German S-100 Class Schnellboot (Fast Boat)
The SBoot Torpedo and Torpedo Tube
Below is my version of the German WW2 G7a Torpedo drawing:
Again like the Hull-2 project it becomes very slow as much research is needed on every part to get the dimensions right.
The German G7a and later G7e Torpedo were both 21" (533.4mm) diameter so for the model at 1/20th scale it can be made from 20mm communications conduit and this will fit perfectly into a "Berocca" (Vitamin B) aluminium tube, the same as the first torpedo's that I produced for Hull-1
For the 1/35th scale I have bought an available resin kit model, this was actually a Mini Submarine model from Verlinden made up of two German torpedo's with the top one having a perspex bubble on the front (warhead section) where the pilot would have been, so I cut and filed this off and made up two almost identical regular torpedo models.
I have painted this with a very light grey matt paint (Humbrol 147) and a metallic blue paint (Tamiya X-13) for the warhead. I used some cellotape as masking tape wrapped around the body to get the line straight between the two colours. My only criticism of this kit is that the fins and prop blades end up larger in diameter than the main torpedo body which isn't correct and wouldn't work in a torpedo tube, however I am not planning on launching these, they will be just mounted on the deck so it doesn't matter.
This photo shows the later Schnellboot model S100 torpedo door fully open, it also shows how the lower part of the torpedo tube slopes downwards at the opening (probably to prevent the prop blades from hitting the tube on the way out) and the complex shape that is produced when cut at 45 degrees.
Here are a couple of drawings of the torpedo tube, the bottom one is the type of tube used on the earlier open forecastle style of SBoot and one can only assume that the S100 series with a higher covered forecastle torpedo tubes were the same shape, although we know that the door opened sideways as in the photo above and not opening up to the top of the tube, which seems a bit of a mistake as it would have blocked the torpedoman's view.
The middle tube drawing is my proposed "Berocca" tube for the 1/20th scale boat, the berocca tubes have the expanded open end cut off and all but one has the bottom blocked end cut off as well. Then 8 slits are cut at all 45 degree points around the tube back about 10mm from the cut end, this allows the tube to be expanded to fit over the next tube behind it. the opening door end is also split for about 80mm (3") lengthwise horizontally and then a thin wedge is cut almost all the way through from the bottom side so that it can be peeled open at the required angle. I then glued some triangular pieces of flattened tube over the created triangular openings and glued them on both sides with "Loctite" brand superglue. once this was allowed to fully dry I cut the end of the tube at 45 degrees. I glued all the tubes together with a long piece of 20mm communications white pvc conduit inside to keep it all in line and make sure the torpedo can slide easily all the way through.
This shows 3 Berocca tubes glued together with a piece of conduit inside to keep it straight.
This picture shows the lengthwise tube split with a flattened piece of ube over the triangular gap.
Another view of the finished split showing the ends.
This what the torpedo door end will look like. Notice that the outside wedge is not as high as the inside wedge due to the 45 degree cut, this is what makes the bottom shape such a headbutt to workout as it isn't just a semicircle.
To join the tubes together cut the end off the tube with a small hobby saw and cut 8 slits around the tube circumference so it will fit over the next tube. The cut off the closed end for the intermediate tubes. you need to clean up the ends to get rid of any burrs.
I split the tube longways with a small hobby saw and cut a wedge out on one side, not quite all the way through to the split so that it stays together.
This shows the tube opened out ready to glue the side wedges on. I used "Loctite" brand superglue.
This shows the two side wedges cut from flattened pieces of tube, the Berocca tube is only around 0.25mm thick and is easily cut with scissors. You can rub the tube with a flat piece of plastic or something on both sides on a flat surface to get it flat and straight.
One of the torpedo tubes finished, these are 400mm long. Now I need another one with the opposite cut. These are actually easier to make than I expected. I have been saving these tubes for years expecting to wreck a few in the process but with the right saw it is a fairly easy task.
Port side tube in place and showing the tube covering below complete with rivet markings.
Port tube in place.
I bought some 4mm high pressure air tube and air fittings and did some testing to see how much air pressure is needed to launch a torpedo, 25 PSI (2 Bar) will probably be enough but at 100 PSI the torpedo flies out of the tube, I'll post some pictures when I've build something more like a real torpedo but I am very pleased with all the work!
I fitted an M5 to 4mm airpipe fitting to the rear of the torpedo tube with an M5 nut glued to the inside of the tube and enough fittings to test it with an air compressor to see how well it would work. I also tried firing the torpedo with a deodorant can with very disappointing results! So I went looking for compressed air at high pressure in a small package and came up with the CO2 cartridge used to inflate (or re-inflate) bicycle tyres, these are small and can push 125PSI, hmmmmm! I went back to the air parts supplier and got some right angled connectors for the tubes as the pipe can then disappear back into the forecastle.
The CO2 cartridge. The thread on these is 1/8" NPT (US National Pipe Thread I believe). The 4mm pipe adapter is 1/8" BSP (British Standard Pipe) so I need an adapter from one to the other.
I found a good Bike shop and spoke to the tech guys to find the best way to connect the CO2 bottle and they suggested this adapter with a valve, as I can screw the bottle on with the valve closed without losing all the CO2. Only problem is I now have a different screw thread to deal with. Also comes with 2 bottles.
I also bought a Valve kit for a few dollars which gives me a few different methods of connecting to the Bike valve thread.
See the test firing below, note that I experimented with the one CO2 bottle a few times and launched the torpedo several times before the video was done so one 16 gram cartridge should launch about 4 or 5 torpedo's, not bad for about $3.99!
Watch the video of the (second) test launch.
(C) Copyright 2014 - 2017 - John Drain