PaulD

My Feedback: (39)

Had a buddy of mine sell a turbine to someone who later complained that the turbine ran eratically and underperformed. He had him send it back which he did including his fuel plumbing. Turns out he had reduced the suction line from the UAT to the pump inlet down to 4mm tubing which has a pretty small ID. The entrapped air in the Kerosene was likely causing the pump to run erratically and making it very difficult for the ECU to control the engine.

SAP 2000 commented on pump flow laws which are o.k. for impeller type pumps, however, the fuel pumps used in turbines are positive displacement so those rules would not directly translate over. What is more likey to happen is as pressure on the discharge side of the pump increases, the volumetric efficiency of the pump would decrease (less flow for a given speed) and the motor rpm would decrease due to increased load. Theoertically, the ECU should then increase the voltage to the pump to try to make up for the reduced flow, however, the ECU is measuring engine rpm and temperature not pump pressure so closing the loop can be difficult esp. if conditions are dynamically changing such as air bubbles appearing in the feed line to the pump. This is also why additional restrictions in the fuel system result in higher pump voltages as the ECU trys to compensate.

Another note is that while the entrained air that appears under low pressure conditions is not "cavitation" itself, it will likely result in cavitation under these conditions.

I was really impressed looking at the fuel system parts supplied by Tom Cook on the Firebird - the fittings at first glance seem oversized, however, they are totally appropriate and well engineered for the application and is what is needed to have trouble free fuel flow in 160+ turbine installations.

A quick google search on cavitation turned up this article which talks about entrained air and the damage it can do under cavitation conditions:

http://www.machinerylubrication.com/...ine-filtration

PaulD

u4eake

Olnico, thanks for your confirmation of the experiment and my theory, but most of all thanks for this thread which will hopefully save a lot of planes from the dreaded 'pfiew' and white smoke :-)
I have meanwhile replaced the filt cluck with a large bore open one, enlarged the pipe inside the tank to 4mm ID, put the 2 small tanks in parallel instead of in series and gave them each their own 4mm ID feedline to the maintank.
These measures have brought max pump voltage from 4.25V to 3.90V and during testing I get no forming of bubbles upto a pumpvoltage of 5V. Furthermore my maintank now no longer collapses when the small tanks are still full and giving full throttle. Collapsing of the UAT is also noticably less, and the collapsing is an indication of the strength of the vacuum.

Still should replace the 4mm ball valve in the suction line by a 6mm one or get rid of the valve all together

I've read somewhere that kero can dissolve upto about 10% of air

When the weather permits, the real test will come : a full throttle vertical climbout.

Didier

I also had some problems with a standard UAT.
My Ultra Lightning is powered by a AMT NL Olympus HP (26 oz/min fuelflow) and after each flight I had a lot of air inside the UAT.
When running on ground , I saw at full power small bubbles entering the UAT and the UAT collapsed also a bit.
I was in shock and I was very lucky no flame-out happened yet!!

I asked Sandor from DIGITECH if he had a sollution.
He made a "special UAT" for me. It's a UAT with 3 big bore nipples.
As the Ultra Lightning has 2 saddle tanks, each tank uses it's own nipple on the UAT. So the T-union is no longer there before the UAT.
After installation, I made a couple of test runs on ground. I was surprissed the side walls of the UAT where no more collapsing.
Better, the UAT is no longer a "moving part"!!!! :-)
I made 6 flights yesterday and can report I have no longer cavitation problems at all.
The UAT is almost full after 7 minutes flight (9 minutes runtime) and lot's of aerobatic (rolling loops, rolling circles) where performed.
The picture shows the air in the UAT after flight.
THIS is the solution if you fly big turbines with a parallel fueltank set-up!!!!! :-)

highhorse

My Feedback: (2)

I would not be shocked to learn that this product [link=http://dreamworksrc.com/catalog/product_info.php?products_id=1596]Hi-Flow Air Trap[/link] , which Todd began carrying within the last two weeks, was a direct result of this thread. Good job, Oli !!

digitech

My Feedback: (10)

we made some 3 nipple setups 2 years ago for multiple tanks

my own p-200sx runs 112k at full power only 5,8 volts.
no cavitation or what so ever.
i think the 3 nipple is the way to go , it also eliminates the T pieces needed for a 2 tank setup when running in parralel.
we will be offering these also when ordering a UAT

Bob.R

My Feedback: (2)

I replumbed my F-16 fuel system with big fittings and 3/16 tygon for a P200 install, but the UAT was still collapsing and foaming the fuel under sustained high throttle flow rates. I made a couple of mods shown below.

Ply plates were epoxied to the sides of the UAT and wrapped with a couple of tie wraps. The UAT was cleaned and scuffed prior to liberally applying epoxy. The bond to the polyethlyene is not great, but it is more than adequate to keep the sides of the UAT from collapsing. Also prevents the UAT from expanding during fueling.

If even a small air bubble forms at the top of the UAT, the high velocity fuel stream hits the air bubble and foams the fuel. Small foamed bubbles coat the UAT bag and ultimately coallesce - a bubble will then burp through the UAT bag. It seems likely that the small bubbles coating the bag also increase resistance to flow. I made a 3/16 fitting that goes lower in the UAT so that the inlet fuel stream enters below any air bubble at the top of the UAT. The only down side, and it is a big one, is to make sure that all air is evacuated from the top of the UAT during fueling. So far, any air at the top of the UAT has been flushed out during fueling.

After replumbing the tanks and modifying the UAT, my pump voltage dropped from 6.0 to 5.2. After several flights with rolling and vertical manuevers, only a very small bubble has formed at the top of the UAT.

P.S. I just received a PST air trap. Good looking piece of hardware.

fast jets

My Feedback: (2)

We have been working on this for some time now, I was not having trouble with trap walls coallescing but I was having trouble with the tank seams cracking when filling to fast.
I really think that if guys would just give our trap a try you would be surprized at how well they work and how simple it is. Fill and fly, nothing more than that.
I have pulled 60 ounces throw or Hi-Flow trap and the Hi-Flow tank fittings that I am working on. The trap showed basicly no sings of coallescing, it would flow way more than that with. Ask Todd at Dream Works, he is running AMT Titans using our traps.

John

kumpol

Hi Guys,
Someone might interesting on ACS STATION for PST AIR TRAP. Cheers Kumpol..
http://image.ohozaa.com/show.php?id=...be05790d5f0f69

Robrow

Jet Central recognise the requirement higher flow capacity in their Mammoth engine fuel supply system, the fuel pump has thicker gears to keep the full power voltage reasonable.

It is also supplied complete with a high flow air trap, (not sure if this is the same as previously mentioned), which has the big bore nipples and replaces the coalescer filter with the central low restriction pleated filter.

Rob.

marc s

A while back I was given a "ball' type UAT to run with an Olympus, I saw the jet fly a few times in the UK before it was shipped abroad the system seemed very cleaver and simple - the only issue being it took up a fair bit of space.
Has anyone had ant experience with this unit, and where/who makes them, I will shortly be starting a project which runs 2 x Olympus turbines.

marcs

olnico

Yes, obviously JC people are open to new/different solutions. This looks like a very nice setup. The only ( small ) problem I can see here is the size of the tank. Given the flow involved, I'd rather have seen a bigger unit like the ones that Sandor is selling for big engines.
By the way, I'd be curious to see what solution Frank Turbines and Behotec and going to come up with on their new monster 300N+ engines.

olnico

Marc, I think that this is a German system. Possibly coming from Turbo Didi. I've seen it a couple of times on the German jets forum...
No feedback available from my side.

I can already feel the nice project coming...

mauryr

Reading this thread 2 ideas come to mind, weird as they may seem maybe there's some good in them?

olnico

Hello guys,
Following my article on RCJI, I am bumping this thread up.
I have been testing the new BF Turbines B300F and the flow requirement on this engine can be as high as 900 ml/min.
All the problems that we have been talking about on this thread are proportionally increased on this engine.
So I had to look for the biggest bore accessories and apply best practices on this engine setup.
I got very nice results with a re-drilled PST air trap, 6 mm brass tubes, re-drilled Dreamworks mega clunks.

Here is the latest fuel accessories table that I made for the article and updated:



Note that the OD column for barbed fittings gives the smallest outside diameter ( non barbed area ).

highhorse

My Feedback: (2)

More of your awesomely thorough work. Thanks again, Oli.


PS: I will continue to ask every now and then for you to pleeeeeeaaaase (!) re-rank the engines listed in the RCJI database (an incredible piece of work) by thrust rather than by efficiency. That would make it SO MUCH EASIER to look up a particular engine, and the efficiency isn't the only thing that's important in the table........

BaldEagel

I second that, if trying to make up your mind which Turbine to get next the first thing to look for is thrust, if they where all grouped together in thrust order it would make life much easier to compare like to like at the moment its a difficult exercise, as highhourse say's efficiency is not the first thing on most people's minds when looking for a turbine.

Mike

mick15

I have for some time now been pressurising my tanks from the gas port of my Jetcats. I use a simple adjustable pressure release valve at 4-5psi dumping excess pressure into the fod screen. I do not use a UAT of any kind.

m

Jgwright

Olivier

Taking Mick's point I wonder how many of the problems with the larger engines can be solved more simply with not using a UAT.

Wren for many years stuck to 3mm tube for the Wren 54 and 44. I have even run a Super Sport on single tank quite happily with 3mm Festo tube. However, I have never used a UAT.

If you want to do some flight tests I can send you a pleated paper clunk to try in your test Phoenix.


John

olnico

Mick, could you post a picture of this setup please ( on the valve side ) ?

olnico

Hi John,
I used to have these ones in my DF planes. I think that the first plane that I had with a UAT was the Mystère IV in 1996.
I haven't used these for so many years. Maybe it's time to give them a try again ?

Jgwright

Olivier

I think you would be surprised with the results. I shall send one off to you. I use it in a standard Dubro tank with the same brass tubing that Dubro supply. Dont be afraid to fly aerobatic manouvers until you are ready to land. If you don't mind running the tank dry it will give you a really good indication how little fuel is left.

John

mick15

Oli, you won't gleen much from a pic, when I get to my computer I will draw you a diagram.

m

Pressure regulator (diagrammatical).

m

haisanjafri

hi guys,

where to use hard jetcat pipe and where to use tygon 6mm? got tomahawk futura tank, bvm uat with P100RX

olnico

Hello Haisan.
Basically, the more rigid calibrated 4 mm Festo tubes go into the Festo connectors from the engine to the pump.

The Jetcat user manual is fairly well written on that matter I guess. You can follow it with the 100RX as the pump max flow is not too high.
http://www.jetcat.de/downloads/rx--e...manual_eng.pdf

However, if you want to reduce the suction drag upstream the pump, tubing from the air trap to the pump inlet can be of a higher diameter.

Here is a little more insight about fuel systems:
http://www.ultimate-jets.net/blogs/f...considerations

REDBULL FRANCE

Test FrankTurbine:
http://www.youtube.com/watch?v=SuxSLY4qtTA#t=43