Blackbird Happy Gas

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Custom Underseat Nitrous Fitting I like doing composite fibre work. Before moving to the USA, I used to do a lot of work - fixing fairings, car body panels and custom work. Over here I haven't done anything and living in an apartment, doesn't really help the situation. However, a friend of mine that I met through the XX board, wanted to fit a happy-gas (ie Nitrous) kit to his Blackbird, and wanted to place the bottle hidden under the seat. This set of photos, with a small amount of writeup, documents the entire process. The nitrous outfit was not done by me - just the custom fibreglassing work. There's a little more to come, which is mainly just sanding and painting work to make it less noticable, as the whole outside is meant to be as stealthy as possible. How it was done Basically I had to fit a 2.5 pound (just over 1kg) bottle of gas between the seat and the rear wheel. Since there isn't that much clearance between the undertail area and the top of the wheel at full compression, this required me to fit the bottle as far back in the bike as possible. It also meant doing as tight a fit as possible too, because no room could be spared for clearance. Then end result is a very tight fitting bottle, but it means that no extra cutting was needed to be done to the seat base or any of the frame, except for a little bit of grinding under the seat latch cross-member. The typical blackbird undertail area before we started. For materials, I used a 0.6Oz straight weave cloth and polyester resin. The weave cloth is used rather than chopped strand because it is much stronger and requires far less material for a given situation. It's more expensive, but given our very limited clearances, I needed something as strong as possible while giving minimal clearance. Trimming the rough edges off the two U pieces. Trying out the basic U-shape for fit. Mmm.... fibreglass. The fitting process started by measuring out a section that was exactly the width of the bottle onto the undertail and cutting it out. Since this was all being done in-situ, it meant having to use small hacksaw blades, knives and dremels wherever needed - there are a lot of complex shapes to the moulding back there. The rear of the slot was right on the lock mechanism and light assembly at the rear of the bike. Since this was a custom fitting, I didn't have any moulds to work from, so it was a start-from scratch excercise. I started by creating two U-shaped sections of glass that were moulded directly on the body of the gas bottle. Two pieces were needed because the entire lenght of the bottle would need to sit in this, and the bottle is not straight for it's entire length, so I just used the straight-sided part of the bottle and made two pieces off this one section. This would give the closest fit possible, and in the end probably resulted in slightly too close of a fit. However, it couldn't have been any bigger as one of the later photos show - the rear wheel just kisses the moulding, so evening placing on say a 3mm of felt to give a bit of lining room would have been a bad thing. For one of the two pieces, I folded the glass around the end of the bottle to give a rough approximation to the end of the "tube" that it was going to sit in. Deliberately not making this pretty because a flat section would be later bonded in - this was just the form work. The shell in the bike being trimmed. With bottle as a test fit. Trimmed and sides fitted. Basic shape is done. Once the two pieces were done, I needed to fit them into the bike. So I trimmed as much away as possible in the body of the bottle and then tack formed the two U pieces together at a slight angle. Again, done in situ so that I could get the angle right - you can't just mould them as a single straight bit because of the clearance issues. Once the tack was complete, I used the basic shape to then continue to trim more plastic from the undertail until I got an almost perfect fit. The tray needs to hold weight, and at this point I had just a U-shaped tube. For weight bearing, I created two L-sections of glass based on a piece of steal as a form. These were tacked onto the outside of the tube and then trimmed to the right length. The undertail is actually curved, so I trimmed them to only rest on the flat section at the rear, which takes most of the weight anyway. The front part would be looked after shortly. Using a marker pen, I drew a line around the glass to show where the plastic met the glass and then trimmed the glass back to the right spot. Dremel cutting disks are your friend. Now that we had approximately the right shape, I went back and properly formed all the currently tacked-together joints, but filling and using a couple more layers of glass over the outside only to smooth it all out. Even at this stage, it was quite a tight fit. Taped and ready to go. After applying the rest of the surrounds To get a nice even weight bearing surface, I needed to continue the little L-shaped pieces all the way around the edge of the moulding. Again, this needed to be done in-situ, so first covering all the plastic and a lot of the frame with tape to prevent the resin from sticking, I then draped a single layer of glass over the edges to give the right formwork. Once set, I popped the piece out and laid in two more layers of glass on the outside to strengthen it up, and also to add more width to the weight-bearing surfaces, so that I could trim them back later on. The Gold Bond bottle in the top was used as a bulk material for when making filler. I normally like to use talcum powder (like Johnson's Baby Powder) but we had none available. This was the next best thing, but it stunk! The beer was for lubricating the tight fitting parts. The silver blackbird in the background is mine. Grinding away for better clearance. Pretty sparks... This is the basic design finished. After that it was just a matter of trimming back the glasswork and then putting a finishing layer on, some filling and then a lot of sanding to make the whole lot look nice. At this point, it was quite evident that once the bottle was in there, it wasn't coming out again. The primary problem was that the piece that holds the rear of the subframe apart and also the catch for the seat was just a little bit in the road. Appropriate application of an angle-grinder soon fixed that problem! and now the bottle fits View from underneath. Notice the small tyre rub Looking from the side. Needs black paint Completed shell Based on this first effort, there are a few things I would probably change. On the right side, I left the plastic moulding that normally represents the side of the tray portion that holds in a disk lock. I thought this might help act as a keying-in point but in hindsight it was more of a pain to deal with than it was worth. In a subsequent revision, I would grind this right off and use a flattened-out side like on the left. Right now the tray is held in by friction and the cupping effects of all the surrounding side pieces, but it would be trivial enough to use a couple of small nuts and bolts drilled through the plastic to hold it all in place. There's no strength needed, just a bit of something to stop the whole lot sliding forward when the bottle is removed. Given the current setup, I could probably lay up a mould for this and create a carbon piece too. However, the biggest problem right now is general clearance and the tight fit. As you can see, the tyre just touches the fitting. Santiago is a big boy and he's still running the stock spring and shock, which will cause the clearance problems. A proper spring would fix most of the rubbing problems. Gas Fitting This bit was not done by me. They're a bunch of photos to show the basic process taken by Santiago and that's about all I know.