Side Elevation
Plan
Reverse Plan
Front Elevation
Rear Elevation
Thunderbird 2 elevations
Quite contradictory measurements on Thunderbird 2 are given in various publications. Consensus seems to be around a length of about 75 metres. This length has been taken to derive all other measurements of Thunderbird 2.
Length: 75m (= 250 feet)
Width (wing span): 60m
Height: 17.6m
Wing length: 15m
Wing width: between 9.6m (tip) and 12.3m (fuselage)
Wing area: approx. 164m2
Pod size length x width x height: 29.8m x 17.1m x 14.9m
Mass: 368,000kg (excluding Pod payload) (= 406 tons)
Weight: 3,680,000N (excluding Pod payload)
Payload mass pod: up to 100 ton (= 90,700kg)
Payload weight pod: up to 907,000N
The mass of a pod is about ⅕th of the total mass of Thunderbird 2 (with a pod inserted). This is somewhat less than one of today's real world freight carrier airplanes, the Ukrainian Antonov An-225 (Mriya) that has a mass of 640 tons. The mass of Thunderbird 2 therefore seems realistic.
Judging by the way Pod 4 floats on water (see the chapter on Thunderbird 4) a pod weighs about 12 times more than is usually claimed: 1,085,000kg. This implies that Thunderbird 2 also has a much higher mass — eight to ten times more than the An-225. For this article, let's stick to the 406/100 tons Thunderbird 2/Pod combination although it is at odds with the observations made in the chapter on Thunderbird 4.
maximum speed: 8,000 km/h (= 5,000 mph = 2,222 m/s = Mach 6) – seems incorrect
Cruising speed: 3,200 km/h (= 2,000 mph = 889 m/s = Mach 2.5) – seems incorrect
Maximum altitude: 30,000 m (= 100,000 feet = 30 km) – seems incorrect
Engines: 2 variable cycle gas turbine engines, 4 vertical take-off chemical rockets in main body (not in landing legs!)
Power: atomic fusion reactor – seems incorrect, nuclear fusion is more likely
Although being able to land and take off vertically from rescue sites, the launch procedure using the launch ramp on Tracy Island still has some merit apart from looking good on screen.
In the air the amount of upwards lift must counterbalance the force by which gravity is pulling the aircraft downwards. This lift can be provided by its wings or by sheer force from the booster rockets. As an old saying goes "even a brick will fly given enough power" Thunderbird 2's shape is partly an airfoil (wing) shape itself and as such the aircraft experiences lift due to its own shape, adding to the other lift-providing forces. A longer discussion on flying and the importance of lift is found in the section "Flying".
The amount of lift through its wings and shape when launched from a ramp is less than when Thunderbird 2 would accelerate along a runway (ignoring the fact it can take off vertically using its VTOL rockets).
Given the fact that the launch ramp is under an angle of about 20° with a weight of over 4.5MN (mega-newton), Thunderbird 2 "only" needs a lift of 4.3MN and a forward thrust of 1.6MN. On screen it takes about 6 seconds to slide off the ramp. Within this time, the forward thrust must build up the lifting force using the red coloured booster rockets at the rear. If lift is by then fully provided by its wings (and shape), a flight speed of 20m/s is required. Therefore, these booster rockets must accelerate Thunderbird 2 from standstill to 20m/s in the 6 seconds before it leaves the launch ramp if it is not to topple over at the end. This requires some 32MW power for this transporter aircraft. And this speed must be a lot higher as not only forward movement is required but also speed to provide lift at least equal to the weight of the aircraft.
Following the "fly a brick" approach, the booster rockets themselves must provide sufficient forward and upward thrust to get the aircraft airborne. In which case the thrust must be 13.4MN which is over eight times as much as the thrust required during "normal flight" to provide lift through wings and airfoil. It will get a very fast horizontal speed as well which of course helps in getting to the rescue zone quickly. After six seconds on the launch ramp the horizontal speed has then risen to 172m/s (620 km/h). Which is extraordinary — one of the faster jet fighter aircraft at the moment, Sänger, would only reach 66m/s within 6 seconds! It is within reason to expect both mechanisms to work to some degree, resulting in a combination of lift generated movement and "brick forward" movement.
When returning to Tracy Island (as in i.e. Ricochet), Thunderbird 2 uses its VTOL rockets to hover above the cliff hangar's runway but in addition it rotates 180° to a nose-forward position while airborne, then lands using its VTOL rockets and rolls backwards into its hangar to be refuelled and prepared for its next rescue operation. A cutaway of the hangar is shown in Thunderbirds Annual 1967.
When Thunderbird 2 arrives at the danger zone it hovers and lands. To take off afterwards, Thunderbird 2 doesn't have the advantage of a launch ramp, but ascends entirely on its four VTOL thrusters and start moving forward using its booster rockets and the turbojets in the tail plane.
Hovering is hanging still in the air or moving slowly — far too slow to have normal lifting principles apply to keep the aircraft airborn. Enter vertical take off. Nicolas Tesla patented ways of vertical take off as early as 1928. Helicopters were the first designs to use this principle and are currently the only vertical take off and landing machines in use. The principle is simple: the aircraft must throw out exhaust gases downwards and in doing so is itself pushed in the opposite direction. It's the same principle that gets rockets off the ground and into space.
Engines of this type are called VTOL thrusters (Vertical Take Off and Landing). Some military aircraft like the AV-8B Harrier II+, have VTOL capability but the last VTOL aircraft were decommissioned in 2011 in favour of helicopters that are a lot cheaper to operate and more flexible.
To hover above a landing or rescue site, Thunderbird 2 also uses VTOL thrusters. It has four of them, clearly marked with red circles at its underside. These four thrusters must compensate for the the weight of the entire aircraft plus pod load — about 1,125,000N per thruster which is about 30 times as much as the thrusters inside a Harrier aircraft. Computers must equalize the thrust of each VTOL engine to avoid an imbalance that might topple the aircraft.
On screen a physical error occurs during landing: the VTOL thrusters shut off when Thunderbird 2 has almost touched down. Precisely at the time you need those thrusters most. Without them Thunderbird 2 would drop to the ground like a brick.
The VTOL air stream downwards is reflected by the ground and moves upward again. The closer Thunderbird 2 gets to the ground, the more effective the VTOL thrusters become. Not only do they slow the descent of the aircraft by providing an upward push against gravity but the reflected airstream also pushes the aircraft upwards. This way, Thunderbird 2 lands on a cushion on air provided by the VTOL exhausts.
Another, rather obvious, continuity error is Thunderbird 2's VTOL thrusters firing from the positions of the hydraulic legs: the thrusters are positioned further forward and inward, inside the red circles on Thunderbird 2's underside.
Thunderbird 2 is accused of being unable to fly in reality, yet it does. An often repeated quote from the world of aviation states that "even a brick will fly given enough power". And indeed, if propulsion is large enough, anything flies. Or more accurately: anything is propelled forward. Nothing beats sheer power to push an object forward or upward, with or without wings.
The art of flying is to move forward utilizing the presence of air to maximum benefit and in doing so, reducing the need for power to a level that can be realized. Anything but brick-power.
Flying through air roughly comes in two quite different varieties: subsonic and supersonic. These are speeds below and above the speed of sound respectively. "Mach 1" is known as flying at the speed of sound, therefore subsonic is below Mach 1 whilst supersonic is above Mach 1. Both Thunderbirds 1 and 2 as well as Fireflash are supposedly capable of flying subsonic as well as supersonic. The now decommissioned real life Concorde airplane could too.
Aerodynamics and fluid mechanics have a set of common names often originating from the French language where initially most of the research on flying was conducted. The illustration at left indicates these.
It took a while before the Wright brothers demonstrated in 1901 what flying (or gliding) was all about. Meanwhile, aerodynamics has become a science of its own where experiments, computer simulations and wind tunnels are daily activities. And Brains knows this topic inside out.
Flying boils down to a properly (droplet) shaped wing that splits the air it moves through into two layers. One layer will move fast over the top of the wing, while the other will move much slower underneath. This difference in speed results in a higher air pressure below the wing and a lower pressure above. The resulting pressure difference gives rise to an upward force (lift) much like buoyant objects under water will be forced upwards. When this upward force supersedes the weight of the aircraft, the wings will lift the aircraft into the air. For this to work, the wings (and the aircraft fuselage attached to them) need to move forward at a minimum speed. This explains why normal aircraft require a runway (or possibly a launch ramp) to pick up speed.
It's important to realize that the air itself basically remains in place. It is the aircraft that moves and as with all things relative, when viewed from the aircraft's point of reference the air appears to move instead. When the aircraft moves through the air it disturbs the air particles, causing a sound wave. The particles themselves are a bit shaken and vibrate but basically remain where they are. This sound disturbance, passed on from air particle to air particle, travels with the speed of sound and will be way ahead of the much slower moving subsonic aircraft.
When Thunderbird 2 flies at subsonic speed (and on screen we never see otherwise) it remains airborn by the same principle of lift. When flying horizontally, the lifting force equals and compensates for its weight. The thrust from the rear engines simply pushes it forward (even if on film they seem to shut off because the Schermuly cartridge has burned out). When climbing, the lifting force plus forward thrust exceeds the weight, pushing the aircraft upwards.
It may look as if those small wings cannot do the job of lifting this heavy aircraft. They cannot. But they don't need to — at least not completely. But let it be stated here that wings, swept forward or backward, both provide lift to fly — but with different consequences.
Thunderbird 2 itself is shaped much like a lifting body, a wing, an aerofoil, providing lift. Whether the shape of Thunderbird 2 proves to be exactly right for the amount of air lift needed, requires wind tunnel experiments and calculations. Especially the protruding tail plane section at the rear causes drag as it disturbs the air flow. Let's assume Brains did all that and the shape came out flying — assisted by the lift provided by Thunderbird 2's wings.
The small wings on Thunderbird 2 may not contribute to lift in large amounts, they are important for steering the carrier aircraft just like they do any other aircraft. The control surfaces on the wings control the aircraft's pitch (tilt up or down) and roll (tilt left or right). The rudders on the rear ramjet block (the vertical parts with the big "2" painted on) control the yaw (turning left or right). However, by tilting the wings themselves, a more efficient yaw is obtained. The wing's lifting force shifts sideways, creating a net force at the same side which will "push" Thunderbird 2 in a circular path so it can change direction.
It may come as a surprise that for lifting purposes, it doesn't really matter whether the wings are straight, swept backward (like Thunderbird 1) or swept forward (like Thunderbird 2). If properly shaped, they all produce lift. Swept wings (both forward and backward) benefit from less air drag (resistance) the same way a knife cuts better when applied diagonally downwards (hence cutting under an angle) than when pushed down straight. This benefit comes with a drawback however: it also provides less lift but the lift/drag ratio is in favour of the swept wing.
In the 1960's, experiments were conducted with forward sweeping wings — and Derek Meddings must have picked up on it for the design of Thunderbird 2. If you look at the airflow around a flying aircraft, the wings cut through the air. Some of the air particles are pushed aside along the front of the edge of the wing. This flow is different for forward and backward sweeping wings and has an impact on the manœuvrability of the aircraft.
With backward sweeping wings air will flow to the wing tips — as happens with Thunderbird 1 and most "normal" aircraft. With small movable parts of the wing near the tip (known as "ailerons") you can influence the stability of the aircraft. A subtle change will produce sufficient torque to stop any rolling movement of the fuselage.
With forward sweeping wings the air moves to the fuselage instead of the wing tips. This makes the aircraft highly manœuvrable (like a bullet can spin around its axis) but also less stable. You need more force to counterbalance any rotation. In these situations, computer controlled navigation (called "fly by wire" — something all Thunderbirds do literally, although the term means something else in aerodynamics) is essential as human reaction is too slow to compensate for these rotations. One of the last forward swept wing aircrafts built for NASA in 1984, the Grumman X-29, needed up to 40 corrections per second. The ailerons at the wing tip are now even better at stabilizing a rolling aircraft — the torque produced by the air near the fuselage can be compensated for by the torque produced by the ailerons as these are further away from the fuselage.
At supersonic speeds an aircraft travels faster than the speed of sound (around 343m/s but this varies depending on the circumstances). Air resistance is the major obstacle to conquer at such high speeds as it heats up the hull of the aircraft. Anything that is heated up expands and at high speeds the temperature can rise dramatically. Railway tracks and bridges leave gaps that can be filled when the structures expand by modest solar heating, thus preventing deformation. The amount of heating in such cases is almost negligable compared to the heating of a fast moving aircraft. They would either require similar (but larger) gaps in the hull to allow for expansion or the hull must be effectively cooled to reduce the temperature increase. Thunderbird 2 is supposed to have a fuselage skin cooling refrigerator unit.
Apart from heat expansion, supersonic flight comes with another problem: shockwaves produced by sound waves that lag behind the aircraft moving at supersonic speeds. Sound is a vibration of air particles that is passed on from one particle to the next. On average, air particles remain in place, they make way to let the shape of an aircraft pass. In doing so, they bump into neighbouring particles and cause a sound wave that travels at the speed of sound. It's not the air particle itself that travels — it only vibrates and stays at (almost) the same location but its vibrating movement is passed on.
When an aircraft flies faster than the sound disturbance it creates, the air in front of the aircraft is unaware the aircraft needs to pass. The warning disturbance hasn't reached it yet. It's a bit like being run over by a fire truck before you hear the siren to warn you it is coming.
When Thunderbird 2 is flying at supersonic speeds its soundwaves move slower than the aircraft itself. This is similar to a boat sailing through water faster than the water waves it creates. It produces "water shock waves"
The illustration at left shows how far the sound wave has travelled when it was created at point A by Thunderbird 2 which has meanwhile moved on, faster than the soundwave, to point B, C and finally D. The three red circles show to what distance the sound, created at point A, has meanwhile travelled whilst Thunderbird 2.has moved from A to B to C and D.
When Thunderbird 2 arrives at point D, it has of course started sound waves along the way. Each of these waves travels in all directions at the speed of sound — slower than Thunderbird 2. The result is that all these sound waves meet each other at a front, known as the "shockwave". This wave is cone-shaped with the aircraft at the top. The cone's surface represents the shockwave. The circular sections of the cone indicate how far a soundwave has travelled in the meantime along the flight path of the aircraft which is on the axis of the cone.
When the energy of all sound waves adds up along the shockwave, the release of this energy can have catastrophic consequences for objects in its path. All energy released collects along the circumference of the circles of the cone (perpendicular to the flight path axis). The smaller the circle, the greater the energy density.
Consider a shockwave cone that sweeps through the ground. The passing of the shockwave at ground level is shown by the yellow parabola. A shockwave caused by an aircraft passing at high altitude (the big circle) may cause windows to shatter. A low flying aircraft (the small circle) with a much higher energy density, may cause destruction of houses or walls. The further away from the flight path, the bigger the shockwave cone section and the less impact is experienced.
Imagine what happens to an aircraft if it was partially touched by its own shockwave. A very small radius means a very high energy density and disruption of that part of the aircraft is quite likely. So it is a wise precaution to fly with such a speed that the shockwave cone completely envelops the aircraft so that no part protrudes.
It will be clear that the faster the aircraft flies, the narrower the shockwave cone as the aircraft's progress is faster than the sound waves that follow it. This limits the speed at which Thunderbird 2 can travel. When it flies at Mach 2, the cone will have an angle of about 20° and all of Thunderbird 2 will just about fit when viewed sideways. When looking from above however, such a cone will have the wings stick out as well as parts of the engine nacelles. This would cause tremendous stress on the hull of the aircraft. But to fit all of Thunderbird 2 inside its shockwave cone, it has to reduce its speed to a maximum of Mach 1.6 which is a far cry from the published cruising speed of Mach 2, let alone its assumed maximum speed of Mach 6. Unless of course Brains has made the aircraft of indestructible alloys and used engines that overcome the drag associated with those high speeds.
It is never seen in a television episode but in one of Frank Bellamy's comics, Talons of the Eagle, Thunderbird 2 needs to escape into space and depends on Thunderbird 3 for refuelling. I think this should be categorised as poetic license by Bellamy. It also contradicts the earlier mentioned maximum altitude of 30km. The cockpit is pressurised and air supply will be available as in any aircraft flying at high altitudes — that should not be a problem for Thunderbird 2. But if it could enter the exosphere, it can only do so if it can act as a spaceship instead of an aircraft as there is no air and its air-dependent engines and wings are useless.
According to Bellamy, to refuel, Thunderbird 3 docks with Thunderbird 2 in a manner almost similar to the one it uses for Thunderbird 5. But without any guiding sensors this seems a much more tricky operation where the slightest momentum of Thunderbird 3 is transferred to and shared with Thunderbird 2, bringing the combination in motion like two billiard balls colliding. Besides, nowhere are there known fuel tanks or hoses in Thunderbird 3 to transfer the fuel.
Returning to the Earth's atmosphere might prove disastrous for Thunderbird 2. Most space capsules enter the Earth's atmosphere in what is basically a free fall downwards. They experience air friction that increases with the speed of the descent (and that may be up to Mach 30 — at free fall it will reach the same speed as is needed to escape from Earth: the escape velocity of 11.2km/s) and the higher density of the lower atmosphere. Thunderbird 2 would heat up and possibly melt. And with a very thin atmosphere, flying down is no option. Space travel is not for Thunderbird 2. Or any Thunderbird craft apart from Thunderbird 3, period.
Thunderbird 2 is claimed to be able to fly at a maximum height of 30km which is in the lower-middle part of the stratosphere layer of the atmosphere. It contains about 10% of the total air mass and is above the troposphere (0 – 13 km) where the airstream jets are located that are used by long-haul international commercial flights. At that height it will encounter less air resistance from the thinner air layers but also find much less air to combust in its ramjets. It seems unlikely that it is able to fly at this height unless thrust is provided by rocket-type engines. Which begs the question: where does it store the fuel for these rockets?
Aircraft that fly subsonic as well as supersonic must meet conflicting requirements imposed by both situations. A versatile engine working in subsonic and supersonic flight is called a turboramjet. The turbo part functions at subsonic speeds, the ramjet part at supersonic speeds. A bit of both works at the transition speed range. In all cases, the engine compresses air that enters at the intake at the front, compresses it, heats it (by which it expands) and throws it out at high speed at the back end, producing a thrust forward. Rather uniquely, Thunderbird 2 does have two different sets of engines instead of a combined turboramjet.
Four subsonic turbojets are housed in the tail plane at the rear end. The specification states they are used for maintaining cruising speed. This must be wrong as turbojets won't work above Mach 1 and Thunderbird 2's cruising speed is supposed to be Mach 2.5. It is therefore more likely that its cruising speed is subsonic (below Mach 1).
The supersonic engines are the ramjets on both sides of the aircraft inside the twin boom fuselage. Because of the supersonic speeds, the jet may fall victim to shockwave energy. To prevent this, the ramjet has a spike whose tip produces a shockwave cone in the air. The spike ensures the engine remains inside its shockwave cone. It is unclear where the shockwave is diverted to or how its energy is consumed inside the ramjet pipe. The air behind the shockwave enters the engine and final propulsion is obtained by the same principle of compression and heating but the thrust of the engine is a lot larger than at subsonic speeds.
Thunderbird 2 is International Rescue's heavy transporter aircraft. The rescue equipment is transported in exchangeable pods. We won't go into the details of the rescue equipment but do have a look at how Thunderbird 2 can fly with and without pods. Specifics on Pod 4 which houses Thunderbird 4 are discussed in the chapter on Thunderbird 4.
The aerodynamic design of any aircraft requires that it minimizes air resistance. In the case of Thunderbird 2 this requires that its hull is continuous. When a pod is dropped, as in the case of a Thunderbird 4 launch, the air drag becomes enormous due to the hole created. A hole in which the center of mass of Thunderbird 2 is situated. Flying forward causes air turbulence when air enters the hole and gets blocked by the rear end of the pod hole with no way to go but upwards or downwards. The twin boom fuselage must be very sturdy to keep the structure of the aircraft intact with such a big hole in the middle. While Thunderbird 2 hovers above the sea to drop the pod, it is kept airborn by using its four VTOL thrusters. In this situation, the aerodynamic shape of the aircraft is of little influence. The strength of the twin boom fuselage that connects front and rear part of the aircraft is paramount to keep the aircraft in one piece.
Some observations can be made on the pod and its contents. Everything in the pod must be secured in place as it will start to move if Thunderbird 2 is launched, accelerates or decelerates — all due to the inertia of the objects according to Newton's Second Law of Motion. If things are not properly secured, the random movement of the pod's contents will interfere with the equilibrium of the aircraft, resulting in instability. Aircraft must be properly loaded to stay balanced the same way that ships must be loaded properly to keep them afloat.
