Downwash on tailplane

In the vast majority of aircraft the C of G (where the weights acts downwards) is forward of the wing C of P (where the lift acts upwards). This produces a pitching moment which tends to make the aircraft pitch nose downwards.

To maintain any given attitude the tailplane must produce a balancing nose-up moment, by generating a downward lift force. This downward tailplane lift depends upon the tailplane area, its angle of attack and the dynamic pressure of the airflow over it. In order to generate donwward lift the tailplane must be either of negative camber or at a negative angle of attack, or both.

The angle of attack of any aerofoil is the angle between its chord line and the relative airflow. If we start by imagining that the airflow approaches the tailplane in a horizontal direction, the tailplane will need to be set leading edge down (or elevators up), in order to give a negative angle of attack.

But the airflow rarely approaches the tailplane in a truly horizontal direction. Ths is because the generation of lift by the wing causes the airflow to be deflected downards behind its trailing edge. This downwashed airflow increases the negativity of the angle of attack of the tailplane.

The greater the lift being generated by the wing or the lower the aircraft speed, the greater will be the downash. So for any given elevator or tailplane angle, the angle of attack of the tailpane will vary with the amount of lift being generated by the wings and the aircraft speed. So when trimming the aircraft at any given combination of weight, C of G position and speed, the angle of the tailplane or elevators must take account of this downwashed airflow.

Downwash from the wings will also affect the way the aircraft responds to flap deployment. Deploying trailing edge flaps increases wing lift and downwash. Most of the extra lift is generated at the rear part of the wing, so the C of P moves aft. This tends to cause the aircraft to pitch nose down.

But the increased downwash increases the negativity of the angle of attack of the tailplane. This in turn increases tailplane down force thereby generating a nose-up pitching moment. If this increased nose-up moment is greater than the nose-down moment caused by the shifting of the wing C of P, then the aircraft will pitch nose-up when the flaps are deployed. This effect is most common in light aircraft where the tailplane is only a short distance behind the wings.

Another effect of the wing downwash is to reduce the effectiveness of the tailplane in providing stability in pitch
If an aircraft suddenly pitches nose up, the tailplane down force must reduce (or be changed into an up force) in order to return the aircraft to its original attitude. These changes in tailplane lift are produced by changes in its angle of attack.

As the aircraft pitches nose-up, the leading edge of the tailplane also pitches up (or at least less down), which tends to reduce its negative angle of attack. This tends to reduce tailplane down force, thereby allowing the aircraft to pitch nose-down back to its original attitude.

But the pitching up of the wing also increases wing lift and downwash. This increased downwash tends to reduce the changes in angle of attack of the tailplane. Try to visualise this situation looking at the aircraft from the left side. As the aircraft rotates nose-up (in a clockwise direction), both the tailplane chord line and the downwashed relative airflow also tend to rotate in a clockwise direction. So the changes in tailplane angle of attack are less than they would have been if the relative airflow had remained unchanged. The overall effect of the changing downwash is therefore to reduce the stabilising effects of the tailplane.

This is of course all a gross simplification whch (I suspect) will add to.

New Era of TUAVs

2001 was the year the tactical unmanned air vehicle (TUAV) came of age. The Israeli Defence Force deployed its first indigenous UAV, the IAI Scout, a quarter of a century ago. The IAI was a short-range, piston-engined tactical reconnaissance UAV with a limited sensor payload. But it was the Gulf war that saw growing awareness of the vehicle’s potential in limited war scenarios.

The US Marine Corps made extensive use of the IAI Pioneer and the hand-launched Pointer mini-UAV while the French army used its simple but effective MART Mk 1 to stand up to the rigours of desert operations.

The British had to rely on the 20-year-old Canadair CL-89 that was a recoverable jet-powered drone launched by a booster rocket. These systems, and others, including the French Fox AT-1 and the Bombardier CL-289 that were operated by the French and German armies, were also used in the various Balkans conflicts over the past decade. One lesson learned from these operations was that these first generation tactical UAVs were particularly vulnerable to cold and wet weather conditions and enemy ground fire. During the Kosovo campaign, a third of 30 allied UAVs were lost to non-combat related causes.

Three were the most advanced and successful TUAVs deployed in the Balkans including the USAF RQ-1A Predator. However, the twin-engine Hunter was less successful. It was developed by IAI and TRW and adopted by the US Army after a protracted development.

Planned as a joint army and navy TUAV, the programme cost the US Department of Defense (DoD) $700m before the naval variant was shelved and more than 50 air vehicles were put into storage. Since 1995, the DoD has spent nearly $5bn dollars on cancelled army and navy TUAV projects, and it was the Balkans conflicts that revitalised the Hunter programme even though eight were lost over Kosovo.

The US Army’s search for a viable TUAV was finally over in 1999 when the AAI Corporation won a $41m low-rate, initial production (LRIP) contract for its Shadow 200. Throughout 2001 the Army carried out necessary initial operational testing and evaluation (IOTE) trials. The full-rate production decision that covered a total of 44 systems worth more than $300m was delayed to the first quarter of 2002 due to a number of technical problems encountered with the Shadow 200.

When the Kosovo campaign ended in June 2000, there were other limited conflicts in the Middle East, west Africa and south-west Asia to open up new markets for UAVs.

In Europe, the Finnish Army took the plunge by ordering the Swiss Ranger system developed for the Swiss government with assistance of IAI. The French Sagem Sperwer short-range TUAV also has been delivered to the Swedish and Danish Armies.



UAV’s are being used in many locations, from Kosovo and Sri Lanka to Botswana

The Franco-German Piver/CL-289 has proved to be a reliable vehicle during its four-year deployment to Bosnia, Kosovo and Macedonia. By the middle of 2001, the German Army had carried out its 1,000th successful CL-289 launch and at the same time it was announced that EADS Dornier would upgrade 140 of the German and French Army TUAVs.

The Belgian Army followed the French Air Force in acquiring Hunter multi-payload short-range TUAVs. However, these were not the TRW variants used by the US Army. Instead, they were a version built by the Belgium Eagle Consortium that is an IAI/EADS partnership. A similar consortium will assemble the Eagle I MALE, based on the IAI Heron that France selected in June 2001. The Israeli UAV was chosen for the $45m contract in preference to the bid placed for the General Atomics Predator. This was ordered by Italy in 2000, and was to be built in France by Sagam as the Horus.

On the other hand, Israel continues to develop its UAV capabilities, as a manufacturer and an operator. IAI’s family of pusher piston-engine twin-boom designs have become the accepted standard of short-medium range TUAVs.

The current production versions of Searcher, Hunter and Heron all are being offered with enhanced payload packages that include SATCOM links and the ELTA EL/M-2055 synthetic aperture radar (SAR) that is able to provide an all-weather intelligence capability.

Israel’s other UAV manufacturer, Silver Arrow, is an Elbit Systems subsidiary that produces a small short-range TUAV recently sold to Botswana, and the Hermes 450 MALE. The latter can carry a 110kg (240lb) payload that incorporates SAR/GMTI and is supported by a compact multi-purpose advanced stabilised system (COMPASS). Data from COMPASS can be transmitted by SATCOM with all-weather detection of targets at non-line-of-sight ranges.

The Israeli Defence Force/Air Force (IDF/AF) currently operates a squadron of short-range Searchers and is now working up a second unit for the Hermes 450. It has over 25 years experience in operating indigenous UAVs, not only in Lebanon, but also along its borders with Syria and Jordan. More recently, Israel has been using UAVs against Hamas terrorists.

Kashmir, the infamous north-west frontier region that has caused two wars between India and Pakistan, has the potential to become an even larger conflict.

In an effort to increase surveillance along their borders, India and Pakistan are deploying TUAVs. Pakistan’s indigenous short-range Vector TUAV is being rushed into service while India has delayed the production of its twin-boomer, the Nishant. Instead, it has preferred to place a $300m order for Israeli UAVs.

This package will include six IAI Searcher II and four Heron HALE systems equipped with EO payloads for day and night missions. The deal also will incorporate the IAI Harpy that is a small delta-wing UAV designed to undertake suppression of enemy air defence (SEAD) missions. This ground-launched UAV can fly to a pre-programmed area where it loiters and seeks electromagnetic emissions. Once a target is detected, the warhead-equipped Harpy dives on it.

Sri Lanka, that lies south of India, has also acquired the IAI Searcher to aid its long-running fight against the Tamil Tigers. Following 11 September 2001, a larger conflict in south-west Asia has emerged.

After it had identified al-Qaida as the network behind the terrorist attacks on New York and Washington, the US embarked on a military campaign against Afghanistan’s ruling Taliban that it said was harbouring Osama Bin Laden. The campaign that was a combination of air strikes and special forces operations, also relied heavily on surveillance intelligence.

From the start of Operation Enduring Freedom, USAF deployed Predator systems to Uzbekistan and Pakistan. Taking advantage of the clear weather over Afghanistan, and the Taliban forces’ lack of air defence weapons, the RQ-1s were able to send back valuable real-time images round the clock.

Since the conflict in Kosovo, the Predators have had a series of upgrades. They include: enhanced IFF equipment, de-icing and turbo-charged engines and modifications to become unmanned combat air vehicles (UCAV).

In February 2001, the UAV was armed with an AGM-114 Hellfire anti-tank missile for a series of live-firing trials at the Nellis ranges using a ball turret to self-designate the laser-guided weapon. It was only seven months later, that armed Predators were being used in combat over Afghanistan.

In March 2001 upgraded USAF RQ-1Bs had been deployed to Macedonia to support yet another NATO peacekeeping force in the Balkans. At the same time the DoD decided to order seven additional RQ-1Bs for $39m as attrition replacements.

Future developments include provision for Predator to launch the Raytheon SilentEyes SUAV, a $5,000 unpowered glider used for spot surveillance or battle damage assessment (BDA).

The longer-range, greater endurance Predator B that powered a Honeywell TPE331-DT turboprop has already flown and a Williams Rolls FJ44-2 turbofan-powered version is scheduled to fly in 2002.

The UK and Australia may consider Predator B as part of their respective future offensive air capability (FOAC). The UAV may also be considered for Air 6000 programmes and even for the UK Watchkeeper project.

The latter is designed to replace the British Army’s Phoenix TUAV, that was deployed to Macedonia during the Kosovo campaign, and more recently to Oman during Exercise Saif Sareera II. It is also the result of a merger of the two programmes, Sender and Spectator, that are short and medium-range systems.

Two of the four bidding Watchkeeper teams, led by BAE Systems that includes General Atomics, Lockheed Martin, Northrop Grumman and Thales, will be selected in the first quarter of 2002. A preferred bidder will be announced by 2004 with an in-service date (ISD) of 2008.

Phoenix will be subjected to a series of upgrades that include Skynet 4 military SATCOM links and improved data links with other platforms such as the RAF Tornado GR.4A and British Army Apache AH.1 attack helicopter.

Another possible enhancement in the pipeline for Phoenix and other TUAVs is an automatic landing system under development by the Sierra Nevada company. The common automatic recovery system (CARS) is for Pioneer, Hunter and Predator, while the tactical automatic landing system (TALS) will be used for the US Army’s Shadow 200. These systems are designed to be integrated into the automatic return systems on datalink loss fitted to most UAVs currently in production.

Looking further ahead, several European countries are actively investing in families of related vehicles to include TUAV, MALE, HALE and UCAV. These include France’s Dassault, Sweden’s Saab and Italy’s CIRA. They are all working in the same direction, towards the possibility of some programmes being merged on economic grounds, or segments integrated into other programmes such as Watchkeeper.

At the moment it has been left to USAF to prove that the UAV is a valuable operational tool in America’s armoury against terrorism. Not only is the RQ-I Predator earning its keep, but it has been joined by its big brother, Global Hawk. Having approved initial engineering and manufacturing development (EMD) in March 2001, the US DoD announced the RQ-4A deployment to Afghanistan eight months later.

Source: www.global-defence.com/2002/surv-uav.html

India, Israel Partner To Develop Three New UAVs

India, Israel Partner To Develop Three New UAVs

By By VIVEK RAGHUVANSHI
Space News Correspondent
posted: 01 March 2005
03:54 pm ET

BANGALORE, India — India and Israel have entered into a new partnership under which Tel Aviv will help New Delhi in its development of remote vehicles.

A formal deal was signed at the Aero India 2005 exposition Feb. 9-13 here between senior officials of the respective defense ministries. Israel Aircraft Industries will assist the state-owned Aeronautical Development Establishment (ADE) here, India’s leading unmanned aerial vehicle (UAV) laboratory, to develop three new UAVs.

Moshe Keret, Israel Aircraft Industries’ chief executive, said Feb. 9 that UAVs are an important segment for collaboration, and the company will be working on defense research and development programs to benefit both countries.

A senior ADE scientist on Feb. 10 said ADE and Israel Aircraft Industries will work to develop three remotely piloted vehicles: the Rustam medium-alti¬tude long-endurance UAV, the Pawan short-range UAV and the Gagan tactical UAV.

Currently, all of India’s UAV needs are met by Israel, and this partnership will ensure that will continue to be the case for at least the near future.

The $100 million Rustam UAV development program will begin officially in June, although work already has begun on planned subsystems. The ADE scientist said this drone is the test case for the overall joint UAV development program. Israel Aircraft Industries and ADE have begun preparatory work that involves testing major subsystems on a manned aircraft here.

The Rustam will be able to remain aloft for more than 24 hours and have a range of up to 300 kilometers and a maximum altitude of 10,000 meters. It will be able to use satellite links to transmit data, thereby extending its surveillance range beyond 1,000 kilometers.

The 1,100-kilogram UAV also will be equipped with a maritime patrol radar and electro-optic sensors from Israel, and an engine still to be determined. The electronic warfare and communications system will be indigenous.

This UAV will be used by India’s three military services and will not be exported, the ADE scientist said.

The Rustam program is likely to be completed in 48 months, during which four prototypes will be produced.

Development of the short-range, vehicle-mounted Pawan is expected to cost $33.2 million. Meant to equip Indian army divisions, the Pawan will be comparable in size and capabilities to Israel’s Eye View, Hermes 180 and Silver Arrow drones, the scientist said.

The 120-kilogram Pawan will have day-and-night surveillance capability, an endurance of five hours and a range of 150 kilometers.

ADE plans to build four Pawan prototypes under this development program, with Israel Aircraft Industries electro-optic sensors for the payload and its own stabilizer platform. The engine will be purchased from outside India.

The ADE scientist said the Defence Ministry will approve the funding in April, and the four prototypes are likely to be completed within 24 months.

The $55.5 million Gagan UAV pro¬gram will feature development of an advanced version of India’s Nishant UAV.

The Gagan UAV will have a range of 250 kilometers and an altitude of 6,000 meters.
ADE will procure synthetic aperture radar and electro-optic sensors from Israel, and develop its own electronic countermeasure systems.

ADE is likely to get the funding clearance in May, and four prototypes will be built within 42 months.

source: www.space.com/spacenews/archive05/israelindia_022805.html