Sender: <marv@lancaironline.net>
To:  lml@lancaironline.net
Date: Mon, 28 Jan 2013 14:47:38 -0500
Message-ID: <redirect-6033572@logan.com>
Received-SPF: pass
 receiver=logan.com; client-ip=17.158.58.247; envelope-from=gw5@me.com
MIME-version: 1.0
Content-transfer-encoding: 7BIT
Content-type: text/plain; CHARSET=US-ASCII
Subject: Re: [LML] Also, does the Primer work?
From: George Wehrung <gw5@me.com>
In-reply-to: <list-6032178@logan.com>
References: <list-6032178@logan.com>

All,

Thank you for the responses!  I have learned a lot.  I also called TCM and Lancair.  It would appear that the consensus is that the IO-550 does not have a separate priming circuit.  The prime function puts the electric boost pump to a higher RPM and thus volumetric output throughout the gascolator and the engine driven fuel pump.  The engine driven boost pump can be bypassed in case of failure or vapor lock.  

The low setting on the electric driven fuel pump should be able to run the engine all but the most extreme flight regimes.  

Therefore, at least on the non-turbo ESes, the High is only used for priming, short use for engine stoppage and to get it running again, or possibly to clear vapor lock or an obstruction.  However, once the engine is running again, it is recommended to go to the Low setting as the High is too much and may flood the engine.  The guys at Lancair use the Low setting for switching tanks, takeoff and landing as most of you all do.

And the priming circuit.  The TCM guys said most likely, I do not have the separate circuit.  That option usually only comes on the Turbo models.  

If anyone has a picture of their fuel manifold depicting the solenoid for the priming circuit I would love to see it. 

I also agree with going out running the engine at a safe altitude and seeing how the engine handles pulling the power off with the boost pump in the low setting and pushing the throttle and mixture up to simulate the go-around/balked landing to ensure it can handle the additional fuel coming in.  

Again, thank you all very much the comments.

George


On Jan 28, 2013, at 6:17 AM, Colyn Case <colyncase@earthlink.net> wrote:

> George,   I don't have the whole answer but maybe one of the engine experts will chime in.
> I do know:
> - engine pump does have a spring loaded bypass so that the boost pump can drive fuel through it if it fails.  (We learned that at the Continental Factory course this week).
> - High boost is a speed function on the boost pump.  I have never seen a IV that didn't have one.
> - I'm not sure what the primer button does (I have both) but I think it has special plumbing.   Many planes don't have this.
> - I need to do some research to understand the relative outputs of the engine pump vs. the boost pump and how that will affect mixture in the event of an engine pump failure.   My expectation is low boost will not be enough and high boost will probably require a mixture adjustment.
> 
> On Jan 27, 2013, at 12:30 PM, George Wehrung 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