I just wonder why F16's have anhedral tail wings?
Is it kind of a design choice to increase maneuverability by compromising stability?
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$\begingroup$ All recent US jet fighters have been designed as inherently unstable to increase performance. $\endgroup$– Rowan HawkinsApr 3, 2017 at 10:23
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2 Answers
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The purpose of the anhedral is to get the tail surfaces away from the wing wake. The distance between the wing's trailing edge and the horizontal tail is low enough so that the tail needs a vertical offset in order to have full dynamic pressure available locally.
Earlier designs moved the tail up for the same reason (Lockheed F-104, Grumman F-9F) until it became obvious that at some angle of attack some airplanes could get into a deep stall. Especially with the wider angle of attack range possible with swept, low aspect ratio wings no position above the wing's plane is safe anymore.
For that reason all modern fighter aircraft position the horizontal tail as low as practical. This in turn has led to situations where ground effect is so strong that other tricks had to be employed to get the airplane to perform as intended.
Stability is not affected, aside from a small positive contribution to the sideslip-induced rolling moment. This is easily compensated by adjusting wing dihedral properly. Or, in other words, the F-16 wing can have zero dihedral because the horizontal tail in combination with the ventral fins reduces the rolling moment of the vertical tail in a sideslip to the desired value.
answered Apr 3, 2017 at 11:15
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$\begingroup$ Thanks for your detailed answer Peter. Maybe this comment belongs to a separate question, but as far as I remember from F-4's tail structure, they also have anhedral tail wings. Although its wings are not aligned in the same level, why F-4's have anhedral tail wings then? $\endgroup$– albinApr 3, 2017 at 11:25
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$\begingroup$ @albin: If I remember correctly, it was to get more lateral area without increasing the fin. Working in the wake of the fuselage, the fin became worthless at higher angles of attack, and lack of directional stability required a limiter for the AoA at 23°. Post a question, and I can explain better :-) $\endgroup$ Apr 3, 2017 at 15:02
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The F-4 has a similar anhedral on its tail. The purpose is to give better manoeuvrability in high angle of attack scenarios. I suppose the same should be true for the F-16, as they frequently enter high angle of attack profiles.
