Mogas in Aviation

Hi Ron,

Thank you for supplying the above video - many good tips (especially about fuel plumbing).

I did not view all of the video, as much  has little relevance flying a 912ULS in Australia.

I had no idea of the far more extensive & complicated fuel supply system needed for the 912iS. With this revelation, two things occurred to me;

The need for such a fuel system is likely to exacerbate,  any potential for fuel vaporisation during hot weather operations.

I stand to be corrected, however to my knowledge, fuel injection systems, return hot fuel to the fuel tank, which can only add to the potential for fuel vaporization. (My common rail,  fuel injected utility has a large in line fuel cooler, on the return fuel line, just before the main tank).

We have very few 912is engines in Australia (ULS being the favorite, by a large margin). Our fuel vaporisation incidents are almost all related to the aircraft on the ground, occasionally on TO role/early climb out. I have never heard of an inflight situation like you describe. 

Hello Sean,

I too was aware of the typical vapor lock scenario.  It generally would happen after the initial flight of the day, where the already hot engine would get heat soaked while parked on the ramp and then the engine would not start after a short down time, or vapor lock on takeoff, or climb out. 

My situation was different, it was due to using highly volatile fuel (high RVP winter blend)... with heated fuel in the tank... and low air pressure.  Had I not climbed to the altitude needed to get over the mountains, or had I not had winter blend fuel in the tank, or had my fuel been Avgas, even with the same fuel temperature this would not have happened.  I'm fairly certain that the vapor lock in my situation was occurring at the fuel pumps (in the tailcone area) and not anywhere near the hot engine compartment.

I suspect that Australia does not have seasonal blends of Mogas due to its fairly warm climate.  Just out of curiosity, do you know, or could find out, what the RVP value of your Mogas is?

Also, could you post a pic or diagram of your inline fuel cooler?

Thanks,

Ron

Hi Ron,

The fuel return cooler, on my ute, looks just like a power steering oil cooler eg below (taken from an advertisement for an aftermarket accessory)

A very quick search yielded the following RVP regulations for petrol supplied to the Western Australian city of Perth:

"...............petrol supplied in Perth is to be compliant with the monthly volumetric average RVP of 62 kilopascals (kPa), and must not exceed the RVP limit of 64 kPa;................................"

Hi Ron,

Testing the RVP of fuel is actually quick and easy after making a test chamber. It takes me about 15 minutes start to finish.  The test chamber can be made from hardware store materials in about an hour. 

When winter fuel is being sold, I run 50/50 mogas and 100LL just in case we get a very warm winter day.  Once I think summer fuel is on tap, I always test the first batch to make sure before running straight mogas. After that I don’t test again until the switch back to winter fuel.  A while back I wrote up these instructions for RVP testing at home - how I do it anyway.   Maybe you will find this helpful.  I have a video also, but never got around to posting it anywhere.