F-22 Underside

As you can see in the picture there are several bulges or bumps in the wing that are located in the aileron and flaps. Somebody told me these are to hide the linear actuator, pushrod, and control horn. However, if the bulge is connected to the wing and aileron how is it possible for it to be there? If the aileron is moving independent of the wing, how is the bulge connected to both at the same time?

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    $\begingroup$ Contrail storage canisters $\endgroup$
    – Richard
    Jul 14, 2020 at 23:43

2 Answers 2


Yes they are fairings for the actuating mechanism for the control surface. I can't speak directly to the F-22's details but, this kind of thing is done on lots of airplanes. The F-22's control surface blister fairings are perhaps a bit more sophisticated and 100 times more expensive, but the concept isn't all that special.

The blister on the fixed structure will have an overlap with the blister on the moving element. The blister on the moving element, like the aileron in the image below, will slip under the fixed part of the blister when it moves down, and there will be additional material forward of the joint that is exposed when the aileron moves up to maintain the contour.

In the somewhat grainy image, you can make out a dark line along the interface between aileron and wing that follows the profile of the blister (along with staining that could be discoloration from seeping hydraulic fluid). There is likely a flexible seal strip to provide the smoothest possible transition but with enough compliance to accommodate the geometric changes in the surface contour, as the two halves of the bulge telescope with each other, and still keep the aerodynamic seal.

enter image description here

In profile it would look something like this:

enter image description here

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    $\begingroup$ What don’t you understand? Please be specific about what is unclear to you. Half the bulge is part of the wing, and half is part of the aileron. They are formed to allow them to move independently as John depicted in his excellent sketch. Unless there is an F22 mech here who can go take one apart for some photos that’s probably about as good of an answer as you’re going to get here... $\endgroup$ Jul 14, 2020 at 15:06
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    $\begingroup$ @MichaelHall Also, I'm guessing than F-22 mech taking this apart, making a video of how it works, and then posting said video on the Internet would likely face a court martial very quickly. $\endgroup$
    – reirab
    Jul 14, 2020 at 15:18
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    $\begingroup$ @LukeJustin The blisters are indeed aerodynamic fairings to cover the actuators for the trailing edge surfaces. The blisters consist of two pieces each, not one. The forward half of them is part of the wing, while the aft half of them is part of the movable surface. As the answer points out, you can see the seem line between these two pieces on each of the blisters in your photo. $\endgroup$
    – reirab
    Jul 14, 2020 at 15:23
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    $\begingroup$ @LukeJustin, what JohnK is describing can be thought about generically like this. Think about the overlapping segments of a medieval Knight's armor. In order for the arm, shoulder, torso and/or legs to have movement and still provide protections, the armor segments are designed to overlap and move over one another to the extent of the design allows. A snakes scales would be another example of this idea in a nature. $\endgroup$
    – Justin A
    Jul 14, 2020 at 16:17
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    $\begingroup$ @JustinA that's not bad. $\endgroup$
    – John K
    Jul 14, 2020 at 16:18

Conceptually, it is a ball and socket. Practically, it is a cross-section of a ball and socket joint. It does not have a hinge. The defined shape of the bulge is not set by its own motion at all and is shaped in the way that it is so that it will maintain its general shape at all possible positions along its plane of motion. I would assume the value is to the aerodynamic calculations and not having to constantly account for drastically different surface area and shape depending on if the plane if flying up or down;keeping values as static as possible. The drawing is pretty accurate in the way it shows what you are talking about, is essentially, a hinge 'cover'.


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