When it came to fixing the foil I wanted to use aluminium bar (25mm square 6060) for the fuselage because I didn't have time to make and layup another one. The tricky part was how to connect it to the bottom of the wooden mast. As luck would have it I'd also just finished making an small aluminium forge that I'd seen on The King of Random site. It cost about $20 to make and was completely idiot proof. Turns out there are hundreds of designs for home forges out there and I've even seen people melting aluminium on a charcoal bbq using a hair dryer as a blower!!!
The King of Random one.
https://youtu.be/lSoWxG30rb0
The one that I'd made using a propane burner ( again lots of designs on youtube) for DIY burners.
So the idea was to cast a connector that would butt glue to the end of the mast and be deep enough so that I could just drill and tap a couple of holes into the connector, drill through the aluminium fuselage and bolt them together.
The quickest way I've found to cast something is to use sand casting. The idea is that you create a copy of the piece you want to cast (the plug) using whatever material you have on hand (wood sealed with spray paint or shellac is perfect). You then place that piece inside an wooden frame and ram damp (not too wet) sand around it. You really ram it in hard because when you then pull the plug out the damp sand holds its shape and leaves a void that exactly matches the part you want. This link shows the general idea.
http://www.the-warren.org/GCSERevision/ ... asting.htm
You can get professional quality parts using really fine sand and mixing it with bentonite clay (crushed clay kitty litter) which binds the sand together much more strongly. But I didn't have time (or inclination) so I just used washed beach sand ('Play Sand' from Bunnings) and used water as the binder.
The plug I used consisted of the end section of the mast with an extra 'foot' on the end that I could spend time getting really square. The foot extended beyond the mast far enough to be able to put a couple of bolts through it and into the fuselage for extra strength. In hindsight I am not sure this was necessary.
Here's the plug and the cast piece about 2 minutes after I poured it!
I roughly cleaned the connector up, cut of the sprue (left over from where the aluminium was poured in) and 5 minute epoxied it to the end of the mast.
I then wrapped about 5 layers of 180gm basalt fibre I had left over from a TT build. This is weaker than carbon but stronger than glass. (if you use carbon you need to put a layer of glass between the aluminium and the carbon otherwise you'll get galvanic corrosion because carbon and aluminium are both conductive)
I was in a big rush to get it done so I didn't bother with making it look good this time round. I had no idea if this was going to hold up but after 5 months and a lot of big hits ( learned in Cairns where a sand bank ran into me every other run) I'm very happy to report it is still going strong and has survived longer than my original wing!
This has worked out so well that my plan is to try casting both the fuselage connector and the baseplate / mast connector in my next build. The mast will still be wood core (for weights sake). The beauty of casting these sections is, firstly, casting takes only a couple of minute to produce the piece and secondly it avoids all the work needed to reinforce the high stress areas which in my first build was a very long part of the process.
There's lots of great info on the web for home casting and if you're just going to do a couple of pieces then the forge can be as simple as hair dryer blowing air onto bbq charcoal. Aluminium melts at around 700 degrees which means it can go horribly horribly wrong if you're careless (wear full protection gear, welder gloves and esp. face covering - read about flash boiling n casting) but at the same time steel melts closer to 1200 degrees so you can use lots of readily available material to make a forge ( the King of Random made his inside a steel bucket and used plaster of paris as the lining).
Also, there are lots of different alloys that you can use for casting. I used whatever I had around which included aluminium cans and profile off cuts. All relatively weak stuff by Al standards. I have read that some of the best material to use is Al alloy from car parts and in particular pistons and housings as they have good flow characteristics that let it flow into fine details of your plug.
The other thing that might be possible to do with casting is to make molds for wings. In an approach called 'lost foam casting' you make your plug out of foam, pack it in sand and the molten aluminium burns the foam out as it enters and fills the space the lost foam leaves. You could hot wire cut female molds of the wing like I've seen others do on this forum. You could then use the lost foam approach to cast the female molds for the wings. This would take a bit of trial and error to get good finish straight out of the sand.
Anyhow, wanted to share this because I'm really excited about doing this in my next build and hope it gets the creative juices going for others to experiment with it.
Matt
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