after some people, knowing my effort to experiment ad measure, asked me about how to insulate the firewall, I decided to share my experience, excuse me for this long rant and for my poor english.
Before to finish my firewall ( F1 Rocket ) I did a few experiment to verify the effectiveness of the thermic insulation and the protection of cables and fittings passing through.
I know that it is very difficult to save our live in case of fire, but I still be convinced that it's better to comply with the rules, result of a lot qualified experience, than decide to ignore them.
Part 23 subpart E , firewall asks for 15' of resistance at 2000F.
If we comply with the suggested material we don't need to do any test.
But I decided to install alu fittings, hi quality aeronautic aluminum connectors and, with my feet at 2'' from the firewall, I do not like to burn my shoes.
So I started to build the samples required, prepared a burner and a thermometer ( thermocouple, in Celsius ).
The purpose was to measure the temperature behind the firewall, the absence of fire or fumes from glue or other material in contact or in proximity of the firewall, the strength and endurance of fittings and the behaviour of thick copper cables passing through the firewall.
Firewall test :The firewall sample was a four layer sandwich : very thin SS sheet (0,002'' ), fiberfrax 3mm, 0,018'' SS, hi temp glue, 2mm glass alu backed.
After 15' at 1037 ?C the sandwich was still in good conditions, the thermometer in contact with the inner surface ( spring loaded ) wrote 553?C at ambient temperature of 09 ?C.
The temperature inside of a black foam rubber (sample of sound and thermo insulation glued on the inner surface of the fuse ) 10 mm thick and 10 mm off the inner surface of the firewall was, after 15', 48?C. Satisfying, but was evident that nothing non metallic shall touch the inner surface of the firewall . Pics 0x-1x.
First fitting test : a SS square ( 0,018'' ) , AN832-6D bulkhead bolted on, 5'' flared versa-tube ( inner side ) a thermocouple inserted in the tube to the nut, direct fire on the fitting.
Result : less than 45 seconds to melt the fitting AND to detach the tube from the firewall ( inner side ). Temperature near the nut 435?C. Pics 2x.
Second fitting test : the same but the fitting protected with a short (2'') 0,002 SS tube or ( same result ) a red ( silicon-glass)hose, and one other tube ( SS fitting ) protruding into fire.
Result : after more than 15' the fitting was still in good condition and the inner tube was strongly
The temps measured ( cabin side) of the versa-tube after 15' : 225?C. Acceptable.
The boiling temperature of brake fluid is greater than 250?C, but the fire side is higher a lot, so high pressure will be developed in the brake circuit, the weaker point of the circuit or the breather must be outside of the cabin. Pics 3x.
Connector test: Connector MIL spec MS3470 series, firewall sample 4 layer , red silicon hose on the fire side of the connector,wires in the fire area.
Result : after 15' the connector was in good condition, not melted, still sealing the firewall. Acceptable. Pics 5x.
High current wire test : AWG 4, epdm grommet, SS Firewall Shield ( Spruce ), big fire barrier 2000 protection covering the fire side of the firewall shield end the first inch of the wire.
Result: after less than one minute the inner side of the grommet started burning. The grommet burned also after the gas burner was turned off.
ANY grommet protecting big wires at the firewall must be a high temp grommet ( teflon or silicon ) and the inner portion of the wire does not touch plastic or rubber things ( grommets, cable ties )for the first 10? minimum.
The copper is a very good heat conductor so the temperature of a thick wire does not change too much in a couple of inches, the protection must be long enough to avoid direct exposition to fire to close to the firewall and the inner side free to allow the heat dissipation.
Others cables, steel or SS, like bauden, are not so good heat conductor, but I suggest metallic clamp and fire barrier protection. Pics 4x.
Link at the pictures: