|January 9, 2008||HOME|
I started off the day with working on the main wheels and brakes. I had already fitted the flanges and axles and was going to temporarily attach the flanges to the gear legs when I ran into a problem. The callout in the plans is for 5/16-20 x 1 1/2" bolts. I found the original bolts that came from Van's and they were marked appropriately and, in fact measured to 1 1/2 inches. All seemed fine except that the OD of the flange measures 1 3/8 inches. Those were the only bolts I had that were close. It turns out that the flange should be attached with bolts with a "grip" of 1 1/2 inches. Bolts ordered and on to something else, Grrrr.
I moved on the attaching the cabin heat box. I haven't figured out exactly how the cable will approach it and I haven't seen how anybody else has done it, but I think it will work.
One more little thing, I safety wired the bolts holding the gascolator.
Time for another fire test! I took a piece of 1/2 inch aluminum pipe crammed full of 18 gauge common electrical wire and packed it with fire block like you would coming through the firewall.
I used off-the-shelf 3M Fire Barrier, allowing it to cure about 10 days. Yes, I started this little experiment earlier.
About 10 seconds after the introduction of flame from the torch, the small pieces of fireblock began to burn.
At 20 seconds, the wire insulation caught fire (remember, this is common electrical wire).
At 1 minute, the fireblock was burning and beginning to expand, but strangely, the aluminum pipe was not melting even though I was applying a balanced flame from the torch.
At 1 minute and 40 seconds, the fire block at the bottom began to burn, but only from direct contact with the flame.
At 2 minutes, the aluminum is cracking and the fireblock is expanding more rapidly.
At 2 minutes and 15 seconds, the top of the pipe is melting away and the crack is enlarged. We wouldn't be anywhere close to a firewall penetration at this point though. The fireblock is expanding to block any openings.
At 2 minutes and 40 seconds, the upper half of the aluminum pipe has sluffed away and the fireblock continues to expand.
At about 4 minutes, almost all of the aluminum is gone and the fireblock is burning, but has not failed.
With the aluminum gone, I couldn't see what was burning and what wasn't.
At a little past 5 minutes, I removed the torch, dowsed the flames and the fire stopped.
The result: My aluminum pipe is gone. That is no surprise, we would be using stainless through the firewall, anyway. The wires break off at the slightest touch. The overall volume is slightly larger than we started with. The mass is reduced by at least half.
I was happy with the outcome. It means that the fireblock continued to work (held back the fire) for 5 minutes even when the aluminum pipe had been melted away. I may try this again with a piece of stainless pipe. This all would have performed better, of course, if the fire had not been able to get to the fireblock from both sides. That would be a more realistic firewall scenario.