Reply-To: Sky2high@aol.com
Reply-To: lancair.list@olsusa.com
From: "Scott Krueger" <sky2high@hotmail.com>
To: lancair.list@olsusa.com
Bcc: 
Subject: The Boost Pump Rule: A Fool Proof Fuel Tool Prevents the “Vapors”
Date: Sun, 05 Aug 2001 15:54:48 -0500
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Message-ID: <F41DgI6bXmdMJOtd3rO0000228f@hotmail.com>

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When I first started flying my fuel injected, Lycoming powered Lancair 320, 
the test pilot (Ivan Checkinov) implored me not to be Russian (or was that 
rush’n?).  He said, “Check lists must require the use of the boost pump 
during take-offs, low power approaches and landings.”  Over time, this 
procedure was ignored because of numerous departures with the pump left 
running until long into the flight (I ain’t no ignor-am-us for nuttin). 
Well, experience and my good angel have conspired to teach me once more.

On the last Friday of Oshkosh 2001, I made another 50-minute flight north 
and touched down on Wittman Field at 8:30 AM.  With the show plane taxiway 
loaded with departing war birds, the orange shirts directed me to 
interstitial Limbo and thence, having lost track of any raison d’etre, onto 
the grass Purgatory alongside runway 9 behind a gaggle of twins.  After 
rattling and rolling along in the heat, I had to sit, idling, for a loooong 
time awaiting departure.  What the heck, it was a beautiful morning to fly 
back home anyway.  During the idling wait, the “idiot” light for low fuel 
pressure popped on several times and the digital indicator showed the usual 
27-psi had dropped to the 12-psi warning level.  Energizing the boost pump 
resolved the fuel problem and got me thinking about something I had read 
recently.

Engines set up without a post-pump fuel return line system are subject to 
hard hot starts because the fuel pump becomes heat-soaked from the engine 
and, when activated by cranking the engine, immediately vaporizes fuel along 
with resulting pump cavitations, the so called vapor lock condition.  
Engines, such as Continentals, can benefit from the down-line flow regulator 
that returns excess fuel to the selected tank while maintaining injector 
system pressure.  Before a hot start, running the boost pump for 1 or 2 
minutes with the mixture at idle-cutoff circulates cool fuel thru the 
engine-driven pump, absorbing a great amount of the heat in the pump and 
thus reducing or eliminating a major factor leading to vapor lock.

In normal idling operation, a return-line system is an important tool in 
keeping the fuel cool, as a rule, because most of the fuel passing thru the 
pump is returned to the selected tank.  In non-return-line systems, such as 
the Lycoming, only the fuel delivered to the engine passes thru the pump 
and, at idle, very little makes the transit.  This allows a hot engine to 
heat soak the pump that can (and did) lead to vapor lock conditions.  Of 
course, these circumstances could also occur on a hot day during a Vy climb, 
pattern work or a long slow descent into your typical Midwest 105-degree 
Heat-index steam bath where cooling air molecules are replaced by lighter 
and useless water vapor that has not quite yet reached the visible state. It 
can also happen in the thin air at a hot, high altitude airport with a high 
density-altitude.

In any event, running the electric boost pump can return enough pressure to 
the system to force the gases back into solution or, better yet, maintain 
the required high pressure to reduce the chance of vapor lock from forming 
during critical operations.

Because U. Ben Slackinoff (a rush’n dingbat pilot) and I now understand the 
rationale behind Ivan Checkinov’s exhortation to use the boost pump – we 
will.  Especially on takeoffs and landings where the loss of proper fuel 
pressure, because the engine pump got the “vapors,” could lead to unwanted 
engine out maneuvers and an overabundance of perspiration on an already hot 
day.

Scott Krueger
Lancair 320 – N92EX


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