Thursday 31 January 2019

Canopy repair - again

In December the Twister had it's annual inspection and after sending off the paperwork I did not get anything back through the post - the LAA normally turnaround a Permit the same day if all is in order.

So after a week I phoned the office and was told - "Oh yeah that's on hold as there is a Repair that has not been approved yet".

This Repair was the one done to the canopy frame and hinges after I got back from the Oshkosh epic in 2017. The Repair paperwork was done to satisfaction (or so I thought) in February of 2018 - so what was the hold up?

Their excuse was that they never received the email I sent which contained all the photos and answers to their questions. Quite frankly I do not believe this story as if the email did not arrive then it would have bounced back to me - which it didn't. It is clear that the LAA don't have any kind of system in place to ensure something is not processed internally. I had assumed all was well as I had not heard back about the Repair.

Anyway on sending the email again it was swiftly approved - except now I had to get an inspector to look at the repair and sign off what I had done - more paperwork!

So I arranged an inspection and he discovered that the reinforcing carbon I had used to thicken up the hinge brackets was cracked at bottom end - not surprising since I had done this repair 'in the field' and so the reinforcing had a weak point which was at the end where it was not really bonded to the existing hinge as it was just butted up to it.

Actually I was happy in a way to have another opportunity to repair the hinges properly this time, so I decided to take the canopy off and repair it at home.

I started off by taking away some of the reinforcing carbon, totally so in the region where it had cracked.

I then made up two small blocks of wood that would sit inside the hinges and allow a clamp to force the carbon up into the corner where it had cracked before - thereby ensuring a complete bond this time round.

The back hinge was not cracked but I decided to do this repair to both hinges anyway to make them right.

The front hinge got a further layup of 3 layers of carbon in a strip which was laid over the entire surface - see pics - to closeout the layup and add even more strength to the hinge. The front hinge is subject to much more flex than the rear one due to it's distance from the retaining wire which supports the rear hinge much better as it is closer to it.

After the carbon work was done I primed and painted the whole area, making a much better job than I did before.

The canopy is now back on and signed off by my inspector - I am now waiting for the Permit to arrive but this has taken more than a week already. In the meantime I have used the time to touch up a few things here and there but hope to get the Permit soon.

If I could start from scratch and build again I would consider reinforcing the inside of the hollow canopy frame with runny flock in the area around the hinges. I would also take away some of the micro in this area and replace it with carbon and also reinforce the hinges as I've done here too.

Canopy off and at home to do the repair - a much better idea than trying to do it 'in the field'.

This shows the crack that developed in the end of the carbon reinforcement - it was just butted up to the end and therefore not really bonded to the round portion of the hinge.

Two blocks of wood, shaped to fit and wrapped in Duct tape to release, enable clamps to force the new carbon reinforcement into the corners of the hinge.

Many layers of carbon were used here - it is easy enough to take away any excess afterwards.

One further step with the front hinge with a layup of more carbon over the entire hinge to close out the reinforcement.

Front hinge with it's new reinforcement. Much stronger now.

Rear hinge. You can see that the carbon has added about double the original thickness of the hinge so now it is 3 times as thick overall.

Time to prime.

Front hinge after paint and back in place on the aircraft.

Outside looking better now - I have since feathered off the edge of the paint too.

I am a donkey

I tried moving around an oil hose recently and that required me to first drain the oil. 

I ended up having to do that twice and each time I did not bother to use a new copper crush washer on the sump plug, also I was not using a torque wrench on the sump plug and have been over tightening it as a result - made much worse by the use of an old washer which provides no 'feel' as to the torque as it does not have any crushing properties once it has been used.

So I ended up stripping out the thread in the sump!

What a donkey...

I discussed the possible fixes with Jonathan the UL Power agent here in the UK and decided that a new sump was the best fix - particularly as it ended up being cheaper than a Helicoil type kit to fix the thread (the best versions of this coil - TimeSert - are very expensive).

So I've had to put a new sump on. In doing so it gave me a chance to see inside the engine. 

I noticed the cam lobes had a bit of wear on them which did not look right to me - the engine has just over 300 hours on it.

I consulted Jonathan about this and he shared it with Patrick in the factory too. This was his response (I also asked about the exhaust valve pic below too).

"Morning Andy

Feedback... 

1. Wear on cams nothing to worry about.  A bit more than normal.. but OK.  (Always check your oil filter mat and magnetic plug for material tho!)

2. Your valve picture... apart from evidence of a tiny leak due to uneven bolting of the exhaust manifold the rule of thumb is 'uniform burnt pizza is good'.

Here is an unofficial  guide to valves..

White deposits from lean  / hot
Black deposits from rich / cool
Brown/reddish burnt pizza is Goldilocks  zone 

With the caveat of 'uniform distribution '

Green is bad. Holes are bad. Uneven is bad.

If your compression/leakdown us good and CHT / EGT good you are a winner! 

Normally all 4 exhaust valves should be similar in appearance.


I wonder if this wear was caused by all the Swarf that was present in the engine, when it was new, after machining? - as evidenced in the first few oil filter changes when checking the filter element (if you remember).

Anyway some lessons learnt. Particularly about always using a new copper crush washer and using the correct torque values - 25nm for the sump plug. All the torque values can be found in the Illustrated parts manual from the UL Power website.

Thread stripped out by Mr Donkey - me.

Old sump coming off - took a few 'love taps' with the rubber mallet to come away.

Oil pickup in the old style iSA engine. The long threads limit movement of the pickup.

A chance to look inside the engine.

This cam lobe wear did not look right to me so I asked.

Another lobe with wear. Strangely the front No.1 Cyl lobe did not appear to have any wear.

Overview of the cam.

Wider view of the above.

No.1 Cyl exhaust valve - even 'burnt pizza' is good. The other 3 looked just like this one.

New sump in place.