Bucaneers development days

THE ARTICLE ON the remaining DRA Buccaneers brought back some interesting thoughts on the amount of work carried out on those aeroplanes at Brough, long after the production lines had closed.

Initially, a metal nose that had first been flown on A&AEE S.I XN927 was resurrected for Nightbird. The whole nose structure of XV344 required re-stressing for this and the mass of equipment installed.

Expanding and monitoring the Buccaneer fatigue life was another major activity at this time. After the accident involving XV345 during a Red Flag exercise in February 1980, the fleet was grounded. Fatigue cracking in a hidden part of the inner wing was found to be the cause and this affected a large portion of the RAF fleet.

The only Buccaneer to fly regularly at this time was also pictured in your article. XW988 flew from HOSM on a strain survey programme. (The Hull Daily Mail ran headlines such as «Nuclear Bomber on secret test flights»!) The fleet was returned to service following a thorough investigation, including extensive analysis and three residual strength tests on cracked wings. This lead to definition of detailed inspection and inner wing replacement programmes to enable the fleet to resume active service.

The Buccaneer fatigue problems had developed from a number of minor changes and the inevitable weight growth that occurs to any airframe during its service life. These could not be Fully represented on the original Full Scale Fatigue Test (FSFT). One ‘minor’ improvement to the Buccaneer S.2 was the introduction of flared wingtips. These were found to slightly increase the wing root bending loads. However, a 10% increase in stress level is generally assumed to halve the life of a component; hence, even small changes can have a significant effect on the fatigue life of an aeroplane structure. This lead to a second FSFT utilising XN982, a low-lifetime former RAE trials airframe. The work done on this new test established Brough as the BAe ‘centre of excellence’ for structural testing, and a world leader with many advanced projects currently running.

This then relates to the letter by Debbie Haynes regarding Tornado wings ‘flexing’. The effect of wing stores is that in symmetric manoeuvres, the store inertia opposes the wing lift to reduce the wing root bending moment (at constant aircraft mass). However, pylon and wing loads in asymmetric manoeuvres may become critical. On any fighter, a number of other factors are as important, such as the effect of pylons and stores on handling qualities and operational limits. You don’t want a fighter to become slower to manoeuvre due to higher drag and inertia! So it is possible that some outer wing mass on the Tornado (the pylon) is to relieve wing root bending without excessively influencing the performance.

I believe that wing fuel management was first used in the Valiant fleet following discovery of major fatigue problems to reduce wing bending loads, i.e. the inboard tanks were emptied first. Modern airliners use fuel management for wing loading and also for trimming, so that control surfaces can be reduced in size.

The final cleared life of the Buccuneer was raised to 260FI (100FI = 1 design lifetime) by extensive analysis and testing. Let’s hope Warton has similar success with the Tornado.

J W Parish

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