Tuesday, May 01, 2012

Air Serpent, update numero dos


Here is a rundown of the status.  Suggestions are always welcome.




Head/nose cone -  Here you see the shoulder mounted.  It will take a couple of additional pieces of masking tape to snug it up at flight time.  It's hard to see on my small screen but there are black tabs glued to the inside of the plastic shell.  The plunger tube is loose in the base and won't support/align the nose well.  The parachute shock cord is attached through the squirter's nozzle.  There is a protruding piece of Kevlar there (also barely visible).  I don't know if I will trim it or paint it.

Upper body - This will attach to the nose via a long piece of underwear elastic.  We'll not from actual underwear.  You can see it at the bottom.  There were several holes in the bottom of the body.  I ran the elastic through the rear hole, knotted it off, and ran it through the forward hole.  This sits beside the plunger tube and should never see any hot gasses.  To firm up the plunger, I poked in chucks of soft foam.  This helped, but I also added the tabs mentioned above.  Until the glue on the tabs sets overnight, I won't be able to assess if more work is needed in this area. Some temporary tape may be added at flight time.  Finally, I screwed a 29mm centering ring into the bottom of the upper body.  The lateral edges were ground down to match the oblong body.

Lower body motor tube - This is 29mm phenolic tubing.  It is long enough to allow for the full throw of the plunger and a 29/40-120 case.  I don't plan on flying it on that much motor, but  I didn't want to exclude it.  The parts so far are sitting at about 12 oz.  The piston is just above the tube (looks like a round spot on my ugly work bench).

Fins - One of 3 main fins is seen above the motor tube.  Near the front is a small decorative fin. This may change or be omitted entirely.

Motor retention - Since the piston is a closed system and the area that requires pressurization is really small relative to most 29mm motors, I want positive retention.  I can't decide whether I want to use the DIY PVC retainer shown at the business end of the motor tube.  This is probably the easiest but is quite bulbous when it sits out in the open. Oh, yeah, I need to remember to place vent holes at the point that the plunger has done it's job...or this thing might pop!