July 2010 Update

11/07/2010 21:03


Engine Firing

Its been an up and down last few months, a few weeks ago I finally managed to get our little 100lbf liquid engine ready for testing, being that its winter here and I was unable to take time off work I set a time for a night test, a daytime test would of been better for a first test but you have to go with what you’ve got.

I had spent the previous few days getting the computer control box wired up along with the control cable to lay out to the test stand, which I might add found behind Dads shed, 12 wire, shielded instrumentation cable, Score! With that all wired up and good to go it soon became apparent with everything setup that we were having valve problems with our fuel valve. We had had issues in the past and thought we had fixed it but not the case, so it had to be pulled and the troublesome wire resoldered in the shed.

I was planning on using pyrotechnic ignition to light the engine so had set about setting that up only to find the igniter for that was a dud (after setting it up!) so all out and that was replaced. I knew it was always going to be hit and miss lighting an engine like this so with David on the computer operating the valves etc. and myself doing the igniter, it was kind of a “now now open” yell to David when the igniter lit, but it was not meant to be, we just got a pad load of propellant out the nozzle and no fire, half expecting that.

We called it a night and I went back to the drawing board to bring back the torch igniter I had made last year. Video here:


But thanks to David, Keith and Dad for helping out that uneventful night, I promise a better show in a few weeks time!

Some pictures.






With the no light of the previous week I resurrected the torch igniter and started designing and making a new one. I spent quite a late night going through Armadillo Aerospace’s news archive and Unreasonable Rockets archive, making notes and looking at pictures, from all this (and after some advice from others) I machined up a new igniter. Different from my previous, I switched to -2AN fittings and welded them to the SS chamber, and made the sparkplug in front of the injection points so by the time the propellants reach the spark they should be fairly well mixed, I also threaded the inside of the end so the whole igniter can screw into a port on the engine, making it easier to swap and change between engines in the future.

The other port in the picture below is to take chamber pressure from.





I’ve done abit of work with composites in the past and have just rekindled my interest again, I have some 90mm dia Carbon Fibre tube coming from Evolution Composites which I plan to test and muck around with for potential tanks/airframes, Ideally I’d like to make a filament winder and play around with that and try and get some decent pressures, but to try my ideas I have at the moment this ordinary tube should be fine.  I know its a whole new art but this experimenting could prove valuable for some other projects I have in mind for the future.



I have also made two 4”dia tanks from aluminium irrigation tubing, one of them I got aluminium end caps welded on, but my welder struggled welding the 1.2mm thick tube because of the properties, I think these tubes were 2013 or something, he managed but from what I gather did not have a lot of fun. I’ll try and find some more appropriate 5000/6000 series tube for welding next time, but in the mean time I made up another tank with machined bulkheads, held in by machine screws, as can be expected this was considerably heavier than the welded tank but was easier for me to make (I need more practice welding alloy that small), both ends have a 3/16th" o-ring and I’ll be quite interested to see what pressure this style of tank can take before it leaks or blows, I’ll hydro the welded tank to destruction as well to see how that fairs.



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