Twisted: The Good, The Bad and The Ugly

First the good.

I spent Tuesday putting G-FUUN together at the airfield.

All went well, the tail planes I am very pleased with - how the mod works and the extra security it provides.

The next day (after moving 5 other planes out of the hanger first - as mine was at the back) I fueled up one tank and decided to do some engine runs and taxiing.

The good news is that the cowling and oil cooler scoop seem to be working very well. The oil temp on a sustained high power run (for 2 mins) stabilised and then actually came down a little bit to hold at 92 degrees. This is exactly in the middle of the required range of 80 to 100 degrees. I was not facing into wind either which I thought would be a better test for it. So far so good...

The cowling and sealed plenum are also doing their job very well. The front two cylinders were actually running too cold and were about 20 degrees cooler than the rear cylinders. I have some plates in front of the front two cylinders already but it seems that they will need to be made bigger still to even up the temperatures.

Now the bad.

Although I thought I had cleaned out all the crap in the fuel tanks I was very wrong. This extra crap got sucked into the pre filters and has most likely blocked them up. Maybe even the fine filter too.

This resulted in rough running of the engine at most revs and a poor throttle response. It did run smooth at the warm up revs of 1,200 though. Maybe the fuel supplied just happened to be correct for the air at these revs - as the ECU does not know how much fuel is being supplied - it just knows throttle position and air temps, pressures etc.

This meant that the engine would not rev out properly on the high power run and the best it could do was 2,500rpm.

After I taxied back and investigated inside the tank there again appeared a heap of crap. I think some of this has come from the top of the tanks and also the 'no mans land' in the middle in between the two baffles which make it impossible to get to 1/3rd of the tank.

Lots more cleaning of the tanks and a thorough flushing out of all the fuel lines plus new pre filters (and a fine filter too I think) and we should be okay.

I had a long conversation with Pete about this and he agreed that according to the symptoms I described that this was the most likely problem.

I also had a chat to Mark Jones (UK agent for UL Power) yesterday at the LAA Rally and he also agreed that this was the most likely cause.

I tested both ignition systems and saw no change and also the EGTs were all the same so it's not an ignition or blocked injector problem.

In the video below you can hear the fuel pumps straining away so they may need to be replaced too if they have become damaged.
Also Pete told me that he does have one 'Red Cube' (Fuel flow meter) installed in the fuel line so he can monitor flow rates - it is an early warning sign if the rate drops that the fuel filters are becoming dirty or blocked.

If you'll remember I was going to have two cubes installed so that the actual fuel used could be calculated but it got too complicated and expensive so I opted not to have any at all. This is a mistake and so I will be installing one of the Red Cubes back in the return line.

As we know from my fuel flow test the other week the hourly rate delivered by the fuel pump is 136 litres so if we are burning 17 litres in the cruise then the Red Cube should show a rate of 119 litres per hour in the return line. The most it should drop to should be 109 litres per hour as this would be on full power which is 27 litres per hour. Any lower figure than the difference between flow and usage and it shows a restriction in fuel flow which would automatically ground the aircraft and warrant further investigation.

Video here: https://youtu.be/YrdZcJ8ZhSA

Now the ugly.

This afternoon I went out to the airfield to configure the Dynon a bit better and start on cleaning out the fuel tanks when I discovered a pool of fuel under the aircraft.

A fuel leak is never a good thing but in this case it was even worse as the fuel had got to the black paint and eaten it. The paint just peeled off. Only the black top coat mind - not the white primer underneath. This just seems wrong to me - that automotive paint cannot handle exposure to automotive fuel. I think something is really wrong here but cannot begin to think about it too much as I will just get more upset. There was another home builder at the hanger (who has painted his own aircraft) and he agreed that something was not right about the paint coming off the way it did.

The photos below reveal just how ugly it is.

The leak BTW was coming from the one screw that I could not Proseal as it is the fastening screw for the threaded tube which holds the fuel tank end plate on and needs to be clear of Proseal to get on and off.

I thought I did this up fairly tight and didn't want to go any further in case I damaged the threaded tube. I think the rubber seal may be to blame as it seems to be protruding out around this area.

It's a bit strange that it leaked now as it did not leak when I filled the tanks up with fuel to clean them last week.