The fatigue testing has been running really well, practice makes perfect as they say! We’ve been busy changing all the joints of the Whiffletree and replacing the engine mount bolts. This is done at approximately 60,000 cycles. We learnt some lessons during the first period when we had rig failures and bits breaking, but this means the second time round, we can monitor things better and avoid this from happening again. In addition, we made a plan with Game Composites to change certain rig components as a matter of course.
We’re currently at 61,500 cycles and we have to get to 71,663. When we run a 24-hour period it gives us 8,640 cycles, so in running another 24-hour period we will be left with only 900 cycles remaining before we reach the finish line and the golden number of 71,633.
Once we’ve reached the 71,633 cycles, this will also us to begin boxing up the airframe in insulation and the week commencing the 21st we will be doing another ultimate load test at 72 degrees Celsius and then a further ultimate load test at a 15% higher load. It will be getting hot in Catcliffe! So keep checking back for exciting news!
Our client, Game Composites, have been liaising with the regulator, the Civil Aviation Authority who is doing the certification for Game Bird 1 aerobatic aircraft and a plan has been developed to damage the airframe and then test it to see how the structure withstands this damage.
This is to replicate what could happen to Game Bird 1 in a real-life situation, for example, if it were to be stored in a hangar and it was to be damaged without anyone noticing whilst inspecting the plane. The testing we’ve already completed has qualified Game Bird 1 for 30 years of air worthiness certification, but with the damage testing we are going to do, this will help further help the plane gain it’s certification.
Game Composites have been on site whilst we have been damaging the airframe. There are seven points around the plane which are to be damaged from different heights and at different energies.
To do this, we fixed a ball into a bag and tied it to a rope and attached it to a crane over the aircraft, all very high tech at the Advanced Structural Testing Centre! Hovering the ball over the targeted point and graduated the string in metres meant we knew how high up we were suspending the ball to drop it onto the marked targets on the airframe.
Damage has been caused on the tail stabiliser and the wing and we then proceeded to run a few hundred fatigue testing cycles. Unfortunately but we got some rather unpleasant and unexplained noises. After a little bit of thinking about things we realised that when heating the airframe to 72 degrees for the ultimate test we had probably baked the grease off the wing pins and the engine bracket interface pin – the joints were running dry!
We were also concerned that we have got a little bit of movement in the engine mount, because over a period of time during testing it has elongated the holes in the composite material forming the aircraft. Not a lot, but enough that the bracket it moving and creating noise. So today we have taken that load bracket out and Game Composites are going to do the repair on these holes by filling them in with resin and putting the bolts back in. Then it will set and take all the play out.
We have slid the big bolts back in the wing spar to clean them up, add a little more grease, and then slide them back in. Hopefully that will cure the groaning noises we are experiencing.
If this all goes as planned today, we are hoping to start running the new set of fatigue testing cycles through the night again; much to Shane’s wife’s delight with his constant checking of the live feed webcam when he’s at home!
ASTC’s fact of the week
Concorde’s first flight was 40 years ago today in January 1976!
Its maiden voyage flew passengers from London to Bahrain in complete luxury, serving champagne, lobster, caviar and fillet steak during the journey.
Concorde flew passengers at supersonic speed during its lifetime, meaning a trip from London to New York was reduced from approximately seven hours to only two hours and fifty-two minutes!
After the Christmas break, we are back up and running again here at the Advanced Structural Testing Centre. Testing is in full swing and we are currently just shy of reaching the 10 per cent mark in the current testing cycle we started just before Christmas. We have a long way to go yet but that doesn’t faze us. During the testing cycle we hear regular creaking from the airframe, but our ears certainly prick up when we hear something new and the aircraft has been making a few unusual noises we are not familiar with.
A creaking sound has been detected at the bulkhead of the aircraft where the baggage compartment is situated, so the client has come up to the Testing Centre to inspect the aircraft and see if they can shed any light to why this may be occurring.
Part of our job is to flag up anything out of the ordinary that we may find during testing and pass these on to the client. In addition, as our role is to test the aircraft and then provide the client data. The majority of our data that is logged onto graphs is consistent and symmetrical, but we get the odd data set where there may be an unexpected spike in the results and flags up a query for us to pass on to the client.
The client will then analyse this data and compare it to their model and give them the chance to inspect the airframe during testing, whilst the aircraft is active in the testing cycle.
For the previous two days, System Services have been at the ASTC. System Services are a technical support company for users of fluid power motion control systems who besides ourselves, work with major international companies such as BAE Systems, Jaguar, Moog and Rolls-Royce.
As we run the testing cycles for the aerobatic aircraft constantly, our hydraulic ring main system and power pack are under constant pressure. These systems have filters on which must be regularly maintained, so the oil within the system is cleaned constantly and meticulously. We have a three micron filter in place meaning there will be no dirt or sediment within the system bigger than three microns. Due to this, we use a specialist company such as System Services who specialise in the maintenance of test systems.
We work very closely with Steve Barrett from System Services as he has an immense wealth of experience and knowledge of the maintenance of test systems, so this gives us the chance to pick his brains whilst he is helping us out here at the ATSC. Shane has used Steve and his knowledge for 30 years after he worked alongside test systems based at the University of Sheffield. Besides his work involving the maintenance and calibration of test systems he also works as a trainer with a wealth of experience, so if we experience something we are unfamiliar with, there is a likelihood Steve will have had first-hand experience of it can help shed a bit of light for us.
As our systems are operating in tip-top condition, we will carry on running through the testing cycle as planned, ready to make any modifications requested by the client should their investigations into the unusual noises we picked up require it.
ATSC’s interesting fact of the week
On this day in 1745 Jacques Etienne Mongolfier was born.
With his elder brother they would go on to demonstrate the first ever flying machine in 1783 first carrying a duck, a sheep and a rooster. Later that same year Jacques Etienne became the first human to lift off the surface of the earth in a tethered fight of a larger balloon!
What a legacy he left behind!
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.
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!