War is Boring recently published a report on the limitations of the F-35 Lightning II when faced with a simulated air-to-air combat engagement against an F-16 Fighting Falcon, one of the aircraft the Lightning II is meant to replace. A flurry of arguments, from Lightning II supporters and detractors alike, inevitably followed. The various claims can be summarized as follows:
- It was an early model F-35A, missing many of the technologies that would give it an advantage
- The F-16 pilot was vastly more experienced in type, allowing him to wring greater performance out of his plane
- The F-35 was not designed for dogfighting, instead being meant to use stealth to attack without being seen
- The F-16 was a twin-seater, and therefore less maneuverable.
- The F-16 was burdened with two external fuel tanks
- The F-35 was carrying no ordinance and was in a clean configuration which should have offered performance increases
- The F-35 pilot reported visibility difficulties resulting from the size of the F-35 helmet
- The F-35 bled significant energy in hard maneuvering, limiting it’s ability to win a turning fight
The controversy raises important questions, not only for the US Air Force, who will rely heavily on the type, but also for international operators who may use the F-35 as the only type in service.The F-35 will inevitably be tasked with a plethora of missions and aircraft’s ability to win a close-range engagement may be crucial.
Two factors, more than any other, influence an aircraft’s abilities in air combat: thrust and wing loading. Thrust is used to maintain energy levels during hard maneuvering. With sufficient thrust an aircraft can hang in the turning fight longer, possibly long enough to force an opponent to disengage. Wing loading affects maneuverability by reducing the energy required to change flight path. Lesser wing loading is better for maneuverability, but it comes at a cost. To achieve a lower wing loading requires either airframe weight be reduced (often not possible) or a larger lifting surface. That larger lifting surface brings a penalty in the form of drag. Drag reduces energy, increases fuel consumption, decreases range, decreases acceleration and limits maximum speed.
In the case of the F-35, the F135 engine is the only engine available and until upgraded (likely in the future) will limit thrust to the same level as available today. Growth possibilities of the F135 engine suggest that future variants might see thrust as great as 50,000 lbs, a significant increase over the current 43,000 lbs. We can assume, rather safely, that the F-35 will see additional thrust become available due to engine performance increases.
Reducing the wing loading of any available variant of the F-35 is difficult. The aircraft has already undergone severe weight reduction programs and it is unlikely that any more weight savings are to be had. That leaves us with increasing the available wing area in order to reduce wing loading. The F-35C variant for the USN has just such a wing with greater area. In order to reduce landing speeds aboard an aircraft carrier, the F-35C is fitted with a larger wing. It is also fitted with larger horizontal stabilizers and wingtip ailerons in order to improve low speed control and maneuverability. Unfortunately, the F-35C is limited to maneuvering limits 7.5g rather than the 9g of the smaller wing variants. The F-35C also carries a weight penalty in the form of the heavier landing gear, arrestor hook and other carrier specific equipment.There is a possibility of creating an F-35D The hypothetical D model would combine the aerodynamic features of the F-35C, with the lighter airframe of the F-35A. This is not to say that we would simply attach an F-35C wing to an F-35A, although for testing purposes it just might be exactly that easy. As a finished design, we would hope for an F-35C sized and shaped wing that offered the 9g limits of the F-35A. Such an F-35D would offer wing loading advantages, but would suffer the drag disadvantages described above. If drag were offset by a more powerful F135 engine, the trade-off might create the most maneuverable variant of the Lightning II family.
I should note that this is hardly a new or revolutionary idea. Lockheed-Martin (builder of both the F-16 and the F-35) once devised a “big wing” F-16 to overcome weight growth in the F-16 series and meant to restore maneuverability. Northrup-Grumman once marketed a de-navalized version of the F-18, known as the F-18L. By removing the carrier specific features of the F-18 the F-18L would have gained a wing loading advantage and improved performance. The F-35 family offers a unique opportunity to increase maneuverability by reducing wing loading.
Only time will tell if something like the F-35D will come to pass.