3 Piece Boot Cowl - A Handy Design

[Steve Pierce]

A friend just built a titanium firewall to replace the stainless firewall on his PA11/AL11 Legend Cub and he saved 3 lbs titanium vs stainless.

 

[skywagon8a]

Interesting, I would not have guessed it to be that much. Now I can understand the interest in Ti.

 

[wireweinie]

Mr. Pierce

What's the proper rivet for the Ti? Monel or is there something else that is less reactive?

Web

 

[Charlie Longley]

A friend just built a titanium firewall to replace the stainless firewall on his PA11/AL11 Legend Cub and he saved 3 lbs titanium vs stainless.

Thanks for the links Steve! After sleeping on it I am going to build a 3-4 piece firewall. I have a slip roller and punches. My “welder” has a good shear I can go over and use.

 

[Charlie Longley]

I used nut plates in the flange so the boot cowl can be removed in sections and used PRC sealant around the flange, front and back.



View attachment 57575

Where did that engine mount lug come from Steve? It doesn’t look stock.

 

[supercrow]

Where did that engine mount lug come from Steve? It doesn’t look stock.

Thrustline mod.

 

[tackdog]

Hi everyone.

For ease of future maintenance when making a 3 piece boot cowl, do you make a ''formed seal'' (I'm not sure of the term that you use?) with heatproof goop like PR812, where the boot cowl is screwed to the firewall's nut plates? Ie: goop one side, petroleum jelly the other and screw them together to form the panel seal?

If you have a avionics maintenance issues, is it easier to make some large removeable panels on top of the dash, or do you remove the windscreen and the top boot cowl panel? I've read that some people use felt to mount the windscreen similar to a Cessna 172, yet others use a caulking compound and I'm not sure if this is a thing that once trimmed and fitted well, you never ever want to remove it again due to the risk of cracking or just being a PITA.

What's the preference for the panel join in the wrapper? A flange / lap seam or a simple overlap with a slight panel edge break?

I'm hoping I can modify the standard parts in my kit when they arrive to suit - they mirror the stock cub setup where the boot cowl wrapper has the fluted formed edge that folds down over the firewall.

Thanks again

Damian

 

[Steve Pierce]

Mr. Pierce

What's the proper rivet for the Ti? Monel or is there something else that is less reactive?

Web

I have used standard aluminum rivets on all the ones I have built so far.

 

[Steve Pierce]

Hi everyone.

For ease of future maintenance when making a 3 piece boot cowl, do you make a ''formed seal'' (I'm not sure of the term that you use?) with heatproof goop like PR812, where the boot cowl is screwed to the firewall's nut plates? Ie: goop one side, petroleum jelly the other and screw them together to form the panel seal?

If you have a avionics maintenance issues, is it easier to make some large removeable panels on top of the dash, or do you remove the windscreen and the top boot cowl panel? I've read that some people use felt to mount the windscreen similar to a Cessna 172, yet others use a caulking compound and I'm not sure if this is a thing that once trimmed and fitted well, you never ever want to remove it again due to the risk of cracking or just being a PITA.

What's the preference for the panel join in the wrapper? A flange / lap seam or a simple overlap with a slight panel edge break?

I'm hoping I can modify the standard parts in my kit when they arrive to suit - they mirror the stock cub setup where the boot cowl wrapper has the fluted formed edge that folds down over the firewall.

Thanks again

Damian

I have not made a seal. The Short Wing Piper series have an airworthiness directive to seal the firewall with a non-hardening seal because they used a fiberglass insulation under the floor that would get saturated with fuel and oil and cause a fire hazard. I have not seen any issues. I have removed the side panels to get access to under the panel but usually access from under the instrument panel using a modified creeper that sits on the front and rear seat bases. The top panel can be removed but the windshield would need to come out. I seal around the windshield with a urethane sealant. At the over laps I brake a flange on one side for stiffness.

 

[Charlie Longley]

I have not made a seal. The Short Wing Piper series have an airworthiness directive to seal the firewall with a non-hardening seal because they used a fiberglass insulation under the floor that would get saturated with fuel and oil and cause a fire hazard. I have not seen any issues. I have removed the side panels to get access to under the panel but usually access from under the instrument panel using a modified creeper that sits on the front and rear seat bases. The top panel can be removed but the windshield would need to come out. I seal around the windshield with a urethane sealant. At the over laps I brake a flange on one side for stiffness.

Steve what thickness/grade of Titanium are you ordering?

 

[astjp2]

When you put the overlap seam on the side, is there any support behind the skin?

 

[Steve Pierce]

I break the adjoining skin to stiffen the seam.

 

[stewartb]

Mine has nutplates.

 

[Mark_Moyle]

I did a three piece boot cowl.. made the bottom panel removable. Didn’t like how you have to peel, bend and wrinkle the boot cowl once a year to access the aileron pulleys and brake components under the floor…

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