Tuesday, September 16, 2014
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Fuel System
July 10, 2010

While flying yesterday, my primary EFI fuel pump died. This was one of the used Subaru Loyale pumps that I got from a junk yard. I am happy with the 300 hours of service that it gave me. The Loyale pumps are getting hard to find and quite expensive, at about ~$350, so it is time for a new style of pump. I have heard very good things about the Walbro GSL393 so have a new one ordered.

While waiting for the new pump, I decided to install a header tank sight gauge. I have a low fuel sensor but have found not knowing the exact amount of fuel in the header to be an issue on cross-country flights when trying to stretch a leg as far as possible.  The end result of not having this gauge is that I had 7.5 gallons of unuseable fuel (I liked to land as soon as my main tank was empty). I think this gauge will increase the utility of the plane to some degree by allowing four hour legs (something around 500 NM assuming no wind). The sight gauge is nothing more than a clear tube connected to the top and bottom of the header tank that runs down the face of my panel. I have it calibrated from zero to seven gallons - the header holds a grand total of 7.5 gallons.

January 1, 2009

ETHANOL - YUCK!!! My fuel tanks HATE the stuff. They get very mushy when ethanol is present so I have learned to avoid it like the plague.

August 21, 2005

Some people have asked about my low header fuel warning light timer circuit so here it is. I have a low fuel sensor mounted about 2/3 of the way up (from the bottom) in my header tank. This is Aircraft Spruce item 6905-400 and is mounted in an aluminum insert that I threaded and glassed into the wall of the tank. This sensor is triggers a DIY KIT 141 timer circuit. This circuit is set to close the warning light relay after 10 seconds of continuous trigger signal has been received. This eliminates the light from flickering due to fuel sloshing. The timer kit is available from HobbyTron.com (item CE-CK1614) and ElectronicKits.com (item CK1614).

90MG-LowFuelTimer-800.JPG

In addition, I have also constructed a cyclic timer circuit for the transfer pump. It is not installed yet but the plan is for it to automatically turn on the pump for x minutes (i.e. 10 minutes) and then off for y minutes (i.e. 5 minutes). The goal being to have a completely automated transfer process. This timer will be on an off-on-auto switch to allow overriding in the event that the main tank is empty.


August 21, 2005

It is finished. I have primered the fuselage but no finish paint - won't even worry about doing this for awhile. Finishing this little project took forever due to the fill/sand/fill/sand routine requiring so many trips to the airport which just aren't as frequent as they used to be.

90MG-HeadTankRepair-2005Aug21-800.JPG

July 4, 2005

Installing the ram air vent. I did not like the having the tube sticking out the top of the fuselage as before. The Q2 is just to sleek to have something poking out the top. The vent line runs into the tank and about one inch down into the header overflow tube. The tube follows the contour of the fuselage to the outside edge of the tank and then into the fuselage. It then follows the inside contour of the fuselage to the bottom where it exits and points directly into the airflow.

90MG-HeadTankRepair-2005July4-2-800.JPG90MG-HeadTankRepair-2005July4-3-800.JPG

July 1, 2005

Pressure testing of the tank. It works - no leaks!

90MG-HeadTankRepair-2005July1-3-800.JPG

June 24, 2005

Glassed the new top-inner skin onto the header tank.

90MG-HeadTankRepair-2005July1-1-800.JPG

June 15, 2005

Fitting the new top tank skin.

90MG-HeadTankRepair-2005June15-3-800.JPG90MG-HeadTankRepair-2005June15-2-800.JPG

June 10, 2005

Tank inside has been re-glassed and threaded inserts glassed/floxed into place.

90MG-HeadTankRepair-2005June10-12-800.JPG90MG-HeadTankRepair-2005June10-13-800.JPG

June 5, 2005

Cleaning up the tank, preparing for additional glass, and new threaded inserts for inlet/outlet fittings.

90MG-HeadTankRepair-2005June10-1-800.JPG90MG-HeadTankRepair-2005June10-3-800.JPG

May 30, 2005


I discovered that I had a mushy header tank and fuselage above the header tank. After several months of this, fuel starting weeping into the cockpit. It was time to repair the problem.

I decided to remove the top of the fuselage over the header to access the inside. After carefully measuring, I made the big cut. Turned out exactly as I had hoped.

90MG-2005May30-HeaderOpen1-800.JPG90MG-2005May30-HeaderOpen2-800.JPG

After taking a good look at the inside of the header, it was clear why fuel was leaking. The fuselage skin that becomes the top of the header had ZERO preparation done to it. There was a light bit of sanding but no additional glass/epoxy. This is a big no-no. Additionally, the joint between the tank walls and the fuselage was fairly poor. In some places there was plenty of flox squeeze out. In others, there was very little flox if any at all.

90MG-2005May30-HeaderOpen4-800.JPG90MG-2005May30-HeaderOpen9-800.JPG

The plan is to now allow a fan to circulate air thru the tank for the next week. Hopefully this will dry the tank and foam. Then I will sand/roughen everything up and apply a ply or two of very light cloth (2 oz) and PLENTY of epoxy. Fuel tanks are the one area of a fiberglass plane that should be over-saturated with epoxy.

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