I can understand what function(s) the flaps serve, but how are they controlled from an internal perspective? Does flipping the switch send signals to an electrical servo? Or is it hydraulics? How are these devices attached to the main wing body, and if they use hinges (which they probably do) where do the hinges connect to? Do these devices have "Control Horns" and "Push-rods" like RC Planes? This can also be generalised to apply to ailerons and rudders too.

EDIT: I'm primarily referring to small GA planes like the C172 and the PA-28 - So while I'd like to hear about air-liners too, I primarily want to know about its implementation in GA aircraft.

  • 3
    $\begingroup$ Which plane? GA and airliner can be different mechanism. $\endgroup$
    – vasin1987
    Commented Sep 5, 2017 at 10:22
  • $\begingroup$ It really depends on the aircraft, and you should narrow your question to a category of aircraft. Gliders have no hydraulic (direct control of flaps) whereas in some fly-by-wire fighters it may be totally automatic (no pilot action needed) $\endgroup$
    – Manu H
    Commented Sep 5, 2017 at 13:35
  • $\begingroup$ Sorry - I'd like to know its implementation in GA aircraft, like the C172 and the PA-28! $\endgroup$
    – user18035
    Commented Sep 5, 2017 at 13:39
  • $\begingroup$ @vasin1987: Different GA aircraft can use different methods. The 150 & 172 Cessnas I've flown use electrically-actuated flaps, via a switch on the panel. My Cherokee's flaps are mechanically actuated by a lever between the seats - where you'd find the parking brake on many cars. $\endgroup$
    – jamesqf
    Commented Sep 5, 2017 at 18:09
  • $\begingroup$ Related: aviation.stackexchange.com/questions/23824/… $\endgroup$ Commented Sep 5, 2017 at 21:03

2 Answers 2


On a light aircraft, the answer is somewhat similar to the mechanism you might be used to in a RC aircraft. The image below shows the important parts - a hinged flap and a "control rod" which is attached to an electric actuator.

enter image description here

This is controlled internally by a simple switch

enter image description here

(Both images source: http://www.weekendcfii.com/frame_c172_preflt.html?c172_preflt.html)

By looking at the actuator of a Cessna 172, it clearly only has one linkage, which implies there is one per flap - and it is situated within the wing.

enter image description here

(Image source: http://aircraftpartsandsalvage.com/product_info.php?products_id=8498)

  • $\begingroup$ So where is the actuator situated - in the wing, or the main fuselage, connected by belts (or gears)? Is there 1 for each side? $\endgroup$
    – user18035
    Commented Sep 5, 2017 at 13:42
  • $\begingroup$ @AnandS answer updated with picture of said actuator. $\endgroup$
    – Jamiec
    Commented Sep 5, 2017 at 13:48
  • $\begingroup$ Wow - nice! What about ailerons? Are they controlled the same way? $\endgroup$
    – user18035
    Commented Sep 5, 2017 at 13:49
  • $\begingroup$ @AnandS Not exactly, they are of course connected to the primary controls so are not electric for starters in this kind of aircraft - they're purely mechanical. $\endgroup$
    – Jamiec
    Commented Sep 5, 2017 at 13:51
  • 1
    $\begingroup$ @Jamiec Yeah, I'm more familiar with how the flaps lever and indicator mechanism works than where the motor is itself (I've worked on creating training devices). The indicator carriage has two micro switches on it and when moving the lever, it closes one of those switches. This powers up the motor to move the flaps (and also the indicator) to line up with the lever (which allows intermediate flap positions if you hold the lever out of the detent). The same mechanism is used in the Citation (although it's hydraulically actuated). $\endgroup$
    – Kyle
    Commented Sep 5, 2017 at 16:40

Flaps have different actuation mechanisms from primary flight controls. Flaps deflection brings a shift of pitching moment with it, and it is done slowly to give the pilot time to adjust the aerodynamic trim. Usually with electrical screwjacks, with a fine pitch that stops the forces on the flaps from feeding back into the motors.

Yes flipping the switch switches the electric motors on. Most jetliners use Fowler flaps, which ride out on their little rails attached to the wing, and clad with an aerodynamic fairing at the trailing edge. This picture (source) shows the rails, flaps, and screwjacks when completely extended.

enter image description here

  • $\begingroup$ Thanks for the info, but I'm sorry I did not mention that I'm looking for its implementation in GA aircraft like the C172 and the PA-28. $\endgroup$
    – user18035
    Commented Sep 5, 2017 at 13:41

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