KC-135 Stratotanker
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The Boeing KC-135 Stratotanker is an aerial refueling tanker aircraft. It has been in service with the U.S. Air Force since 1957.
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[edit] Development
The KC-135 is derived from the original Boeing jet transport "proof of concept" demonstrator, the Boeing 367-80 (commonly called the "Dash-80"). As such, it has a narrower fuselage and is shorter than the Boeing 707 jetliner. Boeing gave the tanker the designation of Model 717.[1]
Developed in the late-1950s this basic airframe is characterized by swept wings and tail, four underwing mounted engine pods, a horizontal stabilizer mounted on the fuselage near the bottom of the vertical stabilizer with positive dihedral on the two horizontal planes and a hi-frequency radio antenna which protrudes forward from the top of the vertical fin or stabilizer. These basic features make it strongly resemble the commercial Boeing 707 and 720 aircraft, although it is actually a different aircraft.
The Strategic Air Command had the KC-135 Stratotankers in service from 1957 through 1991 and with the Air National Guard and the Air Force Reserve from 1975 through 1991, when most were re-assigned to the newly-created Air Mobility Command (AMC). As AMC gained the preponderance of the aerial refueling mission, a small number of KC-135s were also assigned to directly United States Air Forces in Europe (USAFE) and Pacific Air Forces (PACAF). Reconnaissance and command post variants, including EC-135 Looking Glass, Post Attack Command & Control Systems were operated by SAC from 1963 through 1991, when they were re-assigned to the Air Combat Command.
Boeing's 367-80 was the basic design for the commercial Boeing 707 passenger aircraft as well as the KC-135A Stratotanker. In 1954 the USAF's Strategic Air Command ordered the first 29 of its future fleet of 732. The first aircraft flew in August 1956 and the initial production Stratotanker was delivered to Castle Air Force Base, California, in June 1957. The last KC-135 was delivered to the Air Force in 1965.
Four turbojet engines, mounted under 35-degree swept wings, power the KC-135 to takeoffs at gross weights up to 322,500 pounds (146,300 kg). Nearly all internal fuel can be pumped through the tanker's flying boom, the KC-135's primary fuel transfer method. A special shuttlecock-shaped drogue, attached to and trailing behind the flying boom, may be used to refuel aircraft fitted with probes. A boom operator stationed in the rear of the aircraft controls the boom while lying prone. A cargo deck above the refueling system can hold a mixed load of passengers and cargo. Depending on fuel storage configuration, the KC-135 can carry up to 83,000 pounds (37,600 kg) of cargo.
In Southeast Asia, KC-135 Stratotankers made the air war different from all previous aerial conflicts. Midair refueling brought far-flung bombing targets within reach. Combat aircraft, no longer limited by fuel supplies, were able to spend more time in target areas.
Air Mobility Command (AMC) manages more than 546 total aircraft inventory Stratotankers, of which the Air Force Reserve and Air National Guard fly 292 in support of AMC's mission.
[edit] Modifications
[edit] General upgrades
The KC-135Q was the variant modified to carry the JP-7 fuel necessary for the SR-71 Blackbird, segregating the JP-7 from the KC-135's own fuel supply (the body tanks carrying JP-7, and the wing tanks carrying JP-4). When the KC-135Q model received the CFM-56 engines, it was redesignated the KC-135T model, which was capable of separating the main body tanks from the wing tanks where the KC-135 draws its engine fuel.
The KC-135R/T was a receiver-capable tanker, used for pilot training and operational refueling missions. Currently all KC-135R/T models (Receiver capable) are with the 22nd Air Refueling Wing at McConnell AFB, KS.[citation needed] Most of these are used for force extension and Special Operations missions, and are crewed by highly qualified receiver capable crews. If not used for the receiver mission, these aircraft can be flown just like any other KC-135R.
In order to expand the KC-135's capabilities and improve its reliability, the aircraft has undergone a number of upgrades. Among these was the Pacer-CRAG program (CRAG=Compass, Radar and GPS) which ran from 1999 to 2002 and modified all the aircraft in the inventory to eliminate the Navigator position from the flight crew. The modifications were performed by BAE Systems at the Mojave Airport in California.[2]
[edit] Re-engining
All KC-135s were originally equipped with Pratt & Whitney J-57 turbojet engines which produced approximately 13,000 pounds of thrust and, in some conditions, utilized water-injection to boost takeoff power output. In the 1980s the first modification program re-engined 157 Air Force Reserve (AFRES) and Air National Guard (ANG) tankers with the Pratt & Whitney TF-33-PW-102 engines from retired 707 airliners. The re-engined tanker, designated the KC-135E, is 14% more fuel efficient than the KC-135A and can offload 20% more fuel. Only the KC-135E aircraft were equipped with thrust-reversers for takeoff aborts and shorter landing rollouts.
The second modification program re-engined more than 410 with new CFM56 engines produced by CFM-International. The re-engined tanker, designated either the KC-135R or KC-135T, can offload 50% more fuel, is 25% more fuel efficient, costs 25% less to operate and is 96% quieter than the KC-135A.
The KC-135R's operational range is 60% greater than the KC-135E for comparable fuel offloads, providing a wider range of basing options[3].
Upgrading the remaining KC-135E into KC-135R would cost about three billion dollars, about 24 million dollars per aircraft.[4]. According to Air Force data, the KC-135 fleet had a total operation and support cost in fiscal year 2001 of about $2.2 billion. The older E model aircraft averaged total costs of about $4.6 million per aircraft, while the R models averaged about $3.7 million per aircraft. Those costs include personnel, fuel, maintenance, modifications, and spare parts [5].
[edit] Multi-Point Refueling System program
This program adds refueling pods to the KC-135's wings. The pods allow refueling of U.S. Navy, U.S. Marine Corps and NATO tactical jet aircraft while keeping the tail-mounted refueling boom.[8]
[edit] Research and development
Besides its primary role as an inflight aircraft refueler, the KC-135, designated NKC-135, has assisted in several research projects at the NASA Dryden Flight Research Center at Edwards Air Force Base, California. One such project occurred between 1979 and 1980 when special wingtip "winglets", developed by Richard Whitcomb of the Langley Research Center, were tested at Dryden, using a NKC-135A tanker loaned to NASA by the Air Force. Winglets are small, nearly vertical fins installed on an aircraft's wing tips. The results of the research showed that drag was reduced and range could be increased by as much as 7 percent at cruise speeds.[6][7] Winglets are now being incorporated into most new commercial and military transport jets, as well as business aviation jets.
NASA also has operated several KC-135 aircraft (without the tanker equipment installed) as their infamous Vomit Comet zero-gravity simulator aircraft. The longest-serving (1973 to 1995) version was KC-135A 59-1481, named Weightless Wonder IV registered N930NA.[8]
[edit] Electronic warfare
A number of KC-135A and KC-135B aircraft have been modified to EC-135 configuration for use in several different roles.
[edit] Replacing the KC-135
As of 2006, the KC-135E fleet is flying an annual average of 350 hours per aircraft and the KC-135R fleet is flying an annual average of 710 hours per aircraft. The KC-135 fleet is currently flying double its planned yearly flying hour program to meet airborne refueling requirements, and has resulted in higher than forecasted usage and sustainment costs.[9]
The Air Force projects that E and R models have lifetime flying hour limits of 36,000 and 39,000 hours, respectively. According to the Air Force, only a few KC-135s would reach these limits before 2040, but at that time some of the aircraft would be about 80 years old. The Air Force estimates that their current fleet of KC-135s have between 12,000 to 14,000 flying hours on them-only 33 percent of the lifetime flying hour limit.[10] Nevertheless these aircraft are over 40 years old and maintenance costs are increasing, with airframe corrosion being the worst problem.
Between 1993 and 2003 the amount of KC-135 depot maintenance work has doubled, and the overhaul cost per aircraft tripled.[11] In 1996 it cost $8,400 per flight hour for the KC-135, and in 2002 this had grown to $11,000. The Air Force’s 15-year cost estimates project further significant growth through fiscal year 2017. For example, operations and support costs for the KC-135 fleet are estimated to grow from about $2.2 billion in fiscal year 2003 to $5.1 billion (2003 dollars) in fiscal year 2017, an increase of $2.9 billion, or over 130 percent, which represents an annual growth rate of about 6.2 percent.[12]
It has been decided to replace the KC-135 fleet. However, since there are over 500 KC-135 these planes will be replaced gradually, with the first batch of about 100 aircraft to be replaced in the current buy.
Initially the first batch of replacement planes was to be an air tanker version of the Boeing 767, leased from Boeing. In January 2006, Secretary of Defense Donald Rumsfeld announced the cancellation of the KC-767 lease. This followed public revelations of corruption in how the contract was awarded, as well as controversy regarding the original leasing rather than outright purchase agreement. This is also designed to be a cost-cutting measure and is part of a larger reorganization and redefinition of the Air Force's mission that includes the retirement of the E-4B fleet, the cancellation of the Boeing 767-based E-10 MC2A program, as well as the elimination of all but 58 B-52 Stratofortresses. Former Secretary of Defense Rumsfeld stated that this move will in no way impair the Air Force's ability to deliver the mission of the KC-767, which will be accomplished by continuing upgrades to the KC-135 and KC-10 Extender fleet.
In January 2007, the Air Force formally launched the KC-X program with a request for proposal (RFP). The news release announcing the RFP said "The KC-X program is the first of three acquisition programs the Air Force will need to replace the entire fleet of aging KC-135 Stratotankers".[9] The Boeing KC-767 is the leading candidate for the program, competing with the tanker version of the Airbus 330.
Image:KC-135 refueling.jpg An F-15 backs out after refueling from a KC-135. |
Image:Usaf.kc135.taxying.fairford.arp.jpg U.S. Air Force Reserve Command KC-135R tanker taxis for take off |
Image:Usaf.kc135.taildetail.fairford.arp.jpg Tail of an U.S. Air Force Reserve Command KC-135R tanker showing refueling boom |
[edit] Operators
- Template:Country data France
- Template:Country data Singapore
- Image:Flag of Turkey.svg Turkey
- Template:Country data United States
- Italy has been reported in some sources as operating several KC-135s,[13] however these are actually Boeing 707-300s converted to tanker configuration.[14][15]
[edit] Variant summary
- KC-135A - Original production version
- NKC-135A - Test-configured KC-135A
- KC-135D - RC-135A modified to partial KC-135A configuration[16]
- KC-135E - A model modified with Pratt & Whitney TF-33-PW-102 engines from retired 707 airliners
- NKC-135E - Test-configured KC-135E
- KC-135Q - A model modified to carry the JP-7 fuel necessary for the SR-71 Blackbird
- KC-135R - A model modified with CFM-56 engines
- KC-135R/T - Receiver-capable tanker
- KC-135T - KC-135Q modified with CFM-56 engines
[edit] Specifications (KC-135R)
General characteristics<h3>
- Crew: 3: pilot, copilot, boom operator. Certain missions or aircraft (non-Pacer CRAG modified) require the addition of a navigator
- Length: 136 ft 3 in (41.53 m)
- Wingspan: 130 ft 10 in (39.88 m)
- Height: 41 ft 8 in (12.70 m)
- Wing area: 2,433 ft² (226 m²)
- Empty weight: 98,466 lb (44,663 kg)
- Loaded weight: 297,000 lb (135,000 kg)
- Max takeoff weight: 322,500 lb (146,000 kg)
- Powerplant: 4× (R/T) CFM International CFM-56 (F108-CF-100) turbofan engines, 21,634 lbf (96 kN) each}
- Powerplant: 4× (E) Pratt & Whitney TF-33-PW-102 turbofan engines , 18,000 lbf (80 kN) each
<h3>Performance<h3>
- Maximum speed: 580 mph (933 km/h)
- Range: 3,450 mi (5,550 km)
- Service ceiling 50,000 ft (15,200 m)
- Rate of climb: 4,900 ft/min (1,490 m/min)
- Maximum Fuel Load: 209,543 lb (95,006 kg) (31,275 US gal)
[edit] References
- ^ "Historical Perspective, Start of a PROUD MISSION", Boeing Frontiers, July 2006.
- ^ "BAE SYSTEMS delivers final Pacer CRAG KC-135", Aerotech News and Review, 2002-09-20
- ^ [1]
- ^ [2]
- ^ [3]
- ^ KC-135 Aircraft Photo Gallery Contact Sheet
- ^ C-135 Variants - Part 2, by Jennings Heilig
- ^ C-135 Variants, Part 6 by Jennings Heilig
- ^ [4]
- ^ [5]
- ^ [6]
- ^ [7]
- ^ Boeing wins Italian bid military 767s, SeattlePi.com; Italy operates 4 KC-135s, 2001-07-10
- ^ Aeroflight's listing of Italian Air Force aircraft
- ^ Airframe tracking information from Airlinerlist.com
- ^ DoD 4120.14L, Model Designation of Military Aerospace Vehicles, May 12, 2004
[edit] External links
- KC-135 page on Boeing.com
- KC-135 image gallery on Boeing.com
- Official USAF KC-135 fact sheet
- Public domain KC-135 photo gallery at official USAF website
- KC-135 page on awacs-spotter.nl
- Public domain photo gallery of NASA's KC-135A tanker
- KC-135 page at globalsecurity.org
- KC-135 page at fas.org - (not updated since late 1999, but still perhaps useful)
- C-135 page at aero-web.org - Includes specs for many variants
- Smart Tankers (Defence Today)
[edit] Related content
Related development<h3>
<h3>Comparable aircraft<h3> <h3>Designation sequence<h3><h3>See also<h3>
| Boeing C-135 and 707 Military Transport Aircraft |
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| Lists relating to aviation |
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