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RV-10 Starter/Main Power Firewall Penetration

1001001

Well Known Member
I've been working on running conduit and wiring before closing up the back floors. I've made some decisions about routing, but when I review the OP-37 (wiring harness) drawings, I note that Van's has the main power wire to the starter relay penetrating the firewall in the very narrow space between the outer flange of the firewall and the F-1001M Angle, and surrounded by a simple plastic snap-in bushing (Note, I am not using Van's harness kit and am using 2 gauge welding wire for my main power and ground buses from the tail to the firewall).

Clearly, I'm not going to trust my firewall penetrations to plastic snap-in bushings. I have read through tons of threads here on firewall protection and firewall penetrations and have a very good idea of what I want to do for those cases. I don't think the space between the flange and the F-1001M is wide enough for a proper fire-resistant penetration.

My questions are:

1. Where have others run the main power wire through the firewall? Above the starter contactor area? Somewhere else?

2. Did you tie the main bus wire coming from the tail off to a cabin side terminal for feeding the main bus, or go through the firewall first, bond to the starter relay, then return another wire back through to the cabin to to main bus?

3. How many penetrations overall did you make? I presume a minimum of two--one for the main power and another for signal wires, ignition wires/mag grounds/etc. Should ignition conductors be isolated from other firewall penetrations? In this case I could see 3 or 4 total penetrations.

Anyone have some good overall pictures of their penetrations and locations? I have honestly been all over this site looking for these things, as well as many build logs, and am having problems finding what I'm looking for.

Thanks!
 
I made 3 penetrations for wires. One on each side up high for various wires and sensors FWF. The third one was for the main power feed, and (as I recall) was in the stock location using a snap bushing with either a sock of firesleeve up against the firewall, a layer of fire barrier caulk, or both. My thoughts are that penetrations up high on the firewall are unlikely to be the source of a blowtorch shooting into the cabin. So I didn't go crazy over those penetrations. IMO, fire is (most likely) going to be from fuel or oil, both of which are subject to airflow and gravity, so my bigger concern is lower on the firewall and along the belly skin.

There are lots of rationalizations to be made, regardless of how you view these things.

Hope this helps.
 
I'm apparently throwing caution to the wind and installed my #2 main battery cable and starter solenoid in accordance with the kit plans. ;)

I have 4 FW penetrations for wire, the largest being for my battery cable, the others being the alternator power and two for engine sensors and EFII.

Flying in the face of the penetration protection crowd: snap bushings are fine, simply seal them up with a good layer of 3M Fire Barrier, or comparable product.

Now to really stir the pot....there is definitely a LOT of discussion on fire protection on VAF, but what's better than good fire protection? Preventing it in the first place!

I recommend focusing more on eliminating the major sources of fire forward of the firewall, such as the things that normally spring leaks, like carburetors, gascolators & fuel pumps. This may not be possible for many folks with older style fuel systems, but reducing the components and fittings forward of the firewall further reduces the causes of fires.
 
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I ran the fat wires through bullhead pass throughs both on the RHS.
The ANLs and B leads run up vertically into the studs on each side of the cross feed. The starter contractor is next to it.

The bus feed wires come off the back of the firewall pass throughs to the fuse block / CBs

I have 2 of the sleeve type penetrations for sensor wires, field etc. one each side up high.

You could possible get away with less but it would be tight.
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No. 2 battery cable

This is how I did the battery cable penetration for my -8. Used AN931 grommet and heat shrink on cable jacket. Covered with stainless cover plates. Had to enlarge the cover plate hole using a step drill so there would be clearance from the battery cable. Might consider silicon grommets and/or firesleeve to cover.BF165A65-EC98-46EF-9908-5511C00001C2.jpg
 
Here’s what I’ve done with my firewall. Still have a few things to mount Like another contactor, shunts, etc. I’m going with SDS EFI so I have the manifold pressure sensors and fuel pressure regulator mounted.

I think the bottom line is there are a number of ways you can place stuff on the firewall.

Keith
 

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So I took a few minutes today to do some destructive testing in the LavaShield. I have uploade a few pics and will try and best explain what I witnessed.

I did several tests with small coupons about 2” x 3” or so.
I mounted the coupons on a thin piece of aluminum cladding, a .030 piece of 2024 and a 1/16” piece of steel plate I had.
The two pictures show the steel plate tested piece where it has the outline of the adhesive and after I handled it to see if it felt different. I held the torch on the plate for about 1 minute. By then the adhesive had let go and the piece fell off. The torch I was using is for soldering and is fueled by propylene gas which burns at about 2700+ degrees. As for the other coupon tests on the thin cladding the torch basically melted the cladding behind the LavaShield almost instantly. On the .030 the torch melted through the aluminum in about 10 seconds. I did the tests with and without the LavaShield and from what I saw the LavaShield did provide some insulation value to the materials underneath. The LavaShield feels and appears charred after the exposure to the torch which makes sense. It reminds me of burn tests done on Nomex FR clothing.

I am not too concerned about the adhesive letting go as there is ample square feet holding the stuff to the firewall. Also there is equipment screwed on that will hold it in place. All in all I am satisfied that this stuff will by some additional time before burn through of the stainless firewall.

I know this wasn’t very scientific but maybe will help others see what it does.

Keith
 

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Thanks for doing the test!

For the steel test, did you measure the temperature on the other side before it fell off?

Now I'm wondering how to compare the results from 2700 degrees for a minute to (if I remember correctly) DanH's at 1200 for 10 min (which I think is how hot avgas burns?), especially since the LavaShield isn't rated for 2700 :)
 
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Thanks for doing the test!

For the steel test, did you measure the temperature on the other side before it fell off?

Now I'm wondering how to compare the results from 2700 degrees for a minute to (if I remember correctly) DanH's at 1200 for 10 min (which I think is how hot avgas burns?), especially since the LavaShield isn't rated for 2700 :)

Hi Rodrigo,
I don’t have a thermal heat gun so not sure how hot it got but as you can see from the outline in the one picture the steel got hot enough to leave blue marks. That torch puts out a lot of heat so for the lavasheild to survive a minute I think is pretty decent. Also to note there was next to nothing for smoke and the lavasheild will not burn. Lavasheild is rated for 1200 continuous and 2000 intermittently.
If I were to do this again I’d set up the torch to a distance that would equate about 1200 degrees and see what happens over a given time frame.

Cheers,
 
wondering

If people are going through the effort to utilize a fire barrier on the firewall, I am wondering why they are not using SS foil and a layer of Fiberfrax. It would seem that the fiberfrax method would be the gold standard...
 
Hi Rodrigo,
I don’t have a thermal heat gun so not sure how hot it got but as you can see from the outline in the one picture the steel got hot enough to leave blue marks. That torch puts out a lot of heat so for the lavasheild to survive a minute I think is pretty decent. Also to note there was next to nothing for smoke and the lavasheild will not burn. Lavasheild is rated for 1200 continuous and 2000 intermittently.
If I were to do this again I’d set up the torch to a distance that would equate about 1200 degrees and see what happens over a given time frame.

Cheers,

I don't want to buy a torch just to run this test, but I'd be happy to chip in for the materials if you're willing to do it :)

Also, I was wrong, it's 2000˚F, not 1200, for 15 minutes - relevant threads:
https://vansairforce.net/community/showthread.php?t=47587
https://vansairforce.net/community/showthread.php?t=196836

If people are going through the effort to utilize a fire barrier on the firewall, I am wondering why they are not using SS foil and a layer of Fiberfrax. It would seem that the fiberfrax method would be the gold standard...

Well, exactly - I'm wondering if by any chance this product would be a good, easier-to-install alternative. No reason not to (carefully) experiment :)
 
So I took a few minutes today to do some destructive testing in the LavaShield.

My compliments; any test is better than none.

That said, the FAA standard is 2000F over 25 sq inches. The specified heat flux is far more energy than can be applied with a handheld plumbing torch.

There are standards which use a small flame (specifically a Bunsen burner), but they are for checking fire resistance of upholstery and wall covering materials, not firewalls. The exposure time in measured in seconds. Think little Johnnie in the bathroom with his daddy's Bic lighter.

The original FAA-approved burner was oil-fired. It's no longer available from the manufacturer, so the standard will probably change to a propane or NG setup. Most folks who are not chasing certification have already switched to some form of large gas burner. Although not super precise, it's possible to adjust the shape of the burner head so it heats an area about 5" x 5", and calibrate temperature with copper foil, which melts at 2000F.

All in all I am satisfied that this stuff will by some additional time before burn through of the stainless firewall.

You will not burn through stainless at 2000F. The issue is the firewall will glow red, and ignite materials in proximity to it on the cabin side. Please note materials marked "flame resistant" or "meets FAR 25.853" burn merrily when placed in contact with a red hot firewall. 25.853 only requires them to self-extinguish when the heat source is removed.

The important takeaway isn't how to insulate. It is do not place stupid stuff on the cabin side of a firewall. In this context, anything from Lava Shield to cast off baby blankets are fine on the engine side. You can't hurt anything on the engine side; worst case, it's already on fire there. The Darwin Award will go to the dumb SOB who builds in a "fire transfer device"...the aforementioned flammable stuff on the cabin side.

Below, a once popular cabin side "firewall insulation", which turned out to be recycled polyester. I still find it in some older RVs. In the photo, there is no direct contact between the burner flame and test material; they are separated by a 0.019" stainless steel panel. What you're seeing is the effect of red hot metal in contact with a very bad choice....a fire transfer device.
 

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If people are going through the effort to utilize a fire barrier on the firewall, I am wondering why they are not using SS foil and a layer of Fiberfrax. It would seem that the fiberfrax method would be the gold standard...

That's exactly what I'm doing. SS, fiberfrax, SS sandwich. I'm in the process of building a little box out of SS sheet right now, to double up the recessed area of the firewall. Not an easy task, as SS is hard to work with, but I'm getting there.
 
Here’s what I’ve done with my firewall. Still have a few things to mount Like another contactor, shunts, etc. I’m going with SDS EFI so I have the manifold pressure sensors and fuel pressure regulator mounted.

I think the bottom line is there are a number of ways you can place stuff on the firewall.

Keith
Is there a cheaper way to get the servos? I see them for $195 at Spruce.
Thanks
/Martin
 
Is there a cheaper way to get the servos? I see them for $195 at Spruce.
Thanks
/Martin

I did some research for linear actuators before buying these. I was able to find them but the controller I had trouble finding. The actuators are made by acutonix and are relatively cheap about 70.00. Then you have to find the controller.
I finally got fed up looking and bit the bullet when ACS had a thanksgiving day sale. 195.00 is nuts...I think they were 265.00 Canadian. Good luck in the hunt.

Keith

https://www.actuonix.com
www.progressiveautomations.ca
 
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