Back in January 2015 an F-35A was pitted against an F-16D in order to test the ability of the F-35 airframe to perform BFM - Basic Fighter Maneuvers - in a dynamic environment. Essentially, see how well the F-35 can turn, climb, dive, roll, and perform other maneuvers in order to shoot down enemy aircraft and avoid being shot down in return.
The F-16D used is a two-seat variant of the F-16, and has been updated from the original F-16 that entered service in 1978. The D model of F-16 first entered service in 1988, and this particular aircraft was fitted with two external tanks, which do compromise maneuverability. The F-35A used was AF-2, the second F-35 air frame built. The F-35 was in a "clean" configuration, with no externally (or internally) mounted missiles, bombs, or wing tanks.
Some of the results of this test were obtained and published by the military blog War is Boring, and many of the F-35 pilot's observations were not encouraging for supporters of the Joint Strike Fighter.
Some quotes from the pilot's report:
Overall, the most noticeable characteristic of the F-35A in a visual engagement was its lack of energy maneuverability...Even with the limited F-16 target configuration, the F-35A was at a distinct energy disadvantage for every engagement.
No effective guns defense was found during the test...Various techniques were tried depending on aspect, energy, and closure...The result was a target that was continually changing shape/attitude but not actually moving out of the [F-16's gunsight].
The helmet was too large for the space inside the canopy to adequately see behind the aircraft...There were multiple occasions when the bandit would have been visible ...but the helmet prevented getting in a position to see him.
In response, Lockheed Martin and the DoD's F-35 Joint Program Office issued a press release, offering up some explanations for the performance deficit. The press release begins by stating that "The F-35 involved was AF-2, which is an F-35 designed for flight sciences testing, or flying qualities, of the aircraft" this particular airframe is missing some production F-35 features. From the press release:
Aircraft AF-2 did not have the mission systems software to use the sensors that allow the F-35 to see its enemy long before it knows the F-35 is in the area. Second, AF-2 does not have the special stealth coating that operational F-35s have that make them virtually invisible to radar. And third, it is not equipped with the weapons or software that allow the F-35 pilot to turn, aim a weapon with the helmet, and fire at an enemy without having to point the airplane at its target.
Although these sensors and their ability to give situational awareness to the pilot are incredibly impressive (and one of the selling points of the F-35), their addition, plus the addition of the stealth coating, have little to no bearing on the actual observed maneuverability of the F-35A. Although the targeting system being built into the helmet certainly increases the aircraft's lethality, if movement of the helmet is constrained by the canopy, that advantage is also at least somewhat nullified.
The press release goes on to say that "The dogfighting scenario was successful in showing the ability of the F-35 to maneuver to the edge of its limits without exceeding them, and handle in a positive and predictable manner", which is odd, since several statements from the F-35 pilot mention unpredictable control responses at certain angles of attack. One of the final conclusions from the pilot's report is actually "The high AOA blended region was not intuitive or predictable".
Given the statement from Lockheed/JPO, however it seems likely that much of the problem the F-35 faced in this test was related to how the computer and software in the F-35 managed the aircraft's energy and control surfaces. In terms of raw performance data, the F-16 with external tanks would be limited to pulling 7G's or less, while the F-35A is advertised to be able to pull 9G's (the other two models have a lower G limit, the USMC F-35B has a 7G limit and the Navy's F-35C a 7.5G limit). The inability of the F-35A pilot to keep up or defeat the encumbered F-16, combined with the lack of predictable response in certain flight regimes means that the software engineers were probably playing it safe with the flight systems - the data from this engagement (remember, it was back in January) has probably been carefully studied to find out where the aircraft can be improved.
This engagement seems to have been planned as more of a checkpoint than a final destination - a way for the engineers to get some performance data on the F-35 compared to its predecessor. While it certainly is not the best publicity for the F-35 to "lose" this "dogfight", it will be more interesting to see how both aircraft fare the next time this test happens.