PREMIER I FUSELAGES will be produced in two sections, which will be bonded together at the aft pressure-bulkhead. The skins are a sandwich of Nomex-honeycomb core between carbonfibre-reinforced plastic layers, formed on a wooden mandrel using automatic fibre-placement.
First a bladder is slipped over the mandrel, then the inner layer of carbon-fibre is "wound" on. Honeycomb core and local reinforcements are then hand-placed and the outer layer of carbon-fibre wound on. A final layer of fabric, containing metal filaments providing lightning protection, is applied and the completed fuselage section is placed inside a clamshell tool for autoclave curing, the bladder acting as a vacuum bag to hold the skin tight against the female mould.
The tow-placement head is steered over the mandrel surface by a computer, picking up and laying down individual tows to create apertures for doors and windows. There is no cutting out of apertures, as with filament winding. The head can lay down tows in any orientation and precisely maintain that orientation over complex curves. Heat and pressure applied at the head consolidates the composite material to eliminate voids, he says.
Others use fibre-placement, but Raytheon will be the first to use the technique to produce a pressurised fuselage. The Premier I fuselage, is designed for a 0.58 bar (8.4lb/in2) pressure differential, giving an 8,000ft (2,440m) cabin altitude, at the aircraft's 41,000ft operational ceiling.
Cincinnati Milacron has produced three fuselage test-articles for Raytheon, using its prototype tow-placement machine. This handles eight 5mm-wide tows simultaneously, whereas, the two production machines to be installed by Raytheon will each be able to handle up to 24 tows. Each test section represents the 4.1m-long cabin and weighs 135kg. Time taken to produce a section was reduced by 30% from the first to the second article, Bernstorf says, and Raytheon is looking at potential improvements such as fibre-placement of local reinforcements and lightning-protection filaments.
Source: Flight International
