Fuel Filters

[Richard Fitzpatrick]

I have been looking at various options for fuel filters over the past few months. Now, the latest LAA magazine discusses that very subject. However, I still cannot source a "see-through" type fuel filter that I can locate in the Rotax 912 enclosed engine bay; other than the glass one I purchased from LAS some time ago. This though has not been fitted due to engine stoppages reported on other forums and the actual internal filter seeming to be the culprit; It is made in Taiwan but does not require the "spring mod" due to a slight differing internal design; otherwise identical.
The reason for preferring a "see-through" one is as the name implies, so that a cursory check can be made at pre-flight.
Can any reader here recommend a similar type filter, or a suitable internal filter element replacement? At this stage I am avoiding fitting a filter in the cockpit for the same reasons as the article mentions - fuel spill and smell at filter time change (no matter how careful I might be).
Richard
Zenair 701 with Rotax 912

[John Clarke]

What about this one from Skydrive?

http://www.skydrive.co.uk/proddetail.asp?prod=SKY29

[Richard Fitzpatrick]

Hi John,

Many thanks for the reply. However, that looks to be plastic and perhaps should not(?) be located in the enclosed type engine bay.
There are many other fuel filters that can be located in the engine area but all these are mainly metal and hence non see-through. Even the Andair one depicted in the latest LAA magazine may now have a question mark over it.
If no further advice from this forum, it looks like I'll have to use a metal type one in the engine bay and forego the benefit of seeing inside the filter at pre-flight.
Thanks again.
Richard

[John Clarke]

I see your point about the plastic, Richard. To be honest this hadn't occurred to me. I have this type of filter in my engine bay and I've seen several other Rotax installations identical to mine. The engineer who services my engine is quite happy to use this type of filter. Perhaps it could be worth a phone call/email to Skydrive to see if they recommend this filter in the engine bay. I'm rather curious to find out myself now .

[Richard Fitzpatrick]

Hi again John,

I can see arguments both ways, as most of us do. It is comforting to see the innards of a fuel filter prior to flight, even though it can be construed as a whim perhaps and not entirely necessary. However, in the case of a fire in the engine bay I would imagine the plastic filter not lasting long and the ensuing gush of fuel adding greatly to the fire and hence my sphicter muscle activity.
In the same fire scenario but with a solid/metal fuel filter, the danger is greatly reduced, thus giving more time to get down on the ground.
This debate has at least kicked me off the fence (I think). It would seem more prudent to fit a solid metal filter and forego the facility of being able to see into the filter prior to flight.
In the meantime I will see what Skydrive recommend.
Richard

[gasax]

My fuel filters are not located in the engine compartment - but they are glass / chrome types which are very easy to see the state of.

With careful mounting they should be ok forward fo the firewall. See this link http://www.demon-tweeks.co.uk/motorspor ... uel-filter

[Richard Fitzpatrick]

Hi gasax,

That's the very filter I have purchased but at the moment reluctant to fit. I see it is exactly as mine is and will not unscrew internally as the previous ones could do. However, I am still uncertain of the integrity of the internal filter element, as it is this that has "clogged up" causing a few engine stoppages. Do you happen to know if element differs from the previous un-modified filter?
Richard

[AlanR]

In addition to the integrity of the type of filter, the thickness of the filter screen needs to be determined to asssess if it will affect the flow and therefore fuel pressure of your particular engine's requirements. I.e. Is it a 50microns or 100microns or whatever? I can't seem to see the actual spec shown on the Demon Tweeks filter.

[John Clarke]

I only got round to reading Malcolm's article in the magazine this evening. I think I may well look for something other than a plastic filter as well.

[gasax]

I've had those filters installed for the last 5 years. I think it is worthwhile considering what you are trying to achieve when it comes to fuel filtration.

Most certified aircraft do not have fine fuel filters - they do not need them as the jets etc in most conventional carbs can be cleared with a knitting needle (just joking - but I'm sure you get the point). A coarse wire mesh is usually the finest thing in these systems.

The Rotax of course uses rather less fuel and that is split between two carbs - the main jet is fairly small - but we are still talking about keeping 100 micron plus debris out.

Putting any fine filter into the system creates a potential for blockage - just like a fuel flow unit or any other potential obstruction the question is how likely is that to happen and then if it did what would/could you do?

My filters are on the suction of both tanks - they are in the cockpit and can be seen from the pilot's seat. I have had two episodes of debris in the fuel - both from official airfield bowsers. I usually fuel from cans - straining through a filter - so the chances of the filter actually capturing anything is slim.

During both episodes there was no reduction in fuel pressure - most 912 installations have to have a fuel pressure gauge and to be fair it can be quite useful! So both times I had c$$p in the fuel I could see it in the filter and I could judge how bad it was. My fuel system returns to the left tank - so that filter 'sees' a lot more flow and so generally shows contamination first. But that means I can just swap tanks in the event a lot of contamination occured - that would certainly give plenty of time to find somewhere to land.

If however you put a single fuel filter - even one apparently as good as the Andair one, in the engine compartment on a single delivery line - you cannot see it's status and if it blocked then you have no fuel! So with that sort of arrangement you need to very regularly check it. How regularly? Probably every couple of flights - because you do not know if there is anything in the filter without opening it up and during both of my episodes there was no other evidence the fuel was contaminated!

Horses and courses - but you can see why I am happy with the arrangement I have. Yes an element with greater debris tolerance would be an improvement - but really not a big improvement. Looking down at the filters and seeing what is in them is far, far better than having a debris tolerant filter which may or may not have debris in it and which could carry the potential of cutting off the supply.

[Chris Martyr]

I have had exactly the same filter as the one on the Demon Tweaks website that Pete linked us into fitted as a last chance filter on my 1834VW for 8 years now , it is a very good quality piece of merchandise and very easy to service.
As can be seen on the web picture , it is clearly marked IN and OUT to avoid confusion , but note also that the threaded post 0n which the filter screen is mounted also has an arrow [not visible in the picture] which if fitted correctly will mean that the fuel flows from the outside in , as it were .
What I mean is , that if there are any contaminants in your fuel they will be caught on the outer surface of the filter screen making any crud easily visible, and not the inside .
Good shout from Malcolm McBride as well , as some of the F/Fs available from sources that should know better , I wouldn't even fit to my lawn mower .

[Rob Swain]

Kind of on the same subject....

It has been stated that most certified aircraft don't have fine fuel filters. Actually they do - they have a gascolator.

I know a gascolator's 'normal' use is for collecting water, but all the ones I've seen have a quite fine filter in them as well. The design is such that the flow of fuel passes up through the filter to get to the engine, so any crud will tend to drop away from the filter surface rather than clog it.

Do all these Rotax powered beasts not have a gascolator fitted?

[mikehallam]

Both my Rans', 447 Rotax two stroke & the 912 4-stroke have gascolators, can't see how one dare be without on in line.
The principal safety points being (apart from the screen on top) the slowing of the fuel flow to let entrained particles & H2O to drop out & the ease of draining a goodly sample into a glass inspection jar.

mike hallam.

[Rob Swain]

The principal safety points being...

I quite agree.

I was mainly addressing the filter aspect as that is the thread topic, and some people may not be aware a gascolator is a fuel filter as well as a water trap.
The PPL course is most people's introduction to the gascolator when they are taught to draw a sample from it and look for water, but not necessarily anything else as debris often doen't get past the curtis valve.

[AlanR]

Yes the gascolator does have a fine mesh filter but without indivdual in-line filters from each tank, always supposing you have two tanks, should the filter become blocked you have a single point of failure.
Personally I would much prefer to discard the gascolator mesh and install 2 in-line filters from the tanks and before the fuel selector.This then gives me options should the engine start running rough.