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  #1  
Old 06-03-2019, 06:47 AM
I-TERA's Avatar
I-TERA I-TERA is offline
 
Join Date: Jan 2014
Location: legnano (milan) italy
Posts: 29
Default Firewall tests

Hallo builders,

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
attached.
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.

Claudio

Link at the pictures:
https://www.dropbox.com/sh/49ialxn7q...QGuvddEca?dl=0
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  #2  
Old 06-03-2019, 08:14 AM
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DanH DanH is offline
 
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Location: 08A
Posts: 10,360
Default

Clauido, that's good work.

Could you identify the high temperature glue used to attach the aluminum- backed woven fiberglass sheet to the cabin side of the firewall sample?

The sheet of metallic material serving to spring load the thermocouple against the aluminum foil may be acting as a heat sink.

You've again demonstrated why bulkhead fittings should be steel, but not everyone believes it.

Interesting point about the brake fluid vent!

Link below, similar tests of penetrations, from some years ago, start post #38. Note the plastic grommets were on the periphery of the hot spot, not within the 1000C/2000F zone. They still failed. The effective cheap penetration for large electrical cables is the welded tube top hat pumped full of Firebarrier 2000.

http://www.vansairforce.com/communit...resbond&page=4
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  #3  
Old 06-04-2019, 09:19 AM
Kalibr Kalibr is offline
 
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Location: St John, Steamboat Springs, planet Earth generally
Posts: 102
Default

Quote:
Originally Posted by DanH View Post
You've again demonstrated why bulkhead fittings should be steel, but not everyone believes it.
To me, the tests demonstrated that an aluminum fitting need to be properly protected, if someone chooses to use it. The tests demonstrated two good ways to protect an aluminum fitting.
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  #4  
Old 06-05-2019, 05:15 AM
I-TERA's Avatar
I-TERA I-TERA is offline
 
Join Date: Jan 2014
Location: legnano (milan) italy
Posts: 29
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Dan,

I read all your posts with great attention, you job is serious and of great value.

The sheet of metallic material serving to spring load the thermocouple against the aluminum foil may be acting as a heat sink.
I added the pic 01-1. On the inox spring was glued a thermal insulation, not a dewar, but enough to reduce the thermal loss.

Could you identify the high temperature glue used to attach the aluminum- backed woven fiberglass sheet to the cabin side of the firewall sample?

On sample and after on the firewall I used an adesive - sealant normally used for fireplace exhaust sealing ( not for direct flame ). The adhesion is not excellent but enough to hold in position the sheet ( now near two years in service, no sign of failure ), no fumes at 550?C. https://www.fluesystems.com/shop/hig...viromgraf.html

Claudio
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