REFLECTOR:Low fuel light

[Larry Richter]

Folks:
    Okay, I lurk too.  I have been building for a long time (forever?) 
but do have plans to finish it (before I die of old age).

My flying plane is a 1948 Bonanza with Flight Extender tip tanks 
installed in 1961.  I've been flying her since 1984.  This system uses 
no transfer pumps .  There is a vent line consisting of a little tube 
extending down into the slip stream cut off at an angle with the bevel 
forward and a small hole on back side of tube ( to allow some venting if 
the the front ices over- so I have been told).  This tube opens into the 
top of the tank.  (Main tanks have similar vents).  About 1/3 of the tip 
fuel is actually below the level of the fuel line in level flight with 
the line going out to the tip tank inside the wing and then down into 
the bottom of the tank.  This system has a check valve in each fuel line 
from the tip tanks preventing fuel from porting/venting in the wrong 
direction.  I have done all kinds of experiments over the years to try 
to get the tip tanks to unport or malfunction.  To explain all of these 
would make this email very long.  Suffice it to say,  it has been 
totally reliable.   Proper (but very simple) maintainance is mandatory 
to keep it working as the tip gas caps cannot leak and  the vents must 
be open and working.  (My wife occasionally sees me kiss the tip 
tanks--blow into the vent, feel the tank pressurize, and blow back at 
you  when you let go).  Newer "improved" versions of this system 
(Beryl'D Shannon is the latest) used various transfer pumps to eliminate 
problems that do occur if the old system isn't maintained.  These 
systems become maintainance nightmares as they age and fail and end up 
in junk yards.  They can also give you little thrill if you are careless 
and end up with 90lbs of fuel in one wing tip only to find out (too 
late) that the transfer pump on that side has failed.  The only $ 
maintainance I have had to do was replace the O-rings in the check 
valves 10 years ago when I discovered that they weren't "checking" after 
most of the tip fuel ended up on the ground after parking overnight on a 
slope with one wing higher.  And I had to replace the tip gas caps after 
a certified mechanic "cleaned up them thar oily old gas caps n dried um 
out real nice".  Want to ask me again why I am building my own airplane?

Sooo,
    My Velocity has vent lines as per (my) manual with main tanks and 
sump vented to a common manifold on the front of the firewall.  I used 
3/8 inch lines.  When I saw discussions regarding fuel sucking out of 
leaking gas caps and draining the sump and opposite tank, I looked at my 
50+ year old reliable lady and added the check valve to the lines from 
the main tanks to the sump.  It seems to my simple mind that this should 
be equally reliable.  The check valve would obviously cause a problem if 
you expect fuel/air to go "backward" from sump to main tank.

larry richter

John Dibble wrote:

> Yes, I agree that the  pressure will be equal, under static 
> conditions.  The problem is keeping the pressure equal under dynamic 
> conditions like climb, descent, and leaking caps. If connected 
> directly to the manifold, the sump pressure will change faster than 
> the tanks because there is very little air space in the sump.
>
> John
>