Wednesday, 5 December 2018

Maintenance matters, fuel leaks and TPS (again)

I'm pleased to say that yesterday G-FUUN passed it's annual inspection again, so it's good for another year.

Unfortunately I've also had another series of fuel leaks.

I had originally thought they were only coming from the Ali end plates - specifically the central bolt through the fuel sender that tightens the plate (via an ali tube with a thread inside the tank) but as it turns out that was not the only cause.

I've since replaced the ali end plates with new ones and ditched the fuel senders altogether as I now have solid state fuel sender probes. The rubber seal on the Falcon gauges was changing over time and caused some leaks.

The other thing I've done to improve the end plate sealing is making up some thick rubber washers which have a slightly undersized hole drilled in them. Screwing that onto the thread and then putting a large metal washer in front on the outside helps to seal things better than just relying on Proseal. I also made up a smaller washer for the inside which is squeezed between the plate and ali securing tube.

No leaks from the plates anymore!

However recently I got another fuel leak, very small, just weeping out, but very annoying as it took me some time to find out where it was coming from.

To start with I thought it was further up the tank and fixed that supposed hole from the inside with flock - see pic below.

But that was not the cause.

I then bought a UV dye kit which consists of a UV dye and a UV torch. You mix the dye in with about 10 litres of fuel then pour that into the tank. Wait a while then in the dark shine the UV torch and you are supposed to see only the fuel and find out where the leak is from.

Well this did not really help and I ended up leaving it feeling quite frustrated as it still was not clear where the leak was coming from.

When I came back to the job the dye had actually helped as it is orange and visible in the daylight too so does point to where the fuel has been.

A tell tale orange mark from the underside of the wing near the drain finally pointed me in the right direction. It was the ali plate that is bonded into the tank and lower wing skin that was the problem. So I used runny flock to fill in the cavity around the drain and overflow/breather fitting on the inside. Being runny this found it's way into every nook and cranny of this area and sealed up the leak good.

No more leaks again (for a while anyway - fingers crossed).

I will do another blog post about the fuel senders when that is finally sorted as it too has been a bit of a saga and is hopefully soon to be resolved. The manufacturer has admitted to a faulty set of modules for these and the replacements are finally here but stuck in Customs at the moment. 

Finally the Throttle Position Sensor - it has started to fail on me again. Happening when I took of from a bumpy hard runway the other week at Great Massingham.

I checked when I got home and found that it has failed at almost exactly the same number of hours as the previous one - 123 hours approx.

Ironically the next week UL Power released a Service Bulletin which said they are no longer fitting this type of sensor to any new engines in the future. Which to me says they admit there is a problem! 

They are converting to a Hall Type sensor - which does not have the sensing parts touching so therefore is much more robust to the vibrations of an aircraft engine installation.

They are offering the Hall Type sensor as a mod to us older engine users but at a price! Around £600 which is a bit cheeky considering the Hall Sensor is a £25 part. True a new inlet block is needed and an ECU remap and additional wire but £600 is a bit rich.

G-FUUN with it's clothes off for it's annual inspection. It passed again 'without comment'.
New fuel sensor probes - more about those in another blog post.

Fuel tank end plates - now without the Falcon senders and with rubber sealing washers.
Rubber washers I made up to help with the sealing of the fuel tank end plates. These are working well.

Port wing off to fix this fuel leak.

I thought it was coming from this 'hole' part the way up the tank.

Which I fixed with flock but it turned out was not the cause of the leak.
This area around the drain and overflow/breather connections was the cause of the leak and has been fixed with runny flock allowed to run into the area. 

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