I can’t take much credit for the workmanship here as J has been busy with the rivet squeezer and back-rivet plate today. My contribution to this assembly was largely limited to taking the photos 🙂
I *did* debur and scrub the green bits before they were primed, though!
Firewalls are quite important! The firewall in an aircraft is what separates the engine from the rest of the airframe and from the pilot and passengers. This is a good thing, especially given that engines are full of fuel and oil and conditions for burning things!
The function of the firewall is to ensure that if there is an engine fire, the occupants (who in a single-engine plane like the RV-14 sit directly behind the engine) are protected from the heat and flames for long enough to allow the pilot to get the aircraft to safety.
There are various gaps in the firewall, which given what I’ve said above might seem counter-intuitive(!) but they are necessary and all of the gaps and joins are eventually sealed to make the firewall as impenetrable as possible. The holes are either for mounting parts of the engine or electrical system, and/or for feeding through wires for engine controls and monitoring.
The large rectangular holes you can see in the picture below are for the hot-air vents from the engine, and the smaller round holes around the edge are where the engine mount attaches. The others are for mounting the battery box, brake fluid reservoir, starter contactor and battery master contactor, for feeding through the engine controls (throttle, mixture, alternate air and propeller governor) and electrical wiring for engine monitoring (temperatures and pressures).
We hope we don’t ever have to test our firewall to its limits, but it’s definitely a bit we’d like to get right!
Unlike most of the rest of the aircraft, the firewall is made of steel rather than aluminium. In this section, the strength and heat resistance of the metal is the most important thing. I’m a big fan of its properties but steel is a bugger to debur in comparison to the aluminium – it destroys the sandpaper, rather than the other way around. I’m sure we’ll find a better method in time, but our first steel pieces have been in the fuselage so we haven’t really cracked it yet.
As ever, I find the quality and consistency of the rivets done with the pneumatic squeezer to be really satisfying – wherever we can, we use it above the bucking bar + gun method.
The rivet density in the firewall sections is absolutely ridiculous, although it’s reassuring to think how strong it will be as a result!