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7 Answers

Fuel Tank

Asked by: 6498 views Aircraft Systems

For all of the Piper aircraft I have been expose to, Piper fuel systems only have the option to use fuel from either the left or right tank, not from both tanks simultaneously. Why does Piper not design the fuel system to pull from both tanks simultaneously like most Cessna aircraft?   Thank you for the feedback.

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7 Answers

  1. Wedge on Oct 01, 2013

    Some (maybe many) high wing aircraft fuel tanks feed what is called a fuel reservoir by gravitational force. It is basically a single small fuel tank that lies past the fuel selector, but ahead of the rest of the system. The selector is a “T” shaped valve, and you may select to draw fuel from one or both of the tanks. The fuel system still takes fuel from a single tank – the reservoir – but you are filling it with fuel from both tanks via gravity.
    Since low wing aircraft don’t have gravity to aid in fuel flow, manufacturers eliminate the extra reservoir and simply draw fuel from one tank or the other into the system.
    A note, keep in mind that just because the selector is set to both, you may not be burning fuel evenly from both tanks. Factors such as ram pressure from a fuel vent (C172 left tank often burns more fuel because of this), slipping, or banking may cause an uneven draw from the tanks, and on long flights may require some additional fuel management.
    Hope this helps

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  2. John D Collins on Oct 02, 2013

    Gravity feed for the high wing, doesn’t work so well for a low wing aircraft.

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  3. Kris Kortokrax on Oct 02, 2013


    What you are describing is the fuel system for a fuel injected 172S. The carbureted 150, 152, 172 and 182 models have no reservoir tank.


    Not sure what the benefit of feeding from both tanks at the same time might be. Running one tank dry and recognizing a critical fuel situation in time to do something about it would seem to be better that running both tanks dry at the same time. Granted, a pilot should be aware of his fuel situation, but accidents happen all the time due to fuel tanks contaminated with air.

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  4. Cadu on Oct 07, 2013

    I have the same doubt of Dan. Why is not better a fuel system with both tanks option instead of only one as Piper planes fuel system?

    Thanks in advance.

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  5. Mark Kolber on Oct 07, 2013

    It’s not just Piper. It’s all low-wing piston singles with two wing tanks. There might be someone with a real answer but mine is based on what I call the universal piston aircraft design rule – as little aircraft weight as possible consistent with safety. It’s the reason the ailerons in a 172 are corrugated – they can use thinner metal but still have the necessary strength.

    My guess is that it’s simply that the equipment that would need to be used to draw upward from two tanks at a time would add unneeded weight (and probably complexity) to the aircraft without a corresponding benefit to flight safety.

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  6. Chris M on Mar 28, 2014

    I hope this topic isn’t too old to post a reply…
    My experience with Piper, and low wing aircraft in general, not having a BOTH option on the fuel tank selector refers back to FAR 23.951. The FAR basically states that no one fuel pump can draw fuel from more than one tank at a time. There is also a provision for preventing air from entering the system.
    Since low wings don’t have the benefit of gravity to feed fuel into the system, the pump is the workhorse but can only pump from one tank per regulations, thus the choice for only LEFT or RIGHT tanks.
    Adding the option to fuel from BOTH tanks would require 2-3 more pumps and probably just isn’t economically feasible, not to mention the added weight to the aircraft.
    Hope this is helps!

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  7. Dan Chitty on Mar 28, 2014


    Very helpful feedback. Thank you for this great information.

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