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HelicopterTurbine Helicopters › Turbine cut-out mid flight - white smoke!
12-30-2009 01:22 AM  7 years agoPost 21
windy62

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USA

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Have you refueled the heli since the "flameout"?

It appears to me the header tank is still FULL, which means unless there's an air leak between the header tank and the engine, it would appear to be some fadec setting vs a fuel feed problem...

Is it normal to hang the header tank off the side like that??

windy62

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12-30-2009 01:45 AM  7 years agoPost 22
Jerry K

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Houston Area

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The fuel line from the UAT to the fuel pump appears to be to long which can cause the fuel to aerate{vaporize} creating an air bubble. The fact the flame out was followed with white smoke indicates an air bubble, high throttle also suports the aeration{vaporize} thought.

Try relocating either the UAT or fuel pump closer together to shorten the fuel line. Also it is not a good idea to reduce the fuel line size on the inlet side of the pump as was refered to in a previous post. That line needs to be free of any restrictions

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12-30-2009 03:55 AM  7 years agoPost 23
ppridday

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Detroit Lakes MN

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You are correct Jerry. I should correct myself here. I used small pieces of smaller diameter tubing over the fuel tank brass tubing and over the fuel pump nipple and then forced the supplied tubing over top of the smaller pieces. This ensures that NO air will be drawn in at the tubing connections. Sorry for the confusion....

Paul

"There's someone in my head, but it's not me..."

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12-30-2009 02:33 PM  7 years agoPost 24
Chris Bergen

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cassopolis, MI USA

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The fuel line from the UAT to the fuel pump appears to be to long which can cause the fuel to aerate{vaporize} creating an air bubble.
That's odd, In our Intrepid Turbine, the fuel line from the UAT to the pump is at LEAST 12" long, using standard 1/4 OD tygon, and have not experienced that type of problem...

As has been discussed before in another arena, the accel/decel parameters play a HUGE part in how the engine performs when asking it for max perfomance manuevers like a full throttle climb out then STOP. You don't even have to move the stick down below the halfway point, if your decel is too low, just moving from full stick to HALF CAN cause a flameout, with the very telling puff of white smoke. Been there, done that

I do agree, it's not a bad idea to replace old tygon fuel line, it does get hard over time. Also an easy way to tell if you have an air leak somewhere is to visually LOOK at the fuel line going into the turbine. You should see NOTHING except clear fuel...Any sign of bubbles is a strong indication that Matt is correct.

Chris D. Bergen

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12-30-2009 02:54 PM  7 years agoPost 25
Chris Bergen

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cassopolis, MI USA

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A quick question, How do you have your throttle trim set when flying?

Chris D. Bergen

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12-30-2009 06:44 PM  7 years agoPost 26
hazchem88

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W.Mids UK

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I'd be intersted to learn why a smaller diameter fuel pipe in the inlet side of the pump makes a difference.

I have been told before how pipe diameter either side of a pump affects pressure or whatever but don't know the details.

can someone please explain or give a quick overview on this?

thanks

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12-30-2009 07:31 PM  7 years agoPost 27
Jerry K

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Houston Area

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The fuel system on turbine aircraft {models} works under atmospheric presure, there for in order to move the fuel from the tank into the pump, the pump must create a presure lower than the tank. This pressure is refered to as a vaccum. In other words the pump is sucking fuel out of the tank.

Gear pumps which is what the fuel pump is do not like to work at low pressures they can begin to cavitate. So the inlet tubing should provide a minium amount of restriction to the fuel into the pump. Every bit of restriction created in the tubing must be offset by the pump creating a lower pressure in direct proporation to get the fuel moving.

When the pump is "sucking" the fuel by lowering the pressure into a vaccum the kero has the ability to be vaporized in the lower pressure creating bubbles which the pump dosen't like. It only takes one bubble to kill the flame in the turbine. Once the flame is out in the turbine, fuel following the bubble will be injected into the turbine causing the white trail out of the dead turbine as it spools down.

Turbines move a large quanity of fuel compaired to other forms of power. This makes fuel flow in a turbine very critical.

Tygon fuel line is not a very good choice for turbines. A better choice is 6mm poly, a thin wall tube which makes the I.D. larger and it is stiffer making the turns and bends smoother proving less restriction.

The pressure side of the pump runs around 40-60psi making line size less critical so you will see 4mm tube used here almost universily

Jerry

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12-30-2009 08:18 PM  7 years agoPost 28
hazchem88

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W.Mids UK

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hi
thanks Jerry that all makes sense.

But does this contradict what pfriday was saying in an earier post';
" Bell Bloke had some ideas for me to try out and it seems to have cured my problem. This basically was using a smaller diameter fuel tubing all around and then wrestling it over the tank piping and fuel pump nipple."

If I understand this right he put smaller diameter fuel pipe on which would cause more resistance?

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12-30-2009 08:52 PM  7 years agoPost 29
iandavidson99

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Ipswich, England

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Can I just say a massive thanks to everyone who has helped in trying to diagnose the reason for my flame-out.

Last night I had a long and very educational phone conversation with a contributor to these forums and after going over the helicopter with a fine-toothed-comb, it seems the most likely cause of my mid-flight flame-out was down to the fuel pipe going between the header tank and the fuel pump...

This section of pipe was secured to the metal chassis using a tie-wrap (cable-tie) and on inspection it was clearly too tight and pitching the pipe slightly. This, in combination with the fuel pump running flat-out when I asked for full throttle, probably caused this pitched section of pipe to be sucked together and thus cut off the fuel supply to the turbine.

Lesson learnt about tie-wraps and fuel pipes

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12-30-2009 10:28 PM  7 years agoPost 30
windy62

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USA

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What a load of rubbish!! There is NO way that the little fuel pumps used in our hobby aircraft are able to create the vacuum necessary to "Vaporise" kerosene!!

If the line gets totally pinched off, then fuel simply stops moving!! Yes the pump will cavitate, but no "bubbles" are created from any kind of vaccum...

If a fuel line was pinched slightly at one point, then there would be a lower pressure area at the point of the pinch, but as soon as fuel gets PAST the pinch, the pressure rises back again! It's simple hydraulics.

windy62

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12-31-2009 04:50 AM  7 years agoPost 31
Rappy 60

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Paris, France

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Ian,

I guess really the best advise is find someone who has some turbine experience to look it over. Nothing beats a one on one with an experienced turbine operator.

Dale

Load "*",8,1

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12-31-2009 04:55 AM  7 years agoPost 32
ppridday

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Detroit Lakes MN

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Just to clear things up again for all as I mentioned in my 2nd post, I did not use a smaller dia tubing throughout but only small sections (say 5mm long) over the brass fuel tank tubing and fuel pump nipples. Then the normal tubing is stretched over these small nibs of tubing to make a strong seal against ingress of air which would cause bubble and cause the ECU to shut down the turbine... Again, sorry for any confusion that I caused with my first post...

Paul

"There's someone in my head, but it's not me..."

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