renhanxue

If actual Viggen pilot @hilmerby says the previous one looked good I'd say that's a pretty good endorsement of it.

According to the SIPRI arms transfer database 500 (estimated) rb 75's were ordered in 1975 and delivered in 1977-1978. The air force may have modified the missiles after that; I have seen documents discussing plans for seeker head modifications in 1979 (see below) but I don't know to what extent the plans were actually implemented. (Document photographed at a visit to the Arboga missile museum years ago; access was not restricted.)

I have some vague memory that the TRIMSYST circuit breaker should work, because it's necessary to restore function of the normal trim system after touching any of the emergency trim controls. Or maybe what I'm remembering is that I've claimed that before and found out it didn't work? Not sure.

important follow-up questions: do we need an INS alignment chart (ref: the sandwich alignment chart)? does anyone have a precise technical definition of the Swedish term "momentgyro"? I get the gist of what they do (I think) but I want all of the details

"is the Viggen navigation system inertial or not" - the greatest debate in the history of forums, locked by a moderator after 12,239 pages of heated debate, dril references aside, this question has come up a couple of times before, and earlier today @Rudel_chw asked this in a direct message. This post is mostly a reaction to that. My answer to the question is "not really", or "not primarily". It does use dead reckoning just like an inertial navigation system (INS) does, and it does use accelerometers and attitude gyros just like an INS does, but it does not primarily rely on them, so it's not really inertial. Pseudo-inertial? Partially-inertial? Whatever you might call it. An INS by the usual definition of the term only (or at least primarily) relies on accelerometers and attitude gyroscopes to calculate how it's being moved. The accelerometers measure the acceleration of whatever they're mounted to, and the attitude gyros measure the attitude relative to the earth, and if you combine the two you can figure out how the entire system is moving relative to the Earth. That means an INS is by definition ground-referenced (or rather referenced to Earth's field of gravity, I guess). The Viggen system on the other hand is primarily atmosphere-referenced. I've translated a block diagram from the SFI: As you can see, it starts not from inertial measurements but rather from air data measurements. First it uses temperature and air data to calculate the true airspeed. Then the angle of attack is used to calculate an estimate of the vertical and longitudinal speed separately (transverse speed is assumed to be negligible here). This is then combined with attitude information from the FLI-37 ADI and the autopilot's moment gyros to calculate the aircraft's true velocity vector relative to the air. To get the movement relative to the ground (which is what we actually want), the nav program then compensates for wind speed, which is either measured using a doppler radar (ground speed measurement), or forecast wind as programmed into the computer (input with VIND/RUTA/MÅL). The ground-referenced velocity vector is then calculated and integrated every 103 milliseconds to continually keep the aircraft's position updated. This isn't quite good enough though. There are two problems: first, transverse speed (side to side) can't be calculated from air data, and second, the air data system reacts too slowly to really make this precise enough. To mitigate these problems, there's an accelerometer unit that measures acceleration in the longitudinal and vertical axes; acceleration in the transverse axis is taken from the transverse accelerometer that's used for the autopilot's sideslip correction system (y'know that RENFLYGN knob nobody ever touches). These accelerometers react much faster than the air data system, and so they're used to correct the velocity vector calculated from air data. This taken as a whole is good enough. So, in the transverse axis the system actually is a "real" inertial navigation system - it relies purely on attitude gyros and accelerometers to determine movement in that axis. This, the SFI says, is acceptable because the velocity in the transverse axis is usually more or less net zero (the aircraft doesn't typically fly sideways, after all), with only small variations back and forth, so relying purely on acceleration gives sufficient precision. You might ask though, if the aircraft has attitude gyros and accelerometers anyway, why not just go purely inertial? The main answer is that to do that you'd need much more expensive equipment. You need more precision than the Viggen's gyros and accelerometers actually have to make it work well, and probably you'd need a dedicated computer for it too. INS systems were absolute state of the art in the early 1960's when the Viggen was designed, with the Minuteman and Apollo guidance systems being some of the first really practical examples. You couldn't just buy an INS off-the-shelf in the 60's; Saab would've had to design one in-house. INS became a lot cheaper and more reliable in the 80's with better computers and the commercialization of the ring laser gyro. The Viggen system isn't as accurate as a real INS, but at the time it had a significant cost advantage. It's noteworthy that almost the entire system is just a software program that runs in the CK 37. The only hardware it uses that the aircraft wouldn't otherwise have are the two accelerometers for the longitudinal and vertical axes. It also has the side benefit that it's capable of cold starting in two minutes flat because the gyros just aren't that sensitive. True INS systems of the era could take tens of minutes to align from a cold start. It was an engineering compromise: good enough to fulfill the requirements the air force had, but not more complex and expensive than it had to be.

@TOViper, on this page on fly37viggen.com you have a link to ATIS 37 on my Google Drive. That's fine, I'm very happy that people are interested in it, but Google in their infinite wisdom has made it so that even though the file is supposed to be publicly viewable, if you don't have the right link to it, it forces people to log into their google accounts and request access to it before they can see it. That means I get an email and have to approve the access every time. I suspect a lot of people just don't do that, but some do and then I get emailed to approve the request. I don't want to have to do that, so could you please replace the link with this one, which should have the appropriate magic that grants access without me having to know about it: https://drive.google.com/file/d/0B8bCDRcq9BVeSGhTa3dRSU41WGc/view?usp=sharing&resourcekey=0-yyayxaqfe_YfaWn2AkDROw

You're already keeping a change log of edits, clearly what you should do is just adopt the SFI's system where each page is dated individually and changes compared to the base version are highlighted with a black bar in the margin :V

Regarding the inverted plunging spiral, the SFI defines it as different from an inverted spin (there is also an extremely rare non-inverted plunging spiral). A long time ago I translated the relevant part of the SFI, so I'll just paste that here. 24.4 Departure from controlled flight 24.4.1 Superstall and spin If the angle of attack exceeds the permitted limits, some yaw disturbances appear around alpha 25-28°, and at alpha 28-30° there are weak pitch-up tendencies. If the stick is moved forward to counter the pitch-up, the aircraft returns to normal alpha, possibly after overshooting up to alpha ~50°. Note that the angle of attack instrument only shows the area -4° to +26°. If the stick movement forward at the pitch-up is too small or is made too late, such that the angle of attack does not immediately decrease, the aircraft departs into superstall or spin. Superstall is characterized by: indicated alpha 26° (actually around 60°) low rate of rotation (< 40°/s) stable or oscillating nose attitude Two types of spin may be encountered: Oscillating spin (most common) indicated alpha 26° (actually around 60°) moderate to high rate of rotation (> 40°/s) moderate to powerful oscillations in pitch and/or roll Flat spin indicated alpha 26° (actually around 70°) high rate of rotation (up to 120°/s) weak or no oscillations in pitch and/or roll The sink rate in a superstall or spin is around 100 m/s. If the pitch-up occurs without aileron input, the departure usually results in superstall. If the pitch-up occurs with any aileron input active, the aircraft is affected by adverse yaw and the likelihood of a spin increases. [...] The oscillating spin may after ≥15 s diverge such that the aircraft rolls inverted, and from there it usually recovers to controlled flight on its own with control surfaces neutral (but see also the section on "inverted plunging spiral" below). In superstall or spin the pitch authority is good, which eases recovery. Aileron input results in adverse yaw, that is to say rolling right gives a yaw to the left and vice versa. Rudder authority is negligible. Recovery from superstall and oscillating spin is accomplished by moving the stick to a position somewhat forward of the neutral pitch position, with ailerons and rudder neutral. To recover from a flat spin, the yawing rotation must be stopped first, which is accomplished with neutral pitch and full roll input in the direction of the rotation ("stick into the spin"). When the rotation has just about ceased, recovery is accomplished with neutral ailerons and the stick somewhat forward of neutral, just like when recovering from superstall and oscillating spin. If the center of gravity is particularly far aft (aircraft with heavy loads on V7 (wing pylons) and no load on S7 (fuselage pylons)) the pitch-up tendency is more pronounced than with normal CoG positions. To return to a normal angle of attack a stronger pitch down input is required; the stick must be moved close to its fully forward position. These characteristics are not affected to any significant degree by fuselage mounted loads. The characteristics with both fuselage and underwing loads are not known but are assumed to be the same as with only fuselage loads. Stalled inverted attitudes have not been possible to achieve in flight tests. Moving the stick fully forward gives alpha about -30°, there are no pitch-up (pitch-down?) tendencies and when the stick is moved back to neutral the aircraft returns to a normal angle of attack. 24.4.2 Plunging spiral In certain scenarios with a particular type of adverse dynamics, the aircraft can enter an uncontrolled attitude of the autorotating type, here called plunging spiral. The plunging spiral, which can be either right side up or inverted, is considered to be the potentially most dangerous form of uncontrolled flight that has been discovered during the spin tests of aircraft 37. 24.4.2.1 Inverted plunging spiral The most common form of the plunging spiral is the inverted one. The following attitudes/maneuvers repeatably result in an inverted plunging spiral: Somersault into inverted position from oscillating spin (for example while attempting to recover from a spin with the stick fully forward) Stalling the tailfin through so-called "knife flying" (TN: knife edge?) The inverted plunging spiral is characterized by the following: Negative load factor (-1 to -3) Low nose Very high rate of rotation in the roll axis (≥ 200°/s) High sink rate (≥ 150 m/s) Moving the stick back and/or aileron input to either side tends to increase the rate of the roll rotation. The rotation can be stopped by moving the stick fully forward with no aileron input. When the rotation has ceased, the stick is moved back to neutral pitch, and the aircraft returns to controlled flight. 24.4.2.2 Non-inverted plunging spiral The aircraft only departed into a non-inverted plunging spiral on a few occasions during the spin tests. It has not been possible to define any repeatable attitude or maneuver that results in a non-inverted plunging spiral. During the spin tests the non-inverted plunging spiral only occurred on the following two occasions (not repeatable): When recovering from an inverted superstall When recovering from an oscillating non-inverted spin The non-inverted plunging spiral is characterized by the following: Positive load factor (+1 to +3) Low nose Very high rate of rotation in the roll axiss (≥ 200°/s) High sink rate (≥ 150 m/s) In a non-inverted plunging spiral, aileron inputs have no effect. Instead, the roll rotation must be stopped by pulling gently back on the stick until the rotation ceases. When the rotation has ceased, the stick is moved forward to the neutral pitch position and the aircraft recovers into controlled flight.

Regarding the flameout detector, see also

Unfortunately the only tactical field manual I have access to for the Swedish air force strike groups is the 1961 edition with corrections/updates added up until 1967, but that one does have doctrinal advice for rb 04 usage (in its earlier incarnations, carried by the A 32 Lansen). It states that against cruisers and frigates rb 04 is the weapon system of choice, with bombs and armor-piercing rockets as secondary alternatives if missiles are not available. It then outlines these rules of thumb for sizing the strike package: The relevant item here is the 4th item from the top, "Raid eller mineringsföretag" (mineringsföretag = mine laying), against which it suggests deploying anywhere between 1 and 6 full squadrons of 8 aircraft. The two right columns make recommendations regarding sub-targets. Against a cruiser (Sverdlovs in this era), deploy anything between a squadron or a flight (half squadron; 4 aircraft), against a frigate or a destroyer use a flight or a twoship, against any smaller surface combatant use a twoship or possibly a single aircraft. The A 32 didn't really have countermeasure pods (not widely available ones at any rate) so it's two missiles per aircraft. On a side note the Rb 15F's lowest sea skimming altitude isn't fixed; it's "waveheight adaptive". I don't have any information on what that means specifically but it certainly sounds pretty low.

The document doesn't say. If I had to guess I'd say 70% fuel because that's the standard used for the in-flight diagrams in the SFI, but it's far from certain. The aerodynamics compendium has two parts and the graphs in the other part frequently use specific weights to illustrate some point, but then it's always stated what that weight is. So, I really don't know. According to the aerodynamics compendium the RM8A (on the AJ 37) starts compressor stalling at around 20° alpha, leaving only a small margin of error from the limit of 18°. I don't know how the DCS implementation does these days. The RM8B in the JA 37 is significantly better; the alpha limit is 23° and the engine reportedly does not start compressor stalling below 25°, which is the point where the aircraft starts losing longitudinal stability and you risk superstall or spin. That means the AJS 37 should not be able to reach the JA 37's level without compressor stalling even if you exceed the 18° limit significantly. I don't have much to add; if anything I think you might be slightly too generous to the AJS 37 in terms of sustained turn rate, but that's just gut feeling, no numbers to back it up. It's really a pity that we don't have a good JA 37 simulator...

Sounds fun

It shouldn't be possible, isn't that the point? The record attempt described in the book starts out with the assumption that the aircraft could be lightened by 1000 kg by removing the radar, various avionics, the hydraulics for folding the tailfin, the thrust reverser etc and then also increase the engine power by 10%. So if you manage to achieve it in DCS the simulation is overperforming significantly.

If it was ever a thing it's surely long been fixed. Most of the overspeeding problem came from very incorrect weapons drag I think, even negative drag on some munitions even after they had been expended, but there was grumbling about fuel regulator being set to MAN at the time too. May have been placebo or hearsay in the first place. This was years ago at any rate.

I think it used to be functional in some regard? Weren't some of the overspeeding issues related to setting it to MAN?

I don't know how well modeled it is in DCS (probably not very, tbh), but on the real aircraft there's a weird phenomenon with max dry thrust; it decreases slowly with increasing airspeed, but between M0.7 and M.08 the trend reverses and it very slightly increases again (then it's more or less constant up to M0.9 and then it falls off a cliff in the transonic region). The effect is quite subtle though, and I'm kind of doubtful it's sufficient to explain what you're seeing (note how much the drag increases in the same region, for example). It's hard to make out in the charts in the AJ 37 SFI, but you can see it in the JA 37 SFI (note chart is for zero altitude):

For a long time Swedish Air Force Historic Flight's main display pilot for the Viggen has been Stellan Andersson, who I believe is over 70 years old this year. I'd say both he and Gustav 52 are pretty spry for their age

Compared to the "TK1" (typkonfiguration 1) design from late 1962 the production aircraft was shortened by a bit over half a meter, and most of it was taken from the fuselage between the canards and the main wing. On the AJ 37 the aft end of the canards coincide with the front of the main wing; on TK1 they had a gap of several decimeters here. Interestingly on the JA37 they actually lengthened the fuselage in this section again by maybe two decimeters (usually the reason cited for this is that they wanted to fit an extra compressor stage to the engine, but I think it also had some aerodynamic benefits). So, if you compare AJ 37 and JA 37 planform sketches you can see the JA 37 has a gap between the canards and the main wing, although it's not as big as on the original TK1 configuration. JA 37 cannot carry rb 05, unfortunately. It looks like an AJ 37 but it's almost an entirely new aircraft - the engine is different, the airframe is different, the FCS is different, the radar is different, the computer is different, it shares no weapons with the AJ 37 except the rocket pods and the Sidewinders, and so on and so forth.

The elevons do not deflect anywhere near their max angles at high airspeeds, but no, the hydraulics are not strong enough to overcome the force of the airflow over the elevons at very high dynamic pressure. The full extent of these problems was only discovered fairly late in the development process of the aircraft, specifically in 1968 (the first flight was in February of 1967). In order to save weight the aircraft had been shortened compared to the configuration originally studied in the early 1960's, but this led to some very undesirable aerodynamic characteristics in the transonic region, and these problems weren't caught during wind tunnel testing because of the limited capacity and scale of Swedish wind tunnels. The full story of this covers almost an entire chapter of Krister Karling's book on the chief aerodynamicists's perspective of the development* so I won't try to summarize it here, but suffice to say that the elevon servos were already strengthened once at this late stage of development, and that was deemed to be sufficient for a strike aircraft - and keep in mind that's what the AJ 37 is; it's not a fighter. On the JA 37 (the fighter version) that came along 10 years later, they added a whole another set of hydraulic servo arms and resolved the issue. * Karling, Krister: Saab 37 Viggen: Utvecklingen av ett nytt enhetsflygplan för det svenska flygvapnet 1952 - 1971 : Sett ur en aerodynamikers perspektiv. Svenska Mekanisters Riksförening 2002. Can be ordered for 100 SEK here.

Big brain time: if you document the behavior of the real aircraft then people will file bugs complaining it doesn't work as documented and so the module will become more realistic. Everybody wins!

It seems to me to be simultaneously too detailed and too smooth to be based on empirical test data, so I think it's mostly analytical in origin. I'd bet it was made by basically layering four separate charts (one for each reason) on top of each other, and that's why it looks so messy. Also, part of the odd squiggliness in the pitch gearing-limited region probably originates with the "series trim" function which is supposed to alleviate trim changes in the transonic region; it starts kicking in at M0.93.

My chart is from the aerodynamics compendium, which reads like it's written by and for engineering nerds. I'd bet the flight manual version is cleaned up and simplified to avoid giving the pilots information overload. AJ and AJS should have identical flight performance for all practical purposes. Very nice job on the cleanup by the way! I think an extended explanation would be a good idea for the manual with or without the chart, but who doesn't like charts?

Here is a chart of the maximum attainable load factor ("G's") for a clean AJ 37 in SPAK mode (disabling SPAK makes it worse, so don't do that): This chart is not particularly easy to read, so I'll try to explain a bit. On the vertical axis is altitude in kilometers and on the horizontal axis is the Mach number. The solid lines marked with numbers indicate the load factor. You should read them like height curves on a map, and "higher up" = higher load factor. Or, in other words, go outside (or "below") a solid line and you are limited to the number of G's that line is marked with. Then the chart is also shaded to show the reasons for these limits, with a key on the right. It's only mildly cryptic but from top to bottom the reasons are: 18° alpha (angle of attack) limit -22° elevon deflection limit (in other words, load factor is limited by how far the elevons can physically move. technically the elevons can deflect to -27° but part of the deflection range is reserved for roll inputs - this is not a fly-by-wire aircraft so it cannot use the full deflection range for a pure pitch input) "pitch gearing", the continuously variable gearbox that attempts to maintain a reasonably linear relationship between stick deflection force and G loading throughout the envelope (see this post for more details about how it works and why it limits the load factor) elevon torque limit (in this area the load factor is limited by how much force the hydraulics are capable of exerting on the elevons) From this we can see that at reasonably low altitudes, 8 G should be attainable almost up to M1.0, but above that it drops off sharply and especially so at medium to high altitude. The AJ 37 has a really kind of awkward flight control system; it has a bunch of electronics and clever mechanical gearboxes in the control loop to make it more stable and easier to fly, but it's not fly-by-wire, and they were prepared to accept some tradeoffs in order to get a system that would fail safe (if you lose all of your electronics you still have a basic pulleys-and-linkages-and-hydraulics mechanical flight control system to fall back on). On the JA 37 they fixed pretty much all of the issues though (since maneuverability is much more important on an air superiority fighter than it is on a strike aircraft) and the max rated load factor is available throughout the envelope.

The manual would get updates regularly, "ändring 90" means it's update number 90 to the manual. It contains only the pages changed in that particular update, and I don't think it contains all of the bombing section. Unfortunately I didn't manage to find a complete and fully update manual at the national archives, so what's been posted is incomplete. The section on rb 75 is also missing. I won't have any opportunities to fix this any time soon.

Yes, do not disable SPAK; the aircraft is not intended to be flown without it. Without it the flight control system is operating in a degraded mode, called GSA (GrundStyrAutomat), which is only there as a backup in case of systems failure. Without SPAK you do not have access to the full elevon authority, because a part of the deflection range on the outer elevons is reserved for the autopilot and cannot be controlled via the basic flight control system. The aircraft is perfectly flyable in GSA, but because of the reduced elevon authority and general reduced stability, there's a whole bunch of operational restrictions that apply. Some normal operations become outright dangerous without SPAK, like using the thrust reverser for example. Viggen is not fly-by-wire, but it's not quite fully fly-by-direct-linkage-to-control-surfaces either. The basic flight control system is directly linked to the control surfaces, but that's only half of the system. The autopilot is necessary to make the aircraft work as intended.