This week we have been running fatigue testing on our aerobatic aeroplane. We managed to get up to 4,792 cycles out of a mammoth 71,693 before we had a slight technical hiccup…
The loading fixture on the Whiffletree broke due to a failure in the welding. This happened simply because of the continual loading and reloading of the forces applied and began to form a crack in the weld which grew until it eventually failed basically fatigue which is what we are testing the airframe for!. This isn’t forgetting that we are placing a significant load on the structure, +/- 63 kN every 20 seconds! Happily , our colleagues at the Nuclear AMRC quickly re-welded the loading fixture for us, so now we just have to reinstall it to get started with the fatigue testing again. This time, the join has been welded with a much deeper penetration weld than we were specified to start with, so we are very hopeful that this issue won’t recur.
Before anyone begins to worry, there was no damage to the aircraft itself because we had all our test limits tied down. This means when the airframe moves too far, more than it would move when it was cycling up and down, the digital computer control will shut down the cycling and return the actuator to a safe position. We currently only allow the loading actuator to move 3mm outside the specified range during its cycles before it cuts off.
In other news, Show Boss Phil got the chance to go down to The Royal Institution in London to watch the launch of the Soyuz rocket with British astronaut Tim Peake on board yesterday (lucky sod). He was also able to have a look through the archives whilst there and got to peek inside the notebooks of Michael Faraday and Humphrey Davy – not a bad Tuesday as far as they go!
Set Designer Steve and Best Boy Ed are very excited about the launch of Star Wars: The Force Awakens, no spoilers please! Of course, Christmas treats are still being consumed in mass volumes, now so much so, that project Director Lynn says she never wants to see another mince pie again.
We wish everyone a peaceful and joyful Christmas holiday and the team will have more Whiffletree news stories for you when we return in 2016!
ASTC’s interesting fact of the week
On 9 December 1972, the Apollo 17 mission was on its way to the last manned-mission to the moon. 42 years ago today the mission crew were halfway through a rest period, or having a snooze, during their lunar-coast on their way to land on the moon. They were so relaxed that they overslept by 70 minutes and mission control were unable to wake them as their earplugs had fallen out!
This was just over 52 hours into their mission after leaving earth, at this point the crew were 70,200 nautical miles from the moon.
Sadly the Apollo 17 mission wasn’t only the last time humans walked on the moon, it was also the last time humans have left low-earth orbit in the exploration of our universe!
The Apollo 17 mission broke many records, such as breaking the record for the longest total lunar surface extravehicular activities, the largest lunar sample return and the longest time in lunar orbit. Perhaps most interesting, is the fact that the mission was the first and only time a professional scientist has visited the moon, or flown beyond low earth orbit. Harrison Schmitt, a professional geologist, was assigned as the Lunar Module Pilot, rather than NASA training a pilot as a geologist.
The whole Apollo 17 mission is available to view in real-time, with over 200 hours of viewing at http://apollo17.org/
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.
ASTC’s interesting fact of the week round-two, a Sheffield-related achievement!
Did you know, that every single podium place from the last two World Championships and last two Olympics for figure skating, has been won on a pair of skates carrying blades made right here in Sheffield?
The blades are produced by Sheffield-company HD Sports which owns John Wilson and MK Blades. The company originates with Sheffield-based engineer, cutler and Royal Toolmaker John Wilson in 1696. John Wilson blades even provided skates for Queen Victoria and her husband in 1841.
If you are serious about your figure skating, you’ll probably be skating around the ice on a pair of Sheffield-made blades!
ATSC’s interesting fact of the week
This week in 1952 an estimated 4000 people died from the effects of a heavy smog! Reliance on coal fires from both industrial and domestic use combined with cold temperatures and an anticyclone led to the pollution hanging over London for a week.
A change in the weather led to its dispersal. The clean air act was drawn up and passed into law in 1956.
Today we see the problems on a global scale…
Since last week, we have flipped and realigned the aeroplane back on the Whiffletree (we have got it down to a fine art!). We are currently double-checking all the safety settings and limits for the new round of testing; we are always kept busy at ASTC!
The customer has paid us a visit to go through the static verification loads we tested last week in preparation for the aeroplane to be re-mounted back onto the Whiffletree. They were happy with the results and where the strain gauges were positioned ready for the full testing cycles.
Steve then coupled all the instrumentation back in and has done all the necessary checks to ensure that everything will work the way it should when we go back into the testing phase. He’s meticulously gone through all the wiring and initialising the strain gauges, if they don’t initialise it shows there’s a break or a faulty connection. Luckily for us, they’re all fine!
Using previous test data, we have been finely tuning the control system. After this, we will be in a position to run some small five kilo newton (kn) loads, which will help us further verify everything is working in the right way for the full testing cycles.
The client is visiting us on Thursday 3rd December, so we get the opportunity to go through a Test Readiness Review together and if we are both happy, we can sign along the dotted line, press the big red button and testing round two can begin!