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Some aircraft have air brakes in an aerodynamically neutral position with respect to rotational forces on the airframe (e.g. F-15)...

F-15 air brake deployed source

... more often, others have brakes that are aerodynamically neutral by being opposing (lots of examples, F-16, Space Shuttle, here's a Buccaneer)

enter image description here source

... but the Hawk has an air brake that, because of its position at the tail end of the aircraft, and without any opposing force, I would have expected to generate a severe downward pitch as it is deployed, in much the same way as the elevator.

RAF Hawk [source - Ministry of Defence]

It obviously doesn't, so the question is - why not?

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    $\begingroup$ While it's located closer the the center than the Hawk, the F-15 air brake will still cause some nose up force from the drag component. $\endgroup$ – fooot Jul 11 '18 at 14:55
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It did generate a nose down pitch moment, but the tail had enough control authority to deal with it in most cases. Airbrake extension at greater than 450kt produced an unacceptable trim change.

Efforts to increase control authority to counter "phantom dive" caused by tail stall during simultaneous flap and gear extension helped. The solution was to affix a leading edge extension to the tail, but since the tail was all moving it was felt that the structure would not be able to handle the extra load. Instead, the tail LEX was affixed to the fuselage and still gave acceptable results.

enter image description here

A later version, the Goshawk, developed as a military trainer for the US Navy had side mounted airbrakes, though this was done to facilitate the installation of an arrestor hook. This photo shows the LEX just above the side mounted airbrakes.

enter image description here

Hawk mk100 with ventral fins, center airbrake and tail canard LEX. enter image description here

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  • $\begingroup$ Thank you very much, but I'm a bit confused. The diagram you posted shows these tailplane LEX canard extensions (which are present on the Goshawk but not the Hawk T1) AND it shows the smaller ventral fins (which are present only on the Hawk T1 - the Goshawk has a bigger, single ventral fin). Either way I believe the extension you've shown isn't used on the Hawk, and I don't think its ventral fins can have much effect on pitch (are they non-moving? I think so.) $\endgroup$ – Party Ark Jul 11 '18 at 8:13
  • $\begingroup$ The term "tail canard" really confuses me. AFAIK a canard is always ahead of the main wing and is a moving surface. I would call the devices in front of the hor. stab. "strakes." $\endgroup$ – TomMcW Jul 11 '18 at 19:06
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    $\begingroup$ @TomMcW That was the term in the reference and I agree it is not ideal. I used the term LEX since it works through vortex generation and would have been integrated into the horizontal stabilizer if the structure could have supported it. Strakes unfortunately does not work in this case because there are actual ventral strakes in this application and calling both structures the same thing would be even more confusing. $\endgroup$ – Pilothead Jul 11 '18 at 19:17
  • $\begingroup$ @PartyArk Canard extensions were added to the Mk100, which also had the ventral strakes. If you read the explanation of canard operation in the reference, the intent was to increase control authority by generating a vortex across the horizontal stabilizer. I have added a cutaway showing all three features on the Hawk: the side ventral strakes, the center airbrake and the canards. $\endgroup$ – Pilothead Jul 11 '18 at 19:20
  • $\begingroup$ @Pilothead: So call the ventral ones "ventral strakes" and the lateral ones "lateral strakes". $\endgroup$ – Sean May 2 '19 at 3:44

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