Thanks Cuzzy Bro appreciated ;)

WLM,

Sounds expensive!

Where was the noise from? The engine or the EMB? T model or P model?

Sounds like your starter contact. Fuel from aborted/failed start?

Loose connector not allowing enough current - contactor bouncing in and out?

Where? ECD is the holy grail.

The 135 can be a little tricky to the uninitiated!

Igniters typically don't go "bang".

Please let us know what the issue is once you find out.

Sounds like there may have been residual fuel in the chamber on start up. The question would be, why?

Pedal Forces
 

Anybody know by how much (in Newtons?) the pedal forces increase following a number 2 hydraulic failure? Nothing in the RFM - it just says "significantly". CAA medical department issue following knee surgery.

About the same as an EC130? No servo, same fenestron mirror image.

HYD System on the tail is only there for SAS/AP control.

Ask ECD?

Do NOT try to find out by turning "hydraulics off" in flight. :=

Thanks rvdt. Anybody got a sensible answer?

Hi Guys

Well when the EC engineers arrived, sure enough the problem would not repeat itself :confused:

Did every checks possible under the sun and still nothing.. so went for a short flight test and still nothing upon returning..

THEN it happened during the next start... the culprit was my external home made EPS using 2 x 12V + 1 6V batteries (30V) . We made that unit 2 years ago when we could not get a 28.5V StartPac locally. It always worked up to now, mainly running Avionics during ground tests

If using the aircraft battery or the 28,5V StartPac, no issue; but when using the home made cart, the bang bang started and a very slow starter spooling up

So that's what the engineers ascertained the problem to be:O

Recently I did the mandatory fuel system check and started the groundrun with about 180kg in the main tank. The transferpumps were switched off and the fuel level in the main tank was still reducing until reaching about 160kg and thereafter the fuel level in the supplytanks was getting lower. In the ASB EC is mentioning this fact to be normal. I do not understand, why the main fuel is reducing without the transferpumps?


skadi

The transfer pumps supply fuel to the supply tanks via pipes, at a rate that is higher than the engines can suck it up, the excess fuel pores back into the main tank via 'holes' through which the transfer pipes run, above 160kg this means all tanks are essentially connected. Hence the fuel runs through the holes to the supply tank until this point.

At a certain flight attitude you can reduce the main tank further without transfer pumps.

Hard to explain without a diagram.

http://img30.imageshack.us/img30/3640/135tank02.jpg

We had exactly the same; 159 till 139 after XFER pumps OFF, sucking at it for almost 15' before supply tank indication dropped.

I'm thinking the fuel flow of each pump being more than 12L per minute has some inertia to it before it stops flowing back from supply to main tank through overflow.

I did two runs yesterday on one we started with 100KG in the main and this burned off with the xfer pumps de-selected until 52kg only then the supply tanks started to show a reduction. We then did the second aircraft where we drained the main tank to 60kg before we started the test thinking it will take 10kg before we start to see the supply tanks dropping except we didn't. We had 12kg left in the main before the supply showed any signs of dropping.

The third aircraft the day before though started at 57kg.

I am still waiting for an technical explanation for this "phenomenon", the overflow channels are way above these levels, so the answer from RWB2 doesnt satisfy me.


HAPPY NEW YEAR

skadi

Skadi,

The transfer pipes run down to the bottom of the supply tanks, so you get a siphoning effect. Problem is a faulty NRV could in theory, let fuel flow the other way!!

So in every 135 the NRV is faulty? That makes no sense to me.


skadi

Skadi,
Either I have misunderstood your question, or you have misunderstood my answer.
The transfer pipes run to the bottom of the supply tanks, this will cause a siphoning effect so fuel will continue to flow when txfr pumps are off which would account for your fuel anomalies. This is not a fault.
My comment about the NRV is an observation of what might happen if one were to fail.

Bollix.

Does the "phenomena" spoken of coincide with ~ 3 minutes.

If so you will have to dig pretty deep for an answer.

Skadi, post #947

If the main tank was indicating only 12 kg before the indicated levels of the supply tanks began to drop...the aircraft has at least one faulty level-detecting probe in its fuel system....that's no phenomenon, it's a fault.

Were the transfer pump FWD and AFT illuminated when you started the check ?

EPAC please explain your thinking.

Why would there be a faulty probe? All that's happening is the main tank emptying itself due to the syphon effect with the xfer pumps switched off as per AD.

But I might be missing something...

Would that be the well known 'uphill syphon effect'?

TeeS

At last Pilots that understand the architecture of the 135 fuel system!

Anyone have a cutaway pic of a transfer pump?

This seems to violate JAR/FAR certification requirements:

“No engine or fuel pump can draw fuel from more than one tank at a time”

The saying goes, 'There's no such thing as a silly question", but I'll try my best :ok:

Even if the NRV was to fail and the pump was turned off or u/s, how does the fuel still flow through the pump? Surely someone at Airbus would have twigged that this wasn't quite right :confused:

Same way it flows through any other centrifugal pump.

But definitely not like the newly discovered "uphill" syphon.

Google it - listed with perpetual motion machines!

Glad to see you're on the ball, as always Sid. :ok:

With my vast experience of goldfish bowl cleaning and having watched 'Finding Nemo' a couple of times, this reverse siphoning effect going on in the 135 fuel tank seems a bit far fetched. But I guess that's the stage at which we find ourselves.

The source has to be higher than destination. We have been told that the transfer pipes run to the bottom of the supply tanks, the same level as the transfer pump inlet, add a couple of obstructions to a smooth flow, such as faulty nrv, non operating pump, a couple of sharp turns or a pocket of air and syphoning simply can't occur either way.

Having said that, anyone know if the diameter of the tubes is constant or are there different sizes of tube in the transfer system?

How many of us have run the tanks dry whilst sitting on the pad before this ad?

I can only report what I saw.

Have I taken the fuel system apart and crawled around in it? No.

Where did the fuel go, I have no idea.

The collective opinion amongst my colleagues is it's syphoning.

Why would it be uphill????? Aircraft is parked level.

The nub of it all IMHO is where does the XFER pump deliver the fuel to? Does it pour into the supply tanks or does it deliver to the bottom of the supply ?

Well I found this slide.

It looks to me like the XFER pumps are delivering the fuel to the bottom of the supply tanks...


Click me for slide

BS, not that I'm doubting your actions, however one solution is that you turned the prime pumps on and not the transfer pumps off!

When I did the check, after turning the transfer pumps off, the main tank contents remained at a figure over 200 kgs, which I assume is as it should be.

Did you get any feedback from Airbus/Bond after the paperwork was sent in, or have you questioned it outside of an internet forum, as this episode seems rather strange.

Is there a collective opinion about where the fuel syphoned out to? :rolleyes:

Therefore it can't be syphoning can it!

I tried this in the cruise, some years ago, to see what would happen with a double Transfer Pump failure as it didn't feature in the EC drills. There was 255kgs left in the main tank when the supply tanks started going down.

airbushelicopters.com
I hesitate too make this post as too many people want to ridicule and scoff.
But here goes one more time, as a very average Pilot, but some would say a pretty good Engineer!:
If you take the time to read page 5 of the above link you will see that EC know very well about the anomaly of fuel transferring from main tank to supply tanks after transfer pumps have been switched off.
There is no magic or witchcraft at work, just simple fluid dynamics.
The flexible transfer pipes are about 15mm dia and are the [U]only[U]path between main and supply tanks once the fuel level is below the fence transfer ports.
If the head of fuel is large enough, then after the transfer pumps are selected off the syphoning effect will continue pulling fuel through (for want of a better word) a freewheeling pump for several minutes.
The 4 submersible pumps are identical apart from the main tank pumps have NRV fitted, the supply tank pumps do not. There is a very good reason for this, the supply tank feed to the engines is non critical in respect of fuel drain back, the transfer pumps however are critical hence the fitting of NRV/check valves.
Now for goodness sake don't take my word for it, go and ask your Chief Engineers!

Not an IT engineer then, the link doesn't work :rolleyes: :suspect:

Surely the reason there isn't a NRV in the supply tank fuel line is because if there was, not only would we have to continuously have the prime pumps on, if it was to stick, the respective engine would cut off! Nothing to do with drain back!

The link works when I click on it Sid!

Thanks PC, it does now. Must have been caught in the rush!
You're missing a / before the U in the second box if you wanted to underline 'only' in your previous post ;)

Let me do a difficult engineering cut/paste;

"This can be explained by the fuel system architecture of the helicopter and is a normal behavior."

How can it possibly be syphoning if it is the same body of fluid?

???? I think this is nonsense; I should think that the main reason for no NRV is, that as long as the respective engine is running the engine driven fuel pumps are maintaining the fuel feed to the engine by means of suction...thats the reason why you switch the prime pumps off after the fuel flow has been well 'established' (engine started). Even if a NRV was installed in the feed line, the engine pumps need to 'suck' just a little harder to overcome the springload of the NRV. No need to do that.
So, NO, you wouldn't need the prime pumps continuously,
and suppose the NRV stuck in closed position....that can only happen in an engine off situation, and you wouldn't be able to start the engine......stuck in the open position.....you wouldn't notice the difference.

And also SS,... i've been reading a lot of posts of you lately, and also quite some replies to your posts, and I believe I've come across the word 'arrogance' more than once. Must be a reason for that:rolleyes:

....and as to why the main tank continues emptying into the supply tanks for some time after shutting off the XFER Pumps...I don't know, but witnessed it on two machines.

Just thinking...The engines sucking in fuel via the inletport of the prime pump.....transfer pumps delivering the fuel from the main tank to the supplytank. Assuming the transfer fuel lines exits situated somewhere on/near the bottom of the supply tank...the fuel flow generated by the transferpumps is way larger than the suction flow to the engine. Is this creating some swirl effect in the supply tank.....when you suddenly stop the supply from the transfer pumps; the swirl will continue for a couple more minutes, creating static pressure drop at the exit of the fuel transfer line, and thus continue pulling fuel from the main tank. The swirl effect slows in time and after some minutes the static pressure drop ceases to exist and the engine starts sucking from the supply tank........
So I think a lot of sucking is involved:O

so if you did a similar check without switching on the transfer pumps at the beginning of the sequence....no swirl created,.... the supply tanks would start emptying rightaway. (assuming the main tank Qty level is below the overflow channels)

Spot on Yellowbird.

So yellowbird, what cracking pressure is needed in a non return valve?
I'm glad you told us why we turn the prime pumps off after engine start, do you know why we may need to turn them on in flight?
My statement merely highlights the questionable action of placing an obstruction such as a nrv in a crucial fuel line if it wasn't needed :ugh:

Yep, because I question things :ok:

Such as, when you say;
Do you consider it arrogant of me (expecting the obvious answer) to highlight an earlier post;

"Phoinix; We had exactly the same; 159 till 139 after XFER pumps OFF, sucking at it for almost 15' before supply tank indication dropped."

My, thats some swirl effect going on!

Virtually none, they are not spring loaded.