flyrotary@lancaironline.net Mailing List Archive

Cranking amps may exceed 110. If a bulkhead fitting is used you might well be using the hose as a parallel path with your ground strap. This is more than enough current to weld steel tubing. If one start were attempted with the ground strap loose you have used the braid as your ground. In the racer the battery ground strap bolts on with one of the starter bolts. The mating surfaces between the starter and the engine must be free of dirt and paint.

Most people choose the Teflon lined hose assemblies for weight savings. Both Aeroquip and others have Nitrile liners and double stainless braid. Even a cloth cover so as not to saw through an important part or other hoses. Also the SAE specs have similar hoses at far lower cost. You must maintain similar fittings as one is a 45 degree fitting and the other is a 30 degree. Any hose shop can set you up with swaged hose ends and test them to 1,000 PSI if you like. The stainless braid looks racy but you see very little of it on real airplanes.

Lynn E. Hanover

In a message dated 4/4/2013 4:45:18 P.M. Eastern Daylight Time, bbradburry@bellsouth.net writes:

Good points all, Rich.

I am basically doing the conditional now. I have the cowl off and am only running the engine to improve the tuning. That is why I was inquiring about recommendations for fuel hose. With the cowl off, there is a fairly stiff breeze that carries away any fuel vapor. I do suspect that there was some kind of path of least resistance that caused this problem originally. I now have two #4 welding cables attached from each battery to each side of the starter which is mounted on the PSRU plate. During this conditional, I plan to attach about a 12 ga wire from the center iron to each battery just in case the ignition ground is looking for a better path due to the sandwich you mention.

Bill B

From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of ARGOLDMAN@aol.com
Sent: Thursday, April 04, 2013 4:22 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Replacement for Aeroquip fuel hose

Bill,

This probably goes without saying, but it is vital to determine why the arcing is happening. this may be a tremendous safety issue for you (and others)

Arching does not happen in a vacuum (actually it is easier there) but there is a reason. It is possible that your electrical system is using your FUEL lines ( spelled lines full of FUEL) for the grounding of somewhat high amperage loads, such as starter or alternator.

One thing to ascertain is " is your engine adequately grounded". The engine mount is a poor conductor. you need a good grounding strap (line) between the "-" of your battery and the case of the engine. Since our engines are sandwiches and there is a possibility (possibly remote) that there is some resistance between the bread and the meat, your current, wanting the path of least resistance may be using those fuel lines. Perhaps you need a better ground to the mounting bolts of your starter and/or alternator.

I donnknow, if it were me, I would do the fuel line inspection, correction and replacement NOW, before further starting of the engine.

By the way, what is your rationale for delaying until the next conditional to correct a problem where there may be significant current flowing through your fuel lines, especially when there is a fuel smell. You don't smell liquid fuel, you smell the vapor. Lessee vapor mixed with fuel in the proper proportions with some sort of ignition system --lets say an electric shock-- may make your next conditional inspection unnecessary.

Keep safe and fly safely

Rich

In a message dated 4/4/2013 3:01:53 P.M. Central Daylight Time, bbradburry@bellsouth.net writes:

I have several black spots on the SS braid for my fuel hoses they look like they were caused by an electrical arc? I think I can smell fuel around the spots. I plan to replace them at the conditional this month. What fuel hoses are being used besides Aeroquip?

Bill B