A return to model building and flying. Part 2

Metal Bashing

April 2004

The original Lucky Lady was powered by an Elfin 2.49cc diesel. In my collection of recovered engines was a PAW 2.49. This must be considerably heavier and probably more powerful than an Elfin, but it's all I have in this capacity range, so it will have to do. I dread to think where the centre of gravity will end up.

I always tend to build models around the engine and bearers, as it gets around a lot of the problems of trying to fit an engine accurately into something that may not be exactly aligned. With the engine bolted onto the bearers first this is less likely to happen. This process can introduce other less obvious problems but more of that later.

Absolute step number one, was to build a fuel tank. They don't exactly grow on trees these days and I am reluctant to pay US Brodak prices. I used to custom make my own for the F2B stunters, so I didn't anticipate any problems: just how wrong can you be?

tank This was the first attempt all neatly measured out with carfully folded joints. One problem; apart from the fact that when I pressure tested it, one end leaked like a sieve, the folded joints, made soldering the pipes internally extremely difficult. I always do this to avoid the feed pipe possible vibrating and aerating the fuel as it enters the pipe, introducing more problems than necessary. Then came the "piece de resistance", the feed pipe coming out in the wrong pace with it jamming up against the backplate of the engine

tank Oh well, make another one. This time remembering 'why' I didn't use complicated joints on the my stunt tanks. Yet more trivial mistakes with vent pipes, had me chopping up my last Slimfast container for the tinplate and hoping I didn't make a mess of the the third one. The picture on the right is of the inside of tank number 3.

ready

The picture left, is of the unsoldered tank with all the vents in the right place: at last!

All that remains is to solder the joints and pressure test for leaks.

finishedThis final picture right, is of all the relevent bits held together to check that everything was going to fit.

Normally I am used to working on bigger models and having more space to play with. Now the choice of an attractive looking model was coming back to haunt me. I had completely forgotten how awkward to build, a model of this size can be and I do no have the luxury of a simple profile fuselage to simplify matters either. I'm having to cram all the hardware at the front of the model into a very cramped space; as you will see in part 3.

However the whole story is not all depressing. I have remembered a whole load of stuff, from how to soften copper and brass tubing to make it easier to bend, to punching holes to accept pipes, not drilling them, to make soldering then in place easier, and the fact the the simplest methods of construction are sometimes the best.

The only thing I cannot do is tight bend small bore pipe without it collapsing. I have some coil spring benders which to be honest are absolutely useless, none fit the the most common size of pipe.

TIP:

If you want to make your own tanks, do not attempt it with an ordinary mains electrical soldering iron, or a soldering gun. Without giving a lecture, even if they are rated at over 100 Watt, they will produce a mess.

Make sure any surface to be soldered is shiny clean, and use an old fashioned solid copper bit soldering iron heated on a gas cooker

Here's the one I use. Even this copper bit is on the small size.

soldering iron

The bigger the bit the better, An electic cooker would do just as well: maybe not so efficiently. Ordinary electrical multicore solder works fine.



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