Double trouble

I’ve been trying for what seems like weeks now, because it actually is, to resolve the problem with 24ZN’s, my X-air’s, fuel system. Readers might recall that a few weeks ago I took off to make a flight to the north around Périgueux and was dismayed that shortly after take off its engine coughed, spluttered and threatened to cut out before I was able to make it back to Malbec.

The problem was due to fuel starvation caused by low fuel pressure and since then I’ve taken several measures that I think should have solved it. I’ve not been able to confirm this, however, because although I’ve done several long high power engine runs since then, I’ve only managed one take off and landing which was before I’d completed all of the changes that I wanted to and that was not long enough to confirm that all is as it should be.

With an issue like this, you always hope that you’ll find a ‘smoking gun’, a single problem or fault that explains everything. That was the case when I had to deal with a similar issue before I flew 24ZN to France from the UK when I found that someone had fitted fuel tubing of too small a diameter to feed two carburettors at full power, but as I’d replaced most of the old tubing at that time, overhauled the fuel pump and thoroughly cleaned the carbs, I didn’t think that that would happen again this time.

And so it has proven, or at least I think so until I can do a proper test, but until then I’ll go through and explain the steps that I’ve taken. The first thing I found was a length of ‘new’ in 2019 tubing that demonstrated a large amount of cracking that I thought might have been able to allow air to enter the system, causing the drop in fuel pressure. However, after replacing it I cut it open and found that the cracking did not go right through, so in fact it was still fuel and airtight.

Later I found a second length of ‘new’ tubing and the same applied to that, but it convinced me that although I’d only replaced the ‘bad’ tubing three years ago, I should go ahead and replace all of the tubing in the system while at the same time replacing both of the in-line filters that I also only replaced three years ago, even though the aircraft had been very little flown in between. In doing so, I came across a couple of factors that undoubtedly contributed to the low fuel pressure problem.

The outlet from the fuel tanks connects to the first in-line fuel filter, a large plastic one, which in turn connects to a ‘T’ piece connecting the filter to the electric fuel pump and the hand primer bulb. I didn’t touch that ‘T’ piece in the UK while preparing 24ZN for its flight over and when I examined it I found that (a) the tubing connected to it was all very old and (b) the clips securing the tubing to the ‘T’ were also all old style crimp type.

This indicated to me that most likely that ‘T’ piece and the tubing had been in place since 24ZN was built some 20 years ago and further examination revealed that it was wet with fuel, meaning that one or more of the joints were leaking. So here was the first candidate contributing to the reduced fuel pressure problem. I’d already bought the tubing to replace all of the old stuff , although this still left the length from the tank outlet to the filter to be replaced as soon as possible, when the fuel in the tanks has been reduced to a low enough level, and here are the results.

I then went on to the hand primer bulb. When I pumped that I found that it was no longer effective in pressurising the system and in fact it was blowing bubbles back into the fuel filter, indicating that its internal non-return valve was no longer working, probably because it had been damaged by alcohol in the fuel. As I hadn’t replaced that while in the UK, because at that time it was still effective, I thought that both it and the length of tubing connected to its outlet should be renewed.

I then turned my attention to the electric fuel pump. This pressurises the system as it should, but I found that as well as allowing fuel to pass through it when static to feed the engine, its seals also allow fuel to blow backwards towards the tanks. This shouldn’t be a problem however, since as long as the pump can pressurise the system in an emergency, it’s otherwise only used to prime the engine before starting. I did replace the tubing running from its outlet, however, and this brings me to the next issue I found.

The outlets from both the electric pump and the manual primer bulb connect to a second ‘T’ piece which in turn connects to the fuel shut-off valve and the main fuel line. Lo and behold, when I checked this ‘T’ piece, although I’d checked it previously when in the UK, it was also leaking fuel. However, as I already had new tubing and hose clips ready to replace the old kit, this wasn’t a problem and with the new parts in place, that issue too was resolved.

So hopefully, the two leaking ‘T’ pieces that I found will turn out to be the source of the engine’s fuel problems this time around. The engine runs that I’ve since done seem to indicate as much but more testing is necessary before putting the problem to bed. But unfortunately this hasn’t so far been possible because it appears that the new battery that I fitted to 24ZN back in 2019 has given up the ghost.

Starting has been a constant problem and the battery has been losing cranking power surprisingly quickly. Things came to a head today when after having charged the battery overnight, not only couldn’t I get the engine to start, but after only a short while cranking it, the battery’s power collapsed to a level that wouldn’t even turn the engine over. So that’s it until I can get a new battery delivered.

But no problem, I thought. I topped F-JHHP’s tanks up only just the other evening, so while the weather was on the cool side and still calm, why not pull it out and do the flight in that instead? As my Savannah has rather sadly been relegated to the back of the barn while I’ve been trying to resolve 24ZN’s problems, it has become very dusty as I was unable to make the new covers for it that I’d bought the fabric for, before leaving my old house. But after tipping it onto its tail and cleaning its horizontal surfaces with a soft broom, it was ready to be checked and got ready to go. I even returned to the caravan and picked up my Go-Pros that I also mounted ready for the flight.

Eventually it was time to start the engine, which it did after a few turns even though the Savannah’s battery is considerably older than the one in 24ZN. But then, horror of horrors, the aircraft began to roll forward and when I hit the brakes, they had no effect. Luckily I’d started on the flattish area in front of the barn and although I killed the mags immediately and F-JHHP continued to roll unchecked on what was now a slight down-slope, there was enough room to swing around to the right and come to a halt before anything untoward happened.

So the extremely hot weather that we had while the Savannah was in the barn has turned out yet again to be totally unforgiving and has resulted in its brake fluid being expelled from the hydraulic brake system. This happened after extremely hot weather once before, when I flew back to the UK and only found that I had no brakes when I landed at Blois and found that I couldn’t slow down to take the first runway exit. Luckily the runway was long enough to allow me to be slow enough to exit at the far end and coast up to the fuel pump by turning the engine off as I approached it.

I ended up replacing the brake fluid at Headcorn in the UK and had to devise a system using a hand-pressurised oil can to do the job. I never thought that some six years or so later I’d be repeating the process and I’ll have to dig out the oil can and tubing, which I still have and came across again in my storage just the other day.

So there you have it – double trouble, two ULMs and once again, neither of them flyable. It looks as though I’ve got a busy week ahead of me because as well as these two problems, I also have to arrange for an ‘élagage-grimpeur’ (a climbing tree pruner) to come in and remove the branches overhanging the floor slab of my house and deal with a UK family problem. Isn’t retirement wonderful. So restful…