A series of sleek exotic fighter aircraft concepts were explored between 1970 and 1982 in the US. With the fabulous good looks of a fictional spaceship, these Cold War studies were extremely lightweight and often revolutionary in shape and concept. Jim Smith delves into the fascinating story of Bud Nelson’s light fight concepts.
This article stems from a detailed paper called ‘The Third Pass of the Fifth Generation‘. Yes, the title is enigmatic, but it’s possible something has been lost in translation.
The article was published in April 2020 by Kazakhstan Engineering and describes in some detail projects and concepts for very light fighters developed by American aerospace engineer Bud Nelson for first Boeing, and latterly Northrop. These projects spanned a period from 1970 to 1982, and to place these lightweight concepts in context, the Table below shows some first flight dates for other fighters in this period.
|1970||MiG-27, Grumman F-14 Tomcat|
|1972||MD F-15 Eagle|
|1974||Northrop YF-17, GD YF-16 and Panavia Tornado|
|1978||MD F/A-18, Mirage 2000|
|1982||GD F-16XL, F-20 Tigershark|
Militarily significant world events in this period included the closing stages of the Vietnam War, and the Yom Kippur between Israel, Egypt and Syria (1973); the invasion of Afghanistan by the Soviet Union (1979); the start of the Iran-Iraq War (1980); and the Falklands conflict (1982).
A summary of the projects
• Boeing 908-909
This was Boeing’s entry to the Lightweight Fighter competition, and lost out to General Dynamics and Northrop, who received contracts to develop the YF-16 and YF-17 respectively. The general configuration of this aircraft was similar to a YF-16, single-engined, with an under-fuselage intake and single fin. However, the wing appears to be a simple swept wing, without the leading edge strake featured on the YF-16 and YF-17. In addition, the nose of the aircraft was very slender, and would not have provided sufficient space for an Airborne Intercept (AI) radar.
Having missed out on the LWF competition, Boeing was looking to establish a role for the Boeing 747 as an Airborne Aircraft Carrier (AAC), and tasked Bud Nelson designed a series of micro-fighter to come up with a fighter for this. As this would inevitably have to be small, Nelson designed a series of Micro-fighter concepts to meet the desires of the ‘Fighter Mafia’, who had advocated for the LWF program, seeking light weight and extreme manoeuvrability. The first of these was the Boeing 908-625, and later concepts were variations of the Boeing 985.
Microfighter, for operation from flying aircraft carriers. This was a single-engined tailless aircraft, with a wing that bore a passing resemblance to that of the BAC Lightning, and a take-off weight of just 3.7 tonnes. Fins were mounted on the wingtips for directional stability and control, and the engine was fitted with a rectangular rear vectoring nozzle for pitch control. The armament was two cannon on the upper shoulders of the fuselage, and the aircraft was stressed for manoeuvres up to 8.5g.
Designed with a similar intent to the 908-625, this featured a change in armament to carry two tip mounted guided weapons. Otherwise, the wing was changed to a lower aspect ratio, with a planform bearing a resemblance to that of the Douglas Skyray. The tip fins and vectoring rear nozzle were retained.
• Boeing 985-213
The 985-213 was developed as larger, higher performance version of 985-121. The wing planform was dramatically different. Very highly-swept and highly-tapered, this was an arrow wing with conical camber, and was derived from concepts examined in the Supersonic Civil Air Transport (SCAT) program. The wing tips could fold down to improve subsonic lift, and the tail fins were mounted at about about 80% span rather than at the wingtips.
The concept was armed with 2 missiles, carried on the upper fuselage shoulders in a retractable installation, together with a 3-barrel 20mm cannon for ground attack. The concept appears to have a very small radar, and a tricycle undercarriage to allow recovery to an airfield if necessary, the primary operating base remaining the Boeing 747 AAC.
The performance claimed was Mmax 2.2, with supercruise possible to M 1.6. A combination of reduced stability, coupled with light weight and thrust vectoring was expected to allow the aircraft to manoeuvre at up to 8g at Mach 0.8.
The airborne aircraft carrier concept was eventually abandoned, but efforts continued, looking at similar configurations. This now would need to operate from an airfield, and need improved take-off and landing performance, and increased fuel. A twin-engine configuration was examined, with a wing like the 908-909, but variable sweep. This included un-sweeping the wing tips to keep the tip fins aligned. Unsurprisingly, this variant was considered to be too big, too complex, and to have too high a weight penalty.
Light Experimental Supercruiser (LES)
By 1976, the Air Force had concluded that the aircraft was too operationally inflexible, so the concept was reworked to introduce a canard. The wing-tip fins and the vectoring nozzle were retained, and two missiles were to be carried under fuselage. The intent at this stage was for the concept to support to heavy fighters as a front-line interceptor.
The concept continued to evolve, with the design reverting to the highly-swept and tapered arrow wing used on the 985-213, but with a simpler profile. In response to the concerns about armament, provision was made for underwing stores carriage, and vertical variable ramp inlet used. These measured impacted on both weight and drag, and supercruise capability was now limited to M1.3 and max speed Mach 1.8.
Take-off weight was increased to 7.5 tons, and, for comparison, the YF-16A had an empty weight of 6.4 tonnes, and a loaded weight of 9.7 tonnes.
In 1978 Nelson and his team left Boeing and moved to Northrop. At this time, Northrop had the F-5E/F in production, and was working with McDonnell-Douglas on the development of the F-18. Nelson’s initial task at Northrop was to work on the F-18L variant of the Naval F/A-18A, intended for export and for land-based operations. Then in 1980, a lighter and cheaper aircraft to complement what was then the ATF was sought, as the Mission Adaptive Fighter.
Nelson’s concept for this program had the same basic arrow-wing, tip fins plus rectangular thrust vectoring nozzle as the earlier Boeing concepts, but buried and screened intakes in the leading edge, and inward canted fins to reduce radar signature.
Weapons were to be carried in an internal launcher system, which was deployed when needed, but was otherwise within the fuselage to reduce signature and drag. A mix of weapons were proposed including up to 4 air to air missiles, or 40 unguided CRV 7 rockets, or a minigun plus a reduced mixed missile load.
The aircraft was unstable, with a digital flight control system. Avionics for this and other systems were modularised and easily swapped out to expedite repairs and increase aircraft availability. The take-off weight was about 7.7 tonnes, and supercruise capability was sacrificed in the pursuit of reduced signature and high manoeuvrability, the structure being rated for 10g manoeuvres.
• Northrop N-356
This was an export version of the N-353, with a simplified wing, F-18-like intakes, and external weapons carriage under the fuselage. The wing-tip fins were replaced by a single central fin, allowing the carriage of tip-mounted AAMs.
Commonality with the F-18L was sought where possible, and all of the changes in design both added weight and decreased manoeuvre performance. The manoeuvre capability was 7.5g, but up to 6 AAM could be carried.
The USAF took a policy decision in the same period to focus on low observables as the way ahead, and that was that.
So what went wrong?
Some of the aircraft in this saga of wasted effort looked absolutely uber-cool, in a Gerry Anderson kind of way, but ultimately, in my view, the whole program was utterly misconceived and, even if supported by the Air Force, would not have produced an aircraft competitive with the F-16.
This sounds harsh, but the tides of history and technology development at the time were running against the lightly-armed but highly-manoeuvrable concepts that were being considered.
This saga provoked me into thinking in general terms about Light Fighters and their history, and why Light Fighter proposals appeared, and continued to appear seemingly throughout the long history of air combat.
It seems to me that there was a long period, from the beginnings of air combat, right through to about the end of the Korean War, or just possibly the start of the Vietnam War, where there was genuine competition between the Light and the Heavy fighters.
In this period, air combat was overwhelmingly visual air combat, aimed at getting one aircraft’s guns to bear on the other. In these circumstances, lighter aircraft could often out-turn heavier ones, making themselves difficult targets, and obtaining success in a turning fight. Heavier aircraft were generally faster and better armed, and they could obtain success by using ‘slashing’ tactics and avoiding turning combat, and, perhaps taking the combat into the vertical plane if they had sufficient speed and climb-rate advantage.
I wonder whether the proponents of the ‘Fighter Mafia’ were in effect still fighting these conflicts.
After this period, lightweight fighters were still being constructed, but, as set out in my historical piece, were perhaps of greater importance for smaller air arms, or for the Client States of the major powers. Indeed, the Northrop F-5 Freedom Fighter would be an excellent example of such an aircraft.
For the major powers, air combat had been transformed by the development of effective infra-red, and later radar-guided, air-to-air missiles (AAM). These missiles resulted in a technology landscape favouring the heavy fighter, with a radar, possibly two crew, and a mix of IR and radar-guided AAM. Progressive development of radars, missiles, and missile seekers has resulted in a situation where Beyond Visual Range (BVR) air combat is preferred. Short-range manoeuvring air combat is something to be avoided if possible, as the expected result is, all too often, a mutual kill.
As technology is continuing to evolve, lighter-weight fighters are making a come-back, as aircraft like the Gripen and Tejas are demonstrating that highly integrated systems with long-range missiles and highly effective sensors can now be packaged into a single-engined and single-seat airframe. Late model F-16C/D also have BVR capability, but are more often used as multi-role tactical strike aircraft than as BVR Air Defence assets.
The Boeing airborne aircraft carrier concept was doomed, probably from the outset. Against what has proven to be a very successful and very versatile F-16 aircraft, exported around the world, and built in the thousands, the most fully-developed concept, the 985-213, comes up short.
A package consisting of the 747 carrier and four 985-213 offers a capability of just eight AAM, but requires five aircraft, and at least seven aircrew to achieve this. In addition, the vulnerability of the carrier aircraft is such that it is questionable what penetration of enemy airspace could have been achieved.
Efforts to develop a viable land-based version of the aircraft ran into the problem that additional fuel would be required to achieve a useful combat capability, and the most fully developed land-based variant, the Northrop N-353 would end up competing against the same company’s lower risk, but ultimately still unsuccessful F-20 Tigershark.
A detailed article on the F-20 and the Israeli Lavi can be found here.
While there was some interest in the N-356 in the export market, I’d suggest the aircraft would not have been competitive with the F-16, which was being made available for export, at least to some Nations, in the same timescale.
All in all, a sorry saga, and a demonstration that even if it looks uber-cool, it’s not necessarily the right answer. It might, indeed, be the answer to the wrong problem.