Fuel Filter on RC plane

privateBeavis

I am having some reliability problems with my trainer plane. Has a ASP 46 engine and while it seems to run perfectly well on the ground its cutting out on most flights at random.

I'm thinking its either a pin hole somewhere perhaps or dirt in the tank or dirt coming in from the exhaust line. Is it a good idea to have fuel filter on the tank to engine fuel line on this type of plane?

coolwings

If your problem is caused by dirt (burnt fuel residue from the exhaust back via the pressure tube) then the filter will help.
But it could be one of two other possible causes instead.
You might be experiencing some foaming of the fuel caused by vibration. Air bubbles appear in the fuel. They are visible going down a transparent fuel tube towards the engine. The cure is to shorten all fuel lines by cutting away all spare length, just enough to reach the engine, not a 1/4" spare. Next arrange things so the fuel tubing is not against the firewall where it goes through into the engine bay, but is "suspended in the air" by it's own stiffness as it were. Lastly, if these do not work, and they should, a couple of drops or "son of a gun" dashboard polish (yes!) in the fuel and shake to mix. End of bubbles.

The other possible glitch is a slightly over-leaned out engine tuning setting. This is common. The engine generates slightly more heat than it dissipates into the air, and as the flight progresses it warms up until a tightening appears (the beginnings of a seize). the engine stops, cools down and loosens up again before you get to it, and is ready to re-start after landing. Run on lower throttle to prove this cause. If lower throttle produces less heat it takes longer to appear, if at all. Richen the main needle to make it go away. It is most common in new engines which run hotter than they will after they run in, reduce internal friction, and loosen up. But it can be induced in any engine by increasing nitro, or increasing prop size, or a tight cowling around the engine, without richening setting to get more cooling to compensate for the added heat from the extra load. Unscrewing the needle 2-15 minutes on a clock increases fuel flow in and eliminates this.

By the way, if your issue was caused by the engine's tuning being over-leaned, then adding the resistance of a filter would reduce the fuel getting to the engine still further, and thus make the problem worse! You would see the dead sticking appear earlier in the flight, or at a lower throttle than before. You would also consume more glowplugs.

Trust this helps.

privateBeavis

great info there thanks!

Again I'm only guessing here but I think perhaps the air bubbles from vibration may be the culprit cos where we were running it on the ground did see some tiny bubbles in the line at some point. I have the lines as short as they can be I think but as you say it's quite likely its leaning against the firewall, or the padding around the tank might not be optimal.

When I was flying usually had running at about 1/2 to 3/4 trottle so not sure its over heating but I'll chase down the vibration thing first and then look at adjusting the tuning like you said.

Bruthal

privateBeavis wrote: »

I am having some reliability problems with my trainer plane. Has a ASP 46 engine and while it seems to run perfectly well on the ground its cutting out on most flights at random.

I'm thinking its either a pin hole somewhere perhaps or dirt in the tank or dirt coming in from the exhaust line. Is it a good idea to have fuel filter on the tank to engine fuel line on this type of plane?

We used to point the plane straight up and put engine to full revs, if its too lean it will die away and so richen it a small bit and try again. That was the most common cause of your problem there assuming all tubing is installed right.

Bruthal

privateBeavis wrote: »

great info there thanks!

Again I'm only guessing here but I think perhaps the air bubbles from vibration may be the culprit cos where we were running it on the ground did see some tiny bubbles in the line at some point. I have the lines as short as they can be I think but as you say it's quite likely its leaning against the firewall, or the padding around the tank might not be optimal.

When I was flying usually had running at about 1/2 to 3/4 trottle so not sure its over heating but I'll chase down the vibration thing first and then look at adjusting the tuning like you said.

I would say its not uncommon to see tiny air bubbles in the fuel line particularly after starting it after just filling the tank.

coolwings

robbie7730 wrote: »

I would say its not uncommon to see tiny air bubbles in the fuel line particularly after starting it after just filling the tank.

True. They are pretty much always there and if you listen carefully you can hear them go through a running 2-stroke engine. The quantity can vary. they can go straight in with no ill effect, or they can accumulate at the end of the fuel tube where it meets the inlet nipple and make a bigger bubble that is capable of cutting the engine.

The OP said random cutouts. That is the reason I mentioned it at all. Bubbles would appear more random than an over lean setting. Since the lean setting trips after a constant time at each throttle level/climb angle. Full throttle = engine deadsticks soon, half throttle = takes longer to get hot and deadstick.

Bruthal

coolwings wrote: »

True. They are pretty much always there and if you listen carefully you can hear them go through a running 2-stroke engine. The quantity can vary. they can go straight in with no ill effect, or they can accumulate at the end of the fuel tube where it meets the inlet nipple and make a bigger bubble that is capable of cutting the engine.

The OP said random cutouts. That is the reason I mentioned it at all. Bubbles would appear more random than an over lean setting. Since the lean setting trips after a constant time at each throttle level/climb angle. Full throttle = engine deadsticks soon, half throttle = takes longer to get hot and deadstick.

Yes but slightly too lean and it gets a little more lean during flight as fuel level reduces in flight, also how hard ye throttle up to climb, or as i seen plenty of times, the low needle setting being slightly off can cause problems in flight at seemingly random times. Or a leak in exhaust pressurising tube, a change in nitro percentage in new fuel, a glow plug tarnished, lots of stuff.

coolwings

robbie7730 wrote: »

...Or a leak in exhaust pressurising tube....

That's a good spot! Would do it too.

privateBeavis:
If the other stuff doesn't work then that could very well be the cause. A pinhole in the fuel leads might only be visible if they are taken out and pulled between your fingers to stretch the silicone making the hole bigger. Pinholes sometimes appear where the tube goes onto the fuel nipple of engine or exhaust. But these are generally rounded, and the brass tubes coming out from the tank are sharp edged. So check the tank ends of those tubes carefully.