ozief16

My Feedback: (13)

Guys,

Please help, I'm a my wit's end.

I have an Ultra Flash with a P-140. I have the wing tank and the main (fuse tank) standard. I've had three flameouts, all attributable to air (hindsight). All three occurred on 45 degree down lines on flights that included heavy maneuvering with extended down lines. I am 95%+ sure that these flameouts occurred as a result of the wing tank being empty and then with the long down line the maintank feeding air to the UAT until the UAT choked and passed a bubble

To combat this, I built a small (~11oz) tank on the bottom of the main tank. Now all the air that the main tank passes gets caught there and the UAT has a solid stream of fuel, even with a long duration nose down maneuver. This tank is run in series between the main tank and the UAT.

I've made it a habit of running and entire load of fuel out of the plane using the engine fuel pump and the GSU after any fuel system modifications.

Ok, that's the history...now for the problem area(s):

I was seeing tiny bubbles form in the fuel line between the hopper tank and the UAT. Over the course of a gallon being pumped at 4.5v, the total air accumulation in the UAT amounted to 1/3-1/2 the size of a grape. Not something worth worrying about, but curious just the same. After much consternation, my best guess is that I was creating enough of a vacuum in the line to pull any gas in the fuel out of solution (think about a beer bottle opened to the lower pressure of the atmosphere instead of the higher pressure inside the bottle-in fact it looked just like this). I then checked all fittings inside all the tanks...no kinks, and the smallest diameter line is BV clunk line in the hopper tank, everything else is larger (all external lines, ie those outside of tanks, are 6mm hard lines). To test this theory I removed all tanks from the system and retried...similar results (I was thinking drawing through 3-4 tanks in series might be the problem). This however is relatively minor in that it amounts to a very small amount of air and is nonexistent at lower pump voltages (yes, I've pulled all the lines out and pressurized them up to 50psi under water, no leaks).

'THE' problem is that the UAT will pass air every 10-30" at extreme pump voltages (4.5v). In the interest of making a solid video for a couple friends (both VERY experienced jet guys who are also stumped) I put a backlight on the UAT. I can actually watch bubbles form INSIDE the sock. I thought faulty UAT so I replaced it...with two others to include a brand new one straight out of the package. All three do the same. I also tied a GBR CAT...same result. All four air trapping devices have had no more than a gape sized bubble of air, yet all of them have passed air down the line. I allowed all to soak for 48 hours and retested...same.

What I don't know is if a small amount of air going downstream is entirely normal and I'm just gun-shy at this point (I'm thinking his could very well be reality). I've never stared at a fuel line like I have with this setup. I'm am quite sure that my previous flameouts were the result of the main tank passing air in a nosedive attitude to the UAT and the UAT getting overwhelmed.

Anyone that's flown in Vegas knows that an off-airport landing will destroy almost any jet (based on the high landing speeds), so I know I've gotten lucky getting it back three times now. This craziness has to stop! Of note I had a Classic Flash with a P-120 and zero issues.

I'm sorry for the long message, I just wanted all the data out there to prevent the "hey man, maybe it's a pinched line" thoughts. I have torn this system apart and devoted weeks to it at this point

Thanks in advance
Dave

Dave Wilshere

Dave

Did you have a stock CARF set up in the model? Felt clunks? What fuel/Oil you using and is it being used in other jets OK at this time without the micro bubbles?

Does the UAT collapse when running full power in the model?

How is the UAT mounted? Flat or angled? (though the CAT is different and not affected in the same way)

Dave W

ozief16

My Feedback: (13)

Sorry, I should have mentioned that I have BV heavy clunks or comparables around the system. I removed the felt clunks because of perceived restriction issues

Thanks
Dave

ozief16

My Feedback: (13)

Dave, the UAT is mounted at about a 45 with the nipples up (that reminds of a Thailand story). Heavy clunks. Yes the walls of the UAT are partially compressed. They are not flattened by any means however

Dave

marc s

An expert in this matter is Olivier Nicolas, he has done a lot of testing around fuel systems and the possible issues surrounding them - might be worth a PM to him through the forum.

He does post regularily on this forum but seems quieter than normal at the moment so he may be very busy at work (he is a pilot). Be good to get him in on this as he might be able to shed some light on possible issues/causes to your problems.

I am no expert on the technical side but I do know that restriction through fuel lines, barbs and multi-tank set-ups can cause cavitation which will release air bubbles from fuel and may have something to do with your problem.

Hope it get fixed soon.

marcs

Dave Wilshere

I've said before that the Std CARF design WITH felt clunks works, I've flown a lot of Flash models...all stock set up and they work 100% P-70, P80, P-80SE, P-100RX, Hawk 100R, P-120, P-120SE, P-120SX, P-140RX, P-160...no issues! With a felt clunk you don't need that extra tank!

Dave

Xairflyer

My Feedback: (1)

Just one point the extra tank below main won't trap the air as air rises.
How high is your uat ? It is amazing how many installations have the air trap higher than the tanks ( on the engine mount plates seem common for some reason) keep the air trap low as possible, so air will naturally try to escape away from it to a higher point.

ozief16

My Feedback: (13)

Dave,

When I built the plane I used the felt clunks as a result of all the postings (yours being the primary driving my decision). I noticed, however, a rather significant restriction in the fuel system (UAT largely collapsed). I removed the felt and that seemed to solve that problem.

I've tried removing that hopper tank (ie just plumbing around it) just to see if it's causing a restriction that may be driving the problems. It doesn't seem to matter.

XAir,

The UAT is in the cockpit sitting on the floor of the jet (this isn't a particularly tall jet, so that's pretty even with the starter of the motor. It's higher than the wing tank, but lower than the main and as low as it can go)

What I'm really struggling with here is why air bubbles are developing inside the UAT sock. I've never seen that before (I'm no expert mind you).

I have not gone back and tried the CAT since its been soaked. Marcs, does it need to soak for a while to reach full effectiveness?

Does anyone know if a minor amount of air (pinhead size bubbles) is normal? Again, I'm wondering if I'm looking at something normal scrutinizing the heck out of it because I'm skittish now seeing things that have always been there

Thanks guys, I appreciate the time. I haven't flown the jet in over a month now as a result of this mess

Dave

marc s

Not necessary.

marcs

InboundLZ

My Feedback: (10)

Guys,

The "hopper" tank that Dave speaks of is my design. I was having issues with air in the UAT as well...large amounts of air. As matter of fact I had a flame out on my Flash due to air and I had 22oz of fuel still in the main tank. The root of that issue was the baffle came loose and allowed the fuel to move to the front of the tank too quickly. The UAT prior to that always had some air at the end of a flight...I think the biggest problem on the flash is the design of the main tank...it is a long flat tank that is really affected by attitude changes in pitch. It is what it is. With my hopper tank mod you "trap" all of the air in this tank. Now I fly without a care and my UAT is always full of fuel regardless of the amount of fuel in the main tank. The hopper however (9oz capacity) is about half full of air. The design works perfectly. I know for a fact it does improve the reliability of the fuel delivery system.

Dave's problem is no doubt something else...what that "something" is its hard to say. I have not observed the behavior personally as I am TDY currently but I know Dave and he is very thorough on his trouble shooting so I am curious as to what the root problem might be....

jetpilot

My Feedback: (48)

I got rid of any and all flameouts since increasing the suction side to large diameter tanks fitings and fuel lines and also placing the fuel pump right beside the UAT. I try to place the UAT and Fuel pump very close to fuel tank as well. Vents, clunks, etc, never chocking down anywhere on pickup side. Maybe overkill, but i have not had a flameout since! also no fuel filters on suction side.
I started changing all tank fittings to the larger diameter after chasing down partially blocked fitings from aeropoxy or such glue and having similar circumstances as yourself. the regular tank fitings are adequate unless any sort of even minor blockage occcurs. I also quit using the UAT and only use JMP air traps as well as it comes with the large fitings. I used to watch my UAT cave in and that is a very definitive indication of restriction.
The fuel supply is only as good as its smallest opening.
Something else to consider might be the amount of oil be added to fuel or type of oil. sounds a bit far fetched maybe, but sounds reasonable that too much oil will increase its density. We used to think turbines needed alot more oil than they do now and I see alot less flame outs these days for whatever reason.
Good Luck!
Scott

johnls

Over the years I have encountered tiny air bubbles in the fuel line.the first time was on a CARF Lightning and was due to too many restrictions in the fuel system. The second time was on my L39 which had had many flawless flights and suddenly had minute air bubbles in the system. It turned out to be a batch of contaminated fuel.I changed the fuel and the problem went away. The fuel had a slight opaque look and had developed a fungicide.





John

Dave Wilshere

Dave

Mmmm I use Felt clunks on just about everything I build and I have never seen the UAT collapse more than I would expect (sides pulling in 1/8") even with a hot P-160SX.
What overflow outlet did you use in the wing? What size of tube supplies it, how is the tube routed out of the wing tank to the overflow, how long is the tube from the wing tank to the overflow? How are you linking the wing tank to the fuse? Can you run the model with the wing off and just the joining tube? does this make a difference??
I don't see it being the felt clunk...I just dug out the original Flash #1 today for our 50th CJ and that has had the same felt clunks in wing and fuselage since 2006...I don't expect a problem and I have not flown the model since last year.


Dave

bjohnson80

My Feedback: (63)

Every time I have experienced this problem, I simply remove the turbine and make it electric. Electrons in, electrons out. Problem solved.

gunradd

My Feedback: (9)

This thread has nothing to do with electric and EDF troll.

BTW your not going to find an EDF to fly an ultraflash anyway. Go troll the electric forums.

rolsen12

I have 4 Flash and all are set up the way the instructions say and using the clunks that were provided. I have never had a flame out.....

Boomerang1

I have a similar problem with tiny air bubbles forming, I'm almost sure it comes from a felt clunk. The faster the engine runs, the more fuel flows & the more bubbles
form although the size of the bubbles remains the same.

I posted the problem years ago & the most plausable explaination was the restriction of the clunk causes the bubbles to form as the fuel struggles to pass through it.

I suppose the bubbles would eventually gather in a hopper tank or UAT but I don't run one in this install.

The engine, a little Wren 44, does not seem to worry about the bubbles at all & either do I anymore. - John.

JoeEagle

My Feedback: (26)

Gun..

you realize Ozie and BJ are close childhood friends.........

it was a joke dude!!


hey Ozie..i know obvious question but, is all your stuff safety wired???

are you using a Festo SOV somewhere in there? (guess that would be downstream of the UAT.....

gunradd

My Feedback: (9)

OOOPPPPSSS......

Sorry. Thought he was one of those electric guys that force it onto everyone else. Jokes on me now

CraigG

My Feedback: (40)

The few UAT air issues I have had were always resolved by tightening the UAT cap and pickup line fitting. By "tightening" I mean bottoming out with a pair of pliers. The cap, in particular needs to be re-tightned from time to time.

Doesn't really sound like this is your problem but it's something to easily check and eliminate as a possible cause.

Craig

ozief16

My Feedback: (13)

Fellas

First of all, BJ You're a jerk. You must fly out to Vegas and apologize in the form of beer. Immediately if not sooner you Troll!

Gun, thanks for standing up, thats hysterical!

Dave, i have 6mm hard lines everywhere except in the tanks (there I have either large bore tygon or BV clunk line). The vent is a large bore aluminum deal (I forget the manufacturer). All fuel tank brass lines are large bore brass jobbers. Also, Ive tried with and without the wing tank one (to narrow it down to the wing tank). It didn't seem to make any difference. The wing overflow has about a 16-20cm 6mm line on it. I took out the festo 135 degree switchback thinking it might have been a contributor.

Joe-good pickup on BJ! Yes, everything is safetied, or was. All the lines are shoved together right now for testing. It doesn't appear to be coming from the line connections

Craig, that's a great idea. I cranked down one of the three UATs I've tried, I even ran some thin CA in there to seal it. The CAT should solve that problem too. That air trap is VERY nice for anyone that hasn't seen one.

I think the fuel is ok. I've had this batch for a long time (these problems have really slowed down my flying), but I run bio bore and anti static fluid

Guys, keep the ideas coming. I'm thinking more and more that I need to crank down the 10mm nut in the cap on the latest UAT, drop a felt clunk in the main tank and run it. If little bubbles are normal, the engine shouldn't mind. If not, it flaming out in the garage is fine.

CraigG

My Feedback: (40)

Too funny Dave.....brings back memories

Craig

rc4flying

My Feedback: (21)

Dave,

First let me say, I am new to jets and building my first. I have been following some threads to learn. But your problem sounds like an experience I had on one of my giant scale planes. I have used felt clucks in my gas lines since getting into giant scale planes in the early '90s.
My problem started out with a new plane that I just seemed to always have it running lean and hard to tune after I switched my gas tank out to try something new to lose weight in my plane. I switched to a water bottle for my fuel tank and this is when the problem showed its ugly head. What I was noticing were air bubbles in the gas line going to the carb. OK, this is easy, maybe air leaking at the fittings. Nope, i answered this with a pressure test holding the tank under water with pressure applied. Upon closer look when I put the tank back into the plane I now noticed air bubbles starting right at the felt cluck. I wa able to see this happening because the water bottle was a smooth plastic type that I could actually see the fuel in the cluck line right inside the tank. I could not understand how air bubbles could be forming being the line is totally submersed in fuel.

What the problem turned out to be and what I discovered was this. The felt clunks I was using have a secondary paper filter of some kind that can be found when the felt is removed, it is held in place with a spring clip. You can blow air through the clunk and this gives the indication that the clunk is good. But after some troubleshooting I found that, this paper filter was allowing just enough resistance in fuel flow that it was causing what looked like disturbed air bubbles to form after this paper filter. I removed this paper filter, put the felt back on and ran the motor. ALL my air bubbles were gone, and my problem was resolve.

Just maybe, from what I am learning about jet fuel system this possible resistance to the fuel's flow may be causing air bubbles to form in your UAT and giving you your problem.

Just throwing out what I ran acoss in my experiences. By the way I still use felt clunks.

JoeEagle

My Feedback: (26)

yes...enough beer should solve that insult. that and a shipment of kiddie clothes i know you all have been negotiating!

break

er..i know this probably is really stupid but could there be a defect in the stopper of the tank? you had said you pressurized the fuel lines so i am assuming that this was the entire end to end fuel system.

i was also thinking about some weird crack in the fuel pump but that is downstream of the UAT, right? so never mind

+1 on Marc's CAT. JR and I put one in the Ultra Lightning and I ordered a pair for the Ultra Flashes.....they are really cool, and they have HUGE nipples!! hmmmm


and Gun, I hope i didnt jump on your comment too hard...it was just funny since i was talking to BJ when we were reading Ozie's thread, and BJ decided to be "helpful". I, for one will be referring to him as "T" as in Troll from now on!! too funny. and to think he sold all of his 40% stuff-ah well, we're supposed to go fly my jets here in Chicago this year-or so he says.

V/R

joe

ozief16

My Feedback: (13)

Joe,

Good comments on the 40% experiences. I will check the felt clunk for a paper filter

Joe,

Hysterical...that's all I have to say, hysterical. I compliment Gun for defending the forum and compliment BJ for thinking that up. Hysterical, all of it.

Dave