Monday, May 26, 2008

Securing the fins in the Sustainer

Ideally all 24 fin/tube interfaces would be covered with a fiberglass/epoxy layer to maximize strength.  I pondered how to best achieve this since the 4" diameter motor tube leaves only about 1.75" of working radius inside the 7.5" sustainer tube.  Luckily I'd previously bought a 25 foot roll of 1" wide fiberglass cloth at a local composites store and realized this would fit the need perfectly.  I cut strips into 11" lengths (just short of the fin root length) and capped one end (and later both ends) with narrow strips of gaffer's tape.  These caps both prevented fraying of the cloth on the short ends and also allowed me to poke the sharpened tip of a dowel into them so I could extend the strip inside the narrow working radius by holding the back end of the cloth strip then laying it into place (this was impossible to photograph while I was doing the procedure):
By tilting the fin/sustainer assembly so each fin pair pointed up at 45˚ I was able to apply the epoxied strips into all four bottom interior interfaces as well as the two fin fillet areas since gravity would force the resin right where I wanted it:

I should note that I also loaded the exterior two fin fillets with colloidal silica as it increases strength and eliminates resin drip during curing.  I've had this batch of West Systems epoxy and both colloidal silica and microfibers for years but never appreciated the power of the additives until this build.

I then repeated this procedure for the other 18 interfaces (in three batches of six, of course).  

Now the sustainer's on hold until my 2-part expanding foam arrives from Giant Leap rocketry.  I had previously purchased a similar foam, Foam-It, for <$40 at Home Depot but this type failed me because part A had cured in the can.  Better living through chemistry?  Please?  I went to purchase more Foam-It to find it had increased in cost to $96 at three different places!! Inflation rocks.  I decided to purchase the same volume of foam from Giant Leap for $41.  Quite a price difference no?

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