I have a RAM 500 that I have owned for the most part flown successfully for the last 7plus years. Lately I have many flame outs early in the TO roll but only one certain airplane. The engine runs flawlessly in my other airplane so I have concluded my problem is somewhere in the fuel delivery system and not the engine itself. I can sometimes make it quit just by shaking the airplane or bouncing it up and down or by rapid forward and backward movements. This happens with a full fuel tank and a full BVM uat which is orientated level (horizontal). I know that my orientation of the UAT is not optimum but it used to run fine like this so I tend to think that is not my problem.

One of my flying buddies thinks that perhaps my inline fuel filter is trapping an air bubble becasue I have the filter orientated horizonally which is also how it has always been and is infact that may in my two other planes with no issues. He suggests trying it orientated vertically instead and I will try most anything at this point if it might fix my problem. I dont recall ever hearing that the filter orientation mattered.

I am either going to try a new filter in the horizonal config or the existing filter in a vertical config and see if either one helps.

I guess I have three main questions:

1. What is the consensus opinion on filter orientation ?
2. If I orientate it vertically does it matter if the side going to the engine is at the top or the bottom ?
3. Anybody have any other ideas what my problem might be ?

Thanks,

I'd remove the filter for one flight and see what happens. If you don't notice any changes then you can discard the filter issue.

Thats a good idea except that I hate to go unfiltered. I might consider trying it however. I think if I do I will just do a short ground run and shake and rattle the plane and see if I can make it quit or even semi quit (sputter) which it also sometimes does when shaken and bounced.

actually the first thing I will do in the morning is remove the filter open it up and see what the condition is. Then go from there.

Also, if it is accessible (F-86 right?), you can place the filter between the UAT and the main tanks (for peace of mind ), that way you have at least some filtering going on on your engine feed line. If the filter is creating bubbles, then the UAT should eliminate some of them. I think your RAM may also have a filter underneath the cowling, for redundancy.

Have fun!

The specifics or your model aside...ideally the filter should be mounted vertically with the engine side up. This will pass the small bubbles on immediately rather than letting them accumulate into one big bubble which the filter will eventually burp all at once.

I'm wondering about any electrical connections which might be loose?

The recommeded from Jet Cat is to have the filter after the pump to collect any small particles that the pump my give out whilst running i.e. small bits of gearing that come off whilst running also they say have the filter vertical and loose so that it can shake a bit and discard any small bubbles.

Mike

all that would do is trap any crud in the filter as you filled the tank, then as you ran the turbine that crud would be flushed from the filter into the UAT, not exactly the ideal location for a filter

I have a 750 plus for several years, and the UAT placed horizontal,
had the same problems. First of all I've NEVER placed a filter in the
lines. I filter my gas on the way from the filling tank to the plane,
(good filter),; secondly, when I had this problem, I called Carlos from
RTI, and he told me to dissconect the gas solenolid. Guess what,
problem fixed. Never used the solenoid again, and the turbine is
now more powerful than ever.

Hector

Thank you, this is EXACTLY the info I needed. My friend thought the engine side of the filter should be up but he coulndt remember why. This makes perfect sense to me. I'm pretty sure it is not an elctrical connection issue. I'm going to start pursue the filter issue as my first area of concern and if that doesnt fix it I will move on from there. One reason I dont think it is electrical is becasue during some takeoffs where it doesnt flameout immediatly after the start of takeoff roll it will sometimes in mid takeoff roll when I have been able to get to full power sort ot cough or burb which I theorize now to be a bubble that passes but doesnt quite kill the engine. Once airborne the engine pretty much always runs the entire flight perfectly, no flamouts or weird sounds so I dont think it is electrical.

You need to be clear about your terminology. When you say Gas are you saying the propane or the kero ? The word Gas means differnt things to differnt people. My first thought when I read the word GAS was kero ? But after thinking for a second I am not at all sure what you mean.

Hector, just a quick question, what does the gas solenoid have to do with bubbles in the fuel line, unless you meant to write the "fuel solenoid"???

BTW I was at FL jets last week and had an Issue with my Jet Central Falcon powered FB Rafale, it looks like I made two major mistakes:

1) UAT mounted horizontal
2) Fuel Filter between UAT and Pump mounted horizontal

It made the best looking smoke when the engine flamed out that I have ever seen[X(]

Unfortunately it also broke the rear bulkhead supporting the main gears when she pancaked in [>:]

I guess I learned my lesson...

I guess another question that needs to addressed assuming a large air bubble is collecting in my filter is why is my UAT passing air bubbles. That is after all the purpose of the UAT is to NOT pass them. This makes me think I might need to figure out a way to tilt my UAT to somewhat more front end up config. Currently it is perfectly flat or level.

Any thoughts on this ?????

For the record before I get my ears boxed excessivly for having a UAT mounted the way it is, my airplane is a BVM F86 converted from DF and the BVM conversion instructions called for and showed the UAT in a flat ( horizontal ) config.. Thats my stroy and I'm sticking to it untill I get a better one.

I think he means the Kero solenoid and not the Gas (propane). See my post above about terminology.

RCISFUN

I have mounted the UAT in various positions. I spoke with Bob (BVM) and asked him to check my UAT install. He did and told me the orientation as long as it was not upside down did not matter. I am currently flying with one horizontal.

Fuel filter. Our fuel filters supplied have a directional arrow for fuel flow. I never mount them anyway but horizontal and always back near the turbine for easy access and maintenance.

Fuel solenoid: I do not recommend removal for one primary reason. . .safety.! This as most all know, shuts fuel off instantly to the turbine.

On any new install, I enlist the help of others, run the jet and hold it in various positions while shaking. Prior to this, I pump fuel through the pump into a catch can until I am sure all visible bubbles are gone.

Hope this helps. . .

Eric

I think the resoning behind having the UAT vertical is so that any bubbles in the tank are at the top away from the area that the fuel is drawn out of the UAT, for the record filters usually have the inlet to the hollow side of the filter and the exit from around the outside of the filter medium.

If your tank neck is big enough try an Obit fuel filter or one of the paper filters that are used on petrol strimmers etc that usually stops any bubbles from exiting the tank on the way to the UAT.

Mike

For many years I have used the 6 mm Festo filter in all orientations. I used to worry about the big air bubble that you can clearly see that resides in the filter. As you, I worried that it could dislodge and flame out the turbine. I would try different orientations, shaking it, etc. Nothing I have ever done could make that bubble leave the filter.

Bottom line is this: for the Festo filter, orientation does NOT matter one bit. Just install and fly.

When I said gas, I referred to JetA not propane. I know the valve is to restrict the flow of kero,
BUT, that could be another way of looking where the problem is, you don't have to fly it,
just test it on ground.

Hector

I know, I only meant for one flight to try to isolate the fault. Besides the fuel tank should already have a filter in it. The location I suggested was to try to trap any grind from the main tanks.

The most important thing is to kick the filter with your fingers in the first runs to purge it. Once it is purged and all air bubbles are out, it does not matter orientation, because fuel flow does not have enough speed to cavitate and generate new airbubbles.

Once the line is completely purged, you rae free to go....

Perhaps there might be a microscope leak in your fuel filter. Put it under water and test it for leaks

Regards

Nuno

Hello,

Make sure there is not a sharp turn on the outlet of the UAT.

I have seen that, over time, the polyurethane line supplied with the UAT will become less resilient, and it you have a sharp bend, you can get an air leak on the main nipple of the UAT. The bubbles from the leak can sometimes only show up under high power, and in some cases the bubble stream is almost invisible.

If the bubbles become numerous enough, they can collect to form a large bubble in the filter and during a bump or change in orientation the bubble dislodges and you get a flame out.

I remember my RAM 750 doing this and the resultant bubbles displaced so much fuel the turbine would not reach full power. It would run, but at a lower power output.

Good luck with your troubleshooting.

Use the Festo and you don't have to worry about purging air bubbles.

I have perhaps 1/100th the experience of most of you here and am hesitant to disagree, but for SOME reason my results with this exact filter are exactly to the contrary. Big bubble, turn the filter vertically, bubble left, engine burped (but did not quit).

Sorry, Woket....I saw what I saw and once was enuff to make me a believer in others' advice to use loose and vertical mounting.......

Well, let me clarify. I always shake it the first time I put fuel through it to get as much bubble out as possible. But the bubble that is left (the portion that remains and I can never get out) is just fine. It WILL NOT flame out your engine.