Tag Archives: fatigue testing

Gearing up for a big day…

As Mission Controller Shane was away last week and the AMRC was very busy with the exciting budget day reporting hosted by Sky News here at the Advanced Manufacturing Research Centre, the team decided to spend last week re-boxing up the aircraft with insulation and heaters ready for a set of ultimate load testing this week.

The second life fatigue testing was completed successfully the week before and now that the Mission Controller Shane is back, he is currently validating the testing programmes for this week’s testing.

This week’s ultimate load tests will consist of a residual strength test where the Game Bird 1 is pushed up and pulled down on the Whiffletree rig to 72 degrees, applied by a load of 64.5 kilo newtons; the same forces applied throughout the fatigue testing.

Once complete a heated static ultimate load test will pulling down the plane on the rig first with a force of 82.65 kilo newtons, then the aircraft is pushed up on the rig plus 15 per cent of that force.

As we are still experiencing some play in one of the wing pins, Game Composites are currently assessing whether they want to complete some repairs to the damaged bushes this has caused before we go ahead with the testing tomorrow, so Game could well be back on-site with us this afternoon.

As well as Game, the Civil Aviation Authority (CAA) will also be present on-site to witness the tests and we will update as soon as possible, hopefully with some video of the nerve-wracking testing, so you can experience what the team go through when putting the Game Bird 1 through its paces!

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The Game Bird 1 boxed up and ready to go!

 

Plane sailing

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!

Stanley knives and Saturday Morning Kitchen

We starting running the second life of the fatigue testing cycles on Friday and to our delight it ran beautifully well, so ran through Friday night as well. Set designer Steve gave up time on his Saturday morning off to come and shut down the rig safely for the rest of the weekend. Always absolute dedication from us here in ASTC could cause us to miss Saturday Kitchen Live.

We came back in on Monday and started our usual rounds of inspection to find that the engine attachment bracket (the bracket that takes the main load up into the wing spars) was starting to show signs of cracking.

The solution was to take it off, do some hasty cutting up of bits of box section we had and got the whole thing welded up much stronger with the help of our friends at Nuclear AMRC. This time we’ve really gone to town and beefed the bracket it up to help ensure it won’t happen again.

It was ready to reinstall this morning and we are ready to continue with the fatigue testing again today. We have already clocked up about 20,000 fatigue testing cycles out of the 71,633 required for the entirety of the second life testing, so we are getting through it quite quickly now.

Luckily for ourselves and Game Composites, nothing untoward has happened so far during testing with the extra damage we have caused the airframe. Game Composites came in late last week and did some repairs to the rear stabiliser of the aerobatic aircraft because we had noticed a little crease was developing.

It’s quite remarkable the aircraft can be repaired. A Stanley knife is used to cut out the damaged patch of composite material on the fuselage to reveal the foam layer in the middle. The foam is removed and smeared with glue, but not just any old glue is used; the glue has what only can be described as lots of hollow tiny glass balls in it, making it lightweight yet very strong. This replaces the foam and a patch is stuck over the top with resin which we leave to cure overnight.

As the aircraft being hand laid-up (or built by hand), it’s relatively easy and cheap to repair, as any repairs can also be done by manually without having to send it back to a manufacturer. As it would at the hanger or in the field.

With the repairs to the engine bracket made, we will be back up and running with testing today and we will hopefully conclude the second life fatigue testing next week so we can get ready for further testing. Exciting things to come for us!

Passed with flying colours!

Today was a great day! Last Friday, after all the ups and downs, we finished all the fatigue testing after we reached 71 633 cycles.

With this complete it was time for us to move onto the ultimate load test, performed once before, where the aircraft gets boxed in insulation and heated up to a toasty 72 degrees Celsius. This definitely helps take the edge of the February chills we have here in South Yorkshire.

So with the airframe all boxed up as you can see in the picture, we were all ready for the residual strength test to 64.85 kN which the airframe had no trouble getting through.

When this first pre-load test was complete, we moved onto the static ultimate load test which took the Game Bird 1 up to 82.65 kN. This is the highest loading that the airframe has seen to date, so it was a tense time for all involved. The Game Composites team were on site during the testing today, so we were all feeling the pressure!

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The Game Bird 1, boxed in insulation for today’s ultimate load testing.

 

Fortunately relief spread across us all when the airframe passed with flying colours. There was the odd creak which was expected, although this didn’t help with the tension levels when we were all watching!

It has certainly been a very exciting week for us here at the AMRC and guided by the Civil Aviation Authority (CAA), it is now time for us and the team from Game Composites to decide what’s next when it comes to further testing for the Game Bird 1 aerobatic aircraft!

Stay tuned!

Sometimes good things fall apart, giving us a chance to build better for the future…

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.

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The sheared bolts from the engine mount bracket

 

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The failure ripped through the weld on the bracket

 

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!

 

Making sure we have the perfect fit

After everything had been running smoothly last week, we began to notice an increase in movement and creaking of the air frame on the rig which we wanted to investigate.

Our client came in to also see what was going on and together we both decided to take off the wings of the Game Bird for a closer look. We re-looked at the bushings in the wings and realised there were a few tweaks we could make that would hopefully solve the unnecessary movement and creaking sound so these were changed and re-installed.

We also noticed on there wasn’t quite a perfect fit on the pin used at the front of the rig which was contributing to the unnecessary movement we had been experiencing. This was because it had been laser cut, which has the tendency to be a bit rough around the edges!

To solve this, we bored through with one of our lovely machines to make a bigger hole and fitted a brass bush so we could just push that onto the rig and the pin would go straight through it. Now we have a nice, tight-fitting pin which has reduced the creaking, so we are very pleased with the outcome.

All in all, everything took us about a week to complete but we are now back up and running.

Mission controller for the project, Shane, describes the plane running as “beautifully” so we have a very happy office. The alterations have made a great difference to the control so the movements are more progressive.

Shane decided to leave the aircraft to run through the night and has a webcam which is used to check the aircraft when it’s left to run alone. Unfortunately Shane has been checking it constantly through the night, much to his wife’s despair!

The plane did indeed run beautifully which was great news and this greatly increased the speed at which we are progressing through the fatigue testing cycles, having now completed 50,708 out of 71,000!

Here’s a quick video of the Game Bird aircraft during fatigue testing on our new and improved quieter and smoother rig…

 

We are going to run it through the night again which means we will be fast approaching the end of the fatigue testing cycle, when we will have another ultimate load test at high temperature to complete. Stay tuned for more news!

Business as usual here at the Advanced Structural Testing Centre…

Everything is working as it should this week here at the centre and we are rapidly accruing cycles in the fatigue testing of the aerobatic plane.

So it’s business as usual and on with the show. We are now halfway through the fatigue testing having gone through 36,000 cycles and have started running extended cycles of testing setting the rig to perform from 6am until 10pm at night.

Should we get good performance from this rate of testing, we will return to setting the rig up overnight to clock up some more testing cycles.

Watch this space!

Even the best laid plans…

We’ve had a fairly good week at the Advanced Structural Testing Centre since our last post. As mentioned the customer visited us to see the aerobatic aircraft in action on the whiffletree testing rig to check out an unusual creaking sound and to review the data sets captured every 10 cycles of fatigue.

The aircraft is assembled on the whiffletree in an asymmetric way to induce twisting into the wings and fuselage as the load is applied. To achieve these torsional loads, it is necessary to mount the whiffletree on the right wing in front of the centre of pressure (CoP), to induce the correct amount of ‘twist’ in the left wing that is mounted slightly behind the CoP. Loading in front of the CoP wouldn’t happen in normal flight.

This means the right wing is not being tested representatively (it is being over tested). As the root spar of the left wing is smaller, which is the critical wing for testing; so if the left wing is good and the identical right wing with a bigger interface will also be good.

As the right wing is carrying this forward CoP twist it was necessary to put some patches on to stop the flexing of the skin inside and stiffen the assembly, hopefully preventing the unusual sounds, data and make the test run smoother.

The fatigue testing continued on Friday and Saturday morning and on Monday we felt confident enough to let the testing run through the night.

We set the testing cycle going at 4.00 pm and as all good parents do – kept a keen eye on its progress via a webcam – we do like to know what our children are up to! Just after 10pm the shutdown lights came on as the rig was no longer running. A brief investigation on Tuesday morning found the reason for this was a fatigue failure of a rig part.

The part was the thread of an adaptor where the actuator is joined to the load cell; this had fatigued and broken so the actuator could no longer put the loads onto the rig.

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The MOOG controller had then automatically shut down safely. As the actuator became detached it fell onto the engine fairing attachment beam below the representative engine mount causing some damage DOH! This is the worst nightmare of the test engineer! Fatigue testing really does discover every little issue with the entire system.

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The damage has not caused any structural problem to the aircraft and the customer was more pleased that we had tried to run through the night to get the test completed more quickly. Repairs were made by the customer on the same day.

We are now modifying the back end of the load cell to change the broken part to a larger diameter, this is so it will connect directly onto the actuator, hopefully minimising the risk of this failure reoccurring.

The larger diameter part is currently being machined by our AMRC apprentices based onsite at the Knowledge Transfer Centre workshop. A great advantage of being so close to our other centres here at the AMRC is the ability to collaborate closely with our colleagues and our customers, allowing us the flexibility to modify and repair parts at short notice. The apprentices are machining the modified part which should be back with us by the end of Tuesday, allowing us to start testing again on Wednesday if possible.

We are now just under 30 per cent of the way through the testing cycle, so once the modified part is fitted and we are running the fatigue testing cycles day and night, we should run through them fairly quickly!

 

The cycle that broke the camel’s back

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.

Engine mount damage copy

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!