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EC135

Old 26th Jan 2014, 11:03
  #1001 (permalink)  
 
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Sure SS

The narrow point of the swimming pool, is lost on you. No it would not be like the bath plug at the bottom in cases where the unuseable is so high - there is a big difference - think about sharpness of 'fuel out event', (once you have got yourself to the point where you are running out of fuel). The difference between v high and v low unuseable quantities is the main point i make and i think is lost on you.
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Old 26th Jan 2014, 13:17
  #1002 (permalink)  

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AnFI (really!);

From where exactly is your straw sucking up the fuel in the supply tanks?
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Old 26th Jan 2014, 14:26
  #1003 (permalink)  
 
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AnFI, and any others still confused about this:

***before you listen to me, reread post #83, brilliant description***
***I don't fly 135's, but the design features are not unique***

What SS is trying to point out is that the goal of designing small feeder tanks, and it is a common design feature in one iteration or another, is to prevent the scenario you are describing.

Yes, the main tank transfer pumps will move in and out of fuel but they do not supply the engine. They are there to keep the supply tanks full.

The smaller feeder tanks and feeder pumps supply the engine, with significantly less space for sloshing fuel.

Yes, there is a possibility of a pilot moving from hover to forward speed and leaving the transfer pumps in an inappropriate configuration, but it is a known issue. And as was posted, the checklist response will address this.

Finally, if the pilot has turned off a main tank pump because of a light (indicating run dry) then it will not be intermittently sucking fuel later.

-----
I am not trying to start a pi$$ing match, just to point out that the system is not unique, particularly complex, or obviously flawed. Design is compromise. We get paid the big bucks to figure it out.
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Old 26th Jan 2014, 18:25
  #1004 (permalink)  
 
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P&A,
You really need to look back through postings! I recommended reading post 83 to AnFi and he recommended it to others.
Take a look at post 1471 onwards on the Glasgow thread also.
I can't remember anyone suggesting transfer pumps cavitateing, I certainly hav'nt, that would be fairly normal.
My concern with the 135 fuel system is fuel not getting to the supply tanks and being trapped in the main. Transfer pumps spitting fuel into the supply tanks, and the engine pumps then not being able to keep up with demand.

If fuel is being intermittently pumped to a hot turbine, this in theory could cause popping banging etc. on some turbo props when doing a wet start you get this effect.

Hope that's clear, I know I'm not very articulate.

Last edited by PieChaser; 26th Jan 2014 at 18:39.
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Old 26th Jan 2014, 18:59
  #1005 (permalink)  
 
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Working? ... Working?

To state the obvious: When the system is working correctly it works correctly.

The problem is not the big bucks paid to pilots to figure that out, it's the time a pilot has when it goes wrong.

In Glasgow: Engines out, backfiring noises, adequate fuel remaining, experienced pilot and failed autorotation. Reassurance from 135 pilots and engineers.

The explanation will not be obvious until it is known.
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Old 26th Jan 2014, 19:58
  #1006 (permalink)  
 
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Originally Posted by PieChaser View Post
P&A,
You really need to look back through postings! I recommended reading post 83 to AnFi and he recommended it to others.
Take a look at post 1471 onwards on the Glasgow thread also.
I can't remember anyone suggesting transfer pumps cavitateing, I certainly hav'nt, that would be fairly normal.
My concern with the 135 fuel system is fuel not getting to the supply tanks and being trapped in the main. Transfer pumps spitting fuel into the supply tanks, and the engine pumps then not being able to keep up with demand.

If fuel is being intermittently pumped to a hot turbine, this in theory could cause popping banging etc. on some turbo props when doing a wet start you get this effect.

Hope that's clear, I know I'm not very articulate.
I did read the post #83 and referred to that. I was specifically addressing AnFI's obsession with unusable fuel and analogies to swimming pools.

My post was to reiterate that it is not a horribly complicated fuel system, and to support SS in explaining that simply reaching the limit of a transfer pump to reach fuel does not result in unreliable flow to an engine. Just less flow to a supply tank.

Glasgow is a different thread/discussion. That is why I posted here.
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Old 26th Jan 2014, 20:57
  #1007 (permalink)  
 
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Smile

Well I'm pretty happy that people are taking seriously the point i made. it does fit with the witnesses. I don't know the 135 operationally

and/but SS the answer to your question is: at the point where the fuel is becomming unuseable - which must logically be at the top (not bottom) of the remaining 95litres. (and a high unuseable is inherently different from a low unuseable, like the swimming pool) I can't say whether this results in a supply tank being filled with fuel foam or not, nor whether this foam gets to the engine nor how the engine will respond to being fed fuel foam, but it looks on the surface to be something not to be thrown out of consideration without some thought, fair enough? (ESPECIALLY as it fits the information available) Can you be certain it is NOT a factor? If so that's good enough for me.
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Old 26th Jan 2014, 22:29
  #1008 (permalink)  

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SS
AnFI (really!);
From where exactly is your straw sucking up the fuel in the supply tanks?
AnFI (really!)
SS the answer to your question is: at the point where the fuel is becomming unuseable - which must logically be at the top (not bottom) of the remaining 95litres.
Firstly, just to remind you, we don't know that the ac only had 95 litres in it.
Secondly, doesn't foam tend to be on the top of a surface of fluid
Thirdly, the engine sucks it's fuel from the bottom of the supply tank

"Well I'm pretty happy that people are taking seriously the point i made. it does fit with the witnesses. I don't know the 135 operationally"

Just who are these people you think are taking your point seriously!
If not operationally, how?
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Old 27th Jan 2014, 00:21
  #1009 (permalink)  
 
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In a nutshell

If a pickup is sucking air then clearly it is not fully immersed in fuel.

Looking at the schematic, if a 135 were steady on the ground in cruise attitude and the forward transfer pump is not functioning, when the fuel quantity in the main tank drops to ~95 l, no fuel will be pumped to the supply tanks. The supply tanks will run dry and the engines will stop.

What happens when the aircraft is flying and fuel is sloshing around? Partial fuel prior to stopping?

What might a pilot do when he thinks there is sufficient fuel aboard but the engine(s) falter minutes from base?
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Old 27th Jan 2014, 00:40
  #1010 (permalink)  
 
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Ornis,
In a nutshell, if you had read any of the many postings on this topic your question should read:
"What might a pilot do, when he/she sequentially gets a "fuel pump aft" caption cos it has no fuel to suck, a "fuel pump fwd" caption cos it has failed, reducing supply tank indications with fuel shown in the main, an Amber "Fuel" caption, 2 Red FUEL LOW captions with audio when he/she thinks there is sufficient fuel aboard but the engine(s) falter minutes from base?
To quote Silsoe Sid - "round & round & round" etc.

Last edited by Fortyodd2; 27th Jan 2014 at 08:36.
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Old 27th Jan 2014, 07:03
  #1011 (permalink)  
 
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supply tanks act as foam collectors?

well fortyodd would you say that the improbability of the scenario you paint is sufficiently improbable that we can say IT WAS NOT FUEL ?? 1^10-9??, you can't??

1 true but seems probable
2 yup
3 appreciate that Supply tank would act as seperator, which would work until the unfoamed fuel had gone. We don't know what the fineness of aeration would be nor how sensitive foaming is to different additives or blends of JetAorA1.
and also i don't think it takes much detergent contamination to make foam very persistent.

Infact if you think about it the separation action of the supply tank would be to collect a tank of foam.

It would be amazing if this were not fuel related especially with such a complex fuel system with so many permutations of event possible.

Like maybe fuel foam satisfies capacitative fuel quantity detectors.
FSII can also form a gum with water.

The point about testing is that you discover problems that (closed minded) people would not envisage. test and learn
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Old 27th Jan 2014, 08:19
  #1012 (permalink)  

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AnFI (really!)
The point about testing is that you discover problems that (closed minded) people would not envisage. test and learn
Here's a test you might be interested in;
With this mornings daily check fuel sample (after testing that all was well), I placed 1 litre of Jet A1 into an empty 2.27 litre milk container. I shook it vigourously, as you would when mixing a sports drink, for a timed 10 seconds.
Once I finished shaking the fuel in the container, I timed how long it took for the bubbles to go. After 5 seconds all the bubbles had gone.
I then added a quarter of a litre of water to the container and repeated the test, with exactly the same result.

In respect of 'foaming', what have you learnt from that?
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Old 27th Jan 2014, 08:35
  #1013 (permalink)  
 
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Morning Sid,
Glad you know what he's talking about!

AnFI, I have never said that it was not fuel but, if it was a causal factor, then there would have been some clues and cues to the crew that something was about to go wrong for several minutes before it actually did.

"Like maybe fuel foam satisfies capacitative fuel quantity detectors".

But not the thermal sensors that operate the LOW FUEL warnings.

"I don't know the EC135 operationally"

Then how exactly??

Last edited by Fortyodd2; 27th Jan 2014 at 09:29.
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Old 27th Jan 2014, 08:59
  #1014 (permalink)  

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Morning Fo2

Anticipating a certain reply from AnFI (really!), I have since added 5ml of fairy liquid (washing up detergent) to the mix. and again shook vigorously for 10 seconds. After 6 seconds any bubbles had dissappeared leaving an 'island of scum' on the top of the surface the size of a 50p piece.

I suspect that the scum is the residue left from the milk, however without scientific analysis I am unable to confirm.
What I can conclude from these tests;
1. 'Foaming' as described by AnFI (really!), does not occur.
2. I now have a very clean 2.27l ex-milk container.
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Old 27th Jan 2014, 09:18
  #1015 (permalink)  

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AnFI (really!)
FSII can also form a gum with water.
Please tell us, does Jet A1 contain FSII?
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Old 27th Jan 2014, 09:19
  #1016 (permalink)  
 
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Sid,

To make your milk bottle test more realistic, consider what would happen if pumping the resultant mix from one bottle to another with an electric pump, ensuring you are cavitating it at the same time. Also do it outside where it is cold.

edit: I presume during your shake test that the lid was on? Therefore no more air being added to the mix.
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Old 27th Jan 2014, 09:50
  #1017 (permalink)  

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Chop, Describe what you want in order to get the result you need and I'll see what I can do
Temp was 4 deg.

I presume during your shake test that the lid was on? Therefore no more air being added to the mix.
Much like the fuel cap?
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Old 27th Jan 2014, 10:08
  #1018 (permalink)  
 
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Much like the fuel cap
Even you should know the tank is vented to allow air in as the fuel is being used.
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Old 27th Jan 2014, 10:14
  #1019 (permalink)  

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Chop;
Even you should know the tank is vented to allow air in as the fuel is being used.
Of course, Tesco milk containers are renowned for being totally air tight
Besides, if I didn't spill any, there wouldn't be any replacing required
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Old 27th Jan 2014, 10:21
  #1020 (permalink)  
 
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Sid,
I believe if you mix liquid and air in a sealed container, then the air will come out of the liquid quicker than in an open container. Reason being is the sealed container will create a partial vacuum above the surface of the liquid, helping to suck the air bubbles back out.

Last edited by chopjock; 27th Jan 2014 at 10:54.
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