Jump to content
Sturgeon's House
Sign in to follow this  
LostCosmonaut

J35 Appreciation Station

Recommended Posts

I wrote a little piece on the rb 04E based on the SFI's. Figured people might be interested.

Robot 04E (with "robot", abbreviated "rb", being military Swedish for "missile") was the AJ 37 Viggen's signature weapon: a radar-guided, sea-skimming anti-ship missile, developed from the rb 04C which had originally entered service in the 1961 on the A 32 Lansen. The E version entered service in 1975, with 315 missiles produced. Let's have a look at how it works.

gQfyVNX.jpg

Rb 04C or D on a A 32 Lansen.

2099Qhe.jpg

Missiles on the assembly line at the air force's Central Aircraft Workshops in Arboga.

First, some background on the doctrine and use case that shaped the design of the missile. The Swedish armed forces expected the Warsaw Pact to attempt to secure a beachhead on the Swedish coast with a D-Day style invasion: a massive fleet of hundreds of ships with surface combatant screens protecting a core of various landing craft. The AJ 37's raison d'être was to attack a fleet like this. The rb 04E was mainly intended to be used against the screening combat ships, since if their AA was silenced the Viggens would be able to go to town on the vulnerable landing craft with less expensive weapons like bombs, autocannons and unguided rockets. In order to achieve saturation of the defenses and a reasonable chance to actually sink mutually supporting surface combatants, the plan was to deploy at least four but preferably six or more full squadrons in each attack wave (one squadron in the air was two flights of four aircraft, so six squadrons would be 48 aircraft). Since the plan involved launching up to close to a hundred missiles at the same time (or slightly less - some aircraft would be carrying countermeasures instead of missiles), getting the missiles to spread themselves out between different targets and not collide with each other or lock on each other was a very real concern, which will be apparent when we get into discussing the seeker.

Onwards to the technical details!

veEocUg.png

The missile's about four and a half meters long (14 ft 9 in), weighs around 625 kg total (1378 lbs), has a shaped charge warhead that weighs about 200 kg (441 lbs) and is powered by a solid rocket motor that produces a nominal thrust of 195 kp (1.9 kN, 430 lbf) for a nominal burn time of 65.5 seconds (can vary between 60 and 75 seconds depending on propellant temperature). The control surfaces are pneumatically actuated. The seeker is a frequency hopping monopulse radar with a parabolic receiver antenna located under the radome in the front of the missile (the text "TRYCK EJ HÄR" on the radome means "do not press here"). The antenna sweeps horizontally only, 28 degrees to each side. The missile cruises at an altitude of 10 meters above sea level, which it maintains by the use of a radar altimeter.

The AJ 37 can carry two rb 04E's on the inner underwing pylons. When pre-flighting the missile, the mechanic had a panel with five switches and a knob available to him for programming the missile - there really isn't much the pilot can configure from the cockpit. The panel looks like this:

KE6DE5X.jpg

The switches are intentionally only labeled with numbers for opsec reasons - the seeker electronics were highly classified and conscripts were not allowed to know much about how it worked. Switch 1 ("balkläge") is the missile's position on the aircraft; V (vänster, left), C (center) or H (höger, right). The centerline pylon © was initially planned as a possible launch position on the AJ 37 but the electronics to actually launch the missile from there were never implemented. The rest of the switches we'll cover when we get to the functionality they affect.

The missiles can be launched one by one or both together - in the latter case there's an automatic delay of about two seconds between the two, to avoid collisions. Targeting is simple: the pilot simply points the entire aircraft at the desired target, guided by the head-down radar screen, on which either a PPI or a B-scope is presented together with a wind-compensated aiming line (wind speed is taken from the aircraft computer, where it is either doppler calculated by the radar altimeter system or taken from the weather forecast as input during pre-flight procedures). The presentation looks like this:

lbf3RTA.jpgTufAH4q.jpg

B-scope and PPI, respectively.

The number 60 shown in the bottom right means that the range of the display is set to 60 km. The two short, curved lines on the PPI represent the ranges 12 and 24 km respectively, while the line marked "raktframlinje" is the wind-compensated aiming line. Originally, the 12 and 24 km lines represented minimum and maximum firing ranges for the missile, but at some point the procedure was improved to calculate the engagement envelope dynamically based on air pressure, temperature and speed of the launching aircraft (later manuals recommend a max launch range of about 20 km). The pilot can select if the missile's seeker should be in single ("ENKEL") or group ("GRUPP") targeting mode. In single target mode, the missile will simply lock on the first detected target. In group mode, the target selection process is more involved and we'll get back to it in a little bit. The missile can be launched at altitudes between 50 and 425 meters above sea level and airspeeds between Mach 0.7 and 0.92. The aircraft's radar does not need to be radiating to launch the missile, since the targeting is done just by pointing the aircraft the right way. In fact, the missile can be launched completely "blind" - this was particularly desirable on the Lansen, which did not have a radar in every aircraft. The flight lead could do the radar thing and the rest of the flight just launched when he did - a tactic that was also technically usable on the AJ 37. Once launched, the missile is completely autonomous and can no longer be controlled in any way by the launching aircraft.

When the launch signal is given, the missile activates its internal batteries, releases its gyro from being slaved to the aircraft's attitude gyros, unlocks and pressurizes the aileron actuators, and when the batteries have reached full power (after about 0.6 seconds), it separates from the aircraft. 0.7 seconds after separation, the elevators and rudders are pressurized and the missile immediately starts diving at an angle of about 7 degrees. About 1.1 seconds after separation, the missile starts yawing either 2.5 or 7.5 degrees to either the left or the right - which direction and by how much is determined by the position of the knob (marked 6, "kurstillskott") on the switch panel on the missile. After 8 seconds, the missile returns to the launch course. The reason for this is to separate the missiles horizontally.

When the missile's radar altimeter detects that the missile has had an altitude under 120 meters above sea level for more than 100 milliseconds, the automatic 7 degree dive stops and the missile instead follows a descent profile that takes around 10 seconds to reach its cruise altitude of 10 meters. Missiles launched from the right pylon ignite their rocket engine when descending below 130 meters, while missiles launched from the left pylon ignite it upon reaching the cruise altitude, to further separate them in time and in altitude.

mc5OaZL.png

When the cruise altitude is reached, the seeker starts scanning for targets; the scan area (and lock envelope) is shown above. When a possible target is detected, the seeker activates a function called "three-view logic", which means that the ranging function continues seeking forward about 80 meters. Then, the antenna sweep is reversed and the ranging seeks about 250 meters backwards, then the sweep is reversed again and the ranging seeks about 300 meters forwards. If the seeker gets a return again during the first or second reversed sweep, the target is considered valid. If no return is received during the first or second reversed sweeps, the target search continues. On the other hand, if the seeker gets another return immediately after the first indication, caused by the size of the target, the three-view logic function is blocked and the seeker accepts the target immediately.

When the seeker has locked on a target, the range to the target is monitored. The range should be decreasing, since the missile is approaching it. If the closing speed is too low, for example because the seeker has locked on another missile flying in the same direction, the missile releases the lock and starts a new search. The seeker will not lock on targets that are located such that the missile cannot be maneuvered to hit them, either.

In group targeting mode, the seeker will assume that the target ships are traveling in columns, and can be programmed to lock on a target in the first, second or third row as seen from the attacking aircraft, using the target selection switch (marked 5, "målval") on the switch panel on the missile. In order for the missile to lock in group mode, two or more targets have to be detected in the same range sweep, and they have to be a maximum of 2700 meters from each other (this number looks arbitrary, but it's just about one and a half nautical miles). In order to allow for at least some flexibility in the line up, the seeker performs a fictional widening of the antenna lobe by copying detected targets and considering them for the next range sweep as well. This is all perhaps best explained with a picture:

i0DqVkj.png

The "angle jump" function, which can be enabled on the switch panel using the switch marked 4 ("vinkelhopp") makes the missile skip the first possible target it sees and lock on the next one instead, if one is found before the antenna sweep reaches the end position and turns around.

The missile also has an additional targeting mode, called "active + passive", which can be selected on the switch panel (switch marked 3, "följemod"). When this is selected, the missile is basically home-on-jam - if it detects it is being jammed, it will lock on the jammer after one full horizontal sweep. While locked on the jammer (passive targeting mode), the antenna is kept pointed at the signal source and the missile tracks the bearing to it. The range search stays active during the passive target tracking and if a target is detected in the jammer's direction, the missile will lock on that. If the jammer stops transmitting, the missile will keep going "blind" for two seconds; after that it resumes active targeting.

yFQxsVg.jpg

Rb 04E seeker unit.

The seeker keeps the missile pointed straight at the target until it is less than 4000 meters away, at which point the missile starts accounting for the target's speed and leads it. The seeker keeps tracking the target until it has closed to 250 meters, then the missile flies blind the last distance. If the warhead does not detonate when the target is passed, the missile re-starts targeting and simply locks on the first thing it sees (disregarding the single/group target selection and any previous considerations).

At 250 meters from the target, the missile arms its fuzes. The missile is not intended to actually hit the target - the warhead is a shaped charge that is focused downwards, so it is supposed to be detonated above the target. There are three different proximity fuzes - one magnetic, one temperature-sensitive and one based on the radar altimeter, which detects a sudden altitude change when passing over the target. There are two proximity fuze modes, selected with the switch marked 2 ("zonrör") on the switch panel - in mode 1, only the radar altimeter is active, while in mode 2, any two fuzes both giving the detonation signal is required. Additionally, there is also a contact fuze in the nose of the missile, which detonates it after a small delay if it should hit the target directly.

ZElRTCg.jpg

In summary, I find the group mode to of questionable utility since it requires the targets to line up almost perfectly, but I guess they did what they could to try to get the missile to be able to work against large ship formations. In the single target mode though the missile seems to be a pretty nasty piece of business for 1975, especially considering the radio silent mass usage doctrine and the fact that very few aircraft needed to actually radiate to enable a launch. The main weakness was probably that there were so few missiles purchased - about two missiles per AJ 37, total.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

  • Similar Content

    • By LostCosmonaut
      I have a somewhat unhealthy obsession with Swedish armored fighting vehicles (although my disease is not quite as bad as T___A's attraction to communist frying pans and the like). By far the most well known Swedish AFV is the Strv 103, one of the more unusual MBT designs from the Cold War.
       

       
      However, there are also numerous other Swedish armored vehicle designs that I find interesting. Such as the Kranvagn, and the Strv 74.
       

       
      If you are interested in learning more about Swedish AFVs, I would highly recommend consulting this excellent site. Be warned, most of the documents therein are in Swedish, so at least have google translate open in another tab.
    • By Walter_Sobchak
      I don't know why, but in 1919 someone wrote a book about tanks in Swedish.  It's not in a format that allows me to run it through a translator.  Perhaps our resident Swedish tank expert can help us with this one?
       
      <iframe width="450" height="700" src="http://hdl.handle.net/2027/wu.89100067776?urlappend=%3Bui=embed"></iframe>
    • By Serge
      Lets start a thread about the CV-90. Past, present, futur. 
      Link to the Linström's page about the initial Stridsfordon-90 project :
      http://www.ointres.se/projekt_strf90.htm
       
      An interesting SH-MM post about evolution of CV-90 :
      And a summary about contenders for the forseen Czech IFV programme :
      http://below-the-turret-ring.blogspot.pt/2017/08/which-new-ifv-for-czech-army.html?m=1
       
      From a well known blog.
    • By LostCosmonaut
      I was originally going to post this in the J35 thread (since that's turned into the general Swedish aviation thread), but I felt that it'd get more visibility here.
       
      SAAB A36
       

      (via http://forum.valka.cz/topic/view/55568/SAAB-A-36)
       
      During the 1950s, many nations sought to develop nuclear weapons. One of these was Sweden, who hoped that nuclear weapons could help maintain their neutrality during the Cold War. However, when developing nuclear weapons, a delivery system is also needed. For Sweden, that would have been the A 36, a dedicated nuclear strike aircraft and one of the "missing pieces" in the Swedish aircraft sequence (between the 35 and 37).
       
      Development of the A 36 began in 1952, as part of SAAB's 1300 series of projects (which included numerous other designs). The requirements for a Swedish nuclear strike aircraft were different from those of other major countries. The most likely opponent (the USSR) was less than 500 kilometers away across the Baltic, while American bombers would have to fly more than ten times as far to reach their targets. This was evident in designs such as the B-36 and B-52, which had very large wingspans and fuel capacities, as well as large payloads. Additionally, a Swedish nuclear bomber would have to be capable of operating from dispersed airfields, in accordance with Swedish doctrine. Obviously, the Swedish nuclear bomber would end up looking quite different from its American or Soviet counterparts.
       
      Numerous SAAB engineers were involved with the A36 development (quite an undertaking, as the company was developing the J35 at the same time while also producing the J32). Among them was Aarne Lakomaa, a transplanted Finn who had gained fame for developing the Morko-Morane fighter during the Continuation War.
       
      From the start, the Swedish bomber (at this point it had yet to be designated A 36) was designed for high speed. Numerous configurations were studied, with swept wings or delta wings on various designs. Top speed was planned to be around Mach 2, which would have made the A36 almost as fast the J35.
       

      SAAB 1323 (or 1300-23), an early step in the A36 development.
       

       
      SAAB 1371 (1300-71), a proposal which made it as far as wind tunnel testing.
       
      As can be seen from the previous drawings, many of the designs were planned to have two engines. As with other Swedish aircraft of the time, the A36 was planned to use license built British engines. Among the engines considered were the de Havilland Gyron and smaller Gyron junior. However, at some time early in the development of the program, it was decided that the aircraft would be powered by the Bristol Olympus turbojet, the same engine that powered the British Vulcan bomber. However, for use in a supersonic aircraft, it would have required modification, such as the fitting of an afterburner, and a new intake. (The Olympus was eventually developed for use in supersonic aircraft, such as the TSR-2 and Concorde.) With such a large and powerful engine, it became apparent that only a single engine would be needed in the A36.
       
      At such high speeds, the A36 would have experienced significant aerodynamic heating. This concerned Swedish engineers, who were afraid that the heat would damage contemporary nuclear weapons (or even lead to them detonating prematurely). As a result, it was decided that the payload would be carried within an internal weapons bay. This would reduce drag, improving performance, but it would also limit payload, while decreasing the internal volume available for fuel, avionics, and other systems. By the time the A36 design had progressed  to the 1376 and 1377 configurations, payload was determined to be a single 800 kilogram nuclear weapon, carried internally. This is roughly comparable in size to the American Mark 7 bomb, deployed tactically around the same time. As far as I know, no provision was ever made for the A36 to have air-to-air capabilities.
       
      By 1957, the design of the A36 (which had by now received a formal Swedish Air Force designation) was almost finalized.
       
      (SAAB 1376, with chin intake)

       

      (Drawing of SAAB 1377 with dorsal intake, similar to YF-107)
       
      Most documents show the 1376 as the chosen design. 1376 was a moderately sized aircraft, somewhat smaller than the American F-105 (which had a similar role to the A36). The wing was a conventional delta with 62 degree sweep, which would have given good performance in the supersonic regime. I am uncertain whether the A36 would have utilized a variable geometry inlet. A fixed inlet would have had to be optimized for a certain speed; this would mean that the A36 would have been inefficient at low Mach numbers, or been had it speed limited by the inlet design. (Read more about inlet design here).
       
       
      Although work on the A36 was progressing well, by 1957 it was apparent that Sweden could not afford to develop the A36, nuclear weapons, and other vital defense programs. As the A36 would have been relatively lacking in conventional capability, it was decided to cancel the program. (Ultimately, the nuclear weapons program would be shut down during the 1960s as well). Some of the money saved was used to develop the A37 Viggen, which proved to be a competent multirole aircraft during the 1970s and beyond. Ultimately, while it would have been interesting from a technological standpoint to see the A36 fly, its cancellation was probably the right choice.
       
      I have not found any documents showing that the A36 was ever given a name (such as 'Draken' for the J35). Occasionally references can be found to the A36 'Vargen' (Wolf) online, but it appears that these are the inventions of either modeling companies or someone with an overactive imagination.
       
      A36 (1376 design) specifications (approximate):
      Length: 17m
      Wingspan: 9.6m
      Height: 2.5m
      Wing Area: 54m2
      Empty Weight: 9000 kg
      Max Weight: 15000 kg
      Wing Loading at Max Weight: 280 kg/m2
      Payload: 800 kg
      Max Speed: Mach 2.1
      Ceiling: 18000m
      Combat Radius: 410km (?)
      Crew: 1
      Engine: 1x Bristol Olympus Turbojet
       
       
       
       
       
      Sources:
      http://u-fr.blogspot.com.br/2010/12/cancelled-saab-aircraft-projects.html
      http://www.secretprojects.co.uk/forum/index.php/topic,683.0.html
      http://forum.valka.cz/topic/view/55568/SAAB-A-36
×