Watching this Bronco display, perhaps this is an incorrect observation, but it looks like the airbrakes are independently used to counteract adverse yaw. What is the domain of use for these airbrakes? Are they mechanically linked to the ailerons? Are these brakes also used both together?

Mostly why not fight against adverse yaw by coupling the ailerons to the rudders instead?

This can be seen, among other occasions, at about 2:03 in the video. Here's a screen capture:

Bronco airbrakes


1 Answer 1


This is quite common for many larger aircraft with spoilers on the wing. Using the spoilers in this asymmetric way is called roll spoilers or spoilerons. They are usually hydraulically actuated and sometimes fly-by-wire controlled.

The Bronco, however, has them mechanically linked to the ailerons:

The lateral system consists of spring and gear tab-boosted ailerons, augmented by spoilers. [...]

Four fan-shaped, upward rotating, axially hinged spoiler plates are installed in each wing. Movement of the aileron displaces mechanical linkage to rotate upward from the down-going wing, creating additional rolling reaction due to lift loss. The spoilers are positioned with their leading edges 10 degrees below the wing upper mold line with the ailerons neutral. At full stick lateral travel, the spoilers are displaced approximately 86 degrees. Delayed operation, due to the submerged neutral spoiler position, prevents projection at neutral trim and allows aileron trim operation without causing spoiler deflection.

(USAF OV-10A Bronco Flight Manual)

The use of spoilerons reduces adverse yaw, but does not eliminate it. Aircraft with ailerons and spoilerons still need rudder input to coordinate turns. The Bronco is also equipped with a yaw damper:

The yaw damper system supplies a control torque to the rudders proportional to aircraft yaw rate and oscillation frequency and in the opposite direction of the yaw motion.

(USAF OV-10A Bronco Flight Manual)

Additional advantages of spoilerons include improved roll control and more space for flaps, as discussed here: What is the benefit of spoilerons compared to ailerons?

Especially at high speeds, ailerons at the wing tips are not good control surfaces for roll control because they can cause the wing to twist, which can lead to control reversal (How does aileron reversal work?). To prevent this, aircraft like the Boeing 777 do not use ailerons at high speeds and rely on spoilerons (and flaperons, see What are advantages and disadvantages of flaperons?) alone:

Roll control is similar to conventional airplanes. Aileron and flaperon surface deflections are proportional to control wheel displacement. Spoilers begin to extend to augment roll control after several degrees of control wheel rotation. Control wheel forces increase as control displacement increases. Control wheel forces do not change with airspeed changes. The ailerons are locked out at high speeds.

(Boeing 777 FCOMv2 9.20.14 - Flight Controls - System Description, emphasis mine)

  • $\begingroup$ So these brakes never operate both together, and are meant to increase roll rate in the first place. (=reducing adverse yaw is a byproduct of the main purpose?) $\endgroup$
    – qq jkztd
    Oct 7, 2021 at 17:53
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    $\begingroup$ @qqjkztd As far as I could find in the flight manual, they are never used symmetrically for braking. Other aircraft use spoilers for braking in the air (speedbrake) or on the ground (ground spoilers). Reducing adverse yaw is definitely part of their purpose (you could get higher roll rate with bigger ailerons). Another big advantage for larger aircraft is reduced wing bending (since ailerons at the tips induce more wing bending). $\endgroup$
    – Bianfable
    Oct 7, 2021 at 18:09
  • $\begingroup$ I'm a little confused on how these roll spoilers could counteract adverse yaw. It seems like adding more drag to the high wing than the low wing would result in significantly more adverse yaw. Am I thinking about this the wrong way? $\endgroup$ Oct 8, 2021 at 3:39
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    $\begingroup$ @CharlieArmstrong The spoilers are going up on the down-going wing. The picture in the question is not the best choice to show this, but they are currently rolling back towards wings level. $\endgroup$
    – Bianfable
    Oct 8, 2021 at 6:52
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    $\begingroup$ the Hughes XF-11 ( en.wikipedia.org/wiki/Hughes_XF-11 ) is another aircraft with roll control provided partly (or entirely?) by spoilerons $\endgroup$ Oct 8, 2021 at 13:16

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