Are there any performance, or tuning issues with using avgas, or avgas/mogas mix?  (Other than longer term effects on sparkplugs)

 

Thanks,

 

Al

 

-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Al Gietzen
Sent: Monday, July 31, 2006 9:15 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Auto Fuel - composite tanks

 

Not sure where to go with this because there are only a few here with epoxy fuel tanks, and on the Velocity list very few interested in the use of mogas.  I’m suspecting fuel compatibility isses.

 

I first put fuel in the tanks nearly 2 years ago and used Chevron regular. Everything was fine.  When I moved the plane to the airport 3 months ago (tanks empty) I filled with Exxon-Mobile.  Four troubling things have come up in the past few weeks.

 

1.     I have Vance Atkinson site gauge that has a white plastic back plate for easier reading of the fuel level. The small hole through the backing has been swelling shut so the sight gauge no longer works. I contacted Vance who said that there are hundreds of these gauges in EZs using mogas without problems, but he has had 3 incidents like mine in the last three months.

2.     A couple of weeks ago there was suddenly a pinhole leak in one of the gear well enclosures.  These enclosures are part of the fuel tank wall, and are parts that come with the Velocity kit.  These are also made and coated with EZ-poxy.

3.     Looking in through the filler cap I see reddish-purple splotches and streaks on those gear leg enclosures.  Poking and scratching with some safety wire on a stick does not indicate any softness of the surface.

4.     Yesterday, under the leading edges of one of the strakes, I noted an area with some slight surface irregularity.  Pushing on it suggests some sponginess.  This is ½” foam core material, and indicates the possibility of a pinhole leak in the inner skin, and fuel softening the PVC foam.  PVC foam is supposed to be unaffected by fuel.

 

My tanks (strakes) were made and coated with EZ-poxy back in 1998.  At the time I polled EZ flyers about there experience, and talked to reps of various epoxy manufacturers about auto fuel compatibility.  All the evidence said go with the EZ-poxy.

 

Any others with composite tanks having any trouble?  Anybody using Exxon-mobile fuel?  Know of any new additives that are an issue?

 

I’m thinking I should drain this fuel ASAP, but then what?  Other brand?  That expensive Avgas?  Regardless I may be faced with cutting open a strake at some point, but right now we are trying to get first flight done this coming weekend.