From: "R & A Colebrook" <rossann@azstarnet.com>
To: <lancair.list@olsusa.com>
Subject: Facet Pumps and Fuel systems
Date: Sun, 3 Jan 1999 14:58:30 -0700
Message-ID: <01be3764$33055f80$4c28c5a9@rossann.olympus.net>
Mime-Version: 1.0

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Charles Keller:  re your questions on the fuel system on my 235 powered 235.

1. How are the pumps wired?  The pumps are on separate breakers and separate
switches off the essential bus.  No interlocks.

2. Do pumps run all the time?  On the ramp, prior to engine start, the pump
for the tank NOT selected is turned on momentarily to hear it run.  The pump
for the selected tank is turned on to get a fuel sample from the gascolator
and make a quick check for fuel leaks on the ground under the engine.  After
priming, the pump is turned off for engine start.  In the initial flight
tests I turned the pump on for take off, but recently I have not been using
the pump on take off.  There is some kind of a trade here between the risk
of engine driven pump failure versus fuel leaks in the cockpit from
pressurized fuel lines versus available time on take off to switch tanks and
turn on pumps.  I flew a Cessna 210 for years where the manual called for
boost pump off on take off (till the first engine sneeze).  I am flying off
a 6000 foot paved runway with clear ends in Arizona.  I might see it
differently if I was flying off Bill Bartlett's Jefferson County
International with 3000 feet and trees at the end.

3. Has the minimum fuel level been checked for sucking air?  I checked the
fuel flow from a Facet pump with the airplane on the ground with the
tail weighted down to elevate the nose and the gas line disconnected at the
carburetor.  I put a measured 5 gallons in the drained tank.  The Facet pump
pumped out more than 4 1/2 gallons.  I have flown a tank down to 1 gallon
with no problems in relatively smooth air.  The tanks have only the BL76 rib
and no baffles or fuel traps at the fuel exit.  I might re-consider these if
I was doing it over.  My plan for keeping things running with low fuel and
very rough air is to switch to BOTH fuel selection and turn on both Facet
pumps.  I haven't thought up a good way to test this.

Ken Harwood is correct that having two tanks selected, each with a pump on,
will result in flow from the tank with fuel.  That is the fuel management
system in the BOEING heavy iron.  Normal fuel management is with all tanks
on and all pumps running.  Pumps with slightly higher pressure are used in
the tanks to be emptied first and no pilot action is required when a tank
runs dry.  Flow just comes from the next highest pressure pump.  This has
led to the current concern over ignition sources from dry running pumps.  I
have no idea what happens to a Facet pump running dry for an extended period
but  the sound of one running dry makes me think it would soon wreck itself
and quit.

Ross W. Colebrook  (N7828)