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lucien
Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM
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 Posted: Wed Oct 13, 2010 7:29 am Post subject: 912 mechanical pump - fuel lift on vacuum side |
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Hi all,
Does anyone know if there's a limit on the 912 mechanical fuel pump in terms of how far it's permitted to lift fuel? I.e. how far below the level of the pump the fuel level is permitted to be and still be able to lift fuel and provide adequate fuel pressure?
I looked in the installation and heavy maint. manuals and couldn't find a spec for this.
I'm just kicking some ideas around on my fuel system in my titan. The fuel level gets pretty low below the pump at half a tank and below (about 2 feet maybe more) and I'm just curious how close to the edge that is (i.e. without a boost pump).
Thanks,
LS
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LS
Titan II SS |
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Thom Riddle
Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)
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| Posted: Thu Oct 14, 2010 3:16 am Post subject: Re: 912 mechanical pump - fuel lift on vacuum side |
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Lucien,
I don't know the spec you ask for but had no problems with the 912UL Titan I used to own and I let the fuel get way too low on one flight. I think it was about 1.5 gallons remaining when I landed, and this was in a custom aluminum tank with the bottom of the tank at about the bottom of the boom tube (straddling the tube). I used a Facet aux pump for take-off and landing.
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Thom Riddle
Buffalo, NY (9G0)
Don't worry about old age... it doesn't last very long.
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lucien
Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM
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| Posted: Thu Oct 14, 2010 6:11 am Post subject: Re: 912 mechanical pump - fuel lift on vacuum side |
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| Thom Riddle wrote: | Lucien,
I don't know the spec you ask for but had no problems with the 912UL Titan I used to own and I let the fuel get way too low on one flight. I think it was about 1.5 gallons remaining when I landed, and this was in a custom aluminum tank with the bottom of the tank at about the bottom of the boom tube (straddling the tube). I used a Facet aux pump for take-off and landing. |
Hi Thom,
Ok, thanks for the info. The addition of the boost pump is exactly the scenario I'm wondering about. It's not practical for me to put it in parallel, there's just not enough room for all the plumbing. So I have to put it in series before the mechanical pump.
The thing I'm wondering about is the extra flow resistance of the pump when it's off - it's not terrible, but it's quite noticeable - and if that might make an already borderline situation when the fuel level is low even more marginal with the additional drag of the pump (yeah I know I can just turn the pump on, but that's not really what I'm wondering about  ).
I'm just wondering how much margin I have with the approx. 2' or so of fuel lift in the occassional events where I may have low fuel levels to start with.
LS
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LS
Titan II SS |
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Thom Riddle
Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)
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| Posted: Thu Oct 14, 2010 6:17 am Post subject: Re: 912 mechanical pump - fuel lift on vacuum side |
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Lucien,
I don't remember if my Facet was in parallel or series (I didn't build it) but do know that I forgot to use the Facet occasionally on take-off and landings and never had any problems.
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Thom Riddle
Buffalo, NY (9G0)
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Float Flyr
Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland
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| Posted: Thu Oct 14, 2010 4:01 pm Post subject: 912 mechanical pump - fuel lift on vacuum side |
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In order to make sure fuel gets to the 912 mechanical pump place the electric Facett low, close to but downstream of the gascolator. That should be the lowest point of your system. Don't forget to turn the facet on for landing as well as take off just encase of a go around. The Cessna C185 I worked on had a switch which automatically turned on the boost pump with full throttle.. There was also an override switch which would operate the pump at less than full throttle. That may be a good idea for you to rig.
Noel
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