PST and AMT engine performance.
 

Re Ehabs reply.
I always tip the tail of my jets on the ground to ensure the hopper is purged of air (by bringing the tiny bubble to the top front of the tank where the pipe which then takes fuel to the main tanks is located) as the aircraft is refuelled. Because of the tank plumbing layout this results in virtually zero air remaining in that tank after refuelling and, in fact, after landing. But your reply puzzles me . If the UAT is angled to minimise air content when refuelling and to ensure proper running on the ground how does the UAT know when it's airborne and start to break up the bubbles ?

I am not being faceitious, just curious !

No reply to my email to BVM about this subject but I thought David Shulman or SWB might have chipped in on this thread. I would value their comments.

Anyway as I said the PST and AMT jets worked really fine for me last week (just as lots of TJTs did too ) and now we have had some rain in our part of Australia, the total fire ban may be lifted and I can again try the Sabre with the PST and UATincorporating all yof your recommendations.

Many thnaks for all your contributions.

BRG,
David Gladwin.

PST and AMT engine performance.
 

Hi David,

Half your luck on the rain front. We didn't even get enough to register on the rain guages and are still officially drought declared.

I may have to make the trip up to Newcastle to get any jet flying done this summer.

Garrett

PST and AMT engine performance.
 

OK... I'll offer some UAT comments. (much of this has been said already)

First of all, I don't think it is so important to angle the nose up. Many of us have 100% success without doing so. It is dead flat in my F-16

Second of all.... Just because you did have a flame out does NOT mean the UAT caused it. It could be caused by many things including air trapped in filters, Controller hiccups, a piece of crap causing momentary fuel pump stall at idle (the DC electric motors have very little torque at low settings the way we use them) etc.

The UAT works very well when used as directed. I have had 0 flame outs in the air.

I think it is important that any time the UAT has had most of the fuel drained out of it, that it be purged with the pump running, while tilting the plane up and down and all arround. Tilting the tank only may partially speed this process, but will not purge everything, and will not purge filters, etc.

I think the best thing is to do some (the last) of this with the turbine running at full throttle. This seems to help suck out the last of any small bubbles.

I have flamed out once or twice on the runway after emptying the UAT for transport, then NOT following my instructions above I was new to the UAT). The engine would quite as it got to full throttle with the brakes still set.

Bottom line, follow the instructions, and the thing will work perfectly and offer great reliability. I have shut the engine down after taxi back with all tanks empty and 1/3 of the fuel in the UAT with the engine still running perfectly.

I worry too much about felt or sintered clunks clogging or coming apart after time. I will confess that I do not have much experience with the sintered ones.

The UAT has a lot of surface area, and is easy to inspect, so I do not worry about clogging.

My thoughts for what they are worth.

David

PST and AMT engine performance.
 

Thanks David.
The guys in Australia who had problems with the UAT ALL told me that when the UAT was bypassed the problems disappeared. My flameouts on the take off roll happened at exactly the same point and at full throttle so that eliminates ECU/pump problems and the engine performed perfectly on the bench prior to installation. and in the Sabre the Festo filter IS vertical so I doubt if there was air in the filter.

I don't allow dirt into my fuel system, two fine mesh filters in the fuel delivery line see to that.

To me the inevitable conclusion after all these comments seems to be that the UAT can and does work very well indeed BUT needs careful initial set up and consequent handling. The simple properly designed header seems to work just as well in a properly designed and constructed fuel system and requires no special procedures or handling but has slightly more unuseable fuel.

I will carefully shake the BobCat and see if any air exits the UAT and also try refuelling the Sabre via the UAT delivery line to purge the sack and then raising its nose to the vertical and shaking it with the engine running.

If that is all OK I will fly the Sabre with the UAT. If, despite taking all the precautions on this list I have any further problems, my UATs are history and I will stick with the simple header.

Anyone disagree with that or think I am being unreasonable?

BRG,

David Gladwin

PST and AMT engine performance.
 

David,

Sounds reasonable to me! I've found that when you fuel through the UAT the small bubble that is in it is expelled to the main tank(s). If you do not refuel through the UAT then the small bubble is not expelled. In theory, every time you fly the bubble could get larger and become a problem. This could be very bad in an installation where the UAT is concealed. The 15 to 20 degree tilt is just to ensure that the bubble is expelled the next time you fuel. I don't know if you practice this or not but in my opinion, if you completely defuel the model including the UAT then you are asking for problems. The next time you fly you will have to go through the entire process of trying to eliminate bubbles in the UAT sack membrane. (Not a quick process) BVM recommends that you never drain the UAT unless absolutely necessary.

I'm very careful when I fuel my jet not to introduce any extra air in the UAT. When you disconnect the fueling line (fueling through the UAT) pinch the line so that no air enters the line. Then plug the line. Depending on how long the fueling line is---you could put that much air into the UAT. I don't believe that the UAT is overly sensitive----I'm just explaining my methods of fueling. I don't shake my models at all. I've had ZERO flame-outs (both on the ground and in the air). It just may be that due to my carefulness and not defueling the UAT has contributed to my success.

Kevin

UAT redux
 

Sounds good to me, David. Exactly what's been spelled out in the instructions and the UAT and Fuel System addenda on the BVM website for the past year.

This semi-permeable membrane technology still fascinates me, whether producing reverse osmosis drinking water from the sea, keeping the bubbles out of our fuel lines, or in my old line of work, keeping bubbles out of your brain while undergoing open-heart surgery.

Just have to be aware of a few caveats----some of these the manufacturers alert end-users to and others, often for marketing purposes are left up the end-user to figure out.

One thing I know for sure, no matter how hard you blow into the inlet side of a UAT and pump out the outlet port, you will not get bubbles in the outlet line, as long as the bag is sealed around the neck on the inside, it is at least 1/4 full, and there are no defects in the membrane.

Just be aware that in new tanks and in tanks that have been emptied for whatever reason, and in rare cases of cavitation, bubbles can be trapped in the pleats on the outlet side of the membrane.

Problem solution----back fill the outlet port as per instructions if tank is new or has been completely emptied. If you suspect cavitation or are universally paranoid about your $10K++ bird like I am, then eat them Wheaties, pump a little iron, and shake the b'Jesus out of the bird. Will you ever see enough bubbles to kill a JetCat from cavitation???--- probably only if you leave the fuel pump on with your vent plug in, sucking until your feeder tanks collapse. But then you've got another problem!!!

Tom

P.S.---any UAT's that you might make redundant ("If.............my UAT's are history") will have a welcome home in Fond du Lac, WI

PST and AMT engine performance.
 

Ditto Tom's comments! Except send 'em to Mississippi. I invest all of about 15 minutes in the initial setup of my UAT's. And then fly the snot out of them. Lot's of flights and no flameouts.

Semi-permeables
 

By the way, this UAT technology is not new. Dragsters and some of the Reno Air Racers use a similar setup. Looks like a giant version of the metal bubble filter that Tom Cook sells.

They have such a problem with vapor in the fuel lines while taxiing or getting ready for the quarter mile run from the heat under the cowl, that they can switch these into the fuel line temporarily to keep the bubbles from killing the engine.

Tom

PST and AMT engine performance.
 

So Tom,

Does that mean you shake the hell out of a patient on the table after you have opened them up and installed the membrane, but before you commence the open-heart surgery?

Garrett

PST and AMT engine performance.
 

TO be clear.... I only tilt the plane arround if the UAT has been Nearly emptied..... Not a refuel or normal situation.... Just gas and go....

D

PST and AMT engine performance.
 

As a matter of fact I do not allow air into the UAT or header when refuelling as the refuel pipe is connected to a Tetra valve at the end of the airframe refuelling pipe. when tanks are full I close this valve (which does not leak) so that NO air can can get into it.

I am not sure that air in the MAIN tanks is a problem as they become full of air as the tanks drain.

After flight I close a fuel valve after the pump to ensure that no air can enter the pump to deprime it (the JetCat is automatic) and none can enter the engine.

Like I said everything has worked to perfection using the simple header but if you guys can get perfection with a UAT then I am obviously not using it correctly, that will be corrected !
BRG,
David Gladwin

PST and AMT engine performance.
 

Does that mean that Tracy Jensen got bubbles in the brain during surgery cause no one bothered to purge his medical UAT? That would explain a few things.

Bubble on the brain
 

Garrett, after I retired, I thought I would never have the bubble nightmare to contend with any more---and then I started flying turbines-----only thing I don't have to worry about is my Bandit calling a malpractice lawyer if it gets a bubble on the brain!!

Tom

PST and AMT engine performance.
 

Woketman,

Perhaps they shook him a bit too hard?

Or perhaps he figured he could perform the surgery better and cheaper himself than the overpriced, name-brand outfits?

Garrett

BVM UAT
 

Very interesting thread!
I've got 153 flights on my BobCat XL, and have had two flameouts....both caused by the failure of my transmitter timer and brain fade. The old RAM doesn't run well on air.

In order to prevent air from entering the UAT after fueling, I use a 6mm Festo one way check valve in place of the push-in plug.
Push the line into the check valve, fuel 'er up, and pull the line out of the check valve. Fly with the check valve installed. I suppose that you could use a Festo ball valve to accomplish the same thing. There will always be a small bubble at the top of the UAT after flight. That's because it is doing it's job.

A leaking filler plug or filler line will cause you to consume the fuel from the UAT before the mains or header. I have seen this happen. A fellow flyer used a machine screw in place of the plug that he had left at home on the work bench. One trip around the field and he had a flame out. The threads on the screw didn't seal as well as the "dog knots" on the plug would.

I would suspect that many UAT problems are caused by a small air leak in the filler, transfer or supply line fittings. Make sure that all of the lines in your system are leakproof by safety wiring them with .020 safety wire or with tye-wraps. Count the fittings between the fuel vent and the pump. Each one of them is a possible leak. Since the fuel pump sucks (no pun intended), from those tanks, it can suck air through a very small source that will be very difficult to locate.
;)
After saying all of this, I'm sure to have a flame out this weekend.


Harley Condra
BVM REP

PST and AMT engine performance.
 

May be that the answer would be to remove the filter betwen the UAT and the pump? or may be to place it before the UAT in order to keep the sack clean?
Anyway the intructions tells that the uat act as a filter too.

I've not installed my UAT, but now that I'm not 100% sure about it , I may well buy a simple catch tank as David gladwin advises...

Florent

PST and AMT engine performance.
 

I've followed this very interesting thread and would like to put in my two cents worth. In my Boomerang, I switched to a UAT for a while with no problems, filling through the UAT so that only a tiny air bubble is left each time. I've never shaken (or stirred) my plane!
After a transmitter fault caused a crash which damaged the bottle of the UAT I decided that the cost of a new one wasn't justified. I went back to using a simple 8 oz. header(hopper) tank with centre outlet feed as Dave G. mentioned and even with all the throwing about that Ali does with the wild aerobatics he flies, we get no flameout problems.
I've tried various clunks in the main tank from time to time and currently use the felt one with a fine filter 2" up the feed line inside the tank, as well as the usual filters in the system. I'm a firm believer in the old KISS principle.
The Boomerang with the JetCat P120 has put in over two hundred flights so far with this system, all of which are a real test of potential air bubble problems if they're going to happen. So far so good!
I note that no one has mentioned that with many ECU's and/or fail safes, a momentary loss of signal or a glitch can cause a shut down which could be mistaken for an air bubble flameout.
Alan C.

To UAT or not UAT?
 

Hi David/Garrett,
Interesting ideas all round on UAT's. My contention is they are unnecessary as they add areas of failure/leaks etc. (KISS!) I do not use one myself but have used the simple felt clunk with great success, ie zero flameouts ever. An interesting fact of fundemental physics is that when any container filled with fluid and air experiences zero gravity, the air will centre itself instantaneously to the centre of the tank, just like a clunk would at the end of a flexible line.... And you will be surprised how many times aircraft experiences zero gravity during flight. Most flameouts are due to poor plumbing and or poor engine (combustor) design. Most good ECU's will tell you if you had a flameout or an ECU controlled shutdown.
Cheers
Andre

Repeat after me----
 

What has worked for me:

1. Coke bottle with Tygon clunk tube and Dubro large clunk, no hopper---230 turbine flights in a HotSpot====ULTRA-KISS====FEW DOLLARS

2. 2-4 oz cylindrical hopper, no clunk, brass tube centered in tank-----over 100 turbine flights + many D/F flights===SUPER-KISS===FEW DOLLARS MORE

3. UAT mounted horizontally or 15-20 deg upright for easier filling to get the last bubbles out. Neck pointing to the nose on my HS, and to the tail on my Bandit------as of yesterday, 149 flights=====KISS===FIST FULL OF DOLLARS

I think this thread needs a SPAGHETTI WESTERN .wav file and photos of Clint Eastwood and Lee Van Cleefe???


Tom

BMT
 

Hi Andre:

Don't know if you had seen the pics and awards from FIJR, but Joey Tamez flew the stink out of his AD F-16 using one of your engines.
I have seen them bench run at the big meets in the past, but this was the first time I saw one in the air. It was just fuel and fly for Joey, the whole meet. He won best grapics award, but I think he would have won most flights if they had that award.

Very nice motor-------


Tom

PST and AMT engine performance.
 

Hi Andre,

Is this to say that using a geometrically centred clunk means we have been doing our very best to ensure a bubble CAN be sucked out of the header by the pump if you start throwing the model around?

I guess that explains why I'm a software developer rather than a physicist!

Garrett

PST and AMT engine performance.
 

If that is so, just place the pleated paper pickup in the center, on the end of the brass tube. Steve Ellsey proved that even if 95% of it's surface area is exposed to air, it will still only draw Jet A due to surface tension.

PST and AMT engine performance.
 

Guys,

I think the penny just dropped on where some of us could be going wrong.

I don't know about you guys, but I have a 6mm festo fitting in the top of my fuel can. The internal line goes to the bottom of the drum where I have a filter as well as a mesh clunk.

The other line goes to the pump. Now....what if the festo fitting in the top of the can sucks a bit of air? I reckon thousands of itty bitty little bubbles will be pumped into the UAT, probably like foamed fuel.

With a KISS header, this won't cause a problem. The foamed fuel will be purged to the main tanks and the world will be a happy place.

Other the other hand, if you are using a UAT, I suspect you may be filling the membrane chock full of air and undoing the process of the initial purge.

What do you think?

Garrett

PST and AMT engine performance.
 

I take on board the point that Alan Cardash makes that a momemtary glitch can cause a flame out. I have that covered too as I use (and recommend because it works very well, no commerial connection ) the Austrlian made volt logger from MAS.

As well as recording real time and lowest receiver busbar voltage this device also logs, counts and displays any radio glitches. On the Sabre and Bobcat the glitch counters were clear.

Clearly I did not purge the UAT fully so that will be done and the Sabre retested with the UAT. If all goes well the new UAT will go into my BVM F16 PST 600 combo. which is in the works right now.

I will also run the PST in the BobCat and shake the model and see if any air exits the UAT.

All you guys having sucess with it can't be wrong !

BRG,

David Gladwin

PST and AMT engine performance.
 

Garrett,
You may be right but not in my case as I dont use any Festo fittings on my refuelling can, just a Kavan pump and two fine mesh filters.

By the way, light rain here this morning so we may be able to fly at Newcastle soon. You're most welcome to come and stay here overnight before/after flying but cant do it until after the burns on my right hand have healed. (Propane fire at Mangalore due coupling seal bursting ).

BRG,
David.