Thursday, 2 May 2013

Pre-taxy preparation

As XL231 has been stationary as regards moving under her own power for longer than anticipated it was decided to inspect and recify any brake defects as well as any tyres that we did not feel were safe enough to use.

In the end we changed only one wheel on the Starboard undercarriage and cleaned and inspected the braking system. With a complex multi-piston hydraulic system (same as Vulcan B2) leaks and weeps inparticular are going to happen especially, as she is not in daily use. Weeps can be lived with, leaks cannot.

The Stb'd braking system is extremely dry as regards fluid loss and did not require much apart from a good look-over. The Port side required a little more attention.

The front inner braking unit has always been a source of minor leaks from the day XL231 left the RAF. We have always cleaned and monitored it and with use it generally stops. However I noticed the fluid was showing a bit more than I would have liked and so it was decided to remove the brake unit and 'nail it' once and for all. The tube nuts which connect the supply piping are easy enough to undo and replace bonded seals on, but only when removed from the aircraft and this entailed a trip to the bench and hoping the offending tube nuts wouldn't shear off as they are only made of alloy! Luckily they didn't and I replaced one of them with an item that I had removed from XL190 in (well, more years than I care to remember)! The bonded seals were renewed and the whole assembly wire-locked back together before refitting, after John had done his spring cleaning bit!
The main reason I deferred removing the brake unit is the fact that it takes pints and pints of OM-15 hydraulic fluid to bleed the air out until the fluid runs clear. Its a messy job but must be done 100% because any air left, in particularly the maxaret 'anti-skid unit', will render the brakes likely to grab and flat-spot or blow a tyre, an expensive mistake and also likely to un-impress any airfield manager!
I have bled all of XL231's brakes previously after we replaced every hydraulic wheel cylinder seal and I enjoyed it not one bit!

Incidentally we are LOOKING for replacement mainwheel tyres, cuurently we have several spares but, there are 16 on the aircraft, it is the same wheel and tyres as a Vulcan B2, any leads or help would be appreciated.

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