Flight deck



The flight deck of an aircraft carrier is the surface from which its aircraft take off and land, essentially a miniature airfield at sea. On smaller naval ships which do not have aviation as a primary mission, the landing area for helicopters and other VTOL aircraft is also referred to as the flight deck. The official U.S. Navy term for these vessels is "aviation-capable ships".

Early flight decks
The first flight decks were inclined wooden ramps built over the forecastle of naval warships. Eugene Ely made the first fixed-wing aircraft take-off from a warship from USS Birmingham (CL-2) on 14 November 1910. Two months later, on 18 January 1911, Ely landed his Curtiss pusher plane on a platform on Pennsylvania anchored in San Francisco Bay using the first tailhook system, designed and built by circus performer and aviator Hugh Robinson. Ely told a reporter: "It was easy enough. I think the trick could be successfully turned nine times out of ten." On 9 May 1912, Commander Charles Samson became the first man to take off from a ship which was underway when he flew his Short S.27 off of HMS Hibernia (1905), which was steaming at 10.5 kn. Because the take-off speed of early aircraft was so low, it was possible for an aircraft to make a very short take off when the launching ship was steaming into the wind. Later, removable "flying-off platforms" appeared on the gun turrets of battleships and battlecruisers starting with HMS Repulse, allowing aircraft to be flown off for scouting purposes, although there was no chance of recovery.

On 2 August 1917, while performing trials, Squadron Commander E.H. Dunning landed a Sopwith Pup successfully on board the flying-off platform of HMS Furious (47), becoming the first person to land an aircraft on a moving ship. However, on his third attempt, a tire burst as he attempted to land, causing the aircraft to go over the side, killing him; thus Dunning also has the dubious distinction of being the first person to die in an aircraft carrier landing accident. The landing arrangements on Furious were highly unsatisfactory. In order to land, aircraft had to manoeuvre around the superstructure. Furious was therefore returned to dockyard hands to have a 300 ft deck added aft for landing, on top of a new hangar. The central superstructure remained, however, and turbulence caused by it badly affected the landing deck.

Full length decks


The first aircraft carrier that began to show the configuration of the modern vessel was the converted liner HMS Argus (1917), which had a large flat wooden deck added over the entire length of the hull, giving a combined landing and take-off deck unobstructed by superstructure turbulence. Because of her unobstructed flight deck, Argus had no fixed conning tower and no funnel. Rather, exhaust gases were trunked down the side of the ship and ejected under the fantail of the flight deck (which, despite arrangements to disperse the gases, gave an unwelcome "lift" to aircraft immediately prior to landing). The lack of a command position and funnel was unsatisfactory, and Argus was used to experiment with various ideas to remedy the solution. A photograph in 1917 shows her with a canvas mock-up of a starboard "island" superstructure and funnel. This was placed on the starboard side because the rotary engines of some early aircraft created torque which pulled the nose left, meaning an aircraft naturally yawed to port on take-off; therefore, it was desirable that they turned away from the fixed superstructure. This became the typical aircraft carrier arrangement and was used in the next British carriers, HMS Hermes (95) and HMS Eagle (1918).

After World War I, battlecruisers that otherwise would have been discarded under the Washington Naval Treaty—such as the British Furious and Glorious-class and the American USS Lexington (CV-2) and USS Saratoga (CV-3)—were converted to carriers along the above lines. Being large and fast they were perfectly suited to this role; the heavy armoring and scantlings and low speed of the converted battleship Eagle served to be something of a handicap in practice. Because the military effectiveness of aircraft carriers was then unknown, early ships were typically equipped with cruiser-calibre guns to aid in their defence if surprised by enemy warships. These guns were generally removed in World War II and replaced with anti-aircraft guns, as carrier doctrine developed the "task force" (later called "battle group") model, where the carrier's defence against surface ships would be a combination of escorting warships and its own aircraft.

In ships of this configuration, the hangar deck was the strength deck and an integral part of the hull, and the hangar and light steel flight deck were considered to be part of the superstructure. Such ships were still being built into the late 1940s, classic examples being the U.S. Navy's Essex and Ticonderoga-class carriers. However, in 1936, the Royal Navy began construction of the Illustrious-class. In these ships, the flight deck was the strength deck, an integral part of the hull, and was heavily armored to protect the ship and her air complement. The flight deck as the strength deck was adopted for later construction. This was necessitated by the ever-increasing size of the ships, from the 13,000 ton USS Langley (CV-1) in 1922 to over 100,000 tons in the latest Nimitz-class carriers.

Armored decks
When aircraft carriers supplanted battleships as the primary fleet capital ship, there were two schools of thought on the question of armor protection being included into the flight deck. The addition of armor to the flight deck offered aircraft below some protection against aerial bombs. However, to reduce top-weight the hangar height was reduced, and this restricted the types of aircraft that these ships could carry, although the Royal Navy's armored carriers did carry spare aircraft in the hangar overheads. The armor also reduced the length of the flight deck, reducing the maximum aircraft capacity of the armored flight deck carrier. The 23,000 ton British Illustrious-class had a hangar capacity for 36 Swordfish sized aircraft and a single 458 ft x 62 ft x 16 ft ( 140m x 19m x 4.8m) hangar, but carried up to 57 aircraft with a permanent deck park while the 23,400 ton Implacable class featured increased hangar capacity with a 458 ft x 62 ft x 14 ft ( 140m x 19m x 4.3m) upper hangar and the addition of a 208 ft by 62 ft by 14 ft (63m x 19m x 4.3m) lower hangar, forward of the after elevator, which had a total capacity of 52 Swordfish sized aircraft and carried up to 81 aircraft with a deck park, while the 27,500 ton USN Essex class had a 654 ft x 70 ft x 17.5 ft (198m x 21m x 5.3m) hangar that was designed to handle a mix of 72 prewar USN aircraft. RN carriers did not use a permanent deck park until 1943. The experience of World War II caused the USN to change their design policy in favor of armored flight decks: "The main armor carried on Enterprise is the heavy armored flight deck. This was to prove a significant factor in the catastrophic fire and explosions that occurred on Enterprise's flight deck in 1969. The US Navy learned its lesson the hard way during World War II when all its carriers had only armored hangar decks. All attack carriers built since the Midway class have had armored flight decks."

Landing on flight decks


Landing arrangements were originally primitive, with aircraft simply being "caught" by a team of deck-hands who would run out from the wings of the flight deck and grab a part of the aircraft to slow it down. This dangerous procedure was only possible with early aircraft of low weight and landing speed. Arrangements of nets served to catch the aircraft should the latter fail, although this was likely to cause structural damage.

Landing larger and faster aircraft on a flight deck was made possible through the use of arresting cables installed on the flight deck and a tailhook installed on the aircraft. Early carriers had a very large number of arrestor cables or "wires". Current U.S. Navy carriers have three or four steel cables stretched across the deck at 20 ft intervals which bring a plane, traveling at 150 mph, to a complete stop in about 320 ft. The cables are set to stop each aircraft at the same place on the deck, regardless of the size or weight of the plane. During World War II, large net barriers would be erected across the flight deck so aircraft could be parked on the forward part of the deck and recovered on the after part. This allowed increased complements but resulted in a lengthened launch and recovery cycle as aircraft were shuffled around the carrier to allow take-off or landing operations.

A barricade is an emergency system used if a normal arrestment cannot be made. Barricade webbing engages the wings of the landing aircraft, and momentum is transferred to the arresting engine.

Angled flight deck




The angled flight deck was invented by Royal Navy Captain (later Rear Admiral) Dennis Cambell, as an outgrowth of design study initially begun in the winter of 1944-45 when a committee of senior Royal Navy officers decided that the future of naval aviation was in jets, whose higher speeds required that the carriers be modified to "fit" the needs of jets. With this type of deck, (also referred to as a "skewed deck" or "canted deck" or the "angle"), the aft part of the deck is widened and a separate runway is positioned at an angle from the centreline. The angled flight deck was designed with the higher landing speeds of jet aircraft in mind, which would have required the entire length of a centreline flight deck to stop. The design also allowed for concurrent launch and recovery operations, and allowed aircraft failing to connect with the arrestor cables to abort the landing, accelerate, and relaunch (or "bolter") without risk to other parked or launching aircraft.

The redesign allowed for several other design and operational modifications, including the mounting of a larger island (improving both ship-handling and flight control), drastically simplified aircraft recovery and deck movement (aircraft now launched from the bow and re-embarked on the angle, leaving a large open area amidships for arming and fueling), and damage control. Because of its utility in flight operations, the angled deck is now a defining feature of STOBAR and CATOBAR equipped aircraft carriers.



The angled flight deck was first tested on HMS Triumph (R16) by painting angled deck markings onto the centerline of the flight deck for touch and go landings. This was also tested on the USS Midway (CV-41) the same year. Despite the new markings, in both cases the arresting gear and barriers were still aligned with the centerline of the original deck. From September to December 1952, the USS Antietam (CV-36) had a rudimentary sponson installed for true angled deck tests, allowing for full arrested landings, which proved during trials to be superior. In 1953, Antietam trained with both U.S. and British naval units, proving the worth of the angle deck concept. HMS Centaur (R06) was modified with overhanging angled flight deck in 1954. The U.S. Navy installed the decks as part of the SCB-125 upgrade for the Essex-class and SCB-110/110A for the Midway-class. In February 1955, HMS Ark Royal (R09) became the first carrier to be constructed and launched with an angled deck, rather than having one retrofitted. This was followed in the same year by the lead ships of the British Majestic-class (HMAS Melbourne (R21)) and the American Forrestal-class (USS Forrestal (CV-59)).

Ski-jump ramp


Another British innovation is the ski-jump ramp, which came about as a means of improving take off for the VSTOL BAE Sea Harrier "jump-jet" on the small Invincible class aircraft carriers. Initial testing was carried out at the RAE Bedford. They are most common on aircraft carriers supporting STOVL aircraft such as the Harrier, but the Russians also used them with conventional MiG-29s and Su-33s.

The ski jump is a ramp which is curved upwards at its forward end. For STOVL aircraft the aircraft starts by making a conventional rolling takeoff with the jet exhausts set to provide maximum forward thrust. As the plane nears the end of the ramp (the ski jump portion) the jet exhausts are rotated to provide upward lift as well as forward thrust. Rolling over the ski ramp launches the plane both upwards and forwards. As the plane leaves the ski jump ramp it continues to accelerate horizontally until the wings can provide the needed lift.

For conventional aircraft such as the MiG-29 the aircraft just rolls down the runway in the obvious manner. Again, rolling over the ski ramp launches the plane both upwards and forwards.

Such takeoffs allow a larger takeoff weight than an unassisted horizontal launch because the ski jump ramp provides a vertical impetus when most needed, right at takeoff at the slowest takeoff speed; however, ski-jump launches cannot match the payloads made possible by high-speed catapult launches.

These takeoffs use less runway than a takeoff over a flat surface because the plane takes off at a lower speed, using both the ski jump ramp's vertical impetus and the deflected jet engines to generate lift. Ski jump ramp takeoffs are considered safer than takeoffs over a flat top carrier. When a Harrier launches from an American LHA (Landing Helicopter Assault) it might finish its takeoff roll and begin flight at 60 ft above the water. It might not have a positive rate of climb, especially if the ship had pitched nose down during the takeoff roll. Using a ski jump ramp the plane will certainly launch with a positive rate of climb and its momentum will carry it to 150 to 200 ft above the water.

For example, an AV-8B Harrier with a gross weight of 29000 lb on a 59 °F day and a 35 kn wind over the deck would require 400 ft to takeoff using a 12° ski jump ramp designed as on the Principe de Asturias, but 750 ft without the ski jump ramp.

For a MiG-29 launching over the ski jump ramp on the Tbilisi, takeoff speed is reduced from about 140 kn to about 70 kn (depending on many factors such a gross weight).

Carriers using STOVL aircraft and a ski jump ramp do not need catapults nor arresting gear.

With the exception of the United States, France and Brazil, every navy in the world that operates STOVL naval aircraft uses ski jump ramps.

Flexible decks
An idea tested, but never put into service, was the "flexible" or "rubber deck." In the early jet age it was seen that by eliminating the landing gear for carrier borne aircraft the inflight performance and range would be improved, since the space taken by the landing gear could be used to hold additional fuel tanks instead. This led to the concept of a deck that would absorb the energy of landing. With the introduction of jet aircraft the risk of damaging propellers was no longer an issue, though take off would require some sort of launching cradle. Tests were carried out with a de Havilland Sea Vampire flown by test pilot Eric "Winkle" Brown onto the rubber deck fitted to HMS Warrior, and Supermarine designed its Type 508 for rubber deck landings. The flexible deck idea was found to be technically feasible but was nevertheless abandoned, as the weight of aircraft increased, and there were always doubts about the ability of an average pilot to land in this way. The Type 508 was subsequently developed into a conventional carrier aircraft, the Supermarine Scimitar.

Other
Unusual alternatives to flight decks have been proposed for use in the jet age:
 * The Shipborne containerized air-defense system (SCADS) was a proposed modular kit to convert a Ro-Ro or Container ship into a STOVL aircraft carrier in two days during an emergency and quick removal after use for storage. With thirty days of jet fuel, munitions, defensive systems and missiles, ASW helicopters, crew and work areas, radar, and a ski jump, it was effectively a modern merchant aircraft carrier.
 * Skyhook was proposed by British Aerospace, a system using a crane with a top mating mechanism hung over the sea to fuel, launch, and recover a few Harriers to remove the requirement of a deck, allowing launches even from ships as small as frigates.
 * The Convair F2Y Sea Dart was a supersonic seaplane jet fighter that had skis rather than wheels, in the late 1940s the Navy feared that supersonic aircraft would stall at low speeds required for a carrier arresting gear and therefore not be able to land on a carrier. The Sea Dart would land on (smooth) water; then be lowered and raised from the sea via crane.