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Just a heads up to people out there doing their own thing, orange baffle rubber (and I think orange fire-sleeve) does not like fuel and will break down.

History;

While refuelling a Savanah, I would typically unscrew the fuel cap and sit it on the wing next to the filler neck.

This one time, as I picked up the cap, I found a piece of orange 'rubber' sitting on the wing?

Looking under the cap I discovered someone had manufactured 'gaskets' for under the cap, made of glass reinforced baffle rubber (a neoprene I think), checking the other caps I found they were all falling apart!

New seals were made from rocker cover rubber/cork composite.

 

fuelcap_seals.png

Cap_&_seals.png

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Good post. Hope the Savannah has finger strainers in the tanks. Lots of gotchas in the LSA, experimental world.

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This is exactly why LSA including experimental LSA is controlled by the manufacturer & alterations are not allowed. Even though the replacement may appear to be ideal  & serve its purpose as a gasket , it may behave very differently with immersion in fuel that could possibly contain ethanol. It may be of interest to see my recent post in "3300A a tale of two etc" . If we follow the rules there is virtually no place for mods even in Experimental LSA. The option to do as we were able under the "19" home built registration has been taken from us. LSA may server CASSA & RAA well. It does place more regulation on the builder maintainer. I some case it may be a good thing when looking at the pics of those old parts removed.

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2 hours ago, Thruster88 said:

Good post. Hope the Savannah has finger strainers in the tanks. Lots of gotchas in the LSA, experimental world.

If "finger strainers" are what I think they are, in tank strainer, filtering the fuel going out of the tank,  I would suggest they are a hazard in themselves.

 

In tank strainers/filters are not usually easy to access or service. They are subject to fuel "sloshing" during ground opps and when turbulence is encountered. This can lead to partial/total, temporary/ permanent blockage. Blockage = engine loss of power or even failure. 

 

The alternative is an in line filter system that can be easily viewed/inspected and serviced - in my mind the preferred way to go.

 

 

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Posted (edited)

‘Call me old fashioned but I am always mindful of the blood and lives that have been expended over the last hundred years in  learning how to design, build and fly light(ish) aircraft and I will not and do not deviate from established good. design practice.

 

The purpose of the finger strainer is to increase the surface area through which fuel can flow to reach the fuel outlet. Mine have a surface area about two square inches. In other words, you need an awful lot of large chunks of gunk to block a finger strainer, much more than would be required than to block your usual AN6 line.

 

‘’A good filter system has a (corse) filter, then a medium filter (the gascolator screen), then a fine filter  in order to trap the maximum of contaminants without clogging up and lines and fittings should be sized appropriately.

 

‘’As for Savannah fuel caps and gaskets, I just shake my head. Don’t ever use silicon sealer or silicon baffle material(that’s the red stuff) or teflon tape. anywhere in any fuel system. Those products have killed a lot of people used that way.

 

Skippy, with respect, I think plastic in line filters belong in lawn mowers, but then my aircraft is probably twenty pounds overweight for thinking like that 😛

Edited by walrus
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5 hours ago, skippydiesel said:

If "finger strainers" are what I think they are, in tank strainer, filtering the fuel going out of the tank,  I would suggest they are a hazard in themselves.

 

In tank strainers/filters are not usually easy to access or service. They are subject to fuel "sloshing" during ground opps and when turbulence is encountered. This can lead to partial/total, temporary/ permanent blockage. Blockage = engine loss of power or even failure. 

 

The alternative is an in line filter system that can be easily viewed/inspected and serviced - in my mind the preferred way to go.

 

 

As Walrus said, the in tank finger strainer is very coarse. It is designed to allow the passage of contaminants that will not block the fuel line. If even just a few in tank strainers blocked on cessna, piper or beech aircraft in Australia of which there many thousands flying an AIRWORTHINESS DIRECTIVE would be issued.  

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The fact that a manufacturer has the last word is a definite weakness or at least a double edged sword in LSA. Jabiru Engines  are a clear example. 

 

FWIW :

I think that Jabiru have been pretty good with their SBs for their airframe. Recent:  Like the crack in one or two of those control sticks (and they were high hours) - and an SB is produced and  everyone inspects before next flight. 

 

That is how it should be for their engines, also.

 

 

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7 hours ago, walrus said:

‘Call me old fashioned but I am always mindful of the blood and lives that have been expended over the last hundred years in  learning how to design, build and fly light(ish) aircraft and I will not and do not deviate from established good. design practice.

 

The purpose of the finger strainer is to increase the surface area through which fuel can flow to reach the fuel outlet. Mine have a surface area about two square inches. In other words, you need an awful lot of large chunks of gunk to block a finger strainer, much more than would be required than to block your usual AN6 line.

 

‘’A good filter system has a (corse) filter, then a medium filter (the gascolator screen), then a fine filter  in order to trap the maximum of contaminants without clogging up and lines and fittings should be sized appropriately.

 

‘’As for Savannah fuel caps and gaskets, I just shake my head. Don’t ever use silicon sealer or silicon baffle material(that’s the red stuff) or teflon tape. anywhere in any fuel system. Those products have killed a lot of people used that way.

 

Skippy, with respect, I think plastic in line filters belong in lawn mowers, but then my aircraft is probably twenty pounds overweight for thinking like that 😛

All good points Walrus - must admit I hadn't thought about the benefit of a large surface area course "finger"  filter -. You made a good point there however I am still concerned about the inaccessibility/inspection aspect of an  in tank filter.

 

"I think plastic in line filters belong in lawn mowers," - dont think i actually suggested a type of in line filter but now that you have, the discussion broadens;

 

The "plastic" Hengst gauze filters I use are actually specified for a wide range of European diesel  engines. I first came across them in Mercedes diesel cars. Since then I have seen them used in a lot of European LSA class aircraft. True I have used them on mowers but only after they have done  100 hrs in the aircraft.

 

In case you are interested;

Hengst  H102WK

 

D49395001-001.jpg

 

 

Hengst H103WK

H103WK

 

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Hi Skip, looks good but I don’t have a choice. Fuel injected Rotax with a high pressure Rotax filter - about 46psi.

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In absence of a finger strainer, looks easy to get that first orifice clogged up to me.

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I have had those inline filters on vehicles block up to the point whereby the engine stopped completely, and not a skerrick of fuel would get through, even though the filter looked O.K. I would not use one of them on an aircraft engine in a million years.

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22 minutes ago, onetrack said:

I have had those inline filters on vehicles block up to the point whereby the engine stopped completely, and not a skerrick of fuel would get through, even though the filter looked O.K. I would not use one of them on an aircraft engine in a million years.

Well I have been using them for almost 900 hrs - never had a blockage and thanks to filtering all fuel into aircraft, almost 0 material on gauze. I replace them at 100 hrs because they are cheap. I usually blow out the used ones and re use them on my land based engines. 

 

How can "the filter looked O.K" and be blocked?. You put contaminated fuel into the system, or have a fuel system deterioration (gaskets, hoses, etc) of course they will block -  if they didn't they would not be doing their job.

 

You have to remember that all  filters "job description"  involves getting blocked. That what they are there for . That's why you inspect (those that can be inspected)  and replace if needs be and at specified intervals.

 

Getting a blocked filter is not the fault of the filter, its the fault of the person who used contaminated fuel or an internal material  break down  of the fuel system. .

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2 hours ago, RFguy said:

In absence of a finger strainer, looks easy to get that first orifice clogged up to me.

We are still talking about fuel systems ???😁

 

2 hours ago, walrus said:

Hi Skip, looks good but I don’t have a choice. Fuel injected Rotax with a high pressure Rotax filter - about 46psi.

Okay - observation - most fuel filters are placed before the high pressure section - how come yours is under pressure ?? (not that 46 psi is that high)

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Hi Skip, short answer is because thats the way the Rotax elves in der Schwarz Wald designed it. The 912 iS is an electronic fuel injected engine. The filter is about 6 Micron and flows around 75l/min most of which is recirculated back to the header tank.

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1 hour ago, walrus said:

Hi Skip, short answer is because thats the way the Rotax elves in der Schwarz Wald designed it. The 912 iS is an electronic fuel injected engine. The filter is about 6 Micron and flows around 75l/min most of which is recirculated back to the header tank.

I would guess that the Rotax  filter is not a serviceable item ???

 

If the aircraft is "factory" built it might be against the rules however you could put one of my Hengst filters "in line" on the "suction"side, as a  "rock" filter . In the diesel applications, this is where they fit in the system.

 

’"A good filter system has a (corse) filter, then a medium filter (the gascolator screen), then a fine filter  in order to trap the maximum of contaminants without clogging up and lines and fittings should be sized appropriately"

 

Having a transparent casing, makes it  is easy to see (pre-flight inspection) if there is any build up of foreign objects on the filter - either clean or replace

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Skip, yes, it might be possible to put one in the circuit, but it would have handle the flow. The high pressure filter (8 micron) is non reusable and gets replaced every 200 hrs. The filter cannot be placed before the twin electric injection pumps because of the risk of vapor lock in hot weather. 

 

‘’The pumps are fed by gravity through a header tank then Andair gascolator with a 60 micron screen. The pumps can push over 100 psi if necessary. After the high pressure filter is the fuel rail. After the rail there is a pressure regulator and header tank return.

 

The whole thing is IAW Rotax requirements and designed and tested by the Canadian Rotax distributorand Skytek Aviation.

 

People sometimes forget that fuel injection requires:

 

1.Fuel at pressure with no bubbles.

 

2.Electricity.

 

 

Without either the engine stops really really quickly;p

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2 hours ago, Bill said:

I'm interested Skip. Where do I buy them in OZ?  Thanks,  Bill

It was quite a few years ago (bought quite a few, to get the best price) through an importer,  I think it was this crowd  https://www.tooleyimports.com.au/manufacturer/hengst-filters/

 

Application pointers:

 

Make sure you are using the correct fuel line ID - (the "spigots" F & G are 8mm OD)

The "spigots" are not barbed - so hose length and security against movement are important. I tend to cut my hose so that  it pushes all the way, touching the main housing.

I also use good quality fuel injector hose clamps, that are just large enough for the job and only "snug" them down (ie not too tight)

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The high rate of fuel return should improve/fix  vapourization/hot fuel in lines problems of MOGAS.

 

(There is a SL from Rotax requiring fuel returns to be installed  for all their 912 MOGAS engines if people are not aware) 

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If you mount an electric fuel pump directly below or fed by gravity from the tank which is capable of delivering more fuel than the engine can consume at any power setting you will not suffer from vapour locks as you are pushing the fuel through and not just sucking it as the engine driven pump does.

 

As far as in line filters go I use automotive clear plastic paper element filters from supercheap. They cost about $5.00 & have 6mm barbs. It is easy to inspect for contamination being completely clear & I replace it every 50 hours and have a bunch of old ones in the hangar that look as new. I only found a few bits of debris in the first one after the build and I have always without fail used by Mr Funnel when refuelling from Jerrycans

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1 hour ago, RFguy said:

The high rate of fuel return should improve/fix  vapourization/hot fuel in lines problems of MOGAS.

 

(There is a SL from Rotax requiring fuel returns to be installed  for all their 912 MOGAS engines if people are not aware) 

As you will know - fuel vaporisation , in Rotax 91 carburettor applications, is almost always  as a result of heat "soak"  after  engine shut down and usually (in my engine) on hot days (above 30C). It is most usually apparent when trying for a hot start (with difficulty) and taxying (engine running rough). It can also appear on take off run when full power is asked for. It is not an inflight problem, as there is usually sufficient fuel & air flow to keep the over engine fuel lines & fuel cool (below vaporisation). It is not exclusively a ULP issue although more likely than with Avgas.

 

The fuel return that mitigates the problem does three things:

Encourages/intercepts, vaporised fuel to return to the tank

Allows for fuel flow, using the boost pump, when the engine is not running driving out the vapour and cooling the system.

Generates a greater fuel flow (more cooling) in the  system,  at least close to the point of the fuel line splitting to each carb.

 

Fuel injected systems all have a fuel return - I am not so familiar with petrol systems but would speculate it is similar to a diesel  - excess fuel allows for sudden increase in demand (acceleration), cooling and lubrication 

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33 minutes ago, kgwilson said:

If you mount an electric fuel pump directly below or fed by gravity from the tank which is capable of delivering more fuel than the engine can consume at any power setting you will not suffer from vapour locks as you are pushing the fuel through and not just sucking it as the engine driven pump does.

 

As far as in line filters go I use automotive clear plastic paper element filters from supercheap. They cost about $5.00 & have 6mm barbs. It is easy to inspect for contamination being completely clear & I replace it every 50 hours and have a bunch of old ones in the hangar that look as new. I only found a few bits of debris in the first one after the build and I have always without fail used by Mr Funnel when refuelling from Jerrycans

KG - vaporisation is mainly an issue of nil/minimal fuel flow, on hot days, after the engine has been operated and then shut down causing "heat soak" of the over engine fuel lines - boiling/vaporisation of the stagnant fuel in these lines. Some fuel set ups may be better than others for removing the vapour but as far as I know all carburetted  91 engines suffer from the same design problem.

 

Paper Fuel Filters:

I am horrified that you would risk the safe operation of flight by using cheap paper type fuel filters that are unlike to be subject to any sort of consistent quality control. 

The unknown durability of the "paper" and the possibility of it breaking down & releasing fibres to block your carb jets.

Due to the pleated/convoluted nature of the filter, it is almost impossible to visually asses condition/blockage of the filter.

There has been a long standing recommendation that gauze filter medium, uncased in a clear body (for easy visual inspection) are the standard.

The gauze filters, I use, were about $6 each (I did purchase  about 20 to get the best price) but what price would you put on your life?

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Vaporisation is only really an issue above 10,000 feet with Mogas & we are not supposed to go there anyway but yes it happens on the ground with a hot engine which is why the start procedure for a hot or cold engine with my engine is electric fuel pump on for 10 seconds, off then start. Starting is always instant. I don't actually know what the material is in the filters I use. It is coloured orange and designed for use with Mogas. These filters are used extensively in the automotive industry and I have never heard of any problems & I have not had any either. There are plenty of recreational aircraft using them.

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The "spigots" are not barbed - so hose length and security against movement are important.

There's enough reason alone just in that poor design, to not use these Hengst inline plastic filters on an aircraft. What VH aircraft uses fuel piping connections that are not barbed? None, I'll wager. It's an accident waiting to happen.

 

Barbed fuel line connections are standard throughout the automotive industry to prevent fires. Even the cheap Ryco plastic inline filters have barbed tails. 

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11 minutes ago, kgwilson said:

Vaporisation is only really an issue above 10,000 feet with Mogas & we are not supposed to go there anyway but yes it happens on the ground with a hot engine which is why the start procedure for a hot or cold engine with my engine is electric fuel pump on for 10 seconds, off then start. Starting is always instant. I don't actually know what the material is in the filters I use. It is coloured orange and designed for use with Mogas. These filters are used extensively in the automotive industry and I have never heard of any problems & I have not had any either. There are plenty of recreational aircraft using them.

No offense KG but the lower vaporisation point of MoGas/ULP at high altitude is not the " every day/practical" problem for most LSA aircraft - it is the heat soak situation described above..

 

You are indeed lucky that you experience little effect of hot engine /hot day vaporisation, for this is where most pilots have the problem. Like you, I have developed management strategies and rarely have a start problem however on really hot days (I try to avoid flying in the heat of the day) after a fueling/wee landing I can experience rough running during taxi and run up and have on two occasions (over 10 years) had partial loss of power at lift off - aborted with plenty of runway left - backtracked & tried again with success.

 

I am usually an advocate of using automotive "stuff" in LSA type aircraft however there are always exceptions and this is one of them - why use, a  very likely  inferior product, when a better one is  available (& from the automotive world) for a similar price??

 

As for "plenty of recreational aircraft using them" - this just suggests to me that there are those who have little mechanical understanding, influencing their similarly afflicted peers. I dont know of any factory built equivalents that use the off the shelf  mower type filters - that should tell you something.

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