Comparing the variants of the Lockheed Martin F-35 Lightning II

Over the past decade, the F-35 has steadily gained international recognition as, not only one of the most easily identifiable, but arguably the most widely adopted fifth generation fighter in production today. Many customers are lining up to purchase or receive orders for the aircraft, and it seems the F-35 has a long future ahead of it.

Today, there are three variants of the aircraft being produced; and all three sport significant differences. Each variant is suited for a specific environment and tasking, and consequently each have differing strengths and weaknesses. From the F-35A, employed by our own Australian Air Force, to the VTOL capable F-35B, and the more conventional carrier-based F-35C.

In our next gen aircraft series, we have canvased many foreign fifth gen fighters (from those on the drawing board to those in active service), and not long ago we looked at the F-35A in Australian service. Today we will compare all three official variants of the F-35, as well as Israel’s modification program.

F-35A

The first variant is the F-35A. The most popular model by far, and is either being operated by, or on order by, many air forces around the world. It is the smallest and lightest of the variants on offer, with a heavy emphasis on maximising air-to-air capabilities without sacrificing all round multirole performance.

Possessing the most powerful afterburning fighter jet engine on the market - the F135 - it features standard take-off and landing capabilities. This means it is exclusively operated from standard runways and cannot land on a carrier deck without damaging the light, single-wheel, nose gear.

In terms of performance, being the smallest and lightest, it can pull up to 9 G’s (far more than the other two variants) and puts it on par with the F-16 and certain European light fighters in this regard. This capacity gives it an edge during visual-range engagements. When it comes to combat range, the A can operate somewhere between 1,100 and 1,400 kilometres depending on the mission profile and other variables, with a maximum ferry range of around 2,200 kilometres on internal fuel. 

The F-35A is the only of the three main variants to feature an internal gun, something which does add a layer of complexity, but maximises air-to-air and air-to-ground capabilities should other weapons fail.

When it comes to weight, the A variant is the lightest of the three, coming in with a dry weight of around 29,000 pounds. In terms of fuel, the A is claimed to hold 18,250 pounds internally. This is a good amount; contextually this would be almost 3 times what an F-16 can hold internally. It also has a weapons stores capacity of 18,000 pounds, again, a decent rating. All up, the A is rated for a maximum take-off weight of 70,000 pounds.

F-35B

The next variant is the F-35B. Departing significantly from the A design, the Bravo most notably features a modified engine allowing for short take-off and vertical landing - or STOVL - capabilities. While this is its official on-paper ability, the F-35B can actually perform full VTOL take-offs from a stationary position.

The B variant was supposedly designed specifically with the US Marines in mind. The Marines job is to operate from sea and onto land, whether it be island hopping or invading the mainland of a larger country. Unlike the Navy, the Marines rely far more on smaller aircraft or helicopter carriers than large catapult assisted aircraft carriers. The F-35B design allows it to be launched from these small flight decks without catapult assistance.

The F-35B comes closer to what was marketed as the ‘Joint Strike Fighter’, featuring VTOL, and operating both as a land based and maritime multirole strike aircraft.

The greatest trade-off for the B variant is range and stores capacity. To achieve VTOL, the aircraft requires a complex Shaft-Driven Lift Fan – part of what is known as the Rolls-Royce Lift System. This mechanically complex setup adds far more weight than the other two variants, as well as taking up more internal space. The main sacrifice was fuel capacity.  Compared to the F-35A, the B has about a third less internal fuel stores, drastically decreasing its range. To further save weight the B does not feature an internal gun like the A. Instead, a gun pod can be attached.

Performance wise, the B variant is limited to pulling 7 Gs. This is considerably lower than the A, and puts it closer to the Super Hornet in this respect. However, given that the Marines are the primary operator, it is understood that air superiority is not going to be the primary role, but rather strike missions.

So, it is range, in which the F-35B doesn’t match the other two variants. Its combat range is around 940 kilometres on internal fuel, and a ferry range on internal fuel of 1,700 kilometres. This is a notable difference over the others.

The B is heavier than the A, with a dry weight of 32,400 pounds. It also holds less internal fuel, only 14,500 pounds, and a lower weapons stores capacity of 15,000 pounds. In all, the B is rated for a maximum take-off weight of 60,000 pounds, 10,000 pounds less than the other two variants.

Given its medium weight, the Bs thrust-to-weight ratio goes up to 1.04 at 50% fuel, slightly below the As power at equivalent fuel capacity with a ratio of 1.07, and above that of the C. 

F-35C

This brings us to the final of the three variants; the F-35C. Unlike the Alpha and Bravo model, the Charlie is visually quite different, with much wider wings, giving it a larger appearance. It is also fair to say that it is the least common of the three, very rarely appearing at air shows or public displays. It is the least produced of the three, and the only one with no confirmed international customers.

Operated by the US Navy and - to a lesser extent - by the US Marines, the F-35C bridges the gap between the A and B model. It is a carrier-based aircraft like the B, but relies on catapult launch and barrier arrested landings rather than STOVL. The distinctive shape is a result of a larger wing area, giving it better low speed characteristics for conventional carrier launches and recoveries, as well as increasing its stores capacity and range. With foldable wing tips, it can be stored efficiently as with many classic carrier aircraft. Unlike the other models, it features a stronger twin-wheel nose gear, attached to the fuselage via a much more robust landing gear typical of most carrier based aircraft.

The obvious question is why pick the C variant over the B, with its STOVL capability? There are multiple reasons, but the most obvious is the lack of the large, heavy and complex VTOL capable engine found in the Bravo. With the standard F135 engine, the C retains a higher fuel load capacity, and in conjunction with its larger wing surface area, extended range and payload capacity than the Bravo.

For this reason, the F-35C exists primarily as a Navy-centric aircraft with a specific focus on long range missions. Its rugged design came at a slight weight disadvantage, thus sacrifices were made to keep its performance similar to the A model. Notably, like the Bravo, it lacks an internal gun, relying instead on a gun pod if necessary, and its larger wings - which fold at the tips - add a further layer of mechanical complexity in exchange for better aerodynamic efficiency, increasing wing surface area from 460 square feet in the A model to 668 square feet.

In terms of performance, the C variant is limited to 7.5 G. This is slightly better than the B, and we can presume that the Navy puts more of an emphasis on air superiority than the Marines who are more likely focused on supporting troops and hitting ground targets. Beyond this, the C supposedly matches the combat range of the A, somewhere between 1,100 to 1,400 kilometres, and a similar ferry range of around 2,200 kilometres.

The C model is by far the heaviest, with a dry weight of 34,500 pounds, roughly 5,500 pounds heavier than the A model, and 2,000 pounds heavier than the B. The C does however hold 1,500 pounds more fuel than the A, holding 19,750 pounds internally. It also retains the same weapons stores capacity as the A model, roughly 18,000 pounds. It has a maximum take-off weight of 70,000 pounds, the same as the A model, albeit without an internal gun and with heavier internals.

However, power is where the C falls behind. At maximum fuel, the C model has a thrust-to-weight ratio of 0.75, behind the 0.90 of the B and 0.87 of the A. As fuel depletes this difference remains roughly the same between the three. Despite this, it still pulls its weight against the other two.

For a variety of reasons, however, the C variant remains largely overlooked on the international stage, with potential customers usually favouring the more dynamic Bravo model when considering maritime operations.

OTHER VARIANTS

But the story doesn’t end there. Beyond the three official variants of the aircraft, a fourth non-official foreign variant exists. The F-35I - also known as the Adir - a custom variant based on the Alpha, redesigned, and modified by the Israeli Defence Force. Although strictly forbidden, after negotiations the US defence force reluctantly gave permission for Israeli designers to make certain modifications to the F-35A design. This came about after some IAF officials had stated that they believed the F-35s stealth features would only last a decade before adversaries develop sufficient radars to easily overcome its stealth capability.

The Adir has several additions to the original design. Notably it features and undisclosed number of new electronic and physical countermeasures, as well as new sensors. Interestingly, the Israelis also modified the onboard computers to allow for external plug-and-play compatibility, making the integration of other technology easier, but presumably making the aircraft less digitally secure than the standard closed system. Future plans include - in typical IAF fashion - conformal fuel tanks for long strike missions, as well as modifications for domestically produced bombs and missiles. Other future additions include enhanced stealth technology, jamming pods, and a two seater variant which Israel Aerospace Industries claims is in demand by other air forces as well.

As of 2021, a new export variant is also under development, although Lockheed Martin has yet to confirm any specifics about the design or potential customers. It will be interesting to see what develops, and if a two seat variant will emerge.

All three existing variants have between 27% and 40% parts in common, with the C variant being the most unique, possessing 43% unique parts. The A variant, in contrast, shares the most parts with the other two variants. There are multiple reasons why this is important to consider, including availability of parts or lack thereof.

WHICH IS BEST

As we have seen, all three major variants of the F-35 differ greatly for specific roles. The Adir - technically an A model - has its own unique strengths, however unless major changes are made it is essentially an Alpha variant.

For our own Royal Australian Air Force, the F-35A is the most appropriate choice as a frontline multirole aircraft. It offers the most in its stock configuration, the advantageous internal gun, and since Australia doesn’t have any aircraft carriers, the C variant can be immediately disregarded.  The F-35A also offers the best air-to-air capability by far, rated at 9G and supposedly boasting impressive high alpha agility, which may put it in the same ballpark as the F-16. Neither the B or C have this edge, and even the Israeli I variant will lose this edge once conformal fuel tanks are fitted.

Over the decades we have seen some arguments that the B variant may have been better, allowing it to operate from smaller outposts and so forth. If we were a smaller land mass this may have been true, but in practice, long range capability is important for Australia. The B could be extended, just as other countries do with the F-16, but for the sake of practicality the A model already had a good range. The RAAF is a small air force, with a small budget in comparison to many other larger countries. Consequently, aircraft with multirole capability is essential given the limited budget.

CONCLUSION

In retrospect, it has been a long run for the F-35. From its initial development in the late 1990s as the X-35, to the announcement of its full-scale development and adoption by various Air Forces, the Joint Strike Fighter program has suffered a barrage of criticism by the media. Despite this, it has thus far proven itself to be a capable aircraft, constantly being refined as new capabilities are unlocked through upgrade programs.

Despite the long development cycle, the aircraft is still relatively young, and we are yet to see just what the three distinct variants are capable of when put to the test. Already, red flag reports from pilots suggest that the F-35 is a challenging adversary, especially when working in groups. An early criticism by the media was regarding the aircraft’s agility and dogfighting performance, but again, red flag testimonies suggest that encountering an adversarial F-35 within visual range is a challenge, especially given the incredibly fast response of its F135 engine.

With a planned lifespan of 40 more years, the future of the F-35 program has a long way to go, and it’s development and investment by air forces is likely to be very active for the foreseeable future.