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Occasional engine anomally 912S - water?

 
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graeme bird



Joined: 15 Jul 2010
Posts: 399

PostPosted: Tue Oct 09, 2018 11:33 pm    Post subject: Occasional engine anomally 912S - water? Reply with quote

On several occasions now, after some time flying (40+ minutes) the engine has had a minor episode, like one mag has been turned off for half a second. It then continues as normal (with me looking for a field). It seems unrelated to temperature or phase of flight, icing conditions, or turbulence, except perhaps initiating a slow descent.
I have had a good think around the possible causes, and why it's just these last few months; one thing I did was change to using Essso Supreme (no ethanol) from ordinary Shell unleaded; the other was to change the long filler tube to aluminium (classic style).
Recently using the tank drain plugs I have noticed a small amount of water in the fuel (I'm not in the habit of checking this regularly as there was never an issue).
So my current theory is, air is filling the long aluminium tube via the breather and is trapped, when the temperature drops in the hangar condensation forms on the inside of the tube and enters the fuel, either that or the Esso S+ garage supplies it with water in.
It would fall into the starboard side of the tank but after 40 minutes or so the fuel return to the bottom of the starboard side and roll/pitch changes may have mixed the water and fuel sufficient that it is sucked into the port fuel line, into the carb bowl and eventually into the engine at which point the mixture refuses to burn for a beat or two. Once good fuel is back it carries on. The old tube was rubber so this wouldn't have happened.


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Graeme Bird
G-UMPY - Mono Classic/XS FFW 912S, Woodcomp SR3000/3W CS, trutrak Gemini 2 axis AP, PAW, PFLARM core, ads-b out, 8.33khz, mode S, FP-5, Aera500, SD on Nexus, Smart A3
350 hours & 6 years on the Mono, 930 total
g(at)gdbmk.co.uk
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brian.davies44(at)gmail.c
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PostPosted: Wed Oct 10, 2018 12:12 am    Post subject: Occasional engine anomally 912S - water? Reply with quote

Hi Graeme,

A couple of things come to mind.
First, whenever you disturb the fuel system there is a high possibility of
debris moving and temporarily blocking a jet.
Secondly, there is always a danger when you mix fuel containing ethanol with
non-ethanol fuel. Fuel containing 5% ethanol will absorb water until it
reaches its limit and will then undergo phase separation, creating a layer
of pure water. If your 5% ethanol fuel has already absorbed a fair amount
of water and you then fill up with non- ethanol fuel you lower the overall
ethanol percentage of the fuel in your tank and hence its ability to contain
the absorbed water. Phase separation can then take place, probably in
relatively small quantities of water, so this may explain why you are now
getting water out of the drains. The solution is to drain all of the fuel
out of the tank and fill up with Esso Supreme.

This is all theory of course, but worth doing I would suggest.

Regards

Brian Davies

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zwakie



Joined: 03 Aug 2009
Posts: 152

PostPosted: Wed Oct 10, 2018 12:46 am    Post subject: Re: Occasional engine anomally 912S - water? Reply with quote

Suggestion of a by-no-means-expert:

graeme bird wrote:
[...] like one mag has been turned off for half a second. It then continues as normal [...]

Are you saying this 'coughing' only happens once during flight?

If so, then your theory:

graeme bird wrote:
[...] starboard side of the tank but after 40 minutes or so the fuel return to the bottom of the starboard side and roll/pitch changes may have mixed the water and fuel sufficient [...]

will not hold as if that is the case one would expect it to happen more than once a flight.

Also, if this happens only once each flight, Brian's suggestion of debris in the fuel seems unlikely as this does not line up with your description that it always happens about 40 mins. into the flight.

As you were indicating it seems to only happen on initiating a small descend, e.g. reducing power after a prolonged period of non-adjusting the power, I would suspect the carb jet has slowly been building up a minor bit of contaminiation or is getting slightly out of alignment (early stages of it getting stuck completely).


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Marcel Zwakenberg
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Duncan McFadyean



Joined: 18 Jan 2011
Posts: 102

PostPosted: Wed Oct 10, 2018 12:52 am    Post subject: Occasional engine anomally 912S - water? Reply with quote

The other variable (which is consistent with your original theory) is change of season. The temperature differential between warm humid days and cold nights is relatively high at the moment.
I never saw water in the plastic tank either, but have a 'plastic' filler pipe.
Duncan McF.

----Original Message----
From: brian.davies44(at)gmail.com
Date: 10/10/2018 09:11
To: <europa-list(at)matronics.com>
Subj: RE: Europa-List: Occasional engine anomally 912S - water?

--> Europa-List message posted by: "Brian Davies" <brian.davies44(at)gmail.com>

Hi Graeme,

A couple of things come to mind.
First, whenever you disturb the fuel system there is a high possibility of
debris moving and temporarily blocking a jet.
Secondly, there is always a danger when you mix fuel containing ethanol with
non-ethanol fuel. Fuel containing 5% ethanol will absorb water until it
reaches its limit and will then undergo phase separation, creating a layer
of pure water. If your 5% ethanol fuel has already absorbed a fair amount
of water and you then fill up with non- ethanol fuel you lower the overall
ethanol percentage of the fuel in your tank and hence its ability to contain
the absorbed water. Phase separation can then take place, probably in
relatively small quantities of water, so this may explain why you are now
getting water out of the drains. The solution is to drain all of the fuel
out of the tank and fill up with Esso Supreme.

This is all theory of course, but worth doing I would suggest.

Regards

Brian Davies

--


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JonathanMilbank



Joined: 14 Apr 2012
Posts: 250
Location: Aberdeen area

PostPosted: Wed Oct 10, 2018 1:12 am    Post subject: Re: Occasional engine anomally 912S - water? Reply with quote

My aircraft is a Classic with the long aluminium filler tube, which was installed several years ago and I continue to use ordinary unleaded fuel obtained from any large turnover local garage or supermarket. I have changed all my hoses and continue to check the tank bottom outlet coarse filters annually since the introduction of ethanol. No significant dirt nor any water was ever found and all hoses remain in good condition even after 5 years since the last replacement.

By the way, the prescribed method of testing for ethanol employing a glass tube etc never shows ethanol to me, although someone who used to use the chemical testing kit when it was obtainable did detect ethanol. However I take comfort that pilots in at least one South American country are using fuel with 20% or higher ethanol content and seemingly don't report problems.

Since the introduction of ethanol I've never found so much as a drop of water in fuel samples, probably because ethanol "mops it up". Prior to that I did very rarely find a drop or two, usually when the fuel tank hadn't been filled after flight and I'd waited a few days until refilling the tank before going flying again. Consequently I strive to ensure that the tank is filled completely up to an inch or so below the cap immediately after flying, keeping the aircraft tilted slightly to the left when filling to get maximum into the tank. My aircraft's been converted to nose wheel, so possibly more fuel can be accommodated than is normal for a mono and maybe less likely for an empty space in the aluminium filler tube due to deck angle.

It seems to me that condensation droplets which might accumulate in the starboard side of the tank would normally remain in the bottom and wouldn't be able to cross over the tunnel to the port side in most circumstances. The port side is what I have selected for all flights except for the annual permit renewal test flight. Having said all of this, your theory seems plausible in the absence of any other explanation.


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Last edited by JonathanMilbank on Wed Oct 10, 2018 9:01 am; edited 1 time in total
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graeme bird



Joined: 15 Jul 2010
Posts: 399

PostPosted: Wed Oct 10, 2018 1:41 am    Post subject: Re: Occasional engine anomally 912S - water? Reply with quote

Interesting that a bit of ethanol could gobble up the water; I rarely fill up after flying; so I could do that while cold nights persist. I doubt the jet block debris thing as it would be much more pervasive and random; though I did change all the pipes (didn't really twig it would need such a shakedown again).
Never thought of tilting the plan to get more fuel/less air; good tip.

I couldn't say that it only happens once per flight I think it might have been more on an occasion.

I always test the fuel for using the water tube thing but have never seen anything and also never had an issue with ordinary unleaded shell for 5 years.


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Graeme Bird
G-UMPY - Mono Classic/XS FFW 912S, Woodcomp SR3000/3W CS, trutrak Gemini 2 axis AP, PAW, PFLARM core, ads-b out, 8.33khz, mode S, FP-5, Aera500, SD on Nexus, Smart A3
350 hours & 6 years on the Mono, 930 total
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Burrilla



Joined: 25 Apr 2015
Posts: 106

PostPosted: Wed Oct 10, 2018 2:01 am    Post subject: Occasional engine anomally 912S - water? Reply with quote

Probable not related to change in fuel.

How’s the fuel pressure and how old is the Fuel Pump. State of the fuel carb bowls and general health of the fuel system including the carbs?

Alan

Sent from my iPad

Quote:
On 10 Oct 2018, at 10:41, graeme bird <graeme(at)gdbmk.co.uk> wrote:



Interesting that a bit of ethanol could gobble up the water; I rarely fill up after flying; so I could do that while cold nights persist. I doubt the jet block debris thing as it would be much more pervasive and random; though I did change all the pipes (didn't really twig it would need such a shakedown again).
Never thought of tilting the plan to get more fuel/less air; good tip.

I couldn't say that it only happens once per flight I think it might have been more on an occasion.

I always test the fuel for using the water tube thing but have never seen anything and also never had an issue with ordinary unleaded shell for 5 years.

--------
Graeme Bird
G-UMPY - Mono Classic/XS FFW 912S, Woodcomp SR3000/3W CS, trutrak Gemini 2 axis AP, PAW, PFLARM core, ads-b out, 8.33khz, mode S, FP-5, Aera500, SD on Nexus, Smart A3
350 hours &amp; 6 years on the Mono, 930 total
g(at)gdbmk.co.uk




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graeme bird



Joined: 15 Jul 2010
Posts: 399

PostPosted: Wed Oct 10, 2018 10:09 am    Post subject: Re: Occasional engine anomally 912S - water? Reply with quote

Thanks for the response.
The carb bowls are clean, I think there was a small bubble in one when I checked. Re the pump, this would have to be the mechanical pump and I'd expect it to be more likely evident at high power (TO, climb), for the effect of fuel starvation to last longer, for it not to recover so quickly/at all and to show up as low or fluctuating pressure on the fuel pressure gauge.
It was changed last as a result of the rotax SB maybe 3 years ago/ 180hrs.


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Graeme Bird
G-UMPY - Mono Classic/XS FFW 912S, Woodcomp SR3000/3W CS, trutrak Gemini 2 axis AP, PAW, PFLARM core, ads-b out, 8.33khz, mode S, FP-5, Aera500, SD on Nexus, Smart A3
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william(at)wbliss.co.uk
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PostPosted: Thu Oct 11, 2018 10:10 am    Post subject: Occasional engine anomally 912S - water? Reply with quote

Have the gearbox checked for worn splines. I had similar episodes and
did lots of fruitless fault finding re fuel system, ignition, engine
mounts and prop before speaking to Kevin Dilkes (SAS Aviation Services).

New bits, a hole in my pocket and it runs like a sewing machine.

William Bliss G-WUFF


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graeme bird



Joined: 15 Jul 2010
Posts: 399

PostPosted: Sat Oct 13, 2018 12:15 am    Post subject: Re: Occasional engine anomally 912S - water? Reply with quote

william(at)wbliss.co.uk wrote:
Have the gearbox checked for worn splines. I had similar episodes and
did lots of fruitless fault finding re fuel system, ignition, engine
mounts and prop before speaking to Kevin Dilkes (SAS Aviation Services).

New bits, a hole in my pocket and it runs like a sewing machine.

William Bliss G-WUFF


Response appreciated.
I can see that worn splines might add to general lack of smoothness and added vibration particularly when off loading the engine. But I am struggling to understand how it could explain my symptoms. I can see that a resonance and 'chattering' could present a higher resistance maybe, like a chattering supermarket trolley wheel, but why only after 40 min or so and why not more frequently and why in just passive cruise for a fraction of a second? Did you have the exact same symptoms?

I can easily keep filled up and see if it persists. And then also change fuel type.


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Graeme Bird
G-UMPY - Mono Classic/XS FFW 912S, Woodcomp SR3000/3W CS, trutrak Gemini 2 axis AP, PAW, PFLARM core, ads-b out, 8.33khz, mode S, FP-5, Aera500, SD on Nexus, Smart A3
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