a concentric center that was round. YES!!! I love it when things work out like they are supposed to and I don't have to break out the cutoff wheel. The little glitch on the photo was caused by the flash, and is not really there. Notice how dark it is outside in this photo. I had been working on getting it just right for a while!

Yes, it is this small

OK, so the afterburner is small. It has big afterburner envy for sure! I am once again limited to the space I have for components on the bike. The diameter of the tube is 5 inches with a 16 inch length. Since I can inject the fuel in the exhaust pipe way before the afterburner I think it will have enough mixing time to atomize well. Because of this, it should be able to function correctly in the shorter form. Larger afterburners usually need the first half just for fuel and air mixing. This is my theory at least and I will find out if it works out OK.

End ring welding

In my quest to jump around even more, I am now back to the combustor pieces. This is one of the combustor end rings which will hold the flame tube centered as well as providing mounting locations for the end caps on the injector and exhaust sides of the combustor. Since I will not be able to access the inside of the combustor when bolting on the end caps, I welded nuts to the inside of the ring. The hardware that will be used for the combustor is 3/8 inch coarse thread. I am using socket head cap screws just because I think they look really cool. To be honest, they are much easier to deal with when making field repairs too, as you can just grab a t-handle hex wrench and go at it.

Tape over bolts

Since I use a lot of flux core wire I have found little tricks you can use to make life easier. The tape over the ends of the bolts above is one of them. A good tape with high temp ratings will help to keep the flux spatter off of the threads. A petroleum jelly is also good here as it will catch the particles and just wipe off when done. If you use regular masking type tape, just make sure to check for spot flames after each tack weld. If it gets all fired up, just blow it out and keep going. You really don't need to worry about this if you are welding with shielding gas instead of flux wire.

Injector side cap parts

I used three tack welds on each nut, alternating every other flat on the nut. The first weld is on the outside edge of the ring. Make sure that the nuts are tight before tacking so that they sit in their proper flat position against the metal. After welding the nuts I put the bolts in to the nut side of the assembly to the point where they just protruded from the other side of the ring. (As seen in the picture above, the bolts would be screwed in from the top) I then pushed the whole ring assembly down on to some high temp gasket material and turned the bolts in and out just slightly to make indentations on the gasket where the bolts would be located. I then used a razor to cut the gasket by sliding the razor up against the edge of the ring all the way around. Once I had the ring gasket cut, it was a simple matter of a gasket punch to open the holes for the bolts at every bolt indention.

Next time around I may just have a sheet of gasket material laid underneath the steel when laser cutting the rings. It should make the perfect laser cut gasket as it cuts through the steel and gasket material simultaneously.

Assembled end cap

After welding all of the nuts in place, I assembled the end cap to make sure that everything still lined up. OK, I'll admit it..... I wanted to see it put together again too! It just looks cool.

OK, we made some definite progress here so far. I have to remember that some of the viewers of the site are on dialup internet connections though. What does this mean? Part 2 of course!! Before you go take a look though, won't you be so kind as to help out the site a little? If you don't know how, just visit the donation page. When you are done, be sure to come right back and go on to Part 2 of The Overly Awaited Big Update!

Russ W. Moore
Bad Brothers Racing

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