presented on the





Published on the

Spectrum Headquarters


with the gracious

permission of

Mike Adamson

Original series Suitable for all readers



by Mike Adamson

One of the most stand-out aspects of Captain Scarlet is the sleek, lethal Angel Interceptor. Her catapult launch from the Cloudbase flight deck is stunning, and her global reach and the kind of devastating firepower she can lay against the Mysteron Threat often turned the tables for the Captains on the ground. One of Derek Meddings' three original designs for the show, it was practically iconic, and the jet fighter, as such, has emerged in the intervening years, as the very personification of futuristic technowar.

In the '60s the concept of a single-seat fighter aircraft capable of 3000 mph was awesome, but the audience of today is practically satiated with combat aircraft in the post-Star Wars era. X-wings, Y-wings, TIE fighters ... The Viper and the Cylon, the Starfighter and the Hatchet. All those came along by 1980! Then came the A-wing, B-wing and TIE Interceptor, The Last Starfighter, and Hawkwing hunting ZEAFs through the blue, and in the 1990s Space: Above and Beyond, and many others... The aeroplane is very much the symbol of technology itself and it is tempting to conjecture how fictional craft of the past compare to the march of practical science.

The Angel is a primary example of the unavoidable collision of fact and fiction . At the time of its design (a genesis through several stages from the least-practical to the most-) it was flying at twice the speed of comparable aircraft and it safely ignored the aerodynamic laws that real aircraft must obey. Yet today, though production fighters are not significantly faster, there are technological means for achieving almost anything within reason.

 There is no longer anything particularly remarkable about travelling faster than Mach 4. To the present time the record for a jet-driven aircraft is still held by the Lockheed Blackbird, taken during trials in the mid '60s in which every previous record was demolished. Some references place the maximum attained speed as high as Mach 3.6 (a CIA single-seater M-10 variant), though 3.2 is the more commonly quoted figure for the standard SR-71 version. But during the early 1980s Lockheed designed a possible successor to the Blackbird capable of no less than the blistering speed of Mach 8! Since then, certain problems have been rectified, and the maximum speed of the new-generation stealth fighters is classified, though some estimates place it well above Mach 3. Any such a machine, or course, is constrained by the limitations imposed by the technology required to generate the speed. Such aircraft will never carry bomb loads. At best they are interceptors, dogfighters or strategic data gatherers.

 Aircraft design depends on many, many factors; mission requirement, delivery date, funding, new technologies involved. A perfect aeroplane is one in which no corners have been cut and which conforms the closest to the requirement specified by its users, not simply the fastest or the biggest. To size up the Angel in the light of the actual aircraft industry we must consider it as the real thing. So let us begin with the specification.

Spectrum needed an aircraft principally for interception duties but with a certain amount of variety in its possible applications. The interceptor is a breed of fighter whose primary prey is other fighters, indeed any aeroplane is fair game for it. This embodies fire power, long distance targeting, high speed and long range.

The design which answered the requirement could be described in aeronautical jargon as an "acutely swept low wing monoplane arrow-delta with canards and lifting tail". To translate that into English it means the craft has a single, low-mounted wing with a highly swept leading edge and a mildly swept trailing edge that changes the angle of incidence at the juncture to its outboard section. These tip sections, partitioned from the mainwing by a flow separator, or 'dogtooth', are swept down at an angle of 45 (thus generating shockwave lift and propulsion) and taper toward the tip, the centreline with a 0 sweep angle. "Canards" are the small lifting fins mounted ahead of the wings, referred to sometimes as 'stabilators' because they induce stability in the horizontal axis. That heavy T-tail array would also generate lift and the upswept tips have become fashionable because they promote directional stability and reduce drag. These 'winglets' are nothing new, however, one of the earliest examples being in a design proposal during early development of the British Victor jet bomber as long ago as 1949. These surfaces are mated to an almost symmetrical fuselage that is an elegant thing even in this age when Tomcats and Eagles are getting long-in-the-tooth.

 There are two main technical sources for assessing the Angel's internal arrangements. The first is the information written in the 1960s to accompany the Airfix kit (extemporised upon for the 1994 Captain Scarlet Annual), and more recently Graham Bleathman's Supermarionation Cross-Sections book, which provided an Angel cutaway. Each poses technical solutions and arrangements, and while the latter is obviously based on the former, there was room for invention.

One canonical factor is that the Angel, built by International Engineering, is the descendant of a fighter named the Viper. Besides the Galactica spacefighter of that name, there have been two Vipers in real life. First the McDonnell F-23 ultra-fast stealth design that lost out to the F-22 in 1989 (and which has been theorised to have been an intelligence blind, being in fact the prototype of the "Aurora" hypersonic reconnaissance aircraft); and "Viper" is the alternate name sometimes used for the F-16 Fighting Falcon. In many ways the F-16 is like a real-like Angel.

Whatever the authority, basic aircraft engineering dictates certain factors and we can be fairly certain of some things irrespective of source. The body houses, from the nose back, the flight data sensors, fire-control radar, the weapons, the cockpit, the computer, the fuel, the power systems and the engine. Traditionally the main computer is housed ahead of the cockpit but the Angel's narrow nose is cramped for space and the computer appears to have been shifted directly behind the pilot. Building upon today's technologies, as the craft was meant to, we can assume a radar tracking range of in excess of 100 miles (where the antenna would go in that sharp nose is anyone's guess!) , but unless radical developments in missile technology have occurred the interception range would be much shorter.

The missiles are housed in twin blister pods set into the forward fuselage ahead of the cockpit, five visible per battery. The missiles however are so small (perhaps no more than four or five feet long) that on modern technical principals their range would be pitifully short. Presumably above the radar is a housing for a cannon of one sort or another. Though it is stated that a machine cannon is carried, this bay is exceedingly small and a conventional cannon would require an under-fuselage blister, ala the F-4 Phantom II. The available space is enough for no more than a miniaturised rotary cannon ("Minigun") as used on gunships, or perhaps a directed energy weapon perhaps.

Moving back along the fuselage we come to the cockpit. The bubble canopy is a dogfight prerequisite for all-round visibility, but an aerodynamic hindrance in hypersonic performance. The cockpit is laid out in much the manner of a '60s machine and this is clearly inadequate; today we have more advanced cockpit configurations and the G-stress fighters impose on their pilots is still almost beyond bearing. A seat reclining at a much steeper angle is a way of overcoming G-stress (the F-16 epitomises this approach, and pilots can stand 9Gs for protracted periods) and in its present configuration the Angel Interceptor would black-out its pilots in an 8G turn, no more than 10 if they were of exceptional fitness. Also featured in the original configuration is the provision of a two-handed yoke as opposed to a single-handed cyclic stick and this seems especially odd as a pilot needs a hand free at all times to handle the throttle, the computer and the weapons-release programming, missile launch controls usually being mounted on the throttle.

Behind the cockpit we come to the area which in conventional jets houses the main fuselage fuel tanks and such things as generators, back-up computers and pumps. There is ample space for this equipment in the bay between the air intakes, mostly fuel tanks surrounding the centre-of-gravity, and running all the way back to the engine.

At this point it would be appropriate to quote the technical material supplied to Airfix to accompany their construction kit, a famous piece of Anderson merchandise which, uniquely, spent some two decades in continuous production as part of the company's standard range. The notes accompanying the assembly instructions read in part: "The Tail Assembly is an unusual design. Twin turbojet compressors (one each side of the fuselage) serve the rear-mounted ramjet. Bled air serves the pitch jets which give control at high (supersonic) speeds in rarefied air and are also used for Cloudbase landing manoeuvres. For normal landing or reducing air speed quickly, bled air is used as braking jets ... The lower double slit supplies booster reheat warm air."

This implies a supersonic combustion ramjet fed by twin axial impellers just aft of the intake assembly, equipped with afterburner. The concept of bleed air is nothing new, the technique developed in the '50s and used to this day to increase lift by channelling heated engine air through wing culverts, exhausting downward from the leading edge. This is called 'flap-blowing' and enables a heavy aircraft to fly more slowly than would otherwise be possible and retain a high supersonic wing. The McDonnell legend, the F-4, is a 'flap-blower', an efficient one as it has twin powerplants. If a single-engine flap blower experiences engine stall on approach... it crashes.

It is with the engine that design becomes speculation. The most powerful type of engine designed to date is the ramjet, operating only at high speeds. It ingests and heats air through a specially shaped duct and has no induction turbine. However, the turbo-ramjet combines both engine types and enables the ramjet to operate from a standing start. There have been enormously powerful turbojets constructed in the past, the Pratt and Whitney JT-58 that drives the Blackbird being a colossal machine which itself is bigger than an entire Angel fighter but Is still not as powerful as more recent units. In this engine type, most of the compression is generated at the inlet and most of thrust is generated at the afterburner. The Tumansky R-31 engines in the MiG-25 Foxbat are of the same generation, and while they operate somewhat differently, they obey all the same principles.

This leaves us with the Angel requiring an engine no bigger than the current production generation of high output jets, but generating probably ten- to twenty thousand pounds thrust more than these. Such is not impossible, simply very expensive to design and build. Tumansky have built turbojets generating 50 000 pounds thrust to propel the Tupolev Tu-160 Blackjack supersonic bomber. They are, of course, very much larger than conventional units.

To understand engine requirements and, more over, fuel requirements, let us look at the craft as a whole. She seems about 20% larger than the Northrop F-5 (the design on which the earlier WASP Arrowhead fighter, from Stingray, was based) and despite the obvious weight increases due to equipment storage, fuel and strengthening of the airframe, if we are to assume special materials equivalent to all titanium construction, she would probably weigh in at about the same, an empty clean weight of around 10 000 pounds and a gross maximum combat weight of somewhat over twice that. The Airfix notes place the weight at 40 000 pounds which would suggest a much larger aircraft or one with provision for extensive underwing stores, something the Angel does not have, but this figure seems to be show canon, as it has been perpetuated in all subsequent sources. Delta plan form gives her a slightly larger wing area than the F-5, the wing loading, that is the proportion of the aircraft's weight carried by every square inch of lifting surface, being well within conventional limits at the lower all-up weight, and still common enough at the higher. This gives us a machine with a fair glide ability, enhanced by flap-blowing, great stability, and if we are to assume a thrust rating in the order of 50 000 pounds, a thrust-to-weight ratio of about 1.3:1 on the heavier stated weight, as with the ex-Soviet Sukhoi Su-27. This means that she will climb and accelerate like a bullet, with ample excess power at lower speeds and altitudes to achieve sustained turns without loss of height. At the lower speculative all-up weight her thrust-to-weight would go to the unheard-of figure of 2.5:1, which would make her the most manoeuvrable and fastest fighter there has ever been.

The single engine configuration is somewhat puzzling as it necessarily requires the development of an engine with twice the power rating of a twin engine design. Such engines already exist (e.g., the F-101, rated at 31 000 pounds), yet there is then the weight penalty and increased necessary fuel volume. Essentially, a single-engine aircraft is more susceptible to attrition craft lost to engine malfunctions that would not have been lethal if a second engine had been operating. That, however, did not perturb General Dynamics in development of the brilliant F-16, a craft with a superb safety record over the last thirty years, and which embodies much that the Angel is, albeit with only half her speed. Graham Bleathman laid twin complete engines in the mid-body fuselage, feeding a unified reheat outlet.

To achieve hypersonic speed a great deal of brute-force thrust must be mated to a design friendly to the airflow, that is, it must have a low drag coefficient. This means no bulky projections to disturb and slow the passage of the air, a wing with a thickness no more than five percent the distance from leading to trailing edge at the root, and an unobstructed airflow into the engine. Supersonic engines run up against the first barrier to greater speed at this point. Fuel can only burn so fast and when the airflow passing through the engine exceeds a certain figure above Mach 3 it literally blows the engine out like a candle, carrying the fuel out of the engine in less time than it takes to ignite and burn. Critically shaped nozzles and chambers can slow the air until it is almost standing still and the supersonic combustion ramjet, or 'Scramjet' solves the problem at the expense of dictating a super-critical body shape in which all other aspects are subserviated to propulsion.

The next barrier is one that affects the whole aircraft: heat. As greater and greater thrust is required the reaction temperature within the engine climbs to a point at which conventional engines simply melt. There are engineering and metallurgical solutions, the concept of bleeding freezing external air through an arterial system permeating the engine components to carry away the heat, or of simply constructing the parts of materials that tolerate higher temperatures. This also pertains to the external hull of the craft. At the nose, and junctures between fins, tail and fuselage, the skin temperature soars alarmingly, caused less by friction than the piling up of air ahead of the machine and its severe compaction in the instant before it can flow over the hull and escape, compression being the key to the heating.

A Blackbird at Mach 3 is heated to 300 in some areas, 700 in others; it expands by eleven inches and contracts once more on deceleration. The same would be true for any extremely fast aircraft unless there is some material that is impervious to the effects of heat and pressure.

There is such a thing. A recently invented form of spun and woven glass-fibre plastic, ridiculously cheap and simple to manufacture, with the strength of titanium and yet will not scorch until 800 nor melt until 3000. Should an aircraft's skin and airframe be composed of a substance such as this it would avoid the penalties of metal construction at a reduced weight. These exotic materials, including "carbon-carbon," theoretically capable of withstanding any temperature so long as it is maintained in an anoxic environment, may have been included in the design of the F-22 Raptor and the new X-32, X-35 and X-45 fighter prototypes.

(As a commentary on how forward-looking the Anderson organisation was, in the 1967 Thunderbirds Annual, the story Hellfire Valley features a tunnelling machine descending through a volcanic region. The Mole must tow it out of danger but to do so Scott must go outside the Mole and link up, and the suit he wears is said to be composed of, essentially, carbon-carbon. The writers scoured the scientific literature of the day, and forty years on some of it has indeed come true!)

So if we conjecture the Angel as being powered by an exotic-materials turbo-ramjet, with a skin of woven plastic, its performance ceases to be amazing. The only surprise is that it is not actually faster. This leaves us with the fuel requirements: such an engine devours fuel at a fantastic rate, gallons per second, and if the fuel is conjectured to be an ordinary low-octane, chemically-ignited kerosene broth such as the Blackbird's JP-7, a flight of three Angels running at consistently high Mach numbers would need no less than ten yes, ten conventional tanker planes flying in support of them. Clearly, as shown in the series, this is not the case and we must assume that the engine makes much more efficient usage of a very much more powerful fuel. In Graham Bleathman's technical layout the specifications list a paltry 500 gallons of fuel, but it is a exotic, probably synthetic compound, named "Colboltibe."

One or two inconsistencies became apparent during the show regarding Angel operations. The launch sequence was seen in almost every episode but the landing aboard Cloudbase in only one or two. It was shown that the Angel assumed a nose-up posture and made low speed contact with the deck, precision-docking to a section of it raised to about 35. This intimates that Cloudbase must be on the move for Angel landing as with conventional aircraft carriers, or that the Angel has, in fact, a VTOL capability.

The notion of Vertical Take-Off and Landing incorporated in the design is born out in one episode (Manhunt) in which an Angel jet is found abandoned after landing in typical countryside. Yet this, frankly, is absurd. There are, self-evidently, no provisions for VTOL operation (Graham Bleathman's cutaway shows no such concession to the scene in Manhunt), and flap-blowing is not a substitute. The Angel is in all ways a thoroughly conventional jet fighter requiring rolling take off and landing, optimised for speed, not hover, and the scene to the contrary may be assumed to be more a contrivance of plot than of technical forethought. That is a genuine pity as it places at a disadvantage an aircraft that is, on the whole, a remarkably accurate piece of design.

 One last design element (of which Derek Meddings was quite aware) would limit operational versatility the skid landing gear. It was suitable for catapult launch from a prepared system of runners, but not for much else. Wheeled gear would have been logically preferable, enabling the aircraft to operate conventionally from elsewhere without the clumsiness of dragging skids, but, as fighter design in the 1950s highlighted, tucking away landing gear imposes all kinds of penalties on the aircraft, and the design may have attempted to avoid those penalties with a novel landing gear approach. Graham Bleathman's solution was to retract wheels inside the skids, but their tiny diameter and short-stroke suspension make their operation highly dubious.

It is over thirty-five years since the Angel took shape on paper, and we have reached the point at which we have solved problems which kept the Angel a work of fiction. It is now a speculative engineering concept as much as is Craig Thomas's Firefox, an aircraft comparable in certain ways. But the speed of theoretical and practical scientific and engineering advancement being what it is, the ability to build the Angel could come about well before the 2060s. By that time, in all probability, the Angel as it stands could be quite obsolete, underpowered, outgunned and, yes, even slow!

Science moves quicker with every passing year. The age of Captain Scarlet could well be sooner than anyone has ever imagined.