After having a great week last week running the Whiffletree through the night and flying through some more of the fatigue testing cycles, we unexpectedly encountered a failure of the bolts connected to the engine mounting bracket.
That area of the aircraft is more highly loaded during testing than it would be in real life when in-flight, so it is running through the fatigue cycles in an ‘over-test’ situation. Unfortunately the bolts, which are grade 12.9 high tensile bolts, simply weren’t strong enough and had fatigued over time.
The failure caused the bolts to shear and pop off the rig, allowing the engine mounting bracket frame to bend, ripping through the weld and bening the arm of the bracket out of line.
All testing stopped without any damage to the aircraft and we had to remove the whole front engine mount bracket to grind the entire weld out. This took Mission Controller Shane an entire day before we could then pull the bracket back into place and tack weld it together ready for re-welding.
The bracket was sent to our Nuclear AMRC colleagues who welded it back together on Monday. When it was returned we had some re-fitting to do, as the re-welding was done to both sides of the bracket instead of one this time. This caused the bracket to close up slightly from its usual shape so we had to jack it out to make sure it would fit.
The extra strength should serve us well as the fatigue testing continues, so taking the bracket off turned out to be a good opportunity to make some improvements and plan for future preventative maintenance; such as changing the bolts on a more regular basis.
The rig was back up and running this morning, so we conducted a 30 minute test run to bed the rig back in. We will then go round the rig, tighten everything back up and make sure nothing has moved out of place before resuming full testing again this afternoon and evening.
So even though we are only up to 54,400 fatigue testing cycles, should today go as planned, we could be back on 24 hour testing as early as Wednesday; maybe even finishing the fatigue testing completely by Friday!
Pop back next week to see what happens!