Monday, April 28, 2008

Lavochkin La-17 / CAF Chang Kong 1

The Lavochkin La-17 began flight tests in the 1950s and was one of the first Soviet UAVs to enter service. It was a small radio-controlled target drone used for training surface-to-air missile battery crews and interceptor aircraft pilots. The La-17 had a pretty simple configuration with a slim fuselage straight wings and tail surfaces and a ramjet under the fuselage. The drone was air launched and landed belly first. The ramjet was considered expendable.

The La-17 was rather crude however and also expensive to operate because of the need for a carrier aircraft and was soon supplemented by the ground launched La-17M which was turbojet powered and launched from a trolley using rocket assistance. Later improvements added an autopilot, the ability to operate at low-level and a landing skid to avoid damage to the engine when it landed.

The Soviet Union explored using the La-17 as a reconnaissance drone, the La-17R appeared in the early 1960s with a longer nose able to carry a variety of reconnaissance sensors including cameras, TV cameras and radiation monitoring equipment. The last version of the drone was the La-17K which had a different engine based on the engine used in the MiG-21. Some may still be in Russian Air Force use today.

The Chang Kong 1

China received a number of La-17s in the late 1950s but when relations between the USSR and China cooled and stocks of the drone ran low the Chinese reverse-engineered the drone and started to produce their own. The Shenyang B-5 or Chang Kong 1 is their version of the La-17 and continues in production to this day at the Changzhou Aircraft Factory (CK-1G).

The Chinese have continued to improve the CK-1 as it is known with the high manoeuvrability CK-1C appearing in the mid-1980s able to make bank turns of up to 77 degrees and the CK-1E for extra low level missions. A radiation sampling version, CK-1A, was also built for sampling air in the aftermath of Chinese nuclear tests.

Technical details

The CK-1 autopilot stabilises the drone in response to radio commands from the control station though the first 85 seconds of flight are pre-programmed. Up to 24 different command signals can be sent to the autopilot and in return there is a 52 channel telemetry downlink allowing the controller to keep tabs on altitude, speed, engine rpm et cetera. An onboard radar transponder allows the drone to be identified and tracked.

For aerial target use the CK-1 has a miss-distance indicator, infra-red augmentation pods, radar reflectors and smoke generators to aid visual tracking. The CK-1E has flares instead of smoke. The CK-1s these days are powered by WP6 turbojets taken from retired J-6 fighters. The CK-1 has a speed of around 900km/h with a flight endurance between 45 and 60 minutes.

Tuesday, April 22, 2008

McDonnell GAM-72 / ADM-20 Quail

As the Cold War began to develop in the 1950s the US Air Force began to look for new ways to protect their bombers as they overflew the Soviet Union. Height was no longer a defence against the new generation of interceptors and missiles (both ground and air launched). The USAF began to develop decoy missiles that would confuse the enemy air defences. McDonnell pitched a design for a decoy missile that could be carried in a bomber's bomb bay with it's wings folded and then launched when needed. The idea being bombers would carry these decoys along with their weapon load and launch the decoys to confuse enemy air defences. Given more targets it was then hoped that more bombers would be able to penetrate the air defences. In 1956 they were awarded a contract to develop Weapon System 122A of which the GAM-72 Green Quail decoy was a part.

ADM-20 Quail as preserved at the USAF Museum

The GAM-72 Green Quail (later ADM-20 Quail) was a small (for a Cold War aircraft anyway being 3.88m long and having a wingspan of 1.65m) fibre-glass UAV powered by a J85 turbojet. It had a range of 716km and could fly at Mach 0.9.

Pretending to be a B-52

How then could a small drone pretend to be a huge manned bomber? To be effective the Quail had to appear exactly the same as a B-52 would on the enemy's radar. A combination of radar reflectors, chaff, infra-red emitters and electronic repeaters was used to give the Quail as close a signature as possible to the B-52. The design of the Quail with it's slab sides and multiple vertical flying surfaces also contributed to it's radar cross section. (Its kind of ironic that in the days of stealth aircraft here is one that was designed to be exactly the opposite!)

But the Quail not only had to look like a B-52, it had to act like one too. It's performance had to be close or identical to the bomber. The GAM-72 was programmed on the ground before a mission and could fly for up to nearly an hour, changing direction twice in that time and speed also. Later on the GAM-72 was modified to operate at lower altitudes, a barometric altimeter being used to avoid it slamming into the ground. The GAM-72 is an early example of a cruise missile though it never carried a weapon payload.

Service life

In the early 60s the ADM-20 (as it was re designated in 1963) was built in the hundreds. It went fully operational in 1962 and stayed in service until 1978 (it did remain on the USAF books until 1989) though by the early 1970s it was considered obsolete. Improvements in radar technology meant the Quail was no longer considered effective as a decoy. In an exercise in the early 1970s radar operators were able to tell the difference between the Quail and a real target 21 times out of 23. The Commander of Strategic Air Command is said to have written that the Quail was at least better than nothing!

A major reason for the Quail's obsolescence though was the fact that nuclear bombers no longer needed to overfly their targets but could fire "stand off" missiles from some way off. The Quail was, however, the most successful decoy missile fielded by the USAF in the Cold War.

Quail with a B-52 (from Boeing Multimedia Library)

Friday, April 18, 2008

Not Classic Jetliners (4) : Hawker Siddeley Trident

A competitor to the much more successful Boeing 727, the Hawker Siddeley Trident was designed during the 1950s as a short & medium range jet airliner able to carry about 110 passengers. The design, at the time a de Havilland project (the DH 121), was the first airliner with 3 jet engines and the first tri-jet design with the engines all at the rear of the plane, this configuration was was also taken up by the 727 and Russian Tu-154.

The Trident 1, designed to a BEA (British European Airlines) requirement, first flew in early 1962. BEA had insisted on a smaller aircraft than originally envisaged (it could carry 98 passengers) unfortunately other potential customers like American Airlines wanted a bigger aircraft. American Airlines bought the 727 instead which ironically was much closer to the original DH 121 design than the Trident 1. The Trident entered service with BEA in 1964 and was the first civil aircraft fitted with a flight recorder and be equipped for automatic blind landings for use in adverse weather conditions such as fog. In 1966 the Trident was the first airliner to land in fog.

Throughout the 1960s there were continuous improvements to the design including the Trident 1E which was close to the original DH 121 size carrying 140 passengers and the 2E which had further capacity and extra range. The latter achieved a notable sale when 33 were ordered the Chinese national airline CAAC and Chinese air force. One Chinese Trident was lost in mysterious circumstances over Mongolia when Lin Biao was using it to try and defect to the USSR. The official story is that the Trident ran out of fuel. A Trident has also been left marooned at Nicosia International Airport which has been abandoned since 1974 due to the Turkish invasion of northern Cyprus.

The final version, the Trident 3 had a 5m fuselage plug and was able to carry up to 180 passengers. The Trident 3 was actually a 4 engined aircraft as it had a small RB162 turbojet which could be used for take-offs, the Tridents had a reputation for needing plenty of runway to get airborne so the extra boost was especially welcome in the larger Trident 3! The reason for the problems with take-off was that the wing was optimised for high speed (the Trident was one of the fastest subsonic jet airliners) and not lift at low speeds.

Trident development ceased in the early 1970s and small sales continued but total production of the Trident was just 117 when the last example was delivered in 1978. Although technically advanced the Trident was an expensive airliner to operate and had a rival with Boeing's marketing muscle and name behind it. The rival 727 had sales of 1832.

No Tridents are thought to be active today, British Airways who inherited the BEA fleet withdrew them in the 1980s though they remained in service in China until the 1990s. A number of Tridents have been preserved or are in use in various locations for fire training.

Monday, April 14, 2008

Supersonic synfuel and fuel cells

The US Air Force are moving into alternative jet fuel in a big way, indeed they want all of their aircraft to be certified to be able to use a 50:50 blend of synthetic and normal jet fuel by 2011. The B-52 and C-17 has already flown using this blend and the next step is the B-1 bomber which will soon make the first supersonic flight using the blend. The F-15 is also being tested.

The synthetic fuel is a gas to liquid fuel made by Shell, though in the longer term (i.e. 2016) the USAF want to use a coal derived synthetic fuel.

Boeing have also demonstrated a small motor-glider which was modified to fly under a combination of fuel cells and an lithium-ion battery. The battery was used to boost power at take off and landing though the motor-glider flew on fuel cell alone on level flight. Using fuel cells reduced emissions across the board (CO2, infrared and noise) though is expected to be used more for unmanned aircraft.