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As it relates to all this fuel pump question/issue... Let's
all make sure we are specific with a couple of things. Carl, was your
failure in a TSIO or an IO engine? It seems there might be a difference in
pump usage depending on either. The other thing to keep in mind is does
anyone know the gph that can be supported with the pump alone in both
settings? Regardless of type of engine? The *IO* needs approx
26-27gph at takeoff power settings, I suspect the TSIO will need a bit more but
have no real world experience. *MAKING IT UP* - if the low boost setting
will sustain 27gph (plus some acceptable margin) during an engine driven pump
failure, then it could be used, or if it required high boost, then it would need
that setting.
So, given all of this, I picked up the phone and called
Continental...Here's what they told me. They suggested that Low boost does
nothing more than provide a "positive head pressure" to the engine driven pump,
and that if you had an engine driven pump failure, it would most likely require
"high boost" to provide not only the head pressure needed, but the volume needed
to cause the engine to continue to run.
I suspect there is "fudge factor" built into those
assumptions. For example, there are probably different ways the engine
driven pump can fail and depending on the failure mode, it seems that you *may*
need more pressure from the external pump than others. This is probably
why some have said that "low boost" is adequate, where others claim it requires
"high boost".
With that said, I'd offer the below, regardless of engine
type. (continental specific)
a) setup your fuel system appropriately, with the
appropriate fuel flow for high power and the appropriate RPM rise for low
power/idle - do this with a known working fuel system
b) in *any sort of emergency*, it would appear that the
first thing to do it reach for the "High Boost" setting. With a properly
setup fuel system, it should not "flood out" the engine, but may be more fuel
than is needed (and if so, the non-required fuel will be returned via the return
fuel lines)
c) once, adequate altitude has been determined, diagnosis
could reveal that low boost is adequate to "get you home". I suspect there
is a duty cycle that the external pump can support at HIGH vs.. LOW Boost and so
if you can use low to get home, it probably makes sense to do
so.
d) if no emergency condition exists, it seems that Low
boost may be used to avoid any "vapor" issues at 10K and above as most are
taught/learned (I still don't know if this is a TSIO or IO specific learning, my
guess is TSIO based upon fuel flow demands at high MP's)
However the above raises 2 questions in my mind....
a) if High boost is critical in the event of an engine
driven fuel pump failure, then I'd suggest we need to revise our "take off"
procedures to include putting the pump in "High boost" or implement some form of
"ARMED - relay switched" mode ala the Columbias. Fuel demands at TO are
the most critical and because Continental suggests that if an engine driven pump
failed, that you'd need high boost, it may make sense to revise ones procedures
to have that available during TO
b) it would also suggest that it is prudent to switch the
pump to "Low boost" when switching tanks. This should maintain a more
"constant" head pressure for the engine driven pump and avoid any "vapor/air
bubble" issues when switching.
I certainly wish there were more specific data around this
topic, with specifics for the IO vs.. the TSIO, but the above does seem to make
sense and offer the most "backup".
Thots?
Alan
From: Lancair Mailing List
[mailto:lml@lancaironline.net] On Behalf Of Carl La Rue
Sent:
Monday, June 11, 2007 10:05 AM
To:
lml@lancaironline.net
Subject: [Norton AntiSpam] [LML] Re: Boost
switch
Dan, high boost is more useful than engine prime. I had an engine
fuel pump failure at 400 feet after takeoff from Port Columbus, OH, westbound
towards city center. The engine immediately quit. I selected high
boost and it immediately started. The engine-driven pump failure was
confirmed by the Continental dealer who did the repair work. The boost
pump did its job, IMHO.
Carl La Rue
On 6/6/07, Dan Ballin
<dballin@gmail.com> wrote:
With
the current discussion about the recent accident, I am curious
what others
have done with the fuel boost pump switch. It seems like
the
options are for separate switches for high and low, a 3 way Low
-
Off - High and with a 3 way with the High being momentary. I
think I
am favoring the later with the thinking that the high
boost is really
only needed during start for engine prime and as Skip
stated this
precludes leaving the high boost on.
Other
thoughts? Does this apply to the IO-550 as well?
Do any of you
flying, use the high boost for anything else. In an
emergency
would you use high or low boost or try both?
I am doing a IO-550 in a
Legacy.
Dan Ballin
LEG2
#286
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