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".
Evolution
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 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 ever tailhook system, designed and built by circus performer & aviator Hugh Robinson.[1] Ely told a reporter: "It was easy enough. I think the trick could be successfully turned nine times out of ten." On 4 May 1912, Commander Charles Samson became the first man to take off from a ship which was underway when he flew his Short S27 off of HMS Hibernia, which was steaming at 10.5 kn (12.1 mph; 19.4 km/h). 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, 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 Edwin Dunning landed a Sopwith Pup successfully on board the flying-off platform of HMS Furious, 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, however. In order to land, aircraft had to manoeuvre around the superstructure. Furious was therefore returned to dockyard hands have a 300 ft (91 m) deck added aft for landing, on top of a new hangar. However, the central superstructure remained, and turbulence caused by this 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, 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 gasses were trunked down the side of the ship and ejected under the fantail of the flight deck (which, despite arrangements to disperse the gasses, 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 and Eagle.
After World War I, battlecruisers that otherwise would have had to have been discarded under the Washington Naval Treaty - such as the British Furious and Glorious-class and the American USS Lexington and Saratoga- were converted to carriers along the above lines. Being large and fast they were perfectly suited to this role; the heavy armouring 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 during 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 wooden flight deck were considered to be part of the superstructure. Such ships were still being built into the late '40s, 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 now the strength deck, an integral part of the hull, and was heavily armoured to protect the ship and her air complement. Although the armoured carrier concept in this form remained something of a dead end, 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 in 1922 to over 100,000 tons in the latest Nimitz-class carriers.
Armoured decks
When aircraft carriers supplanted battleships as the primary fleet capital ship, there were two schools of thought on the question of armour protection being included into the flight deck. The addition of armour to the flight deck offered aircraft below some protection against aerial bombs. However, to reduce top-weight the hanger height was reduced and this restricted the types of aircraft that these ships could carry, although the Royal Navy's armoured carriers did carry spare aircraft in the hanger overheads.[1] The armour also reduced the length of the flight deck, reducing the maximum aircraft capacity of the armoured flight deck carrier, however the largest part of the disparity between RN and USN carriers in aircraft capacity was due to the use of a permanent deck park on USN carriers.[2] RN carriers did not use a permanent deck park until 1943.
Landing on flight decks
- See also: Arresting gear
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 (6.1 m) intervals which bring a plane, traveling at 150 mph (240 km/h), to a complete stop in about 320 ft (98 m). 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 in order that aircraft could be parked on the forward part of the deck and recovered on the after part. This allowed increased complements, but resulted in lengthened turn-around times 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.
Modern innovations
Angled flight deck
The angled flight deck was invented by Captain (later Rear Admiral) Dennis Campbell[3]. With this type of deck, (also referred to as a "skewed deck" or the "angle"), the aft part of the deck is widened and a separate runway is positioned at an angle from the centreline.[4] 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.[4] 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.[4] 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 fuelling), 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, by painting angled deck markings onto the centeline flight deck for touch and go landings.[4]. This was also tested on the USS Midway the same year.[5][6] It should be noted that in both tests, the arresting gear and barriers remained oriented to the original axis deck. From September-December 1952, the USS Antietam had a rudimentary sponson installed for true angle deck tests, allowing for full arrested landings, which proved during trials to be superior.[7] In 1953, Antietam trained with both US and British naval units, proving the worth of the angle deck concept.[8] HMS Centaur was modified with overhanging angled flight deck in 1954.[4] 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 became the first carrier to be constructed and launched with the deck, followed in the same year by the lead ships of the British Majestic-class (HMAS Melbourne) and the American Forrestal-class (USS Forrestal).[4]
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. They are most common on aircraft carriers supporting STOVL aircraft such as the Harrier, but the Russians also used them with conventional [Mig-29]s.
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. As the plane leaves the ski jump ramp it continues to accelerate horizontally until the wings can provide the needed lift.
Such takeoffs allow a larger takeoff weight than a straight vertical launch because the wings provide some lift even at low speeds, and the ski jump ramp provides a vertical impetus when most needed, right at takeoff at the slowest takeoff speed.
These takeoffs use less runway that 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 it might finish its takeoff roll and begin flight at 60 ft (18 m) 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 (46 to 61 m) above the water[9].
For example, an AV-8B Harrier with a gross weight of 29,000 lb (13,000 kg) on a 59°F day and a 35 kn (40 mph; 65 km/h) wind over the deck would require 400 ft (120 m) to takeoff using a 12° ski jump ramp designed like on the Principe de Astrurias, but 750 ft (230 m) without the ski jump ramp[10].
For a Mig-29 launching over the ski jump ramp on the Tbilisi, takeoff speed is reduced from about 140 kn (160 mph; 260 km/h) to about 70 kn (81 mph; 130 km/h) (depending on many factors such a gross weight)[11].
Carriers using STOVL aircraft and a ski jump ramp do not need catapults nor arresting gear.
With the exception of the United States, every navy in the world that operates STOVL naval aircraft uses ski jump ramps[12].
Flexible decks
An idea tested but never taken to completion was the "flexible deck". In the early jet age it was seen that by eliminating the landing gear for carrier borne aircraft the inflight performance/range would be improved. This led to the concept of a deck that would absorb the energy of landing, the risk of damaging propellers no longer being an issue though take off would require some sort of launching cradle. [13] Test were carried out with a Sea Vampire on the rubber deck fitted to HMS Warrior, and Supermarine designed their Type 508 for rubber deck landing, and the flexible deck idea was found to be technically feasible in tests but was nevertheless abandoned. The Supermarine Type 508 was subsequently developed into a 'normal' carrier aircraft, the Scimitar.
See also
References
- ^ Roberts, British Warships of the Second World War, p62.
- ^ Hone, Friedman, Mandeles, British and American Carrier Development, 1919-1941, p125.
- ^ "History of the Fleet Air Arm".
- ^ a b c d e f "The angled flight deck". Sea Power Centre Australia. Royal Australian Navy. Retrieved 2008-09-15.
- ^ "U.S. aircraft carriers By Norman Friedman, A. D. Baker, III".
- ^ "unknown".
{{cite web}}: Cite uses generic title (help) - ^ "unknown". googlebooks.
{{cite web}}: Cite uses generic title (help) - ^ "unknown" (pdf).
{{cite web}}: Cite uses generic title (help) - ^ http://www.history.navy.mil/nan/backissues/1990s/1990/mj90.pdf
- ^ http://www.history.navy.mil/nan/backissues/1990s/1990/mj90.pdf
- ^ Mikoyan Mig-29, Yefim Gordon, p 84
- ^ http://www.history.navy.mil/nan/backissues/1990s/1990/mj90.pdf
- ^ Thunder and Lightnings - Scimitar 21 May 2007