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From: "Whiting, Brent A" <Brent.Whiting@PSS.Boeing.com>
To: "'lancair.list@olsusa.com'" <lancair.list@olsusa.com>
Subject: Re: Commander singles fuel system
Date: Mon, 13 Nov 2000 14:22:29 -0800
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Frank,

I looked into the commander 114/115 fuel system before doing the builder assist on my Legacy (10/23/2000).  I was interested in the "Both" setting too and I wanted to build it into my fuel tanks before they were closed.  I have fuel system diagrams for the 114.

Some things that I was told:

Commander Aircraft:
The both setting is only for use during takeoff and landing.  Right or left must be used otherwise.  Fuel will not be used equally from both tanks.  One tank or the other will supply more.  I will miss this feature of my 172.

Lancair: (Mark Manke)
Lancair does not support or want anything to do with me setting up a both setting, even if I had all of the system diagrams to do it.  Apparently there was an lawsuit some years ago involving this.

>From a practical perspective, Mark convinced me I didn't want a both setting.  If a fuel pickup unports in a both setting (low fuel), then air will be drawn into the system and the engine will likely die.  A gravity feed high wing will not pull air in.  Once the engine has died, you are now performing emergency procedures at a low altitude (assuming landing).  You will need to switch to either left or right tank.  However, you do not know for sure which tank unported and if you should switch to left or right (or is it some other problem?).  This creates confusion and takes time at a very critical phase.  If you make the wrong choice you may not get the engine running in time.  It is better to just have a left and right.  If a fuel pickup does unport, you have one option; switch to the other tank and restart the engine.  This reduces confusion over what the problem is.

I mostly wanted a both setting so that I did not have to time left and right tanks and keep track of all of that in the cockpit.  It was clear from Commander that a both setting was not going to give me a cruise flight both capability anyway.  The fuel level systems available to us are much more accurate than in the 172 or PA-28 that I fly.  The need to time the tanks is basically eliminated.

Hope that this is of some use to you.  If you still have a need for a 114 fuel system diagram, I could fax it to you.

Brent Whiting
Legacy builder #6

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