Battery Installation

This blog cover the relocation of the battery to the baggage compartment.

Overview
The factory supplied spreadsheet showed a real need to relocate mass to the rear of the aircraft. Currently the factory installs a 5 kg plus battery into a compartment located behind the baggage compartment rear wall and is particularly important for the supercharger installation. It was not practical to install the necessary structure as this needs to be done when the access is available before fixing the turtle deck, so it was decided to locate the battery on the inside the baggage compartment, enclosed by a battery box. 

Another reason is one of the aircraft on the field was a RV8 with the battery in the back fitted onto the fuselage floor behind the back seat - I was advise not place it there as acess is a bear.

Manufacture
The first task was to provide a means for the battery to vent any fumes to the outside of the fuselage. It is envisioned that the door at the front will provide some isolation but a sealed battery box was seen as a necessary item to prevent spread of any fire.

A length of louver was installed in the side panel of the battery compartment.

Battery Vent

A 
A 1.0 mm thick aluminium sheet a box was fabricated to provide a sealed cover over the battery pack open to the the vent shown above. To increase the fire rating of the aluminium the interior was lined with fire blanket cut to fit using a 60 mm diameter Ofla  rotary cutter. A cardboard template was cut, trial fitted and the profile traced with a soft pencil onto the blanket and cut.

The blanket was fixed using high temperature silicone by applying small dabs of silicone and then fixing the blanket. All the seams were coated with a bead of silicone to seal the edge and prevent the blanket fraying. 

Trail fit of blanket
The returns to the flange were removed

The floor had a blanket rectangle cut and covered with 0.016'' aluminium with the edges sealed to the aluminium with silicone and then fixed to the floor under the cover to protect the deck.

Battery
The goal of all this work was to relocate the battery mass from the firewall to the rear of the aircraft. This requires the installation of the two [2] battery's and 4 gauge cables to the firewall.

To save weight aluminium/copper coated multi core cable was selected and sourced from Perihelion Design ,this cable combines the performance of copper wire with the weight advantage aluminium saving 2/3 of the weight of the copper wire.

Note: The weight saved is about 300 grams [0.75 lbs] - hey it all helps

To allow connection of the cables a 25 x 3 mm aluminium bus was fabricated then covered with heat shrink, trimmed providing access to the studs and bolts and fixed with M6 bolts fitted with spring washers. 

Battery installation

The battery's now forms a single block making handling easier.

To fix the battery's M5 rivet nuts were installed into the deck and two [2] length of M5 S/S threaded rod cut and installed. A clamp was fabricated using 25 x 10 aluminium channel extrusion, alodined and then fitted with M5 lock-nuts.

The cable entry's points were marked using a stud with a pencil inserted to transfer the location to the compartment floor. Two holes were drilled to accept IP65 glands to clamp the cables and seal the compartment in the event of a battery failure while supporting  the cables when unbolted from the bus assisting in battery installation.

Cable Installation
The biggest task was to find a route for the cable remembering my aircraft is unique to the factory aircraft. The new manual details the installation of items like fuel and these BIG cables but this was not available when construction begun so this installation is unique. 

Moto: Follow the factory book of words

This installation will be detailed in a separate blog once the factory approves the route past the rear spar.

Comment
Follow the moto

The battery pack weighs about 1.0 kg versus the factory pack of 5 kg requiring a mass to be fixed the stab, calculations show this combination is about 1.5 kg lighter overall.

Starting again the battery would be fitted to the factory specification and additionally look at installing another access hatch on the opposite side and look at fitting the hydraulic pump on that side. This is common practice with a lot of factory aircraft as the pump is a large movable weight with little weight penalty connecting it back to the manifold. 

The key to the c.o.g. is if the nose wheel weight, if it goes over 88 kg you will need a larger mass at the fin. Right now all bets are off and every concept and piece of hardware is up for review and weight reduction.