Actually, there is a good reason NOT to use larger line than necessary. Larger lines mean more oil volume and oil is compressible, causing the pedal to be softer, or more "spongy." That is also the reason to use metal lines when possible - metal, either aluminum or steel, is essentially rigid compared to the compressibility of the fluid. And what we typically call "stainless steel braided" lines are, as far as the fluid is concerned, teflon lines since the steel braid is really an abrasion-resisting layer and does not materially affect the pressure capability or rigidity of the line. Any flexible line expands with pressure application and therefore should not be used unless flexibility is required. Would it be a problem if flex lines were used throughout? Probably not, but if you want the firmest possible pedal you should use metal lines. If the lines are too small there may be a noticeable delay in brake application when operating in very low temperatures. With the short runs used in our planes I doubt if using -3 lines throughout will cause a problem. And why order larger fittings even though the lines are small? No reason to do that, IMO. When I ordered my lines from DH I believe they only had one size AN fitting that came with the standard-length tubes.
Gary Casey
From Skip: This is the same type of line (different manufacturer) that I recently retrofit in my ES. Several other builders I know used this type of line as well. I used AN-3 fittings on my lines, which are perfectly adequate. Perhaps someone out there can explain if there's a benefit to the AN-4's that seem to be the preference of those ordering new lines from DH.
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