Tag Archives: damage tolerance

Time to break things!

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!

Tubes + balls = damage

It’s been another busy work at the ATSC!

The fully assembled plane!The wings are now on the aeroplane (Yay!!)…… but we’re now taken them back off! (Boo!)

The client visited our workshop last Friday to put some damage into the structure of the plane – this is all part of the tests we’re carrying out and the reason that it’s done is to investigate the ‘Damage Tolerance’ of the aeroplane.  If the aeroplane is hit during operation or tools are dropped onto it during servicing it may cause damage to the composite structure. This damage may be invisible to the naked eye but may have caused disbonds in the layers of composite. If the airframe is capable of still meeting the fatigue test with these damages introduced at the start of the test it is assumed that it will be good whilst in service. During the tests we will monitor the points where the damage has been applied to see if the surface/structure shows any sign of the damage increasing.

Drop testingTo create the damage a steel ball is dropped from a known height onto the surface of the aeroplane. If we know the height, weight, and the acceleration due to gravity (g) we know the potential energy (PE) the ball has – physics tells us this is mass x g x height. The formula gives us the PE in Joules and we make the assumption that all of that energy is transferred into the structure of the aeroplane. The impacts were carried out at three different energies so the ball has been dropped from three different heights via three different tubes cut to the appropriate lengths.

On completion of the impact damage routine we then assembled the wings onto the fuselage however the client then decided that some additional damage should be applied to the wing spar so the aeroplane is currently being disassembled.  Hopefully we can re-assemble it in the next few days and then do The Big Flip next week (we’ll keep you posted!).

In other news we’ve maintained our UKAS accreditation for flexible scope testing following our annual surveillance visit! This is an independent assessment of our testing and having this accreditation means that any customer can be sure of our test methods, and that the data that we supply back to them is traceable to an internationally used system of measurement (The SI system)  Well done team!

Photos from top: The aeroplane with wings attached!,  one of the wings with marks of where the damage has been applied (the damage is often invisible to the naked eye).