trimmer fuel valve

[tim kerns]

has anyone installed the trimmer stc on a covered a/c i would like to keep it a flying project instead of tearing it completly down

[Twofieros]

I've got the STC for my tripacer. I have not begun the install yet and I will be doing it on a bare frame. I have reviewed the instructions but that is all I have done so far. I just felt inclined to comment. The fuel valve requires some rerouting of fuel lines. The most difficult will be the ones on each side. The passenger side is routed to skip the gascolator under the right seat and it passes under the seat rather than behind the instrument panel. You would have to remove some of the interior fabric to get to those lines. The same holds true for the pilot's side. You will have to open up that fabric as well to get everything done. There is a new location for the fuel drains which are under the pilot's side just inside of the gear leg. The entire job can be done but if you think you can avoid all fabric work when doing this, you cannot.

All of that is from memory so exact locations may be off. In general it should give you a good idea of what you will be facing. I see that you are from Ohio. You are welcome to come down and take a look at my frame and the STC to get an idea of what you will be facing if you want.

Tim

[Steve Pierce]

I have done it on a bare fuselage. I think it can be done on a covered fuselage but would require the interior fabric or panels be removed. It would be a pain. You can install the Dakota Cub or Univair fuel valve without modifying the fuel lines. The Dakota Cub valve has a Both position.

[Stephen]

I've installed the Trimmer Fuel mod on a covered plane. Interior fabric work on the right and left side will need to be done. On the right side have to run a fuel lines forward of the door, which joins the aft fuel line under the right seat. I cut a couple of holes in the fabric and fished the fuel line down then patched it. If you have interior panels instead of fabric it should be easier. The left side has the same set-up which I think I was able to use some of the original fuel line. You will have to open the fabric where you install the new fuel valve on the left side. It is a pain, but it's a good improvement.....no more switching tanks for T.O. and landing. I recently saw a good T.Pacer bit the dust because the pilot forgot to switch tanks on T.O.....

The whole project should be able to be completed in a couple of days. With some of the work staged to keep it flying.

[tim kerns]

hey stephen i will get with you on the fuel systm and i sent you a money order today thanks

[Stephen]

Thanks Tim, we can chat in a couple of weeks. Off tomorrow!!

[dplunkt]

What is the advantage of the Trimmer system over just replacing the valve with a Dakota Cub valve. If you can put it on "both" then you would no longer need to worry about the right tank being under 1/3 full. Am I missing something? Trimmer rerouted the lines to accomodate the seaplane door.
Dan

[JohnW]

What is the advantage of the Trimmer system over just replacing the valve with a Dakota Cub valve. If you can put it on "both" then you would no longer need to worry about the right tank being under 1/3 full. Am I missing something? Trimmer rerouted the lines to accomodate the seaplane door.
Dan

I think you might be missing something. The L-R-Off valve isn't the issue with the "1/3 tank" problem. Really, relocating the fuel valve as much as would be NECESSARY wouldn't actually REQUIRE repiping the system very much at all! The issue is the ROUTING of the right side fuel feed lines in the original design. The right side lines make a large "U" around the cabin door. The rear line has to go UNDER the lower door frame in order to meet back up with the fwd line (BTW, the very early Pacers with the right tank installed only had the REAR fuel outlet. The front line and tee was added by a Service Bulletin. Splicing this tee into the system "takes place" pretty high up, just above the cross tube that forms the lower "support" that the instrument panel rides on. When the right tank is less than 1/3 full and you are taking fuel from it (only, with the original valve), it is quite possible when maneuvering to "unport" the front tank line. Now, with a "full rear fuel line" at such "attitudes", the fuel that the engine needs to stay running can quite possible STOP FLOWING when the front port is "sucking air". This is cause by the simple fact of Physics that "liquids flow not only "downhill", but also "through the path of least resistance". At the right attitude, air can be drawn through the unported front line because the fuel level IN THE TANK may actually become LOWER that the "other end of the fuel loop that ends at the carburetor"! The rear line remains "filled with fuel, but the "lower part" of the piping system is free to "draw from" the open-to-atmosphere front tank outlet, and the carb "RUNS OUT OF FUEL". The part of the fuel line "downstream of" the tee will flow normally, UNTIL THE AIR THAT IS ENTERING FROM THE UNPORTED FRONT OUTLET is all that is left in that line! Engines just don't run as well on air as they do on fuel... You might think that the lines would draw fuel anyway, but if the tee is higher than the fuel available to the rear line, the path of least resistance becomes the source of AIR from the unported front outlet. This "breaks suction" and the fuel in the rear line will NOT flow past the tee. Wow, huh? Such a tenuous grip on flight.

Simply installing a On-Off-Left-Right valve in the original system does ABSOLUTELY NOTHING to mitigate the possibility of having fuel in the left tank at that attitude and starving the carb. The "attitude" when all this happens is when the left wing is LOW and the right tank is less than 1/3... having 18 gal of fuel on the left side doesn't change a thing if it is "below that tee". No change was made.

Yeah, Eddie's mod also solves "a problem" with the seaplane door installation...but I wouldn't agree that this was his PRIMARY consideration in rerouting the lines (well, maybe is WAS the causal factor in the first place, but rerouting the lines the way he did SOLVES the "unported front right tank outlet" nicely). The L-R-On-Off valve in itself has pretty much "nothing to do with" the termination of the AD.

[MN_flyer1]

I was looking at my Univair valve. It sure would be simple to modify to a "Both" selection. Has anyone done this type of mod? The problem with the routing of the right tank rear fitting would still concern me with a potential loss of fuel in the system. I have the Aux tank installed.

Tim

[Steve Pierce]

You would have to cut the groove in the center plug to keep fuel from going around and out. It is a specialcut in a round part to hold an o'ring.

The Dakota valve would use the same routing and doesn't flow the same out of each tank at all times but does end up feeding even on the low end. Trimmer re-routes the lines under the seat and they flow more eveny. Most L-R-Both systems use a vent between both fuel tanks to help them feed the same.