In level flight at 400 knots, what happens when the speed brakes are extended?
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1$\begingroup$ I'm guessing the speed brake would rapidly depart the aircraft... $\endgroup$– Ron BeyerCommented Oct 1, 2019 at 13:24
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$\begingroup$ Not true. The boards will be effective at all stages of the flight. What is the reason why you said that? $\endgroup$– George GeoCommented Oct 1, 2019 at 13:27
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2$\begingroup$ I forgot they were tail mounted devices on the F-16, I was thinking of the large flap that opens on the top of some aircraft. $\endgroup$– Ron BeyerCommented Oct 1, 2019 at 13:32
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1$\begingroup$ F15 has an "flap" on spine, it is top air brake , used for landing and in flight to slow down at any speed but it will not be fully open. $\endgroup$– George GeoCommented Oct 1, 2019 at 13:44
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1 Answer
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Because the speed brakes are tail mounted, and because they deploy upwards and downwards equally, pitch should not change. The airplane's fly-by-wire system likely dampens any slight pitch changes caused by the buffeting.
The only photos I've seen of the speed brakes open are of them fully open, not partially open. So they may open gradually with different deflections up and down, or with different resulting air loads up and down, or both, or neither. But in any of those four cases, the FBW should correct for pitch excursions by deflecting the other control surfaces.
answered Oct 1, 2019 at 16:43
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$\begingroup$ True, but ideally the pressure would have to be equal top /bottom. This is not the case with the body lift and chines of the F16. $\endgroup$ Commented Oct 1, 2019 at 17:23
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$\begingroup$ How do you know that they open symmetrically @George Geo? Top and bottom part angle may be different to keep pitch moment zero. $\endgroup$– Jpe61Commented Oct 1, 2019 at 19:08
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$\begingroup$ Jpe61. The F 16 speed brakes are deployed always symmetrically up /down 60 degrees(same piston work to operate them ). Could be stopped at any angle. For landing is less because they risk to touch the ground. $\endgroup$ Commented Oct 1, 2019 at 20:37
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3$\begingroup$ This first thing that comes to mind is, you slow down. Shouldn't that affect the pitch? $\endgroup$– user14897Commented Oct 1, 2019 at 23:35
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1$\begingroup$ No need to toss around minus points when someones asks a legitimate question @George Geo. The fact that the speedbrakes are operated by single piston/pair does not automatically mean they open symmetrically. $\endgroup$– Jpe61Commented Oct 2, 2019 at 12:30