Fuel Line Size for O-360

[taildraggerpilot]

The reg is correct. I think Trimmers STC uses 3/8 lines to the fuel valve and then 1/2 inch to the strainer and engine with a both poistion in the valve. Similar to some Cessna systems. He has also plumed the system like a Maule eliminating the right hand under seat gascolator. Our 180 Pacer is gravity fed with 1/2 lines. The fuel valve does not have a both position and we have ram air on the caps as well.

Brian.

I went back and looked at the drawings, the Trimmer fuel mod uses 3/8 in. lines for the entire plumbing installation.

[taildraggerpilot]

http://www.trimmeraviation.com/

I did not see any prices listed at his site, but he's a great guy, give him a call. I think his fuel mod is great, I never take it off the both position. The discussion about larger diameter fuel lines going through smaller fittings is partially correct in that it is some restriction to fuel flow. But, you are still better off by getting a higher fuel flow with the larger line, because it will obviously carry more fuel, but when it passes through a smaller fitting the fuel will accelerate at that point. Even with a restriction you are still better of in terms of fuel flow with bigger diameter lines. I ran 3/8" lines to the fuel selector and 1/2" from the selector to the engine.

Using a larger line between orifices (small fittings) will only reduce the line losses along the tube, but the pressure drop we are talking about is on the order of .01 psi between using 1/2 in. line and 3/8 in. line (neglecting the fittings). Regardless of whether the flow accelerates through the fitting, it is still acting like an orifice (thus providing a pressure drop) and the only gain as I mentioned earlier, is attributed to less line friction which is negligible.

[Stephen]

Ben, I'm not sure I follow, so please correct me, are you saying that the fuel pressure drop is only .01 psi between 3/8" tubing and 1/2". Regardless of the length, pressure, number of bends or number of fittings? I've don't have the ability to even detect that kind of difference.

For the 0320, 3/8" obvisiouly is fine. The only reson I switched to 1/2" after the fuel value was that since I would be using the both position, I might as well continue on with a higher flow and I had the fittings. But, it mostly goes for naught, because the flex fuel line to the carburetor (I think) is 3/8". I made enough of those flex lines one would think I could remember. Clearly, there's an inverse relationship between age and memory, at least for me.

Heck, I switch my vote (oops, wrong word) to Brian's reply.

[stevesaircraft(Bri)]

I looked at Trimmers web site and can confirm that it is 3/8 all the way. More than likely, Trimmer is able to get the fuel flow with the both position and using the pressure caps. Our Pacer does not have a both position, therefore the 1/2 inch system to get the required fuel flow. Trimmers fuel system probably requires that fuel selector be in the both position for takeoff and landing in order to get the fuel flow.

Brian.

[Steve Pierce]

Stewarts have a 180 hp in their Pacer and I remember they didn't use a fuel pump. I don't remember them saying anything about having to change the fuel lines. I have a copy of their paperwork, I will see how they did it.

Brian, What is the requirement on this? Your Dad gave me an equation once using engine horsepower and amount of flow? I will have to dig up my notes.

[taildraggerpilot]

[quote="Stephen"]Ben, I'm not sure I follow, so please correct me, are you saying that the fuel pressure drop is only .01 psi between 3/8" tubing and 1/2". Regardless of the length, pressure, number of bends or number of fittings? I've don't have the ability to even detect that kind of difference.quote]

No, the .01 delta P between 1/2" line and 3/8" line is only for the portion between the fuel selector and the gascolator and is the delat for the line loss only, fittings are neglected. I also assumed 360 degrees of bend.

[Stephen]

Interesting Ben, did you measure or calculate that?

[stevesaircraft(Bri)]

This is Steve,

The Fuel flow requirement from the FAA is .5 lbs X hrsp + 150%. OR .5 x 180 = 90 lbs. divided by 6 (fuel weight per gallon) = 15 gal x 150% = 22.5 gal per hour minimum fuel flow for 180 hrsp. Now the tricky part is how this measured. The fuel system has to be completely empty, with the aircraft set up in a 15 degree nose up attitude. If using fuel pumps it is assumed the engine pump will produce the same as the electric pump so the test is conducted at the outlet of the electric pump. If a complete gravity flow system, the test is conducted with a hose attached to the outlet of the gascolator and raised 19 inches above the carburetor. This is to represent the atmospheric pressure of .5 inches. ( minimum carb inlet pressure). It turns out that at 19 inches above carb is about even with tank outlet. Now, you introduce fuel in the system one gallon at a time until you get the required fuel flow. On our 180 with 1/2 inch lines took 3 gallons ( creates the head pressure) to meet the flow requirement . This becomes placarded as "Unusable Fuel". On our 180 STC with the constant speed we used original 3/8 lines with fuel pumps and it took 2 gallons to meet the requirement. The pressure tubes on the caps has never been an FAA consideration with us. We have them on our 1/2 line Pacer, but not on our STC constant speed with 3/8 lines.
I have not talked to Eddie about his testing, but from our experience, my suspicion is with the two 3/8 lines plumbed into a both position and 1/2 from there out, will create enough head pressure to operate within the requirements with 2 to 3 gallons unusable. There is plenty of fuel available in level flight with 1/4 tanks or better with 3/8 lines on gravity, but it does become marginal with full power in a nose high attitude with low tanks. The critical scenario is a balked landing go around with low fuel. The "unusable" is supposed to be enough to get you around the patch for the second try.

Steve.

[Steve Pierce]

Thanks Steve. I did find my notes but didn't have all that down. I remember installing the headerless system in a Super Cub and the stc/kit came with pressure caps. I asked if I needed them for the C90 and they said it was part of the fuel requirements for the O-360 STC. I think it is placarded for less than 36 gallons also. Now I know why. See I learned something today. Thanks.

[andya]

Just recieved this great news this morning in email......
:P
Hello to all,

We are very pleased to announce that the FAA has issued to us the STC SA02306AK for the installation of the Lycoming O-360 180 horsepower engines for installation on Piper PA-16, PA-20 & PA-22/20 aircraft. The engine models approved for installation are Lycoming O-360 A1A, A1D, A2A, A2D, A2E, A2F, A3A, A3D, A4A, A4M, A4N, & A4P.

There will be some lag time in getting the engine mounts produced.

Pricing will be determined as soon as the engine mount production cost are determined and the mounts are available.

Thank you all for being patient during the lengthy STC process.

Eddie Trimmer
Trimmer Aviation LLC
P. O. Box 361
Willow, Alaska 99688