Boots for firewall piercings?

[Marty_d]

Hi all,

After some advice.

My CH701 has rods from the rudder pedals through the firewall to the noseleg for steering. These rods go through vertical slots as they need to move up and down as the noseleg suspension moves.

I bought a piece of silicone sheet online, but at 2mm it's too thick to deform enough to make into a boot that can move around in the middle while fixed (sandwiched between aluminium collar and firewall and riveted) at the edges.

Has anyone found a solution to this? I'm thinking something preformed, like the Dektite flexible fittings you can get for roof piercings. But lighter and smaller of course.

The slots are 20mm wide X 100 tall.

Thanks, Marty

 

[onetrack]

Here's one blokes solution, Marty (link below). The three biggest problem that I see for your requirement, in trying to find a commercially-made boot, are;

 

1. It seems that all boots are designed to fit round or square holes. I have yet to find a boot that fits a slot, and which allows substantial movement in a straight line.

 

2. There are grommets, and there are boots. Many grommets offer a wide range of shapes, but they're not designed to allow a substantial range of movement, as boots are designed to do.

 

3. You really need the material to be fire resistant. As a result, silicone would be the best choice, it's very heat and fire resistant (450°C), and self extinguishes once the flame source is removed.

 

I think this bloke has produced a workable solution, even if it's not professional-looking. I wouldn't trust those PVC or nylon cable ties, though, I'd be looking at something more durable.

 

https://www.kitplanes.com/diy-firewall-boots/

 

[Marty_d]

Hi OT, 

Yes - saw that one. That's a backup plan, it'd be good to do the out of silicone though (less messy!)

[Kiwi]

Not fire proof,  but should keep the cold and fumes out.

[Marty_d]

30 minutes ago, Kiwi said:

Not fire proof,  but should keep the cold and fumes out.

Thanks, that's the kind of shape I want, but in lighter silicone.

[skippydiesel]

Have you considered wool felt.

 

It comes in diffrent grades, thickness, fire resistant, durable and cost effective.

 

I have home made felt witches hats, as draft excluders, on my aileron /wing root holes - work a treat.😈

[Thruster88]

Perhaps  a fire blanket or one of these welding blankets could be used, make a form out of wood, fit blanket material around form and join the seam with high temp silicone.

 

https://www.vevor.com.au/welding-blanket-c_10056/vevor-carbon-felt-welding-blankets-2-pack-508mm-x-914mm-flame-retardant-welding-blanket-up-to-1800-f-heat-resistant-safety-protection-blanket-3-5mm-thickened-carbon-fiber-fireproof-insulation-mat-p_010421956361?adp=gmc&utm_source=google&utm_medium=cpc&utm_id=21271593978&ad_group=163180832818&ad_id=699136035035&utm_term=&gad_source=1&gad_campaignid=21271593978&gbraid=0AAAAACYOjau14XBmePs9-F5M-n41S3zEd&gclid=Cj0KCQjwoMXQBhDcARIsAH-eEtvXRPrzkvdVRBWQb84ev-zKWuCVrAUwmIbJnrIkFM4d51QVjle-klcaApICEALw_wcB

[Marty_d]

4 hours ago, skippydiesel said:

Have you considered wool felt.

 

It comes in diffrent grades, thickness, fire resistant, durable and cost effective.

 

I have home made felt witches hats, as draft excluders, on my aileron /wing root holes - work a treat.😈

Wouldn't felt let gas through? Part of the purpose is to stop carbon monoxide.

[onetrack]

That's a firm Yes. Wool felt has no ability to stop CO2 getting through it - even though it has some uses in filtering some chemical smells and chemicals with large molecules.

 

CO2 has small molecules that pass easily through the relatively porous regular wool felt material. But if you employed wool felt containing activated carbon particles (charcoal) in it, then the CO2 would be trapped by the activated carbon.

[Blueadventures]

Hi Marty  This is one method.

DIY Firewall Boots.docx

[Marty_d]

28 minutes ago, Blueadventures said:

Hi Marty  This is one method.

DIY Firewall Boots.docx 226.79 kB · 1 download

Thanks! That's the same article OT linked to.

[skippydiesel]

 

 

12 hours ago, onetrack said:

That's a firm Yes. Wool felt has no ability to stop CO2 getting through it - even though it has some uses in filtering some chemical smells and chemicals with large molecules.

 

CO2 has small molecules that pass easily through the relatively porous regular wool felt material. But if you employed wool felt containing activated carbon particles (charcoal) in it, then the CO2 would be trapped by the activated carbon.

I hadnt thought about the potential for wool felt to pass CO (Note: CO2 /Carbon Dioxide, is not the realy nasty one, its CO /Carbon Monoxide ).

 

Seems to me that, other than a "rubber" concertina boot,  with gas tight fitting to rod & firewall, would be your only option for a good seal. Even the home made silicon boot will likly be be gas permeable.

 

😈

 

 

[onetrack]

My apologies Skippy, I meant to write CO, knowing full well that CO2 is carbon dioxide - I just had a late evening brain fart.

 

Yes, there could be gas leakage potential with the home-made boot, I guess that would depend a lot on the thickness and evenness of the silicone RTV spreading. 

 

Another approach would be to fabricate a mold and make a boot from silicone rubber. I've done this myself for the manufacture of a mold to make a rubber mounting.

 

It's easy enough to purchase the chemicals for manufacturing silicone molds. However, the material only seems to come in pink colour - I'm not sure if Marty is right into pink, for his aircraft colour scheme. 😄 

 

https://www.flowresins.com.au/products/pinkysil?srsltid=AfmBOor7DvBhG6bxCiGN5nzFHphpt09AkjRyaN_ZCCErwLIZ1YMc7Cya

 

 

[onetrack]

Or ... you could simply check the dimensions of a larger size, off-the-shelf rubber shifter boot, off eBay - typically for big American pickups - and see if that would do the job.

 

https://www.ebay.com.au/itm/277258163920

 

 

Edited May 24 by onetrack

[onetrack]

There's actually a whole pile of YooToob videos of people sewing up their own custom-shaped shift boots (or gaiters as they're also known)

 

https://www.youtube.com/watch?v=oaPqzw2eGJk

 

[onetrack]

You can also purchase "rubber bellows" for hydraulic cylinders, which are designed to keep contaminants away from cylinder shafts and seals.

 

These are also available in silicone rubber, and they have the advantage of being vastly more flexible over a longer range of movement, than a simple gear shift boot.

 

https://www.steerforth.co.uk/standard-rubber-bellow-gaiter-p-4433.html

 

[onetrack]

I'm on a roll here! Another option is - Kelpro produce a range of CV joint boots. Many are for specific vehicle fit, of course - but they also produce about 3 sizes of "universal fit" boots.

 

If you find the Kelpro part number, a Google search on the Kelpro part number will usually bring up the boot dimensions - or some sites selling them will provide dimensions.

 

The only problem with the CV joint boots that I can see, is that the base is designed to fit a circular CV drive forging, so you would need to fabricate a metal adaptor that screws to the firewall, and which would have a circular top to allow the securing of the larger diameter of the CV joint boot to it. The CV joint boots are exceptionally durable, I'm pretty sure they're nitrile rubber. Nitrile rubber is not as flame resistant as silicone rubber, but it's not highly flammable, either.

[facthunter]

Anything flammable is not desired forward of a FIREwall, OR as a seal. It also has to be Fail safe.  ie not impede movement.  Nev

[skippydiesel]

Tangential thoughts:

 

Prevention is usually better than cure.

 

In this context CO poising is best prevented by making sure your exhaust system is in good order. 

 

I would think that few, if any, light aircraft firewalls are gas tight.

 

Their main purpose is to:

• Slow the effect of an engine fire
• Reduce engine noise and heat (& cold drafts)

       - on the inhabitants of the cockpit.

 

Your focus on taxi fume exclusion, is commendable but may not be achievable and inhibiting you achieving a workable (rather than ideal) solution.

 

From what I have read (& experienced with the occasional paddock basher) exhaust fumes can enter the passenger compartment, via all sorts of other routs, not just the short rout through the firewall. You may be going to a lot of trouble to prevent exhaust fumes through your steering rod holes, only to find the gas is entering through the floor/tail cone/etc.

😈

 

[skyfox1]

Try early LandRover  high and low gear stick  boots fit perfectly for the 701 

[IBob]

Hi Marty, my kit came from Oz, and the then dealer supplied bellows type 'rubbers' to go on steering rods and throttle rods.
I don't have the details of those, but he also supplied a pattern for making a protruding collar round the rod slots, attached to the firewall, which the big end of the bellows then fitted neatly over. It looks an odd shape, but when you rivet it's ends together to make an oval, it is angled so that it attaches to the firewall in line with the rods (not perpendicular to the firewall as a single width band would). See Boot Bracket, below.

Boot Bracket.pdf

Edited Sunday at 08:11 AM by IBob

[pmccarthy]

4 hours ago, skyfox1 said:

Try early LandRover  high and low gear stick  boots fit perfectly for the 701 

Funny I have both of them on my desk at present and was thinking they would probably work.

[BrendAn]

On 23/05/2026 at 10:35 PM, Marty_d said:

Thanks! That's the same article OT linked to.

aren't there any zenith builder forums you could ask the question on. there must be plenty of info from people building the same aircraft.

[GolfWhiskeyHotel]

I used "cut down" early mini drive shaft boots. siliconed to the firewall works on a Jabiru

[sfGnome]

Thanks for starting this thread Marty, and thanks to all who provided advice and suggestions. I’ve been putting this off, and it’s given me the gently prod to finally get my act together.