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4 Answers

Gravity-fed Fuel System

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Aircraft Systems, General Aviation

I'm confused as to why the CE-172S has an engine-driven fuel pump when the fuel system is gravity-fed. It it because the fuel is drawn by gravity to the reservoir, where the pump then takes over to get the fuel throughout the rest of the system? Does the pump simply provide more pressure and gives better fuel flow? Realistically, how bad is it when both fuel pumps fail in flight?

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4 Answers



  1. John D Collins on Jan 03, 2015

    The engine is fuel injected. The pumps provide the positive pressure to move the fuel from the tanks to the throttle body and then to the fuel distributor and finally to the injectors which continuously stream the atomized fuel into the cylinder above the intake valve. More fuel than is required is passed to the throttle body with the excess fuel is returned back to the tanks from the fuel throttle body.

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  2. Gary S. on Jan 04, 2015

    The electric fuel pump provides a backup to the engine-driven (mechanical) fuel pump in case the mechanical pump fails. That’s why it’s recommended that the elect. pump is switched on at critical times like take-off and landing.

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  3. Drew on Jan 04, 2015

    I was taught that the C172 is a gravity-fed system; the high-wing design, as opposed to the low-wing, allows fuel to naturally gravitate toward the bottom, which is the natural path for the fuel system. The answers seem to imply that the engine-driven fuel pump is required for engine operation. Does the gravity-feed/high-wing design not matter? Does provide any benefits Thank you.

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  4. Auxiliary fuel pump | Ask a Flight Instructor on Apr 08, 2015

    […] about the fuel system. One of my doubts already was answered at this post asked by Drew at the link http://www.askacfi.com/27340/gravity-fed-fuel-system.htm but, follow the next one:   As we know, generally we have two schematic possibilities in a […]

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