lowandslow1(at)hotmail.co
Guest
|
 Posted: Fri Oct 17, 2008 10:41 am Post subject: Fuel Vent Lines |
 |
|
Just as a word clarification C so that terms aren't used incorrectly.� The fuel system in a Kitfox is "gravity feed" and fuel pressure to the carb or engine fuel pump is "head pressure" from a gravity fed fuel tank.� Strictly gravity only.� There is no "siphon action".� Designers have to determine that the fuel tank is high enough in normal flying/attitudes (nose high/nose low) and fuel line size adequate to provide a certain fuel pressure or head pressure for the fuel consumption of the engine used.� If your engine installation requires additional pressure to the�engine pump than head pressure can provide C an electric pump must be installed prior to the engine pump or carb (ala low wing aircraft).� Fuel line size�and head pressure to the�engine is all that insures that an adequate supply of fuel is maintained to the metering device C unless you have a fuel pump located at each tank outlet to supply increased fuel flow.� Most small aircraft under 140 hp C 3/8" line is used C that will that will supply more enough fuel for engine consumption.� As engines get larger C fuel line size goes up C 1/2" C 5/8" C etc.� The only time fuel is "sucked" or "siphoned" from�a�tank�is if you have a pump located at the tank.
�
It is extremely important that the fuel lines and the vent lines be angled down to the header tank or on a constant slope C problem areas are at the wing pivot and the horizontal routing to the header tank.� Especially in the vent line.� Air and fuel�must have an unimpeded path and a way to get out and�into the upper wing tank C if both lines to one tank have a low or high�spot� you could run into a fuel lock situation on that side.� Installed correctly and under normal flying and fuel conditions C the vent line has fuel in it and should correspond to the level of fuel in the tank.� In a long C steep C nose down descent with low fuel C your fuel pickup will be higher than the fuel level in the tank C as the fuel runs to�forward to the�front of the tank.� The tank is still vented C fuel to the header tank is supplied only by the remaining fuel in the fuel line from the pickup to the header tank.� Leveling off routinely will then raise the fuel level above the fuel pickup/screen and will flow back down into the header tank.� The air being displace by the fuel will go up the vent line and into the fuel tank.� If the vent were blocked then air would have to travel�upstream against the fuel going down into the header tank.� If it is on a constant slope this should not cause a problem other than fuel will not fill the header tank as fast as it has to make room for air in the line going up.� This is why the vent line is important.
�
If you look at aerobatic biplanes with a center section upper wing mounted fuel tank C you will see a forward fuel pickup. This is for nose down attitudes.� Most Cessna's have a forward pick up location C we can't because of the folding wing design.� The fuel line would have to run down the forward doorpost frame. (Which it does in a Cessna)�
�
There is nothing wrong with a single vent line to one tank or a vent line to each tank.� Because we have a folding wing design we cannot have a interconnecting vent line (wing tank-to-wing tank) like a Cessna�that they use to�help even the fuel burn from each wing.�In a perfect world (no slip nor skid C wings level C no turbulence C etc) Kitfox dual vent lines are used to keep fuel burn equal.� The fuel vents on the "filler caps" provide�a very�slight positive pressure in the tanks C but mainly to fill the void of used fuel.� Make sure the caps are on correct and the gaskets are sealing.��One of the�reasons for the long periscope vent line on the cap is to get the vent into static atmospheric air.� The low pressure on top of the wing where the fuel cap is can cause siphoning of fuel C which is why a gasket check is a good idea.
�
The reason that the vent line from the header tank needs to be a constant slope to the tank vent boss is to ensure that you don't create a "trap" for air.� A dual vent line system helps to ensure positive flow to the engine just incase one vent line were to become blocked.
�
Depending on your engine installation it is possible run the fuel low enough that there is not enough head pressure to supply the carb C even though there may be fuel in the header tank.� I suggest a standby electric fuel pump (Faucet 4-6 gph)�be mounted�below the header tank outlet that can be turn on during takeoff/landing and low fuel situations.� I installed one in my fuel system.� To insure positive pressure.
�
I would:
I would check the fuel caps first to make sure they are not blocked C pointing forward and the gasket seals.�
Ensure that the fuel and vent lines to each tank are on a constant slope to the tank.
Verify that the fuel level in the vent line corresponds to the level of fuel in the tank.�
�
Andy
You live life beyond your PC. So now Windows goes beyonget='_new'>See how [quote][b]
| | - The Matronics Kitfox-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Kitfox-List |
|
|
|
Get Email Distribution Too!
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
