Fire and Forget

By the end of my last post, we’d got as far as the 1950s in terms of the development of air warfare, an interesting period of transition, particularly for fighter technology. With the development of the jet engine and supersonic flight, the potential of these faster, lighter aircraft was beginning to outstrip that of the slow, lumbering bombers they ostensibly served. Lessons were quickly learned during the chaos of the Korean war, the first of the second half of the twentieth century, during which American & Allied forces fought a back-and-forth swinging conflict against the North Koreans and Chinese. Air power proved a key feature of the conflict; the new American jet fighters took apart the North Korean air force, consisting mainly of old propellor-driven aircraft, as they swept north past the 52nd parallel and toward the Chinese border, but when China joined in they brought with them a fleet of Soviet Mig-15 jet fighters, and suddenly the US and her allies were on the retreat. The American-lead UN campaign did embark on a bombing campaign using B-29 bombers, utterly annihilating vast swathes of North Korea and persuading the high command that carpet bombing was still a legitimate strategy, but it was the fast aerial fighter combat that really stole the show.

One of the key innovations that won the Allies the Battle of Britain during WWII proved during the Korean war to be particularly valuable during the realm of air warfare; radar. British radar technology during the war was designed to utilise massive-scale machinery to detect the approximate positions of incoming German raids, but post-war developments had refined it to use far smaller bits of equipment to identify objects more precisely and over a smaller range. This was then combined with the exponentially advancing electronics technology and the deadly, but so far difficult to use accurately, rocketeering technology developed during the two world wars to create a new weapon; the guided missile, based on the technology used on the German V2. The air-to-air missile (AAM) subsequently proved both more accurate & destructive than the machine guns previously used for air combat, whilst air-to-surface missiles (ASM’s) began to offer fighters the ability to take out ground targets in the same way as bombers, but with far superior speed and efficiency; with the development of the guided missile, fighters began to gain a capability in firepower to match their capability in airspeed and agility.

The earliest missiles were ‘beam riders’, using radar equipment attached to either an aircraft or (more typically) ground-based platform to aim at a target and then simply allowing a small bit of electronics, a rocket motor and some fins on the missile to follow the radar beam. These were somewhat tricky to use, especially as quite a lot of early radar sets had to be aimed manually rather than ‘locking on’ to a target, and the beam tended to fade when used over long range, so as technology improved post-Korea these beam riders were largely abandoned; but during the Korean war itself, these weapons proved deadly, accurate alternatives to machine guns capable of attacking from great range and many angles. Most importantly, the technology showed great potential for improvement; as more sensitive radiation-detecting equipment was developed, IR-seeking missiles (aka heat seekers) were developed, and once they were sensitive enough to detect something cooler than the exhaust gases from a jet engine (requiring all missiles to be fired from behind; tricky in a dogfight) these proved tricky customers to deal with. Later developments of the ‘beam riding’ system detected radiation being reflected from the target and tracked with their own inbuilt radar, which did away with the decreasing accuracy of an expanding beam in a system known as semi-active radar homing, and another modern guidance technique to target radar installations or communications hubs is to simply follow the trail of radiation they emit and explode upon hitting something. Most modern missiles however use fully active radar homing (ARH), whereby they carry their own radar system capable of sending out a beam to find a target, identify and lock onto its position ever-changing position, steering itself to follow the reflected radiation and doing the final, destructive deed entirely of its own accord. The greatest advantage to this is what is known as the ‘fire and forget’ capability, whereby one can fire the missile and start doing something else whilst safe in the knowledge that somebody will be exploding in the near future, with no input required from the aircraft.

As missile technology has advanced, so too have the techniques for fighting back against it; dropping reflective material behind an aircraft can confuse some basic radar systems, whilst dropping flares can distract heat seekers. As an ‘if all else fails’ procedure, heavy material can be dropped behind the aircraft for the missile to hit and blow up. However, only one aircraft has ever managed a totally failsafe method of avoiding missiles; the previously mentioned Lockheed SR-71A Blackbird, the fastest aircraft ever, had as its standard missile avoidance procedure to speed up and simply outrun the things. You may have noticed that I think this plane is insanely cool.

But now to drag us back to the correct time period. With the advancement of military technology and shrinking military budgets, it was realised that one highly capable jet fighter could do the work of many more basic design, and many forsaw the day when all fighter combat would concern beyond-visual-range (BVR) missile warfare. To this end, the interceptor began to evolve as a fighter concept; very fast aircraft (such as the ‘two engines and a seat’ design of the British Lightning) with a high ceiling, large missile inventories and powerful radars, they aimed to intercept (hence the name) long-range bombers travelling at high altitudes. To ensure the lower skies were not left empty, the fighter-bomber also began to develop as a design; this aimed to use the natural speed of fighter aircraft to make hit-and-run attacks on ground targets, whilst keeping a smaller arsenal of missiles to engage other fighters and any interceptors that decided to come after them. Korea had made the top brass decide that dogfights were rapidly becoming a thing of the past, and that future air combat would become a war of sneaky delivery of missiles as much as anything; but it hadn’t yet persuaded them that fighter-bombers could ever replace carpet bombing as an acceptable strategy or focus for air warfare. It would take some years for these two fallacies to be challenged, as I shall explore in next post’s, hopefully final, chapter.

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The Development of Air Power

By the end of the Second World War, the air was the key battleground of modern warfare; with control of the air, one could move small detachments of troops to deep behind enemy lines, gather valuable reconnaissance and, of course, bomb one’s enemies into submission/total annihilation. But the air was also the newest theatre of war, meaning that there was enormous potential for improvement in this field. With the destructive capabilities of air power, it quickly became obvious that whoever was able to best enhance their flight strength would have the upper hand in the wars of the latter half of the twentieth century, and as the Cold War began hotting up (no pun intended) engineers across the world began turning their hands to problems of air warfare.

Take, for example, the question of speed; fighter pilots had long known that the faster plane in a dogfight had a significant advantage over his opponent, since he was able to manoeuvre quickly, chase his opponents if they ran for home and escape combat more easily. It also helped him cover more ground when chasing after slower, more sluggish bombers. However, the technology of the time favoured internal combustion engines powering propeller-driven aircraft, which limited both the range and speed of aircraft at the time. Weirdly, however, the solution to this particular problem had been invented 15 years earlier, after a young RAF pilot called Frank Whittle patented his design for a jet engine. However, when he submitted this idea to the RAF they referred him to engineer A. A. Griffith, whose study of turbines and compressors had lead to Whittle’s design. The reason Griffith hadn’t invented the jet engine himself was thanks to his fixed belief that jet engines would be too inefficient to act as practical engines on their own, and thought they would be better suited to powering propellers. He turned down Whittle’s engine design, which used the forward thrust of the engine itself, rather than a propeller, for power, as impractical, and so the Air Ministry didn’t fund research into the concept. Some now think that, had the jet engine been taken seriously by the British, the Second World War might have been over by 1940, but as it was Whittle spent the next ten years trying to finance his research and development privately, whilst fitting it around his RAF commitments. It wasn’t until 1945, by which time the desperation of war had lead to governments latching to every idea there was, that the first jet-powered aircraft got off the ground; and it was made by a team of Germans, Whittle’s patent having been allowed to expire a decade earlier.

Still, the German jet fighter was not exactly a practical beast (its engine needed to be disassembled after every use), and by then the war was almost lost anyway. Once the Allies got really into their jet aircraft development after the war, they looked set to start reaching the kind of fantastic speeds that would surely herald the new age of air power. But there was a problem; the sound barrier. During the war, a number of planes had tried to break the magical speed limit of 768 mph, aka the speed of sound (or Mach 1, as it is known today), but none had succeeded; partly this was due to the sheer engine power required (propellers get very inefficient when one approaching the speed of sound, and propeller tips can actually exceed the speed of sound as they spin), but the main reason for failure lay in the plane breaking up. In particular, there was a recurring problems of the wings tearing themselves off as they approached the required speed. It was subsequently realised that as one approached the sound barrier, you began to catch up with the wave of sound travelling in front of you; when you got too close to this, the air being pushed in front of the aircraft began to interact with this sound wave, causing shockwaves and extreme turbulence. This shockwave is what generates the sound of a sonic boom, and also the sound of a cracking whip. Some propeller driver WW2 fighters were able to achieve ‘transonic’ (very-close-to-Mach-1) speeds in dives, but these shockwaves generally rendered the plane uncontrollable and they invariably crashed; this effect was known as ‘transonic buffeting’. A few pilots during the war claimed to have successfully broken the sound barrier in dives and lived to tell the tale, but these claims are highly disputed. During the late 40s and early 50s, a careful analysis of transonic buffeting and similar effects yielded valuable information about the aerodynamics of attempting to break the sound barrier, and yielded several pieces of valuable data. One of the most significant, and most oft-quoted, developments concerned the shape of the wings; whilst  it was discovered that the frontal shape and thickness of the wings could be seriously prohibitive to supersonic flight, it was also realised that when in supersonic flight the shockwave generated was cone shaped. Not only that, but behind the shockwave air flowed at subsonic speeds and a wing behaved as normal; the solution, therefore, was to ‘sweep back’ the shape of the wings to form a triangle shape, so that they always lay ‘inside’ the cone-shaped shockwave. If they didn’t, the wing travelling through supersonic air would be constantly being battered by shockwaves, which would massively increase drag and potentially take the wings off the plane. In reality, it’s quite impractical to have the entire wing lying in the subsonic region (not least because a very swept-back wing tends to behave badly and not generate much lift when in subsonic flight), but the sweep of a wing is still a crucial factor in designing an aircraft depending on what speeds you want it to travel at. In the Lockheed SR-71A Blackbird, the fastest manned aircraft ever made (it could hit Mach 3.3), the problem was partially solved by having wings located right at the back of the aircraft to avoid the shockwave cone. Most modern jet fighters can hit Mach 2.

At first, aircraft designed to break the sound barrier were rocket powered; the USA’s resident speed merchant Chuck Yeager was the first man to officially and veritably top 768mph in the record-breaking rocket plane Bell X-1, although Yeager’s co-tester is thought to have beaten him to the achievement by 30 minutes piloting an XP-86 Sabre. But, before long, supersonic technology was beginning to make itself felt in the more conventional spheres of warfare; second generation jet fighters were, with the help of high-powered jet engines, the first to engage in supersonic combat during the 50s, and as both aircraft and weapons technology advanced the traditional roles of fighter and bomber started to come into question. And the result of that little upheaval will be explored next time…

The Red Flower

Fire is, without a doubt, humanity’s oldest invention and its greatest friend; to many, the fundamental example what separates us from other animals. The abilities to keep warm through the coldest nights and harshest winters, to scare away predators by harnessing this strange force of nature, and to cook a joint of meat because screw it, it tastes better that way, are incredibly valuable ones, and they have seen us through many a tough moment. Over the centuries, fire in one form or another has been used for everything from being a weapon of war to furthering science, and very grateful we are for it too.

However, whilst the social history of fire is interesting, if I were to do a post on it then you dear readers would be faced with 1000 words of rather repetitive and somewhat boring myergh (technical term), so instead I thought I would take this opportunity to resort to my other old friend in these matters: science, as well as a few things learned from several years of very casual outdoorsmanship.

Fire is the natural product of any sufficiently exothermic reaction (ie one that gives out heat, rather than taking it in). These reactions can be of any type, but since fire can only form in air most of such reactions we are familiar with tend to be oxidation reactions; oxygen from the air bonding chemically with the substance in question (although there are exceptions;  a sample of potassium placed in water will float on the top and react with the water itself, become surrounded surrounded by a lilac flame sufficiently hot to melt it, and start fizzing violently and pushing itself around the container. A larger dose of potassium, or a more reactive alkali metal such as rubidium, will explode). The emission of heat causes a relatively gentle warming effect for the immediate area, but close to the site of the reaction itself a very large amount of heat is emitted in a small area. This excites the molecules of air close to the reaction and causes them to vibrate violently, emitting photons of electromagnetic radiation as they do so in the form of heat & light (among other things). These photons cause the air to glow brightly, creating the visible flame we can see; this large amount of thermal energy also ionises a lot of atoms and molecules in the area of the flame, meaning that a flame has a slight charge and is more conductive than the surrounding air. Because of this, flame probes are sometimes used to get rid of the excess charge in sensitive electromagnetic experiments, and flamethrowers can be made to fire lightning. Most often the glowing flame results in the characteristic reddy/orange colour of fire, but some reactions, such as the potassium one mentioned, cause them to emit radiation of other frequencies for a variety of reasons (chief among them the temperature of the flame and the spectral properties of the material in question), causing the flames to be of different colours, whilst a white-hot area of a fire is so hot that the molecules don’t care what frequency the photons they’re emitting are at so long as they can get rid of the things fast enough. Thus, light of all wavelengths gets emitted, and we see white light. The flickery nature of a flame is generally caused by the excited hot air moving about rapidly, until it gets far enough away from the source of heat to cool down and stop glowing; this process happens all the time with hundreds of packets of hot air, causing them to flicker back and forth.

However, we must remember that fires do not just give out heat, but must take some in too. This is to do with the way the chemical reaction to generate the heat in question works; the process requires the bonds between atoms to be broken, which uses up energy, before they can be reformed into a different pattern to release energy, and the energy needed to break the bonds and get the reaction going is known as the activation energy. Getting the molecules of the stuff you’re trying to react to the activation energy is the really hard part of lighting a fire, and different reactions (involving the burning of different stuff) have different activation energies, and thus different ‘ignition temperatures’ for the materials involved. Paper, for example, famously has an ignition temperature of 451 Fahrenheit (which means, incidentally, that you can cook with it if you’re sufficiently careful and not in a hurry to eat), whilst wood’s is only a little higher at around 300 degrees centigrade, both of which are less than that of a spark or flame. However, we must remember that neither fuel will ignite if it is wet, as water is not a fuel that can be burnt, meaning that it often takes a while to dry wood out sufficiently for it to catch, and that big, solid blocks of wood take quite a bit of energy to heat up.

From all of this information we can extrapolate the first rule that everybody learns about firelighting; that in order to catch a fire needs air, dry fuel and heat (the air provides the oxygen, the fuel the stuff it reacts with and the heat the activation energy). When one of these is lacking, one must make up for it by providing an excess of at least one of the other two, whilst remembering not to let the provision of the other ingredients suffer; it does no good, for example, to throw tons of fuel onto a new, small fire since it will snuff out its access to the air and put the fire out. Whilst fuel and air are usually relatively easy to come by when starting a fire, heat is always the tricky thing; matches are short lived, sparks even more so, and the fact that most of your fuel is likely to be damp makes the job even harder.

Provision of heat is also the main reason behind all of our classical methods of putting a fire out; covering it with cold water cuts it off from both heat and oxygen, and whilst blowing on a fire will provide it with more oxygen, it will also blow away the warm air close to the fire and replace it with cold, causing small flames like candles to be snuffed out (it is for this reason that a fire should be blown on very gently if you are trying to get it to catch and also why doing so will cause the flames, which are caused by hot air remember, to disappear but the embers to glow more brightly and burn with renewed vigour once you have stopped blowing).  Once a fire has sufficient heat, it is almost impossible to put out and blowing on it will only provide it with more oxygen and cause it to burn faster, as was ably demonstrated during the Great Fire of London. I myself have once, with a few friends, laid a fire that burned for 11 hours straight; many times it was reduced to a few humble embers, but it was so hot that all we had to do was throw another log on it and it would instantly begin to burn again. When the time came to put it out, it took half an hour for the embers to dim their glow.