The great advantage to using zip-ties for joining is they can be adjusted as you build. They are light and incredibly strong. I used them with PVC conduit tube and ply bulkheads to build the “”Blimp”. This is where I started again, this time with PVC tubing and PVC foam bulkheads.
I knocked up a test to see if the foam bulkhead could take the strain of the nylon zip-tie which can be sharp. The tube took up a tilted position. I redid the test three times using different wraps until I got a self locking result with final straight pull through.
Using tubular stations brought another development line. Each solution also showed a weakness, and by trying to solve it, brought another knot. This is called ‘praxis’, learning by doing.
The final process involves temporarily holding the frame together to get the spacing correct. A 5mm hole is drilled through and through the longeron into the frame. All frames and bulkheads are done at the same time. The longeron is then turned 90 degrees. Two zip-ties are used, starting on opposite sides, The 5mm hole in the frame is enough to locate the longeron. Using a single 200mm tie is possible, but it can be clumsy in confined spaces and time consuming. The extra block weighs 0.165gm. which is reasonable for all the avoided frustration.
Once we had agreed the drawing Layout One.1 was a good starting point for a build, I started the process of converting the outline drawings to working ones. This means placing the 28 lengthways 15 mm pipe (longerons) inside the outer skin. I started with the 900 mm Station and made it the Master. This has a registration box that is used in each seperate Station, and remains identical throughout. My initial idea was to print the Station on to paper and use that as a template to cut flat boards. The registration box stops the programme deciding what size each one is best for you.
Two things happened about the same time, I bought a laptop projector and Davy Jamieson introduced me to underfloor heating pipe. At 16 mm it has 2 layers like the PVC plumbing pipe, but it has an added layer of aluminium. When you bend it it retains the shape. I redid the drawings with 15 mm and 16 mm pipe and projected the drawing directly on to a board, taped in the registration box on the board and the feet of the Workmate and tripod on the floor
I built a frame called a Strong Back to support and keep all the Stations properly spaced and in line. I should have stayed with my first plan of using aluminium extrusions. It is more expensive but it would not have twisted and warped like the timber in the centrally heated atmos. However this failure has lead to a solution which could give great benefits to structural frame strength and building simplicity, more later.
Charles and I then lashed the structure together loosely with zip-ties. At this stage nothing is really finalised, the drawing is one thing, what we have here is another and it can be useful go with what evolves rather than rigidly pursue an ideal.
I made a start on a Sketchup 3D drawing to have something to point sticks and throw rocks at. The first task is to cover the rider and front wheels. I wanted to keep a simple shape, and deal seperately with the head above the shoulders to give minimum frontal area. The body frontal area is determined by the height and width of the shoulders, and the height of the knees as they cycle. The wheels cause a lot of turbulence. If you enclose them, then the body has to be wide enough for steering clearance at full lock. If you try to pursue one aspect of a design for purity of function it has a terrible habit of showing up flaws in another area. I don’t like compromise, but trying to find the best balance of the least offensive solutions is often the most you can hope for. I had already been through this with the “Blimp”, so that seemed a good starting point for development.
Building the drawing in two parts and combining them was too much lke hard work and showed up how difficult the real construction could be. So I combined the head faring into the main body, at the cost of increased frontal area.
This looked OK until I put in the clearnce for the feet. This gave two ‘nostrils’ which appeared to be scooping air into the body.
I added an air-dam but this unbalanced the look badly, I tried an elliptical dam guiding the air around the wheels and away again, but again it looked very difficult to build and keep light. The dam would have be able to to rise over Speed Bumps, adding complication, weight and jamming.
In order to divert the air around the feet I lowered nose, and the tail, to smooth the air flow and balance the shape.
Charles wants a Velomobile, a small human powered car, to complete a challenge of cycling round Britain. Charles Barnard is a long distance cyclist, he warmed up by doing Lands End to John O’Groats followed by 4,800 kms round the perimeter of France, then capped that by cycling 864 kms along the Pilgrim’s Way, up and over the Pyranees, to Santiago de Compostela, in Galicia, N.W.Spain. All of these expeditions have three things in common, weather, wind and sun. Singly and in combination these elements can be very wearying, to the point of psychological collapse. The answer, Charles decided, is a Velomobile. The shelter will keep you dry and the aerodynamics will reduce the effort required. If the reduction is only 10%, it is cumulative, day to day, and then over 100 days cycling results in a saving of 10 days in simple terms. That is a lot.
The outcome of our next meeting was although Charles appreciated the 5 examples what he really wanted was my illustration version. I explained he had been seduced by a prettier picture and it is really unwise to set off on a trek round Britain in a untried trike. So I incorporated some of the shape ideas into one of the 5 and set to work building a 3D drawing in Sketchup, which I had only just started using.