Aircraft carriers are one of the most iconic types of ship you will come across. They are floating cities, and can have thousands of crew on board. These mobile air bases are capable of deploying short-range fighter planes to any destination around the world. Not all the world’s armed forces have them however; in fact today, there are less than 40 operational aircraft carriers, divided between the navies of around a dozen countries.
Aeronautically speaking, an aircraft carrier is a fully operational floating runway, with similar features to an asphalt runway on land.
The USA has by far the largest fleet, with various large-scale aircraft carriers (supercarriers), and a number of amphibious assault ships usually used for helicopters.
These are the largest type of aircraft carrier in operation today, and at the moment only the US Navy is in possession of them, with 10 supercarriers in its fleet. The British Navy has two of these ships under construction, due to be ready in 2018. The Chinese Navy also has a supercarrier in an early phase of construction.
Supercarriers are around 300m long and can carry up to 80 fighter jets, in a range of configurations.
The flight deck
The flight deck of an aircraft carrier is obviously the most important part of the ship, and the hub of its activity, being where the aircraft take off and land.
Aeronautically speaking, an aircraft carrier is a fully operational floating runway, with similar features to an asphalt runway on land. There are though, of course, a number of specific systems and design elements that you will only find on one of these floating runways.
The earliest flight decks were wooden ramps built on the top of adapted warships. The first flight to take off from one of these warships was in 1910, from US ship USS Birmingham. Just under 10 years later the first aircraft carriers that resembled those of today began to appear, with a full-length flight deck. The British ship HMS Argus had a purpose-built wooden platform across the full length of its hull to provide unobstructed take-off and landing. This full length deck, however, meant that there was no control tower or structure from which to command the ship, so eventually this configuration was replaced with the type of deck seen in today’s ships, including a tower on one side to serve as a control centre for the aircraft operations and a command area from which to captain the ship.
Take-off and landing on an aircraft flight deck is also something which has evolved with the changes in flight deck designs. On the earliest carriers landing aircraft were actually brought to a standstill by the flight deck crew itself, by literally grabbing hold of the aircraft. Later on, the arrestor cable system became commonplace, with tail hooks being installed on aircraft to bring them to a standstill over a very short distance (in most cases these systems can stop an aircraft travelling at close to 250km/h in just two seconds). Catching one of the arrestor cables however is no easy feat, and contrary to what one would think, as soon as the aircraft touches the deck the pilot will increase the engines to maximum thrust. The reason for this is simple – on such a short runway if something goes wrong with the arrestor cables, the pilot needs to have enough thrust to be able to take straight off again!
In terms of take-off, the most common system used is the aircraft catapult. The first catapult systems were actually trialled as early as 1904 by the Wright brothers, using a weight and derrick setup. Today’s aircraft carrier catapult systems however, consist of a track embedded into the surface of the flight deck with a piston or wire attached to the base of the aircraft to literally launch it down the runway at high speed. A number of propulsion systems have been used, ranging from steam, air pressure and hydraulics, and even gunpowder! A number of new systems are currently being developed using technologies such as electromagnets.
A number of other aircraft carriers also use a ski jump runway design. More apt for STOVL (short take-off and vertical landing) aircraft, this type of flight deck benefits from a shorter runway and converts the aircraft’s forward motion into upward motion and a positive rate of climb directly after take-off.
A number of different take-off and landing configurations have also been tested and used on aircraft carrier flight decks. In the mid-1940s the British Royal Navy tested the first angled flight decks. This deck was designed to accommodate a runway positioned at an angle from the centreline, therefore maintaining a longer runway for jet aircraft with higher landing speeds, while also optimising the deck space for a larger tower area and also offering the possibility of simultaneous take-off and landing operations. Newer versions of this design including a wider deck have now become standard for modern carriers and supercarriers. The space is optimised to include a large control tower, simultaneous take-off and landing operations and also an area for aircraft stands.
Optical landing systems
Without doubt, landing on an aircraft carrier is one of the most difficult task pilots will ever face in their career, however technology has thankfully evolved to make this slightly easier. Given the extremely short length of the aircraft carrier runway, and that while at sea the traditional visual aids approach systems found on a runway on land don’t exist, a type of optical approach system has been developed over the years. On the earliest carriers, pilots relied on their own visual judgement and also on the help of other crew members (otherwise known as landing signals officers or LSOs) who physically wave them in using different coloured flags and wands. Later on the LSOs guided the pilots by radio and also by changing the colour and position of the lights on the deck itself to order the pilot to go around again if necessary.
Nowadays pilots landing on a carrier have the benefit of a fully equipped optical landing system, or OLS. This is a powerful lighting device installed on the flight deck that uses a system of lights in green, amber and red to tell the pilot whether the glide path of the aircraft is correct or not. A horizontal row of green lights indicates the optimum glide slope, and a series of vertical lights, varying in colour, tells the pilot whether the aircraft is too high or too low. There are also other indicators that tell the pilot to abort the landing, or give other commands. There are a number of different variations of the OLS, using new and updated types of lenses, but all of them are based on the same principal.