Er_c
Registered Users
- Joined
- May 1, 2017
- Messages
- 16
- Reaction score
- 1
When I purchased my Skybolt ferrying it back from TX to CA at the first stop I filled both tanks and low and behold it left two gallons of avgas on the ramp through the fuel vents. The bad news is the vent lines ran down the gear struts and directly onto the brake rotors. I stood back and watch for a few minutes with the very real realization that my newly purchased Skybolt may soon be a pile of ash on the fuel ramp. When I got home along with a few other squawks I decided to address the fuel venting issue. My first idea was to run the vent lines up above the main fuel tank to create a sort of air gap and prevent it from venting fuel overboard, then move the lines away from the brakes. At the recommendation of friends, I opted to put check valves on the fuel vents. This worked well however when filling the tank with cold fuel on a hot day I notice it would build some pressure in the tank. However, I was assured that the pressure wouldn’t be enough to damage anything and as soon as the engine was started the pressure would be relieved. I tested the system with both tanks and all seemed well…until. The other day I topped both tanks and headed off to a near by airport for a few hours of office work.
After departing in the downwind I switched from the main to the aux and continued my climb out for about ten minutes everything was fine then heard a loud thump. Looking around in confusion as to what the noise was I noticed the gas cap on the main tank was sticking up about an inch higher then normal. I thought the gas cap was coming off and opted to switch to the main tank to burn off the incase the cap came off and landed at a near by airport. Upon further inspection I saw the whole gas tank had expanded and puffed up like a balloon. What I though was the gas cap coming off was the entire filler neck sticking up an inch higher then normal.
What had happened was… the fuel return from the fuel injection system had dumped some of the fuel from the aux tank back into the main tank, this over pressurized the main tank. This had obviously been happening all along on the ferry flight home, however without the check valves it simply dumped the fuel overboard through the vent lines.
Interesting side note when I adjusted the K factor on the fuel totalizer I used the 9 gallons in the aux tank to find how much fuel I was burning and it turns out I was off by almost 4 gallons an hour because it was dumping fuel overboard.
At any rate I’m now working on removing the severely damage main tank and it appears that the wing must come off in order to get it out. Can anyone confirm this? Also needles to say I plan on re-working the fuel vent system again and have read through some other posts on biplane forum but if anyone has some in site of pictures of how their vent system is ran or better ways of doing it I would appreciate it.
Another question I have is would it be possible or make more sense to have the aux tank just drop the fuel into the main tank so you don’t have to run the engine out of fuel to know its empty?
After departing in the downwind I switched from the main to the aux and continued my climb out for about ten minutes everything was fine then heard a loud thump. Looking around in confusion as to what the noise was I noticed the gas cap on the main tank was sticking up about an inch higher then normal. I thought the gas cap was coming off and opted to switch to the main tank to burn off the incase the cap came off and landed at a near by airport. Upon further inspection I saw the whole gas tank had expanded and puffed up like a balloon. What I though was the gas cap coming off was the entire filler neck sticking up an inch higher then normal.
What had happened was… the fuel return from the fuel injection system had dumped some of the fuel from the aux tank back into the main tank, this over pressurized the main tank. This had obviously been happening all along on the ferry flight home, however without the check valves it simply dumped the fuel overboard through the vent lines.
Interesting side note when I adjusted the K factor on the fuel totalizer I used the 9 gallons in the aux tank to find how much fuel I was burning and it turns out I was off by almost 4 gallons an hour because it was dumping fuel overboard.
At any rate I’m now working on removing the severely damage main tank and it appears that the wing must come off in order to get it out. Can anyone confirm this? Also needles to say I plan on re-working the fuel vent system again and have read through some other posts on biplane forum but if anyone has some in site of pictures of how their vent system is ran or better ways of doing it I would appreciate it.
Another question I have is would it be possible or make more sense to have the aux tank just drop the fuel into the main tank so you don’t have to run the engine out of fuel to know its empty?
