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From: Robert R Pastusek <rpastusek@htii.com>
Subject: RE: [LML] Re: Also, does the Primer work?
Thread-Topic: [LML] Re: Also, does the Primer work?
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I would add that the fuel flow changes with boost pump on or off. Important=
 that you know which way your engine is set up (with or without low boost o=
n) to achieve the correct fuel flow on takeoff. On my TSO-550E, this varies=
 by about 4 GPH with/without low boost. This is within the allowable allowa=
nce of fuel flow for my engine, but if the fuel system is set up to flow at=
 the top end of the allowable range (mine is), the addition of low boost co=
uld deliver enough fuel to flood the engine.  Again, it's important to know=
 what you have/how your engine is set up, and to operate it accordingly.

Bob

-----Original Message-----
From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Paul=
 Bricker
Sent: Sunday, January 27, 2013 8:46 PM
To: lml@lancaironline.net
Subject: [LML] Re: Also, does the Primer work?

George,

Questions I also had while building my ES.

First, there is a bypass circuit on the engine driven fuel pump. That's how=
 the electrical pump can get fuel to the engine when the engine driven pump=
 fails.

The priming works by just forcing fuel through the spider and injectors.
It pools in the intake until it runs out the overflow ports (and on the han=
ger floor, tarmack, nose wheel, etc.)

I had a document on the flow rate/pressure for the Dukes pump in both Low a=
nd High modes, but I can't find it now. As I remember in the low pressure m=
ode it would provide more fuel then I needed for cruise LOP, but not max po=
wer at sea level. Since this was to allow we to get somewhere to land I con=
sidered it sufficient. I ran an IO-550N. If you're running TSIO you may nee=
d to plan on reduced power.

I originally wired my AC with the LOW-OFF-HIGH switch, and went to OFF-LOW =
later with a mom PRIME button. Too much fuel forced into the 550 can make i=
t stop running, so a momentary HIGH seemed safer to me. From what I've read=
 one failure mode of the altitude compensating fuel pump can be very danger=
ous. There are threads on this in the archives.

In the ES at least HPAT is (was?) training to take-off with LOW boost ON.
It always made sense to me. I don't know about other Lancairs.

Paul Bricker

On 1/27/13 10:30 AM, "George Wehrung" <gw5@me.com> wrote:

>As a continuation to my previous post, referencing the build manual=20
>chapters 14 and 23:
>
>Chapter 23: wiring:  denotes a Single Pole Double Throw rocker switch=20
>for the LOW-OFF-HIGH positions of the fuel boost pump.
>
>Chapter 14: Firewall Forward, depicting the fuel flow does not show a=20
>separate routing for the fuel primer circuit.  So how does the primer=20
>function work?  Is it merely pushing a higher volume of fuel through=20
>the circuit?  I know it's necessary for hot starts to quickly circulate=20
>the cooler fuel to the manifold but does it somehow bypass the=20
>gascolator and the engine driven fuel pump?  This would make sense if=20
>it did as some aircraft call for pushing in the primer and possibly=20
>holding it in to keep the engine running in the event of an engine=20
>driven fuel pump failure.
>
>So then why do I only have a low selection of the boost pump?  Should I=20
>replace my boost pump switch with a three-position LOW-OFF-HIGH switch.
>Should I have the boost pump on LOW for takeoff, descent and landing?
>
>Thanks again
>
>George
>
>
>
>
>--
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