This week the team have completed the ultimate load test on our aerobatic aircraft under heated conditions. The test involved applying 82 Kilo newton’s (kN) of force through the load mounting bracket that acts through the main wing attachment points. The load is spread through the airframe and reacted down through the Whiffletree all under heated conditions of 72 degrees Celsius!
The ultimate load test involved loading the airplane up to replicate positive and negative g forces of 15 g. This load was applied just once in each direction and is the biggest load test the plane will complete.
It is a pivotal point in the testing programme, and takes the airframe to 150 per cent of maximum operating load so it was ‘squeaky bum’ time for the aircraft designers and a real relief that the test was passed successfully.
So we now have a green light to go ahead and start full fatigue testing as soon as we have made some modifications to the Whiffletree requested by the customer. We’ve installed some steel metal reinforcements to the engine mount block to ensure that the load is spread evenly through the engine mounting interface on the aircraft.
The reinforcements were laser cut by our friends at the AMRC Design Prototyping & Testing Centre and welded by our Nuclear AMRC colleagues. So we’re in good shape to start the fatigue testing cycles in earnest, getting as many cycles as possible completed before site shut down for two weeks over the Christmas break.
The full fatigue testing programme is made up of 71,633 ten second cycles of +/-10 g. This will take five weeks if we run the programme eight hours a day. These testing cycles have to be constantly monitored to ensure we are hitting the loads, that the data being received from the strain gauges is correct and to visually inspect the aircraft as testing progresses to make sure no cracks appear in the structure.
Luckily the team will be sustained by a multitude of festive snacks that have been appearing in the office this week, including mince pies and Quality Street chocolates. Although half a tub of Quality Street chocolates disappeared this morning and the finger of suspicion has been pointed at the mission’s best boy, Ed. Whether the accusations are true or not will require more verification, stay tuned.