darryltarr

My Feedback: (2)

Hi Marc, and Mark,

I am using the JMP accumulator in my Hawk with the P-200SX. It was in fact me who convinced a good friend of mine to use one of these on his Hawk (Marc S build).

It is by far a superior product. Mark, you were concerned that you can’t see inside but if there were any issues they would clearly show up on the outlet side of the unit, you could look at the fuel flowing from the unit to the fuel pump.

Like I have said this unit is awesome, just as Tom Antlfinger has mentioned in his post.

I have a spare one here and will lend it to Olivier to test, if you guys want, but trust me, it is the way to go for these bigger turbines.

Regards,

Darryl Tarr

Malcolm Kay

My Feedback: (11)

Oli.. full marks ! this thread has been one of the most informative and valuable that I have read, I myself suffered four flame outs in my JL 1/6 F16 with a new 160 sx and luckily I was able to bring the plane home without damage every time due to flying in ideal conditions, subsequently I changed the whole fuel system replacing with double vents, and bigger tubing , still the problem remained, since I cant actually be in the plane when its flying ,I can't see whats going on, save to say that the flameouts usually ocurred after pulling back the throttle after a maneouver then opening up again ...i replaced the BVM UAT with a german design twice the size , with built in festo's but still the problem ocurred, i have now ordered Tom Cooks Air trap and will fly again and hope this cures my problem... I even returned my 160 sx to jetcat usa to complain ,but they tested extensively and found it perfectly ok.also i used the anti static tubing that Bob wilcox supplied just to be on the safeside, less that old argument about static applied.. so hopefully I had covered all angles........................MK

Jet Legen Agent
Jet Cat Agent
Futaba Team Pilot

olnico

Malcolm,

I see only one way to solve your problem: simulate the flight conditions.
You can do that by following the procedures I laid down in my last RCJI article ( pre-maiden procedures and tests ).

This will enable you to see what is going on in the workshop, to take your time and have a good thinking about it. You'll find the solution to your problem for sure...

Try to sort out your problem with a transparent air trap before fitting the JMP aluminium model. It seems that you have a clunk problem. Bear in mind that the capacity offered by the BVM UAT offers 10 seconds of buffer at full thrust.
So when your engine is flaming out, you have to realize that the condition that led to the flame out occurred 10 seconds earlier approximatively.

olnico

When I have finished setting up the system, I do a stress test in real conditions without the engine running. I just loop the fuel line that is supposed to feed the engine back to the fuel vent ( possibly with a Tee in a 3 tank configuration ). This way the system runs on a closed loop.
I then enter the engine test menu and rum the pump at whatever voltage is needed ( 6v in the P-200 SX case ). I can then have a good look at what the system is doing at a simulated full load.
While doing this test, I move the plane in all the possible positions ( ie: nose up, nose down, both sides, inverted ). I always keep a good look at the air trap behaviour and any air bubble entering/exiting it, as well as at the engine fuel feed ( which is looping back to the tank and not connected to the engine on this test ).
I also do the same test while feeding the fuel back to the my Jersey modeller field tank ( open loop ). This way I can see the behaviour of the fuel clunks when the tanks empties.

Try to remember in what position your plane triggered the flameout condition ( t-10seconds ). Then place your pane in this position and watch the UAT behaviour in the pump test run mode. Then try to understand what your clunk is doing during this sequence.
I have had similar problems with the F-84G and P-160SX running on the BVM UAT. The UAT was not offering enough buffer protection in my case...

Robrow

Oli, how do you simulate the real pump load/pressure differential which includes engine back pressure (case + fuel injector pressure)?

Rob.

marc s

Darryl,

Good to hear you are having good results from the unit, it helps to have referrals.

I fitted a 'ball' UAT a few years back to an Olympus turbine, seemed like a very simple device, wondered if anyone has had experience of this type of UAT....

marcs

olnico

As far as I have experienced it to this stage my answer is simple: you don't need to.
This load is negligible compared to the pushing capability of the pump with a Jetcat engine.

Robrow

OK, you may find a problem in this area as you gain more experience, this also affects the feedback to the ecu as the operating conditions of the fuel pump are different under a real stress test. This may be the type of problem which Staale is experiencing in the other thread?

Rob.

David Gladwin

Sorry if I have missed it and its already been said but I have found that the Orbit clunk with inbuilt filter screen causes cavitation when used with larger engines, they work very well indeed on engines upto, say, Supersport size but I simply could not achieve full rpm on my Wren 200 XL. Only when looking at the fuel lines through a magnifying glass could I see the TINY bubbles in the fuel. Replacing the Orbit with a standard clunk and the problem disappeared.

Heartily endorse the positive comments about the PST Bubble trap, works a treat and the engine, PST 1300, on my Reaction continued to run, but not at full power, with only about half an inch of fuel left in the bottom of this tank.

Another ideal hopper tank is one of the old JPX oil tanks, they are VERY strong and rigid and when fitted with large bore tubes, center pick up etc., have never given a moments trouble on engines as powerful as my AMTNL Pegasus HPES and JetCat 200.

Regards, David Gladwin.

olnico

Sorry Rob,
I don't really understand what you mean.
I am talking about testing the fuel system under realistic flight conditions. Not the engine system.
In this type of test, the pump is set to a higher volatge that what is achieved at full thrust conditions. In that example: 6v for the P-200 instead of 5,5v. This largely makes up for the load difference given by the engine downstream.

BaldEagel

David

I am using an Orbit clunk without a UAT on a 120SX without problems, (Supersport= 17.4Lbs 120SX= 30Lbs) I have been able to run the fuel down to approx 3mm depth in the main tank before any bubbles came up the feed line, the majority of the clunk was not immersed in fuel, I think your bubble problem may have been elsewhere rather than the clunk, where you using the Orbit clunk with or without a UAT? What size tubing was supplying the pump?

Mike

David Gladwin

The ONLY thing I changed was the clunk, problem cleared, was/am using larger Tygon. The filter was new so not clogged, and yes I have used an orbit clunk on JC 120 but nothing larger. So after the Wren experience I limit the Orbit to the Supersports and JC 7 and PST 600 thus anticipating any slight clogging which MIGHT affect the larger engines. The mesh is extremely fine.

Regards, David.

Robrow

OK Oli, I will try to explain a little more.

The fuel system begins with the refuel point and ends with the engine vapouriser needles; it also includes the fuel computer which in our case is the ecu.

In order to simulate real fuel system conditions you either have to artificially load the pump or run the engine (as Staale is doing) simply increasing the pump voltage will not do this.

As an example: It is not unknown for fuel pumps to cause what appears to be a fuel supply problem, the pump may have a nominally on spec fuel flow when not under load, but as back pressure is increased a u/s pump will not be able to cope with demand. This can happen even with a new pump, the quality of electric motors used does vary.

I have a simple rig that I cobbled together years ago when I started making my own engines and fuel pumps; the rig gives pump rpm, voltage, current and inlet/outlet pressure. Back pressure can be varied between zero and 100% with a valve.

Hopefully that makes things clearer

Rob.

i3dm

My Feedback: (51)

Great thread - signing up !

Craig B.

Hi Mike,

You will be able to run one for a while but it is only a matter or time before the orbit clunk (and similar felt ones) clog and start to cause an obstruction. Problem is, unless you are lucky and get to see vapor bubbles emanating from your fuel line out of your header tank upon startup one time, the first knowledge of it you will have will be a shut down in flight. You get bacterial growth forming plaques in these things (and in fuel) which probably contributes to the blockage problem.

I first came across this problem with a Simjet 1200 installed in my Renegade at a jet meet in Adelaide in 2000. Don't think for a moment that they can't also affect the smaller engines, just because they don't 90% of the time. These fuel pick ups were designed for use in PETROL applications where fuel flow rates a re very low, not the high flow rate applications we are using them in. They might be chemically compatible but they are not FUNCTIONALLY compatible. Use them at your own risk. Better still, set up a test rig with you fuel pump on a regulated power supply. Grab some of these filters, old and new and test by slowly increasing your pump voltage to the point the fuel on the suction side cavitates. Even better, stick them in a soft walled, rectangular header tank and see how you get on. Be prepared to be alarmed at your findings. You will then probably ask yourself why half the stuff on the market is for sale!

David, I remember discussing this issue with you a long time ago when you were having issues with vapor bubbles and your Wren in one of your hawks. Glad the change eliminated the problem.

Regards,

Craig.

olnico

OK Rob, now I see what you mean.
The way I've designed my test is to be able to put the plane in flight configurations/positions without the hassle of an engine running ( which would render the positioning and observation of the air trap nearly impossible on large planes ).
I've covered the elimination of the last fuel system element ( ie the engine ) by checking the pump voltage difference with and without it during the blank test / engine test.
For example, on the P-200SX the voltage difference at 750 ml/min is 0,3V. I'm simply doing the fuel test 0,5V higher than the max load.
The next step would be to place a tapered tube at the end of the fuel line to simulate the engine fuel injection system load.

BaldEagel

Craig

I have never been able to find a similar clunk to the Orbit as its very large, has a filter membrane in a cage around the outside and felt I belive internally, inspecting my fuel supply lines during start up and after a run I have never seen a bubble small or otherwise, I don't use a header tank or UAT so have eliminated that as a potential problem, in fact after two years and over 200 flights with the same Orbit clunk I have not had a problem or any bacterial growth, this of course could be due to the different climatic conditions between the antipodies and the UK.

Mike

SAP_2000

This is not my experience.
See [link=http://www.rcuniverse.com/forum/fb.asp?m=9381070]Post 89[/link] and then [link=http://www.rcuniverse.com/forum/fb.asp?m=9384181]Post 99[/link] in the 200sx thread.

The pump easely pumped 750cc in 52 sec even with a restrictive fuel valve @ 5,5 pv but could not deliver the 750cc the p200sx needs at full throttle (112k) pr minute when running the engine in real life at pv 6,2. Only got 109-110k @ pv6,2 so the engine itself must create a considderable amount of back pressure.

On a well working system. When you unplug the hose from the engine and putting it in a bucket or closed loop and run the pump at the same voltage as the max rpm voltage, the pump will pump quite a bit more than the enginge consumes at max rpm because there is no (almost) any pressure left on the pressure side of the pump anymore.
I hear the fuel pressure in our engines is typically from 2-5 bar.

I remember some general specs from geared bilge and fresh water pumps used in in boats and cabins. If a pump is rated at say 500 liters pr minute @ 1 meter pumping height, it would typically pump 350 liters a minute @ 2 meters because of higher pressure on the pressure side.

Will test this with a manometer the next time I have an engine in the test bench.

ww2birds

My Feedback: (14)

FWIW, I've seen the Wren 160s run on the testbench here in the USA and the fuel pressure going into the engine is over 80psi, or 5-6 bars. Sounds compatible with the 2-5 bars in the previous post.

Dave

olnico

Hi Staale,

As I said in the P-200SX post, I measured a drop of 0,3V at full thrust condition between an open system and one with the engine.
Since I have an old P-200 out on the bench right now, I will do some more testing again.

u4eake

Hi all,

I have also been struggling with bubbles in the fuel with my P160 in my T22 warrior. Probably the cause of my 5 flame outs so far, of which the second one did quite a bit of damage to the plane (repaired).
The 2 last flame outs both occurred while going vertical full throttle.
I am also using the BVM UAT. I have a felt clunck in the main tank (2l), brass pickup tubes in the 2 side tanks (0.4l each) which are put in series. 6mm tygon tube until the UAT, then 4mm to the pump and turbine. 4mm ball valve in the suction line and fuelfilter and fuelvalve between pump and turbine. So in all quite a restrictive fuelsystem.

BUT it used to work for the 25 first flights. On the video you can even see a full throttle vertical without problems, while these days 2 consequative attempts on vertical have both resulted in flame out. My guess is that the felt clunk has clogged a bit and with the cold temperatures, fuel is thicker and the P160 consumes more.

Observations :
After a flight there would be air in the UAT, even if the main tank was still far from empty.
Full throttle the UAT would collapse a bit, not until the sides touched the sac, but still quite noticable.
No kero leaks could be observed.
After standing on its tail for a week (UAT in upright position), there would always be an airbubble in the line to the pump. Even when the UAT was made completely airfree, after a week there would be an airbubble in the line and in the UAT.

I changed piping to 6mm tygon all the way to the pump and got rid of 20cm pipe between pump and turbine. I replaced tie-wrap safeties with wire safeties. Got rid of a festo connector in the push line. No avail.

Further obervations :
When refueling there would be no bubbles forming in the UAT. When reversing the refuel pump and drawing the fuel back through the UAT, the UAT would collapse and bubbles would form.
Same when running the fuel pump in test mode at 4.00V. UAT collapse and bubbles forming in UAT. Bubbles regulary also reaching fuelpump (audible but not visible)

Replaced UAT with an identical one from a friend : no avail.

Then I thought of an interesting experiment : I filled a verterinary syringe (without needle) half with kero, got the air out, put my finger on the top and sucked it vacuum.
Result : the kero starts sparkling and foaming like a fresh pint of beer !!

So it's clearly the vacuum that gets you. My guess as an engineer is that this is not actually cavitation (vapourbubbles should then collapse when pressure is normal again, which they don't) but it is air that's dissolved into the kero and that comes out under vacuum. Much like caisson's disease with divers (nitrogen dissolves in the blood at high pressure and forms bubbles when pressure drops rapidly) or with beer or coca cola (CO2 is dissolved in the coca cola or beer to make it sparkle when pressure drops).
Ofcourse air gets plenty of opportunity to dissolve in the kero when we shake the can to mix our oil.

This would also explain why I get a bubble in the line and UAT after a week. When standing on its tail, the main tank is well below the UAT, so the weight of the fluid in the line places the UAT under slight vacuum. Air slowly dissolves in the UAT, but also in the sac inside the UAT. The air that dissolves inside the sac goes up and collects in the line to the pump. Air ouside the sac collects in the UAT.

This also explains why regulary the bubbles in the UAT reach the pump. Those outside the sac stay in the UAT, but those forming inside the sac go straight to the turbine and cause a flame out when they've combined into a big enough bubble (my filter does an excellent job at combining the small bubbles).

In all pretty much the same story as olnico, exept that I think it's dissolved air instead of vapour bubbles from cavitation.

Now how to solve it ?

I see 2 possibilities :
1) Make sure there is little or no vacuum (big bore and short feed lines) so no air dissolves, but this ain't always easy.
2) Make sure dissolved air can't reach the tubine. (a central pickup with no sac may do better here then a UAT)

The PST airtrap may score well on the second solution. It has no sac that will capture and collect bubbles forming inside it and send them to the turbine.

Where can I order such an airtrap ?

Discussions on my theory and confirmation of the syringe experiment are welcome !

olnico

Thank you for the feedback.

I've tried your experiment and got the same result. However I am not sure if the bubbles are made of air. That could be CO2 released by the kerosene or some kind of intermediate gas.

Anyway, the result is the same: as soon as the pressure in the system is dropping below a given value, the liquid will cavitate and the bubbles will take a long while before dissolving again in the fuel.
They'll typically end up in the engine or in the air trap if triggered upstream.

Just as a reminder. The Bernoulli law says that when the diameter of the pipe decreases, the pressure in the pipe decreases.
So watch out for any restriction in the line that could cause cavitation on the suction side of the pump...

Hinckley Bill

My Feedback: (569)

Rob and all contributors,

Just found this thread and to say it's informative would be a massive understatement.....thanks to everyone for providing desperately needed information to the rest of us.

Rob,

Any chance you could provide some additional information/pics on your "simple rig" for testing?


Bill

alanjets

hi all thanks for all the info could anyone tell me where can in find the pst bottles in the uk

olnico

u4aeke

I talked to a General Electrics engineer a couple of days ago. Yo were right. These bubble that appear when applying low pressure to kerosene are air bubbles.
Kerosene can trap an impressive amount of dissolved air that will release as micro bubbles as the pressure drops ( either when an aircraft is climbing or depression is applied to the system ).
This is why real size aircraft have their pumps in the tank...