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What would you do?
Interesting issue reared it's head on the condition inspection I'm working towards completing on the 801. My IA pointed out my fuel supply lines may be a bit too small (3/8) ID. Neither he or I were comfortable with the rubber auto fuel lines used to connect the tanks to the solid lines in the fuse. That is what prompted the question, "are these lines to small for the application?" .
This is the Franklin 220 Hp installation, further research indicates other a/c's with this PP utilize 1/2" lines and the 43.13 suggests the lines it was built with are too small.
I understand that ex aircraft are not necessarily held to the 43.13, but this looks like a solid benchmark to aim for. I looks like a complete retrofit is in order...
What would you do?
Replies to This Discussion
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Permalink Reply by Daniel Niendorff on
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Well, a couple of thoughts here.....
First, are the current rubber fuel lines over 10 years old? If so they need to be replaced anyhow. But if not they may be adequate if they pass fuel flow testing. Fuel flow testing should test the flow of the whole system from tank to carb, or injector spider. To find out if the flow is enough, you will need to know the fuel consumption of your engine at full power. This can typically be found in engine the manual. Then just measure flow and see if you have 150% of that value (125% if you have fuel pump also). That will answer if the lines are adequate for you. Just be aware that you need to measure flow at level pitch and climb pitch.
All fuel systems are unique - testing your system provides your answer. For an example, my 801 has 3/8 lines and I flowed 30 gal/hr in my fuel flow tests. But it was less at climb pitch, with lowest flow tank flowing 22.5 gal/hr. That was adequate for my IO-375 at 195 Hp. Yours will be different, even with the same diameter lines.
If you do decide to replace, I highly recommend the speed seal PTFE hoses (see ANplumbing.com) for flex lines - lasts forever. If you go hard lines, I would recommend 3003 versatube - as it is very easy to work with, and of course also lasts forever..
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Permalink Reply by Guy Zindel on
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Exactly the percentages we're looking at, we'll be flow testing this week, but it'll likely be a wast of time as the Stinson 220 frank stc calls for 1/2" lines... Thanks for the tip on the speed seal.
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So is the speed seal stuff less expensive than the an alternatives? Will any of the fittings adapt to an, or will I need to run them all the way to my fuel pump?
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The speed seal fittings are not cheaper (as I recall at least). But they are easier to assemble. No mandrel needed to put together the ends.
There are a whole variety of fittings you can put together. The selection is nearly endless. I’m assuming you have NPT - hose barb fittings for your rubber hoses at the tanks. You would want to change those out for NPT - AN fittings appropriate to the size line you decide to run. If you are upsizing lines, you will be upsizing all the fittings from tank to engine…..
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Permalink Reply by Bob Pustell on
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Are you gravity feeding your fuel to the mighty Franklin or using pumps? That will determine your tube size needs as well. I am partners in a 1958 Cessna 175 that was set up at the factory for gravity feed with 3/8 fuel lines to the carb. Mine was retrofitted with a Lycoming O-360 conversion and the STC allows the smaller stock fuel lines to remain in place but requires the addition of an engine driven fuel pump backed up with a firewall mounted electric fuel pump, very similar to the layout of Cherokee fuel systems exept for the high wing part.
If your 220 Franklin is being gravity fed the fuel I would think half inch lines are needed for sure. If you have fuel pumps I don't think it's as big a problem. Your flow test should tell you for sure. Good luck.
For what it worth, Stinson 108's with 150 HP Franklins and gravity feed use 3/8 fuel lines. 108's with 165 or more HP use half inch fuel lines. In the Stinson world, at least, if upgrading engines and therefore fuel lines, one needs to upgrade the entire fuel system to the larger size - including the gascolator, fuel selector valves and the threaded bungs in the fuel tanks (yes, you need to remove the old smaller bungs and weld in larger ones to allow a larger size fitting to be screwed into the tank).
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Let us know how your fuel flow testing goes……. Curious minds want to know.
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WILCO
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The half inch system flowed just shy of 3 gpm, and that was through the bottom of the steves gascolater. I'm sure it would be higher at the carb.
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