lml@lancaironline.net Mailing List Archive

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 on) 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 allowance 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 could 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 hanger floor, tarmack, nose wheel, etc.) I had a document on the flow rate/pressure for the Dukes pump in both Low and High modes, but I can't find it now. As I remember in the low pressure mode it would provide more fuel then I needed for cruise LOP, but not max power at sea level. Since this was to allow we to get somewhere to land I considered it sufficient. I ran an IO-550N. If you're running TSIO you may need 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 it 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 dangerous. 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 chapters 14 and 23: Chapter 23: wiring: denotes a Single Pole Double Throw rocker switch for the LOW-OFF-HIGH positions of the fuel boost pump. Chapter 14: Firewall Forward, depicting the fuel flow does not show a separate routing for the fuel primer circuit. So how does the primer function work? Is it merely pushing a higher volume of fuel through the circuit? I know it's necessary for hot starts to quickly circulate the cooler fuel to the manifold but does it somehow bypass the gascolator and the engine driven fuel pump? This would make sense if it did as some aircraft call for pushing in the primer and possibly holding it in to keep the engine running in the event of an engine driven fuel pump failure. So then why do I only have a low selection of the boost pump? Should I 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 -- For archives and unsub http://mail.lancaironline.net:81/lists/lml/List.html -- For archives and unsub http://mail.lancaironline.net:81/lists/lml/List.html