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It occurs to me that the thermal fuses could
be mounted against the firewall, under the firewall blanket. They're not much
larger than resistors and distributing them around the firewall would
give an indirect engine fire indication and would also guard against the
situation that Brad Simmons discovered. 144 dC fuses are available at Radio
Shack, and would fail at 291 dF. This is slightly above the prepreg cure temp of
270 dF that Lancair mentions for the Legacy. They imply the other
models are cured under the same conditions but the factory should be able to
confirm that.
Lancair's website also states that the
IV materials strength and stiffness was tested at 170 dF. Perhaps a
fuse designed for a temperature between 170 and 270 dF would give warning when
there was still an adequate reserve of strength while reducing the
possibility of a false alarm.
In addition I have read that titanium
is difficult to machine because it doesn't transfer heat easily. For example,
the heat from drilling a hole tends to build up rather than dissipate into the
surrounding metal so the use of coolant is required. Low heat transfer is what
we're looking for in this application- has anyone considered using it as a
shield for fiberfrax or the blanket? -Bill Wade
We are in the process of repairing a IVP engine fire
that was centered on the passenger aft side of the engine compartment, and the
firewall blanket just barely did it's job. There is signifigant scorching
around the perimeter, through every penetration, and around the cowl attach
flange.
Brad Simmons
Airframes Inc.
Milan,
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