Rotax 912 80hp Is the gascolator on my airplane enough of a fuel filter

Hi Michael

The installation manual contains the information you need.  The reference to no using a plastic filter refers to the outside construction.  The information that says do not use paper refers to the filter element inside the filter itself.  

You should have a coarse filter at the pickup of your fuel tank.  It should then to a gascolator at the low point of the fuel system. After that your fine filter.  Generally the fine filter is found within the fire zone, on the firewall or between the gascolator and mechanical pump. Given heat and the possibility of fire no plastic body filters should be used.  (glass filter bodies are also not recommended as they can crack leak in hard landing or vibration) 

Cheers

My last aircraft (European origin) used exclusively Hengst H102 WK & H103 WK in line filters. Baldwin make a very similar filter and have a wider selection of this type.

Several of these filters were fitted (& I carried a spare, never used) on all (x3) lines delivering fuel to the engine.

These filters are;

Light weight - Almost indestructible - Transparent leak proof casing - Gauze filter medium- Low cost - Easy to replace

In tank (finger) filters are a hangover from the past, that are better replaced with an easily inspected/serviced in line filter as above.

My current aircraft uses in tank finger strainers/filters and a single gascolator. 

The gascolator has the option of fitting two diffrent micron (filtration measure) gauze  filter medium - the finer one (can't remember its size off hand) meets the Rotax standards.

This system creates a weak point, in that all fuel must pass through the gascolator. No alternate supply rout, in the event of a blockage.

Gascolaters are recommended to be located at the lowest point in the fuel reticulation system - this facilitates their principal attribute, water separation. They are relativly heavy, complex and much more expensive & harder to service than a disposable, in line filter that can be installed at any suitable/accessible point in the fuel system.

Whatever filter system you adopt, should always be supported by  good fuel hygiene practices ie the use of a filter funnel when refueling.😈 

I use strictly mogas with 10% ethanol. For the past 11 years I’ve use automotive clear plastic filters with paper elements without any issues. They are placed in a no heat area near the fuel tank though.

"I use strictly mogas with 10% ethanol. For the past 11 years I’ve use automotive clear plastic filters with paper elements without any issues. They are placed in a no heat area near the fuel tank though."

That's fine Sam however everything that I have read, recommends gauze filters.

I have also heard of people using & swearing by the sintered bronze type. 

I guess they all work - the question is what is the best for a small aircraft.

# Pleated fabric/paper filters;

Have been known to break down (just parroting here) are harder to assess for contamination (pleats can fill before giving a visible indication).

# Sintered bronze;

I suspect they are prone to blockage - only ever seen them used on mowers etc. For the most part the filter appears quite small - I would be concerned about the surface area available to accommodate contamination without blocking.

I would advise;

A gauze filter medium of an appropriate micron

Transparent casing to facilitate inspection

All in one (in/out spigots & filter casing) "plastic" construction for leak security & light weight.

Example;

Baldwin BF7850  &  BF7863 (not to scale)

Be careful with plastic filters. Ethanol with some of the plastic filters causes the plastic to soften. I’ve seen this a few times and Flight Design had a mandatory replacement with a metal filter because of this. Personally I’d stick to a metal filter. You can’t damage them, they have a fine metal mesh screen inside and they unscrew for any cleaning so they are a lifetime filter.