Hi All:

      What are the advantages of running muffler pressure to the fuel tank in a CL plane that is to flown on suction?


                                                                                                                Tia,

                                                                                                                Frank McCune

     Hi Bill:

     Thanks for the reply.  I will fly two planes today with muffler pressure and then I will be able to determine for myself if there is an advantage.

    I will get back to you about my findings.

                                                                                     Be well my friend,

                                                                                     Frank

 

Another advantage if you fly on grass is in the winter when the grass is dry. With an open vent we've had grass bits from our field accumulate in the tank and then the craptrap, with the open vent being the only entry point. A line to the muffler makes it a closed system so no more bits piling in in the craptrap.

Also to help avoid this(and sucking it into the venturi), we crank the plane standing up and only set it on the ground while the pilot is putting the thong over his wrist.
Rusty

As for crap in the system: it's also a good idea to put a filter over the venturi.  I have some fine-mesh nylon that's the same mesh size as pantyhose but is stouter (and it's purple!).  Use the right sized O-ring to hold it onto the venturi and you'll never have to mess with it.

Bru-Line used to sell them as did K&B for R/C car use. I don't think Bru-Line is still in bidness. I liked them, and have some filters, both coarse and fine. I'm not using them, either. I just asked the wife for an old pair of pantyhose, and got them without a lot of fuss, once I 'splained what I was going to do with them! I was not allowed to remove them, however.  Steve

I have a piece of metal mesh taken from a Tettra air filter about 10 years ago. It's kept in place with 1/2" silicone tubing that also serves as venturi extension to keep places clean. I like it. I think it also makes engine run better, maybe some turbulence thing.
Where could I find more of similar mesh? L

I have a piece of metal mesh taken from a Tettra air filter about 10 years ago. It's kept in place with 1/2" silicone tubing that also serves as venturi extension to keep places clean. I like it. I think it also makes engine run better, maybe some turbulence thing.
Where could I find more of similar mesh? L

I don't know what your mesh looks like, but there are permanent coffee filters that are made of a fine stainless steel mesh that seems about the right size to me.

If you can find a lab supply house in your economic zone that sells to individuals, they'll have a huge selection.  In the US we used to have Small Parts, but they've been bought by Amazon and it's now impossible to distinguish mesh with a 32-inch grid from mesh with 32 wires/inch.

Hey Frank:

What engine, what run, and how were you checking for sameness?

If you're not trying for a stunt run it probably doesn't matter.

If you're running an engine tuned for a 2-4 break, I'm very surprised that you didn't notice a difference.  I would expect that without a uniflow tank, possibly running on atmospheric pressure, that you'd start with a good 2-4 break and end up in a solid 2.

If you're running an engine that needs a wet 2 run (i.e., an LA 46 the way it's typically run), then unless the difference is extreme the only way to tell is by timing laps.  My LA 46 generally speeds up from about 5.4 second laps to about 5.2 second laps over the course of a flight, with a non-uniflow clunk tank on muffler pressure.  I have a Tower 40 on a similar tank that speeds up about twice as much.  I would like the runs to be dead consistent.

      What are the advantages of running muffler pressure to the fuel tank in a CL plane that is to flown on suction?

   If you add static pressure, the fractional change in pressure as the the fuel runs out is lower, so change in mixture over the run is less. For old-style muffler 4-2 break engines, the exhaust pressure is an important adjustment. I can recall many happy hours experimentally plugging or opening holes in chip mufflers to get what I wanted.

    Brett

     Hello All:

     I tried running the engine in three different modes and the results were:

     1. Uniflow with muffler pressure to uniflow vent.

     2. Uniflow with uniflow vent open to the atmosphere and filler vent plugged.

     3. Both uniflow and fill vent open to the atmosphere.

     I could not see any difference in the way that the engine ran in these three modes.

     I was my "pit man" who suggested that we try these different mods and he too concurred that he could not hear or see any difference in the way that the engine performed.

   Either you don't have very much pressure, or you have substantial leaks somewhere. If nothing else you should have a pretty good change in the needle orientation from pressure to no pressure.

    Brett