REFLECTOR:Low fuel light

[Scott Derrick]

Chuck,

Let us know how the Gami's work out.  I'm lucky that my IO360 will run 
50 to 75 LOP now that I have the EI installed.  I wonder how much better 
things would be if I caughed up the dough for a set of Gami's.

Scott


Chuck Jensen wrote:

> Brett,
>  
> I suspect the point is, why did the air get into the sump or how logical 
> is it that air is actually in the sump or, if that is not logical, then 
> it does point to a faulty instrument.  An investigation tree might look 
> like:
>  
> Air in sump:
>     1.    From the either tank? 
>                 No, both tanks were full and fuel outlets were always 
> covered
>     2.    From the vent line?
>                 No, the sump vent line is open and there is no source 
> for the line to be pressurized to blow air into sump
>     3.    Did the sump become starved for fuel from the tanks and pull 
> air in through the vent?
>                 No, flow paths open and if it was that starved, the 
> engine would have stopped.
>     4.    Was air in the sump all the time and just hadn't been vented off
>                 No, the vent to the sump was always open and air should 
> have been displaced by gravity flow of fuel.
>     5.    Do we know for sure that there is air in the sump?
>                 No, we only infer that because we are getting the low 
> fuel signal.
>     6.    Is it logical that air is actually in the sump?
>                 No, not if it is vented off and there is not pathway or 
> mechanism for air getting into the sump
>     7.   If air in the sump is not the problem, then what is?
>                 Then, it would seem to be a faulty instrument (float 
> only semi-buoyant) or a faulty signal. 
>  
> and so on.  Of course, if any of the answers in the question-path are 
> wrong or different than we think, then that limb breaks off the tree.
>  
> I don't mean to insult anyone's intelligence because this is pretty 
> simple stuff.  I've found difficult problems can be simple to solve with 
> a structured approach and simple problems can be difficult to solve with 
> a shotgun approach.  I've used both!
>  
> With that said, I'm still working on the unbalanced tank draw-down 
> problem.  I have a long trip scheduled next week, so I'll be able to 
> test the theory that I'm unbalanced (which comes as no surprise to a lot 
> of people) and that I need to shim the rudder slightly. 
>  
> I just installed a new set of GAMInjectors this morning so I'm looking 
> to get some good "lean test" numbers to see if the balance has 
> improved.  I was confident that my engine was "pretty good" in that area 
> because it does run smooth.  NOT.  There was 2.1 gph difference between 
> peak EGT across my cylinders as I leaned out.  1.0 gph is OK, 0.7 is 
> acceptable and and <0.5 is an excellent target.  That's probably why the 
> 540 started to run rough in the LOP region.  In sum, mine numbers were 
> kind of pathetic side. 
>  
> The single gph or two that are saved will probably never recover the 
> cost of the injectors but if running cooler and smoother increases TBO a 
> hundred or two hours, now we're talking real money.  And, like many 
> things, it feels good for it to be right!
>  
> Gotta go.  Have some OSH flight planning to do.
>  
> Chuck
>  
> 
> 
> min@tvbf.org [mailto:reflector-admin@tvbf.org]On Behalf Of Brett Ferrell
> Sent: Saturday, July 26, 2003 9:06 AM
> To: reflector@tvbf.org
> Subject: Re: REFLECTOR:Low fuel light
> 
>     Why would you jump to the assumption it's air in the tank?  Without
>     a sightglass, or replacing that run of tubing to the sump neoprene
>     or something, we don't have any idea what's causing the indication. 
>     Could just as easily be a defect inside the instrument.  My whole
>     contention was that, if air is entering the sump, it's probably for
>     the best b/c the alternative is most likely to pull a vacuum on the
>     tank.  Air doesn't displace fuel without a reason.
> 
>      Brett
>      
> 
>         ----- Original Message -----
>         From: alventures <mailto:alventures@msn.com>
>         To: reflector@tvbf.org <mailto:reflector@tvbf.org>
>         Sent: Friday, July 25, 2003 5:56 PM
>         Subject: RE: REFLECTOR:Low fuel light
> 
>         Al,
> 
>          
> 
>         This thread started with Rene's problem with occasional low-fuel
>         warning with plenty of fuel on board.  How is the air getting
>         into the sump tank if the strake tanks have enough fuel to keep
>         the strake-to-sump fuel lines submerged?  The sump vent seems
>         the most likely route.
> 
>          
> 
>         Keith
> 
>          
> 
>             Yes, I agree with that; assuming of, course, that the
>             intermittent warning is due to a low level in the sump tank
>             and not a problem with the float switch, or something else.
> 
>              
> 
>             After giving the issue more thought, the valve in the sump
>             vent seems to make sense.  Although it is one more thing on
>             the checklist, and not convenient to get at.  And it doesn't
>             preclude fuel exhaustion in the case of a leaky fuel cap. 
>             If we are going to keep a simple gravity feed system from
>             both tanks, we have to pay attention to the fuel caps, and
>             be aware of one tank level dropping faster than the other.
> 
>              
> 
>             Let's see; if we could just find a different place to put
>             the fuel cap; someplace that doesn't happen to see about the
>             maximum negative pressure of anywhere on the airplane.
> 
>              
> 
>             Al
>