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  #1  
Old 06-04-2021, 08:52 AM
DanH's Avatar
DanH DanH is offline
 
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Location: 08A
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Default Firewall Penetrations

From a previous thread...

Quote:
"...Yes Mickey, I constantly come across RVs that have firewall penetrations made with nylon snap bushings covered with a blob of "high temperature" red RTV such as Permatex Silicon Gasket Maker or similar. This is crazy..."

I guess you ought to address this with Vans. Referring to RV-10 plans, section OP37-2 figure 1, electrical harness, Vans says drill a 1/2" hole for firewall penetration of the battery cable and use a SB500-6 snap bushing...

It may not be what YOU consider airworthy, quality, or whatever you want to call it but it is spelled out in the plans that way. Someone with little or no experience in this hobby is going to follow the plans...
...which is a very good point.

That inexperienced builder may wish to learn more. Like most issues, God is in the details.

At typical operating temperatures the snap bushings will be fine.

Snap bushings combined with a good sealant choice actually performed at a reasonable level in a fire resistance test, maintaining a gas tight seal for roughly 1-1/2 minutes when adjacent to, but not encompassed by the hot spot. That said, sealant choice is an integral part of bushing performance, and there were significant differences in sealant. The popular orange Permatex was not a good choice, as it appeared to be highly flammable, and would serve as a fire transfer mechanism, bringing open flame and smoke to the cabin side.

In the same hot test, a simple tubular pass through filled with intumescent sealant performed much better than the basic snap bushing and sealant. It never lost a gas tight seal, even when subjected to the full 2000F, and did not itself transfer flame to the cabin side. The test was ended when the cabin side tefzel wire insulation ignited via its red hot copper core.

The popular eyeball style pass throughs were not tested, but their performance is going to be predictable. Aluminum eyeballs should be expected to melt if encompassed in the hot spot, but maintain integrity if held below 1000F, more or less. Steel eyeballs would maintain integrity regardless, but may not remain gas tight when the wire insulation melts.

Read here:

https://vansairforce.net/community/s...8&postcount=38

https://vansairforce.net/community/s...8&postcount=40

https://vansairforce.net/community/s...9&postcount=42
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  #2  
Old 06-04-2021, 09:29 AM
blytle blytle is offline
 
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Default

That is “How” It is done. Thanks Dan!
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  #3  
Old 06-04-2021, 09:31 AM
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Mike S Mike S is offline
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Default

Dan, thanks for posting this-----I have tried to find these tests in the past, but they seemed to be lost in never-never land.

Moved to the Building Tips forum to make it easier to find in the future.
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  #4  
Old 06-04-2021, 10:19 AM
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It's Dan's testing that caused me to think a lot harder about my FW penetrations, and make them better. In the end it cost very little additional time or money. Still far from perfect, and no idea if it will make any difference if I have a FWF fire, but I think they have to be better than a snap bushing with a bit of RTV.

Here's how I did it:

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  #5  
Old 06-04-2021, 10:34 AM
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Default Wraps

Quote:
Originally Posted by rv8ch View Post
It's Dan's testing that caused me to think a lot harder about my FW penetrations, and make them better. In the end it cost very little additional time or money. Still far from perfect, and no idea if it will make any difference if I have a FWF fire, but I think they have to be better than a snap bushing with a bit of RTV.

Here's how I did it: ...
What is the shielding on the exhaust pipe?
What is the wrap on the Intake pipe? Silicone?
I may need to protect things as well.
My penetrations are very similar. Steel eyeballs and fire sleeve pathways.
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  #6  
Old 06-04-2021, 11:15 AM
PhatRV PhatRV is offline
 
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I have similar radiant heat shields to protect the fuel lines and the control lines from the radiant heat generated by the exhaust pipes.
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  #7  
Old 06-04-2021, 11:29 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by rv8ch View Post
Here's how I did it:

Attachment 12244
Thanks Mickey, I forgot about tubulars with a firesleeve wrap. Should have tested it with the others, but I suspect they will perform well, in particular if used in firewall locations which are not likely to be subjected to full fire intensity. The basic concept is that fire follows airflow, so locations near the outlet are likely to be a lot warmer than a location at the top of the firewall, as you pictured.

FWIW, I am also using a wrapped tubular pass though for the one penetration which carries a bunch of small wires. It's far over on the right side, out of the likely high temperature region. Used a wrapped fitting there so I can easily add and remove wires for my experiments. All the others are filled with FireBarrier 2000.

BTW, pick up some ordinary shiny aluminum tape, as used in modern residential ductwork. A reflective wrap on those throttle and mixture cables will significantly slow radiant heat transfer.
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Last edited by DanH : 06-04-2021 at 11:32 AM.
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  #8  
Old 06-04-2021, 11:44 AM
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bjdecker bjdecker is offline
 
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Default On melting...

...Looking at the myriad of AN426AD rivets that attach the firewall to the substructure and imagining what happens when those melt; little jets of fire come in to the cabin from everywhere...

Those probably should be solid monel rivets if we're going to be serious about it.
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  #9  
Old 06-04-2021, 12:25 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by bjdecker View Post
Those probably should be solid monel rivets if we're going to be serious about it.
Different subject, easily addressed. No worries here.
.
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  #10  
Old 06-04-2021, 01:44 PM
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rv8ch rv8ch is offline
 
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Default

Quote:
Originally Posted by wirejock View Post
What is the shielding on the exhaust pipe?
What is the wrap on the Intake pipe? Silicone?
I may need to protect things as well.
My penetrations are very similar. Steel eyeballs and fire sleeve pathways.
The exhaust pipes have "heat shield" on them to try to reduce the radiant heat that goes to things near the exhaust, like cables and hoses. I used both store-bought heat shield from Van's and "home made".

http://www.rv8.ch/heat-shield-home-made/

I don't have any wrap on my intake tubes but they have rubber joints that connect the tube to the "sump". I don't think these are silicone but some kind of rubber. I've got more pictures here: http://www.rv8.ch/engine-photos-after-test-flights/

I've updated the clamps there to "constant pressure" clamps. Just added some pics: http://www.rv8.ch/sds-intake-tubes/

@DanH - thanks for the tip on the aluminum tape - will have a look at that. So far I think the heat shield on the exhaust pipes is working pretty well, but I have not pulled the cowl in a good 20 hours - need to do that soon.
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Last edited by rv8ch : 06-04-2021 at 02:14 PM.
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