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How good was the JA-37 Viggen?

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    How good was the JA-37 Viggen?

    I always thought that the performance of JA 37 has always been somehow underrated. To some extent it can be attributed to the lack of export sales and the Sweden's neutrality - there were simply not enough information, rumors from exercises etc., to generate some sort of the consensus on the Viggen's performance. Also, despite the originality of the design, there are practically no books dedicated to the development of Viggen family, what makes extremely difficult to trace all the in-service upgrades and modifications, which, as usually in Sweden, can be expected to be rather extensive.

    The fighter variant JA-37 came to live as a deep modification of the Viggen's first generation planes. Its first flight took place in 1974, while it entered squadron service in 1980 (for reference, the AJ version prototype flew in 1967). As a result, the aircraft is commonly disregarded, as people say that it offered phantom-like capabilities while being produced in the same period as the teen fighters. That however, is not entirely true.

    The JA-37 had a number of modification in comparison to AJ-37. The main differences were:

    - Uprated RM8B engine, with the thrust increased from 115.6 to 125 kN, was used. The responsiveness of the engine was also greatly improved (and the smoking was reduced).
    - An Oerlikon KCA cannon, famous for its performance (range in excess of 2 km), was added.
    - The onboard computer, air data computer, inertial navigation system etc. were updated (most of these systems was actually borrowed from the F-14...)
    - A pulse-Doppler PS-46/A radar was introduced. It sported a lookdown/shootdown capability as well as ability to track up to 2 targets while scanning. I've came across some information that it benefited from solutions used in F-15 AN/APG-63, but no specifics were given. The cited range is almost always given as either 48 or 75 km, what looks awfully like the case, where everybody is citing an old brochure, with no clue of the real performance.
    - The initial armament consisted of 2 SkyFlash missiles, combined with 2-4 Rb. 24 (AIM-9J). Later, it was upgraded to Rb.72 (AIM-9L) and Rb.99 (AIM-120B). It is worth noting that after the AMRAAM upgrade it was common to see a Viggen with 4 such missiles.
    - Cockpit was fitted with 3 CRT screens. The HOTAS was introduced at some stage, but I'm not sure if it was there from the beginning.

    The JA 37 went through numerous upgrades, often benefiting from the Gripen's technologies. The most important were:

    1985 - introduction of the data link (encrypted communication between up to 4 fighters and ground control), which allowed passive firings about a decade before any other country sported such system
    1987 - flares, ground controlled secondary information via data link, Rb. 74
    1990 - radar upgrade, improved resistance to jamming and multi target tracking (I don't know the specifics)
    1992 - automatic gun aiming (from what I've heard, extremely effective)
    1996 -1998 - upgrade to the JA-37D standard - Rb. 99, cockpit upgrades, MIL-STD-1553B databus introduction, U95 jammer pod, flare and chaffs dispensers BOY 401, ECM and ECCM suites enhancements, TARAS terminal (improvement to data link).

    These are the main upgrades I am aware of, but there were probably multiple more.

    Another poorly known aspect of Viggen's capabilities is the airframe performance. Recently, a performance manual of JA 37 Viggen became available thanks to this guy:
    Below are presented some of the E-M diagrams, given for different armament configurations (examples in the table).

    Click image for larger version

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    I must say that I have some problems with understanding how the instantaneous turn rates are to be determined. The problem here is with the Nz G limit lines. They are changing from 7G at 0 meters, to 4G at 8 and 12 km. I have never seen such behavior on E-M diagram, so I don't know what to make of it, as usually the G limit is not changing with the height. If anyone have any suggestions how to read it, I would be thankful. Nevertheless, even if we assume that at 4 km the airframe is limited to 6G, and at 8 km just to 4G, the turning performance of Viggen is still quite good. Its sustained turn rate at 0 km, with A-A configuration is about 13.3 deg/s, so in the Phantom's ~14 deg/s ballpark. However, its instantaneous performance is rather spectacular, with 24.5 deg/s, so similar or even better than some of the teen fighters. The performance suffers rather badly with the increase of height (again, the G-limit question), but the instantaneous turn rate at 4 km (18.5 deg/s) is still great (for comparison, at 4570 meters the clean F-16 block 50 has 18.8 and F-14D in A-A configuration has 18.1 ). The acceleration of Viggen is a bit less spectacular, as at sea level it takes about 30 s to accelerate from 0.55M to 1.05M, so similar to F-4, and much slower than F-16 (about 20 s).

    It seems to me, that the case of Viggen is similar to Tornado ADV - a very good weapon system, inside a rather mediocre airframe (in comparison to teen fighters and MiG-29/Su-27). Still, I would say that it had a clear edge over the MiG-23/F-4/Mirage F-1 generation (excluding F-4F, which is debatable) and thanks to the upgrades it remained a very competitive aircraft up to its retirement. However, there are still many aspects, which remain unknown, at least to me:
    - what was the performance of the PS-46 radar? How greatly it was improved during service?
    - what is going on with the G-limit - height dependence?
    - how did it perform in actual training exercises, are there any rumors?
    - and finally, why this marvelous aircraft seems to be forgotten by all aviation authors?
    Attached Files

    - what is going on with the G-limit- height dependence? Typical Delta behavior. At height or alpha, thrust is the limiting factor (drag)

    idem for instantaneous turn rate Vs sustained


      I have wondered for some time how the Automatic Gun Aiming works on Viggen and Gripen.
      It would make sense to me, if the aircraft could detect the distance, position and speed vector of a designated enemy, and once the pilot has achieved an approximate firing position, the aircraft would enter an auto pilot mode, where it would create a perfect deflection shot, firing the cannon at the right time. Then it would return controls to the pilot.

      Is there any aircraft with such functionality?


        I've read that Mig29 had something similar.. during an interview at Le Bourget an engineer said they had trouble with the gun that wasn't reliable enough, though, it was only half a problem, as with automatic firing, the target would be hit with the first shells and destroyed.. trouble was more about having to fight a second opponent after that. But I never heard about it again

        If someone has any info about it... could be nice to read more


          1985 - introduction of the data link (encrypted communication between up to 4 fighters and ground control), which allowed passive firings about a decade before any other country sported such system
          Nice capability, but MiG-31 had a datalink before then, and Su-27 had a roughly contemporary one as well.


            Technically the Sabre hog (D) had one too

            (Such was the F-94)
            Last edited by TomcatViP; 2nd May 2018, 21:14.


              Congratulation to the Russians for introducing a digital datalink,
              20 years after it appeared in J-35A Draken!


                I didn't know that multiple J-35A fighters could share situation information between each other. That's really impressive thing to do in 1959


                  The Soviet datalink suite Vozdukh/Lazur was in VVS operation in the 60's already, on various MiG-21s etc, simultaneously with J 35A and Stril 60, and just about as capable (in terms of streamlining GCI)

                  The MiG-31 datalink suite was way more advanced, but came later. More akin to the 1985 upgrade of JA 37 as mentioned above.
                  Last edited by Dr.Snufflebug; 5th May 2018, 16:42.


                    More akin to the 1985 upgrade of JA 37 as mentioned above.
                    Exactly, hence why I mentioned it.

                    Funny to see how easily some are triggered though.


                      Mentioning that the MiG-31 had a datalink before the JA-37 Viggen is useless information.
                      That is just trolling, and got the deserved answer.
                      Saying the the MiG-31 had a datalink, and then comparing the features is useful information.


                        Originally posted by APRichelieu
                        Mentioning that the MiG-31 had a datalink before the JA-37 Viggen is useless information.
                        That is just trolling, and got the deserved answer.
                        Saying the the MiG-31 had a datalink, and then comparing the features is useful information.
                        Well, he clearly meant that MiG-31 had a comparable datalink suite (planes exchanging information etc) before JA 37 received one.

                        Your snarky remark about J 35A having a datalink (without specifying features) long before, adding sarcasm-laden things like "congratulations Russians" and so on was pretty much uncalled for, and ultimately rather ignorant, given what I wrote above. But whatever, no point in bickering about that, it detracts from what I assume the OP wanted to discuss.

                        edit: Also, will you guys please stop using hyphens when talking about Swedish aircraft? There never was a "J-35A" or a "JA-37" or whatever.
                        Last edited by Dr.Snufflebug; 10th May 2018, 20:15.


                          perhaps we should end this nicely started thread on a better way:

                          I recommend browsing the user chanel...


                            I always thought that the performance of JA 37 has always been somehow underrated.

                            I don't think it was always the beast fighter aircraft at its time.
                            If it looks good, it will fly good !
                            -Bill Lear & Marcel Dassault



                              Great read about Viggen intercepting the SR-71, achieving a radar lock!



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                                  Thanks for the very interesting information made available in your post about the JA-37 Viggen.
                                  In fact, the JA-37 Viggen were among of the highly advanced fighters in the 80s, since the JA-37 had been described as the most advanced fighter in production from Western Europe in the 80s too, and this mention was never really challenged even in Europe.

                                  There are several reasons that could have been restricted the sales of the JA-37 (second-generation AJ-37) for others countries, among those: the high cost of acquisition and operation of the JA-37, such lack of political weight from Sweden and particularly the restriction imposed by the United States who had provided many advanced technologies used by the JA-37. In fact, there were rumors that even nations that had obtained U.S. approval in the 1980s to receive F-16A/B/C / D, but the same nations were not given permission from U.S. to buy the JA-37 from Sweden.

                                  This latter fact may seem like an urban legend nowadays, but the United States had such strong interest in strengthening indirectly the Sweden, since the neutrality of the same could not have been questioned by the former Soviet Union, so in the case of JA-37 Viggen should have quite important mission for NATO in case of war against the Soviet Union: to block the fly of the Tu-22M2/3 across the Sweden territory for both naval attacks on the North Atlantic or ground attacks in the United Kingdom and northern France against the OTAN.

                                  Then JA-37 had been the second generation from AJ-37, as well as the AJ-37 were able to perform intercept missions or ground attack through the changes of the modules from radar system in the own air bases during the refueling and rearming between missions, however the AJ-37 had not been capable to use BVR (Beyond Visual Range) missiles.

                                  Therefore JA-37 has been described as an interceptor with a secondary capability to attack ground targets as the same manner of the F-15C / D, however JA-37 had been completely redesigned in relation to AJ-37, as well as the JA-37 were equipped with more advanced avionics and weapons.

                                  Just as important as the new electronic items and weapons introduced in the JA-37 , it had been increasing in its maneuverability over the AJ-37. In fact the JA-37 received a new reinforced structure with parts in titanium and carbon fiber, so that had been increased the structural limit at the 12G, as well as the increasing in rudder height and elevons on the wings from 03 in the AJ-37 to 04 in JA-37. Another important change were the use of a Fly-By-Wire system in the JA-37.

                                  The T / W ratio has been very close to 1, since the JA-37's empty weight (12,500 kg / 27,558 lb) and maximum thrust power (12,000 kgf / 26,455 lbs) that actually puts it in the same category as the 4th Generation fighters.

                                  Overall, the JA-37 has been described as 9G maneuverable fighter, while the AJ-37 would be in the 7G category.


                                    Saab Sk37E Viggen 37809/SE-DXO to the skies again

                                    On 15 May 2018, Saab Sk37E 37809 marked as F15-61 took to the skies again. The dual seat Viggen belongs to the Swedish Air Force (Flygvapnet) Historic Flight since her last operational flight on 4 September 2007.

                                    It was kept in airworthy condition and stored at Stens, home of Skaraborgs flygflottilj F 7.