Hi Fred
"When you took your described precautions (BID'ing the tunnel, and
> foaming the tank bottom), were you aware of the tank's tendency to
> absorb fuel and consequently expand"
Yes I was aware tank can expand. The foam is not applied directly to the
tank, I have a piece of mylar under the tank and the foam is underneath
the mylar, thus the foam is not bonded to the tank, the tank can move if
it cares to. The foam should support a good majority of weight of a full
tank, not rely on just cantelevering hold of aft BID layups. You can see
in Jims pics that the plastic just kinda flowed. The BID in tunnel should
relieve the sharp edge stress riser of the aft factory layup. I have the 3
BID tapered so there is not a sharp edge ending. If the tunnel of the tank
wants to expand, I can not see that the additional BID would causing a
crack to occur.
I attached a pic of Steve Hagars top of tank, if you had 3 BID on top of
tank when it was flat, not that you would want to do such a thing, but if
you did, I don't think it would cause cracks to occur. On the other hand
the tunnel layup and the lay ups on the aft base of the tank are all that
is supporting the majority of the weight of the tank. If I didn't already
have CPM bonded in, I would 3 taper BID the base supports as well. I think
the foam will take a real load off all 3 by not allowing the tank to
cantelever as compared to not having foam.
Ron Parigoris
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