I would like to thank all those who responded to my question about when
to turn on the fuel boost pump when flying a Lancair IVP.
Based on info gleaned from the posts, it appears that the answer is
“whenever it is necessary depending on your specific plane.”
As some never use their boost pump after engine start, others turn it on for
take off, others turn it on at 3k feet or 6k feet or 10k feet or after reaching
cruise at 24k feet, it appears that there is no dependably consistent answer
that would apply to every plane, even in identical environments (temperature,
pressure etc). We are left to figure it out on our own. But at
least I know a little bit about why, thanks to your feedback.
It appears that the “right” answer is all over the board
because of at least the following reasons (there may be more):
- Fuel flow set-up varies from plane to plane
- The internal leakage of the metering pump varies
considerably from unit to unit
- Vaporization level
and rate of the fuel, because of heat and thus cavitation in the
engine driven pump, especially if that pump is also heat saturated
from the engine operation, varies from plane to plane
- Fuel flow varies from
plane to plane because of varying mounting locations of the fuel boost
pump
Not everyone is happy with these seemingly
random and unpredictable (especially on your first flight) variations. Bob
Mackey typifies the sentiment of many with:
It seems that the job of fuel flow regulation is
relegated to the pilot. The pilot has access to two pump switches, a mixture
knob, and a fuel cutoff valve. With those tools he attempts to keep the fuel
flow to the cylinders within a narrow range of acceptable mixtures. If he
fails, the engine quits now, or overheats, detonates, and may quit later.
It appears to me that the safety of these pilots and
their passengers could be
improved more by fixing the flaws in the fuel supply
and injection system than by learning better switchology.
The posts that came in were mostly helpful and very informative.
Some were not. I’ve listed brief excerpts of some “Helpful Comments”
below. (I deleted my original “Less then Helpful Comments”
section in an attempt to not embarrass anyone to the point that they would be
tempted to hunt me down and kill me. There are enough of those people out
there already.)
Helpful Comments:
Everything from Gary Casey, especially: “If the flow is
predictable, then why is there so much effort required to "set up"
the system for each engine? I'm not sure, but the internal leakage of the
metering pump surely varies considerably from unit to unit.”
Mike Easley’s Continental Fuel Injection Setup PDF.
Scott Krueger: “On the other
hand, a fuel injected engine, say a Lyc 320 with an RSA style fuel system,
generally requires that some level of fuel pressure must be maintained so the
stinking throttle body can match it to the air via pressure measured
by some weenie tubes in the induction stream so that ultimately it
can deliver the correct fuel flow to the injectors. The ideal pressure is
about 26 psi, but the system only gets upset if the pressure drops below 12 psi
(fluctuations between those values don't seem to make much difference).
How can such variation happen? Well, one way is vaporization of
the fuel because of heat and thus cavitation in the engine driven pump,
especially if that pump is also heat saturated from the engine operation.”
And: “If you haven't already
considered a test pilot for the first flight, you should do so. If you
haven't at least been to an HPAT ground school, you should go before you
fly. You should be current and flying something that is high performance
and complex now. You should also be in contact with your aviation
insurance company as they may have some "suggestions" about your
training in order for you to obtain hull coverage.”
Colyn Case:
“If you haven't taken the APS course I HIGHLY recommend it. I went in
thinking I would learn the fine points of LOP operation and came out realizing
how very easy it is to destroy your engine doing pretty much what we've all
been taught to do. This is all backed up by hard data. ...and now
you can take it on line cheap. Check out http://www.advancedpilot.com/ for only
$395.”
Bill Maddox:
“I see only one way this accident problem can be reduced…that is to
set up a program with either of these schools as a pre-requirement to flying
this equipment. I said this some time past on this site and nothing has changed
other than the accidents keep developing at a faster rate than it should be.
I think training in the sims is a must and invaluable. Sitting at a desk and
hearing about a situation is one thing, but really being in one in a sim is
where the real training occurs.”
Bob Mackey: “A reliable system is one that stays within its
proper operating range
even when its inputs are out of spec. It appears from the published
accounts on this forum that the fuel flow varies with fuel supply
pressure….It appears to me that the safety of these pilots and their
passengers could be improved more by fixing the flaws in the fuel supply and
injection system than by learning better switchology.”
To Safe and Happy Flying
John Hafen
N413AJ
To be flying in the Spring (not sure which year)