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Posts Tagged ‘SAAB Gripen’

A fighter for Canada

Posted by picard578 on December 21, 2015

Introduction

Canada is a Western country that at the first look has most at common with Russia. It is huge, but vast majority of its population is concentrated in a narrow swath of land to the south, near the US-Canadian border. It borders United States to the south and west, while to the east is rest of the NATO and to the north is inhospitable Arctic, with its vast natural riches and strategic importance.

Defense of northern Canada depends mostly on three or four forward operating locations – fourth one is the only with permanently assigned squadron, and that one consists of transport aircraft. Only the far east and south of Canada have proper air bases. CF-18s are based in Bagotville to the extreme south-east and Cold Lake to the south-west. Extreme north is patrolled by long-range patrol squadrons using CP-140 Aurora aircraft; no fighter aircraft are present there on a continuous basis, despite primary mission of Canadian fighter jets being to patrol Canadian airspace. Main warning system is a chain of radar stations making up the North Warning System (DEW Line). Read the rest of this entry »

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Gripen C upgrade proposal

Posted by picard578 on December 20, 2014

Introduction

Similar to the F-16 upgrade proposal, this proposal will take an existing aircraft – Gripen C – and adress its greatest shortcomings with minimal redesign. Read the rest of this entry »

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Comparing modern fighter aircraft

Posted by picard578 on August 30, 2014

Nature of air to air combat

“Those who cannot remember the past are condemned to repeat it.”

—G. Santayana

Fighter aircraft exist to destroy other aircraft, and allow other aircraft to carry out their missions without interference from enemy fighter aircraft. That being said, there exists a colloqial – and incorrect – use of term “fighter aircraft” as being applicable to any tactical aircraft, even those that are primarly or exclusively designed for ground attack, such as the A-10 and the F-35. Task of the aircraft is to enable pilot to bring weapons systems in position for a successful kill.

You never make a big truck and tomorrow make it a race car. And you never can make a big bomber and the next day a . . . fighter. The physical law means that you need another airplane. . . . You should do one job and should do this job good.

—Colonel Erich “Bubi” Hartmann, GAP Read the rest of this entry »

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Aircraft signature reduction measures

Posted by picard578 on March 9, 2014

Rafale

rafale1 Read the rest of this entry »

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Usefulness of thrust vectoring

Posted by picard578 on April 13, 2013

With introduction of thrust-vectoring F-22 and Su-35, many claims have appeared, such as that thrust vectoring aircraft are most maneuverable in the world and that addition of thrust vectoring alone guarantees that fighter in question will be unrivalled in maneuverability, excepting of course other thrust vectoring aircraft. These claims hold that addition of thrust vectoring by itself is enough to turn otherwise-sluggish fighter aircraft into supreme air-to-air machine. Things are more complex than that, however; effectiveness of thrust vectoring depends on aircraft’s aerodynamic configuration, speed and altitude.

To discuss thrust vectoring, we must first know how non-TVC aircraft behave. Major parameters that impact aircraft’s performance are:

  1. weight
  2. lift, which can be approximated through wing loading
  3. excess thrust, determined by thrust to weight ratio
  4. drag

One of advantages of thrust vectoring is allowing aircraft to enter and recover from a controlled flat spin, yawing aircraft without worrying about rudder, which looses effectiveness at high angles of attack. However, aircraft using close coupled canards instead of thrust vectoring have also demonstrated flat spin recovery capability, example being Saab Gripen. But while thrust vectoring reduces drag during level flight, thus increasing the range, close-coupled canards add drag and decrease lift unless aircraft is turning, thus improving the range.

But to see what impact thrust vectoring has on combat performance, we have to take a look at parameters I have defined above. Mass of aircraft determines inertia – thus, heavier the aircraft is, longer it takes to switch from one maneuver to another quickly. This results in slower transients, making it harder for pilot to get inside opponent’s OODA loop – in fact, mass is defined as a quantitative measure of an object’s resistance to acceleration (to clear common mistake in terminology, acceleration can be in any direction – in fact, what is commonly called “deceleration” is mathematically defined as “acceleration”). But to actually turn, aircraft relies on lift. Lift is what allows aircraft to remain in the air, and when turning, aircraft uses control surfaces to change direction in which lift is acting, resulting in aircraft turning around imaginary point. It can be approximated by wing loading. But turning leads to increase in angle between air flow around the aircraft and the aircraft itself (this angle is called Angle of Attack), which results in increased drag. Increasing drag means that aircraft looses energy faster, and once fighter’s level of energy decays below that of his opponent, he is fighting at disadvantage. Loss in energy can be mitigated by excess thrust, which can also be used (usually in combination with gravity, aka downwards flight) to recover lost energy. All of this leads to expression “out of ideas, energy and altitude”, which basically means “I’m in trouble and have no way out”. Nose pointing allows aircraft to gain a shot at opponent with gun, and was crucial for gaining a shot at opponent with missiles before advent of High Off Bore capability, which shifted requirements more in direction of ability to sustain maneuvers at or near corner speed (minimum speed at which aircraft can achieve maximum g loading; it is usually around M 0,6 – 0,9). It must be noted that, while lift and excess thrust of aircraft can be approximated by wing loading and thrust to weight ratio, heavier aircraft will require higher thrust to weight and lift to weight ratios to achieve same turn rates as lighter aircraft.

Thrust vectoring, as its name says, results in shifting of the thrust. Due to modern fighter aircraft’s center of gravity and center of lift never being behind its nozzles, shift in thrust results in aircraft rotating around its center of gravity, resulting in massive increase in Angle of Attack. Thus, comparision non-TVC aircraft turning and TVC-equipped aircraft turning would look like this:

TVC

This is result of forces described above acting on aircraft. In this model, assumption is that aircraft can reach angle of attack required for maximum lift both with and without thrust vectoring, which is true for all close-coupled-canard aircraft, but not necessarily for tailed and long-arm canard arrangements.

Thus, forces impacting turn ability of non-TVC and TVC aircraft would look like this:

forcesforces_resultants

It can be seen that thrust vectoring increases angle of attack, and thus drag (as entire airframe at high AoA drags far more than just control surfaces plus airframe at far lower AoA), while reducing thrust avaliable to counter the drag – and, in case of very high AoA values, lift avaliable to pull aircraft around. While TVC can improve turn rate even at combat speeds, it happens only if aircraft is unable to achieve angle of attack that is required for maximum lift, one example being F-16, which requires 32 degrees AoA for maximum lift but is restricted to 25,5 degrees by FCS due to departure concerns. Angles of attack in excess of 35 degrees are unsustainable, however, due to massive drag they cause, resulting in very large energy loss, turning fighter into a deadweight in very short order. “Benefit” of extreme AoA values is also not unique to thrust vectoring aircraft: while TVC-equipped X-31 achieved maximum controllable angles of attack of 70 degrees (compare to 60 degrees for another TVC design, F-22), whereas close-coupled-canard delta-wing Rafale and Gripen are able to achieve controllable Angles of Attack that exceed 100 degrees, with Gripen being able to sustain Angle of Attack of 70 – 80 degrees. Further, X-31 without TVC was unable to achieve more than 30 degrees of alpha, even momentarily, whereas without TVC F-22 is limited to 26 degrees, though not due to issues of lift but rather controllability. As such, TVC actually improved instanteneous (and possibly sustained) turn rates of both aircraft by allowing them to reach angle of attack required for maximum lift, which is between 30 and 40 degrees of AoA. Aircraft that use TVC during combat to achieve angles of attack beyond lifting capability of wing actually sink in the air, as opposed to turning, but if they are unable to achieve maximum lift capability without TVC, then TVC does indeed improve their turn capability. Close-coupled canard configuration, on the other hand, drags less in turning than TVC one as it achieves same lift at lower angle of attack, resulting in far lower fuel consumption. This is important as in visual-range fight, most kills have been historically made when one of aircraft fighting ran out of fuel; thus aircraft with less fuel consumption per unit of weight is (assuming similar fuel fraction) more likely to win the fight. Specifically, maximum lift for close-coupled canard is greater than that for just wing at any AoA past 10 degrees AoA; in configuration analyzed in this thesis, lift is greater than baseline value by 3,4% at 10 degrees AoA, 34% at 22 degrees AoA, 9,4% at 34 degrees AoA, 7,2% at 40 degrees AoA and 18,3% at 48 degrees AoA. Thus aircraft does not need to achieve as high AoA for same lift to weight and lift to drag values, consequently allowing pilot a choice (assuming other values are similar) wether to achieve same turn rate as opponent and outlast it due to using up fuel far slower than it is case with fuel-hungry thrust vectoring maneuvers or try to outmaneuver it with higher turn rate.

Neither is main “benefit” of thrust vectoring, post stall maneuverability, anything new. Aside from close-coupled canard designs, which have extensive post-stall maneuverability, Russian Su-27 has demonstrated stall recovery capability and post-stall maneuverability. It is also important to note that John Boyd was able to do Cobra in F-100, and other pilots did it in J-35 Draken. While TVC certainly improves post-stall capability, capability by itself is useless in multi-bogey scenario, as it bleeds energy very fast. As such, thrust vectoring is tactically useless for most fighter aircraft, especially in age of high-off bore missiles, as usage of thrust vectoring would leave then slow-moving aircraft very vulnerable. Further, Cobra – one of main “poster maneuvers” for TVC – is easy to see in advance, and if done, leaves fighter without energy and at opponent’s mercy; so while usage of TVC may surprise pilots that do not know what it allows, it is suicide agains pilots that are aware of it.

TVC does not necessarily increase security either, as resistance to departure and superstall which it provides are inherent advantages of close-coupled canard designs. However, it does allow non-close coupled canard configurations to recover from these conditions.

Using TVC for maneuvering is beneficial for tailed aircraft, however, at two regimes: at velocities well below corner speed, and during supersonic flight at high altitudes. Simple reason for that is that in these two regimes, flight surfaces are not very effective. At very low speeds (150 knots – M 0,23 – and below), large control surfaces’ deflections are required for turning due to weak air flow, thus increasing drag – and even when surfaces are fully deflected, aircraft responds comparatively slowly. This also includes takeoff and landing; as result, aircraft with thrust vectoring can take off and land at lower speeds and in shorter distance than same aircraft without thrust vectoring; this capability can be useful if parts of air strip have been bombed (though it is always smarter not to require air strip at all). During supersonic flight, tail finds itself in wake behind the wing, which reduces its effectiveness. Thus thrust vectoring can be used to compensate for this effect. Further, at high altitudes (12 000 to 15 000 meters) aerodynamic control surfaces are less effective, and there is less drag, which means that thrust vectoring provides greater benefits and less penalties. As dogfights happen at altitudes of 1 500 to 10 000 meters, and speeds that start in transonic range, thrust vectoring is obviously not effective for WVR – and, therefore, real world combat.

In level flight, thrust vectoring allows for trimming, thus increasing range due to reduced drag. 3D TVC nozzles can also reduce drag by optimising their shape. Further, thrust vectoring can add STOL capability to otherwise-CTOL aircraft, but it is always better to look at simpler, lighter and cheaper options. If aircraft lacks roll authority, TVC can be used for pitch, freeing up tail control surfaces to improve roll rate – examples of this are F-22 and Eurofighter Typhoon.

TVC (especially of 3D variety) can also provide ability to quickly point nose in a certain direction, but this is only useful in one-on-one gun-only dogfights (which do not happen in real world) as it leaves aircraft with seriously depleted energy and thus vulnerable to opponent’s wingman, and/or its target if attack was not successful. This is especially problematic in age when HOB capability is becoming increasingly common. But even in such unrealistic dogfights, TVC does not garantee victory. In upper set of images, F-22 is seen from Rafale, pulling a turn; OSF is clearly visible, showing that Rafale’s nose is pointed towards the F-22 (allegedly, Rafale won 2 out of 7 engagements; further, while IRST does have high off-bore capability, video camera is fixed):

rafale F22

F-22 does have major advantage in thrust-to-weight ratio over Rafale, however, allowing it to recover some of energy lost through TVC usage simply by flying straight and level for short time. But against aircraft with higher thrust-to-weight ratio, TVC usage will be even more problematic.

As for air shows, in this video, at 0:50, MiG-29 can be seen doing Cobra:

http://www.youtube.com/watch?v=ra3sr4HqF3E

At 1:54 and later, several S-35 Drakens can be seen doing Cobra:

http://www.youtube.com/watch?v=jqiDEcfSnXs

Reason is simple: while TVC-aircraft relies on TVC to provide both lift and forward motion, close coupled canards allow for lift production beyond 100 degrees of alpha, while forward motion is provided by inertia. Energy loss is high, but so it is with thrust vectoring, and neither version of Cobra has any real tactical application.

Edit 19. 6. 2013.

Here is link to a video recording of DACT from which upper row of screenshots in image comes (thanks to Jeneso):
http://www.youtube.com/watch?feature=player_embedded&v=oGuWadoTgkE

Another one (just recording):

www.youtube.com/watch?v=B4rNPouCggk&feature=player_embedded

Edit 22. 8. 2013.

mwuzi1

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Saab Gripen vs F-35

Posted by picard578 on March 16, 2013

AIRFRAME PERFORMANCE

Contrary to some claims, F-35 has rather simple and conventional aerodynamics. Basic configuration is similar to F-16, however lack of LERX, and use of lower-performance but stealth-friendly chimes for high AoA lift enhancement, means that it will have far less body lift than F-16 to help compensate for its high wing loading, and wing lift will also be smaller at high AoA. Result will be (for a modern fighter) disastrous turn rate.

Further, it has internal carriage, which adds drag compared to low-drag AAMs and pylons, and its far higher weight also means more inertia that has to be overcome.

Gripen is, on the other hand, built for maneuverability. Close-coupled canards, wing-body blending, and wing shape all help increase lift during maneuvers, allowing aircraft to both achieve higher angles of attack, and to turn tighter at same angle of attack. Particularly canards create vortices that reattach air flow to the wing at high angles of attack. Aside from helping air flow over the wing, Gripen’s canards also help air flow over the body. Canard also has advantage over tail as the control surface – as center of gravity for modern aircraft is towards rear of the aircraft, usage of canard results in longer moment arm than it is case with tail. Further, Gripen has large degree of wing-body blending, and it’s wing loading is also far lower than that of F-35.

While thrust-to-weight ratio is below 1 for both aircraft, Gripen has far lower drag than F-35, partly compensating for F-35s superior thrust-to-weight ratio. While F-35 achieves maximum of Mach 1,6, clean or not, Gripen can achieve speeds of over Mach 2 clean.

SITUATIONAL AWARENESS

First thing that can be noticed about both Gripen and F-35 is that neither has rearward visibility from cockpit. In Gripen’s case, attempt was made to attenuate the problem by installing rear-view mirrors onto the canopy forward frame. However, while Gripen’s visual and IR signatures are far lower than F-35s, Gripen itself does not have IRST, which means that F-35 may be able to detect it first.

WEAPONS

In gun department, Gripen uses German BK-27, a 27-milimeter revolver cannon which was also supposed to be equipped to F-35, but in the end, F-35 received 25-milimeter rotary-barrel GAU-22. In air-to-air combat, BK-27 has a large advantage over GAU-12 in that delay between pilot pressing the button and full rate of fire being achieved is just 0,05 seconds, as opposed to 0,4 seconds for GAU-22. Further, on F-35, trap door must open if gun is internal (and assuming it wasn’t open already), possibly adding another 0,5 seconds to process. Maximum rate of fire is 1 700 rpm for BK-27, and 3 300 rpm for GAU-22. Muzzle velocity is 1 025 m/s for BK-27 and 1 040 m/s for GAU-22, but BK-27s shells – weighting 260 g as opposed to GAU-22s 184 g for HEI and 215 g for AP – will bleed off speed slower, and be less affected by wind and other air turbulences.

Therefore, in first half of second – which is crucial in dogfight; rarely will opponent fly in the same directon for full second or more – BK-27 will fire 14 projectiles massing 3,64 kilograms, and GAU-22 will fire 16 projectiles massing 2,94 – 3,44 kilograms, but only assuming that F-35 pilot opened gun doors beforehand – if he didn’t, GAU-22 will not fire any projectiles at all. GAU-22 may be a sign that US have (finally) understood that 20 mm cannons are not sufficient for modern air-to-air combat, similar to WW2, when they delayed introduction of 20 mm cannons instead of 50 caliber machine guns as main fighter armament well into Korean War. However, it is more likely that it was thought of as compromise between air-to-air and air-to-ground combat, considering that F-35 is primarly ground attack aircraft.

FORCE PRESENCE AND SUPPORTABILITY

While F-35A costs 197 million USD flyaway, Gripen C costs 40 million USD flyaway. As such, Gripen can provide almost 5 times as large force as F-35A can. Further, due to Gripen’s lower maintenance and turnaround times, same force will be able to fly far more sorties. Gripen is also designed to operate from roads, and has STOL capability, something that F-35A lacks, though not the (even more expensive) F-35B.

5-TH GENERATION?

According to this article, Lockheed Martin’s definition of 5-th generation fighter is following:

— stealth
— high maneuverability
— advanced avionics
— networked data fusion from sensors and avionics; and
— the ability to assume multiple roles.

Comparing F-35 and Gripen, it can be seen that while F-35 is stealthier on radar, Gripen has far lower IR and lower visual signature. Unlike F-35, it also has high maneuverability, and both aircraft have advanced avionics and multirole capability, while networked data fusion will be avaliable on Gripen NG. F-22 has high maneuverability but is not multirole, while Rafale and Typhoon only lack stealth. Thus, F-22, F-35, Typhoon, Rafale and Gripen NG are all equally 5-th generation aircraft, with Gripen C/D being just one step away.

And while another article defines fifth generation fighter as “being able to operate in anti-access environment featuring integrated air defenses…”, that capability can also be achieved in several ways, radar stealth being just one aspect of survivability, and rather limited one considering proliferation of passive sensors.

Further reading

Comparing modern Western fighters

Comparing modern fighter aircraft

Dassault Rafale vs F-35

Fighter aircraft engine comparison

Fighter aircraft gun comparison

NATO main battle tanks comparison

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Saab Gripen analysis

Posted by picard578 on February 16, 2013

Program history

SAAB Gripen is a result of relaxed-stability fighter rush initiated by (at the time) revolutionary F-16 fighter aircraft. It is not surprising that SAAB opted for delta-canard layout they themselves pioneered in 1960s, but other options were also evaluated (and rejected). This was influenced by testing programme of Viggen in late seventies, which verified benign high AoA characteristics of the layout. To Sweden, choice of small, cheap but highly capable fighter aircraft was obvious.

In 1979, after cancellation of too expensive B3LA project (a development of subsonic trainer and light attack aircraft), Swedish Air Force carried a reexamination of its requirements. Conclusion was that only affordable option was development of multirole aircraft capable of carrying out air superiority, ground attack and reconnaissance missions. Thus the JAS programme was born, drawing name from specified requirements (Jakt – fighter, Attack – attack, Spaning – reconnaissance).

In March 1980, Government endorsed the plan, but insisted that foreign contractors should be allowed to bid for the contract. As a response, Swedish (state-owned) aircraft industry formed a JAS Industry Group, comprising Saab-Scania, Volvo-Flygmotor, Ericsson Radio Systems and FFV to manage the bid by Swedish industry. Formal proposals were requested in 1981, and JAS IG submitted their proposal on 1 June 1981. After evaluation of proposals, it was decided to go forward with JAS proposal. On 30 June 1982, a fixed-price proposal was signed between the FMV and IG JAS for 5 prototypes and 30 JAS-39A aircraft. Following month, name Gripen was selected for the aircraft.

Ericsson was tasked with developing multi-mode radar, while FFV developed navigation and attack systems.

Mock-up of the final design was unveilled in early 1986. However, development of Flight Control System caused delays in final assembly of the aircraft, with first Gripen rolling out of assembly on 26 April 1987, after 7 years of development. First flight was achieved on 9 December 1988, but after its sixth flight, on 2 February 1989, aircraft veered off the runway and carwheeled. Following that, FCS was fixed, and on 4 May 1990, JAS-39-2 flew with new software. Fifth and final prototype flew on 23 October 1991. Testing showed drag to be 10% lower than predicted, and airfield performance was also better than specifications. In June 1992, contract for second batch of aircraft was approved.

On 4 March 1993, first production Gripen (JAS-39-101) made its flight, with second production aircraft delivered for service testing on 8 June 1993. It soon crashed during air display over Stockholm due to the pilot loosing control and having to eject. Following the accident, further flight testing was suspended until FCS was revised. Revisions included changes to canard deflection angles in combat mode. Testing continued on 29 December 1993.

One JAS-39A was converted from production line to serve as prototype for twin-seated trainer, JAS-39B. It features 65,5 cm fuselage stretch, and rear cockpit that is, except for lack of HUD, identical to the front one.

On 12 June 1995, SAAB and British Aerospace announced joint development of export variant. In 2001, joint venture was registered in Sweden as Gripen International. As Gripen was designed solely for Sweden’s needs, Export Baseline Standard was developed, resulting in C and D variant of the aircraft. Soon, Swedish Air Force decided to also acquire the new version, with last 20 aircraft of Batch 2 and 30 aircraft of Batch 3 conforming to EBS specification.

EBS featured retractable inflight refuelling probe on the port air intake, full-color English-language cockpit displays in Imperial units, new computers, night-vision compatible cockpit lightning, FLIR and reconnaissance pods, more powerful air conditioning system, OBOGS and stronger wings with NATO standard pylons.

In December 2004, BAe sold large portion of its stake in Gripen International to Saab, finally selling remaining 10% of their stake to Saab in June 2011. On 26 April 2007, Norway signed an agreement on common development of aircraft, with agreement between Saab and Thales Norway following in June, concerning development of communications systems. In June 2007, NATO Link 16 was added to datalink systems of Gripens in Swedish service.

On 23 April 2008, Gripen Demo (requested in 2007) was presented, serving as demonstrator for Gripen NG. On 27 May 2008 it had maiden flight, and demonstrated supercruise ability on 21 January 2008, flying at Mach 1,2 without reheat.

In 2010, Sweden awarded 4-year-contract for improving Gripen’s radar and other equipment. On 25 August 2012 Sweden announced plan to buy 40-60 Gripen NGs, following Switzerland’s decision to buy 22 Gripens of the same variant. On 17 January 2013, Sweden’s government approved decision to buy 60 Gripen E’s, with first deliveries in 2018.

Unlike with Viggen, Gripen’s test flights revealed no aerodynamic, structural or engine deficiencies; in fact, all of them were better than predicted. Only structural “fix” was added strake behind each canard surface.

Basic data (Gripen C)

Length: 14,1 m

Wing span: 8,4 m

Height: 4,5 m

Wing area: 25,54 m2; 30 m2 with canards

Wing loading:

326 or 383 kg/m2 with 100% fuel, 4 AMRAAM and 2 Sidewinder

287 or 337 kg/m2 with 50% fuel, 4 AMRAAM and 2 Sidewinder

266 or 313 kg/m2 with 50% fuel and 2 Sidewinder

(*depending on wether canards are counted)

Thrust-to-Weight ratio: (80,51 kN – 18 100 lbf – thrust)

0,95 with 50% fuel, 4 AMRAAM and 2 Sidewinder

Fuel fraction:

0,27 (6 622 kg empty, 2 400 kg fuel) – 2 270 kg fuel was for A version’s “peace setting”; C version has only war setting

Weight:

6 622 kg empty

7 997 kg with 50% fuel and 2 Sidewinder

8 605 kg with 50% fuel, 4 AMRAAM and 2 Sidewinder

14 000 kg max takeoff

Maximum AoA:

>100 degrees (aerodynamic limit)

50 degrees (FCS limit)

Speed:

Mach 2,0 dash

Mach 1,15 cruise

Combat radius:

Ground attack, lo-lo-lo: 650 km

PS-05/A:

Range: 120 km vs 5m2 target (80 km vs 1m2 target)

Operational G capability: 9 g

Flyaway cost: 38 to 44 million USD (in FY 2013 dollars)

Cost per flying hour: 4 700 USD

Design

General

Saab Gripen is designed as a lightweight, highly maneuverable fighter. Close-coupled canard + delta wing arrangement was chosen to optimize maneuvering performance while also providing acceptable strike capabilities. Testing programs have verified excellent recovery capabilities for both Gripen versions. Further, delta canard configuration has inherently good battle damage tolerance due to “overlapping” surfaces, as well as positive trim lift on all surfaces, high maximum lift coefficient, good air field performance, and spin recovery capability. Floating canard also offers stable aircraft if EFCS fails.

To minimize weight, 30% of the structure is carbon-fibre composite. Aircraft is inherently unstable, and SAAB claims that it is first inherently unstable canard fighter to enter production.

While Gripen has low wing loading and good lift at high angles of attack, as well as relatively short wingspan, its thrust to weight ratio is below 1 at combat weight. Aircraft has operational service life of 8 000 flight hours.

Fuselage

One of things that can be noticed is large degree of wing/body blending, similar to F-16, which results in higher lift during maneuvers, as well as little or no interference drag that usually originates from wing-body juncture. Only exception to that are intakes, which are in side arrangement, with flat surfaces used for mounting canards. Body itself, having a “waist” noticeably thinner than parts immediately in front or aft of it, is clearly designed for transonic maneuvre.

Two small strakes are visible on the upper fuselage, located just behind canard surfaces, and single strake can be seen at bottom of fuselage; their purpose is to help enhance directional and lateral stability at high angles of attack.

Canards

Saab Gripen has canards that are relatively large compared to the wing. Canards are positioned close in front and slightly above the wing, and are tilted upwards, with large sweep-back. Location of canards at sides of air intakes prevents obstruction of air flow.

Primary purpose of close-coupled canards is not to act as control surface, but to increase lift at high angles of attack, where aircraft relies mostly on vortices to provide lift, by strengthening vortices generated by the wing and preventing their breakdown. Size and angle of Gripen’s canards are used to achieve as good as possible separation – vertical and horizontal – between canard’s tip and wing’s lifting surface, thus allowing for maximum vortex lift during high-alpha maneuvers – improvement of lift due to the close coupled configuration could be up to 50%, when compared to lift produced by surfaces in isolation. While thrust vectoring only increases maneuverability at very low speeds, and in supersonic regime, close-coupled canards are effective at any speed, though level of effectiveness varies with speed. As such, aircraft with close-coupled canards can have smaller wings for same lift at higher AoA (improving roll rate), being able to turn tighter at any air speed than otherwise possible with same wing size and angle of attack value, and achieving higher instantenenous turn rate. This also means that aircraft will be able to have lower wing span for same wing sweep and lift values, improving roll rates; smaller wing and reduced angle of attack also mean reduced drag when turning, allowing fighter to maintain energy better. However, downwash from canards also reduces wing lift at low angles of attack, reducing maximum payload fighter can carry.

Compared to LEX, canards are more versatile. Aside from being able to act as a control surface, canards can adjust position so as to produce maximum lift at any given angle of attack.

While Gripen managed to achieve angles of attack between 100 and 110 degrees during flight testing, normal AoA limit is 50 degrees as extremely high AoAs have no tactical use. Further, position of canards contributs to the fuselage lift of the fuselage just behind the canards during the turn, and canards themselves create lift, both in level flight and in turn.

Canard also has advantage over tail as the control surface – as center of gravity for modern aircraft is towards rear of the aircraft, usage of canard results in longer moment arm.

Canards can be tilted forward to nearly 90 degrees in order to aid braking during landing.

Wing

Wing itself is standard delta wing, offering large surface area, large volume and high strength for its weight. Shape of the wing ensures creation of vortexes at high angles of attack by wing’s leading edge, improving lift; wings are also equipped with small LERXes to strengthen said vortices. Another high lift device are leading edge flaps, which are used to increase lift at high AoA. When deployed during high-alpha maneuvers, flaps improve lift; however, they can also cause vortex breakdown. They also redirect air flow towards root of the wing, countering the tendency of air flow over delta wing to move towards wing tip. While usage of flaps can reduce drag, it only happens at speeds near stall speed, while in most other cases they increase drag. When flaps are not deployed, dogtooth leading edge configuration results in creation of single strong vortice at each wing, helping lift by countering tendency of delta wings to move air flow towards wing’s tips, and leave rest of the wing in stall. Wing is neither anhedral or dihedral, being located at half of the hull height. Due to wing’s (lack of) thickness, external actuators are required to control elevons.

Due to the Gripen being aerodynamically unstable aircraft, usage of delta wing also results in large trimmed lift during level flight, improving maximum lift by 10-20%, possibly more. Combination of close-coupled canards and low wing loading further improves air field performance, allowing for STOL capability.

While mechanism of lift creation at high AoA create additional drag, they increase lift and thus turn rate. But what some ignore while talking about drag “penalty” of close-coupled arrangement is that flow separation, aside from causing loss of lift, also causes major increase in pressure drag.

Rail launchers are located at wing tips, improving weapons loadout and allowing two missiles to be carried with minimum increase in drag, as well as improving lift/drag ratio of the wing.

Air intakes

Gripen’s air intakes are two-dimensional intakes, similar to those used at RA-5C. Intakes are separated from aircraft’s surface by fuselage boundary layer splitter plate, and provide adequate handling of fuselage boundary layer. High-alpha testing revealed no deficiencies in intake performance.

Fin

Tail fin is small relative to fighter’s size, compared to that of other Eurocanards and F-16. This might theoretically result in problems at high AoA; but usual way to change direction of aircraft is to rotate around X axis and pull nose up, and Gripen has additions on lower surface that may make fin unnecessary for directional stability.

Cockpit

One of major downsides of Gripen is its cockpit. While it allows good forward and side visibility, rearward visibility is very limited. This is dictated by its strike requirements, where exhaust from cooling unit is located behind cockpit to hide it from ground-based IR sensors. While SAAB did attempt to attenuate the problem by installing mirrors on forward canopy frame, it is only a partial solution.

Cockpit originally featured three monochrome multi-function displays, and wide-angle holographic HUD. It also has HOTAS controls that allow pilot to select many functions without lifting hands off the control stick or throttle. Ejection seat, unlike in previous aircraft, is not SAAB’s, but from Martin-Baker.

Engine

Engine is based on General Electric F-404 engine. Version used in Gripen, lincense manufactured by Volvo, had thrust boosted from 16 000 to 18 000 lbf (that is, from 7 257 to 8 165 kgf).

Operational characteristics

Gripen is capable of taking off and landing on roads, and could be capable of using unpaved runways. It can take off from 800 meter long snow-covered landing strips. Landing distance is reduced to 500 meters through usage of canards as air brakes, which is activated automatically when nose wheel establishes ground contact, as well as usage of elevons and large air brakes located at each side of fuselage behind the wing.

Further, it can be maintained by team of one specialist and five minimally-trained conscripts, and has very good combat turnaround time – less than 10 minutes. Gripen requires 10 man hours of maintenance for each hour in the air, and mean time between failure is 7,6 flight hours. Engine can be changed on road by 5 people in less than one hour. Airplane’s on-board systems include built-in “self-test” capabilities, with data being downloaded to technician’s laptop. All service doors to critical systems are at head level or lower for the easy access. Result is that Gripen requires only 60% of maintenance work hours of Viggen.

Aside from providing superior agility, Gripen’s FBW system is capable of automatically compensating for combat damage, including disabled or destroyed control surfaces – for example, using canards if aelirons are disabled.

Handling

Due to its aerodynamic layout, Gripen can be “parked” at 70 to 80 degrees of alpha. When giving adverse aeliron input, flat spin starts at up to 90 degrees per second rotation, and can be stopped by pro aeliron input. Aircraft has demonstrated spin recovery capability for complete cg and AOR range, as well as control capability in superstall, allowing recovery. During the spin testing, in one occasion when spin entrance was gained by wild maneuvering in afterburner, surge in thrust was recorded at high AoA and side-slip angles, but was immediately followed by instant recovery to full power.

Aircraft has operational G load limit of 9, and ultimate limit of 13,5 Gs.

Weapons

Gripen is armed with single Mauser BK-27 cannon, housed in a fairing on port side of aircraft’s belly (can be seen here). It currently also uses Sidewinder IR AAMs, though these are to be replaced with IRIS-T missiles. BVR missile is AIM-120 AMRAAM, though aircraft is also capable of using MBDA Meteor, Matra Mica, and BAe Sky Flash (built in Sweden as Rb-71).

For anti-ship combat as well as ground attack, it can carry SAAB RBS-15 missile (though only Mk3 version of the missile supports land attack missions). Dedicated air-to-ground missiles are AGM-65 Maverick (built in Sweden as Rb-75).

Fact that Gripen uses revolver cannon is a large advantage over aircraft using Gattling guns: while Gattling guns typically take 0,5 seconds to achieve full rate of fire, revolver cannons take only 0,05 seconds. As such, while M61A1 will fire 25 rounds in first half of second, weighting total of 2,5 kg, BK-27 will fire 13,45 rounds, weighting total of 3,5 kg. Larger caliber also ensures greater damage-per-hit, important due to stronger airframes of modern fighters.

Aside for gun, Gripen also has 6 missile hardpoints on wings. Two of these are in wingtip configuration, ensuring minimal drag in flight, while other four are mounted on low-drag pylons. Another hardpoint is located at the bottom of aircraft’s hull in centerline configuration. It is usually used for fuel tank carriage, though it can also carry targeting pods as well as ground attack ammunitions.

Sensors & EW suite

Gripen is equipped with radar PS-05/A, that is capable of detecting targets with RCS of 5 m2 at distance of 120 kilometers, which translates into 80 kilometers against 1 m2 target.

EW suite is built around AR-830 Radar Warning Receiver, with receiveing antennas at front and back of missile launch rails. BOL dispensers are bult into ends of missile launch rails and have capacity of 160 chaff packs or flares; BOP/C dispensers are built into the fuselage, and BOP/B into end of the wing pylons. Lattermost can trail BO2D towed repeater RF decoy, which can be used at supersonic speeds.

Gripen’s limited sensory suite in versions so far is a large shortcoming in combat – namely, lack of IRST, which means that Gripen pilot will have to rely on visual detection (not possible during night, insufficient in bad visibility conditions) or on opponent using his own radar (relying on opponent being an idiot should never be part of any plan). This was realized by SAAB, and Gripen NG will be given IRST; earlier version of Gripen, however, will either have to be retrofitted with an internal IRST system, or settle for using FLIR pod for both air-to-air and air-to-ground missions (if possible). That is probably connected to the fact that Gripen was always intended as a defense weapons, and could thus rely on directions from the ground.

Signature reduction

While the fact that Gripen is relatively small aircraft automatically means smaller IR and visual signatures, there were some specific attempts made at further reduction. Just behind cockpit are located ducts, which are used to release exceess heat from heat exchangers, reducing Gripen’s IR signature as seen from ground.

As far as radar signature is concerned, care was taken to reduce frontal RCS, though side RCS is not likely to be large as long as radar emitter is not at precise 90 degrees angle relative to the aircraft, which would result in return from aircraft’s side surfaces – in particular tail, nose and intake surfaces.

Datalinks and communications

Flygvapnet pioneered the use of datalinks in the combat aircraft, fielding first versions on SAAB 35 Draken in mid 1960s. Gripen is equipped with four high-bandwidth, two-way data links, with range of around 500 kilometers. This allows for exchange of targeting information and other data, even when one of aircraft is on the ground. One Gripen can provide data for four other aircraft, as well as get access to ground C&C systems and SAAB-Ericsson 340B Erieye “mini-AWACs” aircraft. It can also allow fighters to quickly and accurately lock on to target by triangulation of data from several radars. Annother possibility includes one fighter jamming the target while another tracks it, or several fighters using different frequencies at the same time to penetrate jamming easier.

Gripen NG

For Gripen E, SAAB has stated that empty weight will be under 7 000 kg, and engine also apparently has 22 500 lbs of thrust. It also has 3 300 kg of internal fuel, achieving 1 300 km combat radius with 30 minutes loiter time in AtA configuration on internal fuel, or 1 800 km with no loiter time. OTIS IRST will also be added.

Gripen NG will be significantly cheaper than other 4,9 generation aircraft, such as Eurofighter Typhoon or Dassault Rafale, and with 22 ordered by Switzerland and 40-60 by Sweden itself, it has prospect to achieve success on export market as well. Some sources place flyaway cost at less than 50 million USD; my estimate is that it will likely be around 45 – 55 million USD per aircraft.

According to some reports, wing area is double of Gripen C’s, fuselage is 20% longer, but it is made out of carbon nanotube reinforced polymer composites, reducing weight compared to Gripen C. All images of Gripen NG to date, however, seem to be using Gripen C / Gripen Demo as basis (Gripen Demo is test aircraft built by using Gripen C airframe, and images that could indicate wing area don’t show any difference in fuselage dimensions). Another presentation also shows Gripen NG’s empty weight as 7 120 kg, and wing loading as 317 kg/m2 in combat configuration with 50% fuel. (Interesting point is that same presentation states that IRIS-T will be able to shoot down BVR missiles from other aircraft, though slide in question is not entirely clear). OTIS IRST will operate in 3 – 5 and 8 – 11 micron wavelengths.

Conclusion? I won’t draw conclusion about NG until it is airborne and in service.

Image of Gripen landing. Take note of air brakes and canard position:

JAS-39 Gripen landing

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Saab Gripen NG

Posted by picard578 on October 14, 2012

Two months ago, I have contacted SAAB about Gripen NG and changes it will have when compared to earlier versions of Gripen (A, B, C, D – Gripen NG encompasses versions E and F).

I got following answers:

1) Gripen NG will be equipped with imaging IRST (imaging IRST works similar to IR camera and can create video image from IR radiation it receives). It will be forward-looking only (FLIR).

2) Airframe will be increased in size, and wingspan will also increase. Wing area will increase, so wing loading, while slightly higher than for C/D models, will still be low.

3) Cockpit will not be changed; rearward visibility will be facilitated by mirrors.

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