Larry Driskill

I snuck away this afternoon to go fly my 1/2A wing stuff. Temps in the 70s and almost calm winds singing a soft siren song I did not resist.

My Litehawk with the carbed VA (yes, oh yes, I know VAs should be allowed to breath freely but this unjustice has already been done) was working great for 1/2 a tank (Fuji) then appeared to go lean. If I throttled back it would recover a bit but only for a moment.

Land, refuel, relaunch and everything is copacetic for . . . 1/2 a tank.

So I thought " there is an air leak that does not get uncovered until the 50% marker. " Land test with a syringe, do the visual stuff, - Nada.

Refuel, relaunch - 1/2 way thru the blues return.

So, no apparent air leaks, no apparent dirty fuel, clean needle, taxes up to date, livin' cleanly and with only one woman . . . what should I check next?

Edit and add some photos: OK, Pigg is probably gonna say something like " Stick with what you know. Get a bladder."

'Did that. Please see Photo 3 for the proof. The bladder version works great, goes fast, runs a full ounce without whining, but so should the Fuji.

soarrich

My Feedback: (98)

It might be fuel foaming. The tank looks like it's held real tight. Check you prop is balanced.

burtcs

Larry:

Try 1/4 turn or so richer. You're running fine till 1/2 tank and then going too lean. This is not uncommon for my 1/2a Texico either. This really hurts to fly rich but if you want the least 1/2 tank to be just right you gotta do it.

HTH - Steve B.

Larry Driskill

Good points. You are correct about setting it richer at launch and that helped, but after a staggering launch due to richness it still got lean about 1/2 way thru. The prop is pretty well balanced and there could be foamin' (did not see any) as the tank is pretty well snitched up against a thin piece of foam padding.

cncswiss1

mount the tank loosly, tightly sinching it up makes it foam more.. use more foam and (fairly loose) rubber bands instead of zippies

Larry Driskill

Thank You, I will try that when the nice winds return and I can sneak quitely.

combatpigg

My Feedback: (3)

Fuel foaming creeps up slowly as more aerated fuel molecules convince the solid fuel molecules that they are having a great time at the bubble party. Larry, you could try to build the first 1/2A Tettra tank, with a collapsible liner? Isn't there a lightweight foam tank liner that is used in motorsports to prevent foaming? Something that our fuel doesn't attack?
There is a dense foam that camera equipment is packed in that makes a nice tank insulator/ holder, just run an undersized holesaw through it by hand, or hot wire an undersized hole through it, then squeeze the tank in.
I don't understand why you would jeapardize your precious freetime messing with those suction tank things anyway, they don't really work that well.

cncswiss1

you could try snapping a baby bottle liner in that fuji can to make a bubble-less tank.. the cap seal will be the tricky part, but those fuji cans are real tight.

ptulmer

My Feedback: (5)

Larry, If foaming is the problem, make a balloon tank adapter for the fuji tank. The last one I made didn't have a pickup inside and was 1/2" in diameter and would run perfect until it was completely empty. If you are interested, I should have a picture somewhere... but the idea in my head is to use the balloon as a bladder inside the can to prevent air/fuel foaming. (not a pressure bladder)

ptulmer

My Feedback: (5)

You know, the only thing about this idea that bothered me was the bottle liner would be folded on the top where you put the cap on, but there is something that would work. I don't know a nice way to say it except for calling it a men's birth control and safety device.

soarrich

My Feedback: (98)

I thought I read something about not using any latex with Norvels, something about it screws up the glow plugs.

ptulmer

My Feedback: (5)

Rich, I don't know how it applies to latex, but the rubber bulbs will cause problems in the long term. You have to replace balloons often enough to not risk a rupture, so long term effects wouldn't come into play.

Remby

My Feedback: (3)

Can this setup be flown, bypassing the perssure line so it is only suction? If so, see if it still leans.

If it still leans, I would suspect a leak in the fuel line inside the tank. Just a guess..

Do these engines varnish?

Larry Driskill

Remby:

The VA with the RC carb will draw fuel, but I have always ran it with muffler pressure to help keep fuel at the needle on the RC LiteHawk wings that can maneuver pretty quickly. I had drilled one carb out to try and get more air involved, but this one is stock.

I'll check again, but I'm pretty sure there are not any fuel line leaks, but that is exactly what it acts like.

The VAs don't seem to varnish as easily as the Coxes. But, good point. I'll pull the head and have a look at that dude. Could it be that the RC version turning a bigger prop and carrying more load would varnish when the CL version turning 30,000 didn't? Maybe so?

Plus, I run 20% castor, 30% nitro in my 1/2As and so there is plenty of castor there to varnish if the conditions were right.

And I think trying DR's and Pigg's tetra/condom idea is a good one. 'Kinda like the idea of a Fuji/Trojan fuel tank.

combatpigg

My Feedback: (3)

I think where some guys have tried balloon tanks and failed is from:

A. first of all, not sucking every last bit of air out, then clamp the line off.

B.then fill the balloon with a medical type syringe that has just fuel, no air in it.

C.The other failure point is putting too much fuel in the balloon and creating a false pressure

D. Toss the balloon after every flying session.

Remby

My Feedback: (3)

Larry,
The idea was to fly once without pressure to see if it still leans, to eliminate something wrong there(block in the pressure line). It should still fly good enough for the test, but perhaps you know better on that.

I would just try and replace the (in the tank) lines, not sure how much trouble that is. It sounds like a bad fuel send line.

combatpigg

My Feedback: (3)

If you try to fly a plane capable of high Gs without pressure, all you will get is alot of flameouts.

flyswatter

With my VA and no pressure, the engine would rev good and I would set the needle at max less two-three clicks. Everything seemed to be perfect, but then I would get flame outs at launch! It would happen right after the plane left my hand. This produced a number of very short, frustrating flights.[&o]

With a crankcase tap and a bubble bottle tank, the launch would go well, but then the engine would never get up on the "step". Engine appeared to go rich(?) and the rpms would go from low to high in an oscillating manner until the tank was emptied. It sounded like a WWI ignition interrupter throttle! I suspect a leak in either the line or tank caused the problem.[&o]

So enough already! I have since gone to a bladder tank which should eliminate the problems.

combatpigg

My Feedback: (3)

With thecrankcase pressure tap, alot of folks forget to use a check valve, to keep the tank pumped up. It's amazing how much pressure can get developed. Fuel injection beats carburetion all day, any day.

flyswatter

cp, I did not forget. You are again telling me something I did not know. I was not using a check valve with the crankcase pressure. I have never used one, but this is my first experience with a VA cc pressure tap. In the past, on TD and Norvel fuel systems, if I remember correctly, I have used cc pressure taps (without check valves) successfully. Should I be using a cv in all cases? What does the cv do, eliminate fuel feeding back to the engine through the pressure line?

D Bronk

A check valve ,will allow pressure, to go in 1 direction only,depending how it`s installed in the line.You want, to build pressure ,in the Tank.A Two stroke, has nearly as much negative pressure(vaccum), as it has, positive pressure.The "pulse", is a constant push & pull.Without the valve, You end up with vaccum, equalizing the positive pressure,at the Crankcase.So ,you are actually working off Venturi vaccum, and gravity,but that will work too..

CP; Are you making your own Valves, with, a Ball and seat ,in a tube, or ,do you have a source for us..Also, how much better, will the fuel Atomize, as opposed to a muffler Tap..Will this in fact Inject fuel..My sleds, all have Have a "pop off valve", in their fuel pumps .These type of pumps , are opperated off Crankcase pressure, but, they have Tank "return lines", to prevent over pressurized Conditions at high Rpms,and ,allows for a consistent,fuel pressure condition, through the entire RPM range..I`ve never tried a Crankcase Tap, on any glow engines,but you have me thinking..I should give it a shot, on the Baby Foras`..Is the ballon tank, a better system, than a gravity feed system ,and, is the oneway pressure tap ,a better system than both of those.The muffler tap without a check valve where does it stand ,amongst these systems,it`s open to the atmosphere, so, that one can bleed off pressure too..HMMmm

Larry Driskill

OK, I knowingly violating rule number one of chasing down a problem. I have made more than one change at a time toward solving the going lean event.

I discovered the nose block was a bit loose in the foam and so injected some poly-u around the foam to bass joint and tightened that up.

I inspected the fuel lines and then tested the tank by pulling a vacuum on it with the syringe and then clamping it off with hemostats. Several minutes later it hissed at me when I removed one clamp.

I changed the foam behind the tank, but did not go to rubber bands yet as I would have had to pull the engine to get them on.

I ckecked the engine for leaks and found none.

I'll check the prop balance.

Inspecting the liner for varnish I found very light signs and so scoured the liner with 0000 steel wool wrapped around the barrel of a ball point pin. When a TeeDee was well varnished there would be brown on the wool after the cleaning effort. No such residue here. I doubt that there was enough varnish to be the problem.

I will try and remember to pick up some Armor All and, if I still have the leaning, try a drop or two of that in the fuel to suppress foaming.

Andrew

Dave --

Texas Timers carries a full line of fuel and bladder fittings. Here is a link to the [link=http://www.texastimers.com/accessories/pressure_bladders.htm]bladder page.[/link]

combatpigg

My Feedback: (3)

Foremost is the company that makes check valves and small fittings. KK used to sell a tiny check valve, so tiny, it inserted into the fuel line. Larry, you bring up another point that is important, a solid mount that ties in well to the rest of the plane. Sounds like you're in hot pursuit of the problem, not many of us have the patience to try just one fix, then go to the field......go home to try another fix, go to the field.......

flyswatter

DB & cp, ok, ok, I got it! Never thought about the ebb and tide of the pressure wave in the crankcase. Geez, that may explain some of the problems I was having with the bubble tank. I ran the engine today with a bladder tank and all was well. Thanks for your help and the brain stimulation!