renhanxue

It changes the radar pulse duration. It only has an effect when CI is showing a PPI - no effect on B-scope. I think it's supposed to help with detecting small targets, especially at sea, but I'm not sure, and I'm not sure which mode is supposed to be better for that either. See SFI AJ 37 del 2, page 25. I have no idea if it has any in-game effect either.

That when the series production contract was approved by parliament, not when it entered service. Granted, for OP's question it doesn't matter, but I know an opportunity to clarify obscure Viggen trivia when I see one. ;) So, getting to the "well, actually": the unclassified document Beskrivning bombkapsel 90 mentions on page 7 that prototype development was complete by 1991, the series production contract was signed in 1992 and delivery was complete by spring 1997. It's a fascinating document by the way with an amazing level of detail for being unclassified - highly recommended for nerding out.

According to the SFI, you have it right and "no function" means that the radio is turned off entirely. In NORM+LARM mode FR 24 is in receive-only mode and its push to talk button does nothing if you press it. Normally you're not supposed to use FR 24 to transmit at all, it's an emergency backup radio with very weak output (3 W antenna power) and AM only. I don't know why they didn't unify the PTT buttons but presumably it was cheaper/easier to have two.

Sorry if that came off as overly dismissive. I'm sure there are devices for which your tones are actually realistic (the RWR on the A 32 Lansen is a quite likely candidate, for one) - I'm only questioning if they're authentic/realistic on the AJS 37. I mean, it's entirely possible that they are, but given the fact that app 27 already has some synthetic tones (and can also generate synthetic tones based on the input from an external pod), and that an updated variant of it only has synthetic tones, I'm not so sure about the authenticity in this case. There was even talk at the design stage of implementing some form of threat categorization in CK37, and while that was never implemented, it sort of hints at greater ambitions here. I don't think there are any strong realism arguments in favor of any particular side in this case, is what I'm saying. We simply don't know exactly how apparat 27 worked. Or maybe RagnarDa has access to information that I don't.

hilmerby was a Viggen pilot in real life, so I believe he'd be pretty familiar with how it worked in reality.

Apparat 27 doesn't generate tones with pitch higher than 5 kHz in reality. If the incoming PRF is higher than 5 kHz (or if you're carrying the U22 jammer pod and it detects a CW signal), a synthetic "ambulance tone" is emitted instead. I'm not sure if this is implemented in the game though. It's not explicitly stated in the SFI, but considering the above, I don't believe App 27 converts the incoming signal directly to audio. It might, but I'm doubtful. Your complex tones are interesting, but I'm not sure if they're realistic. I don't think any of us here has heard what it actually sounds like in reality (it was a notoriously secret part of the aircraft), so claiming that yours are "more authentic" is going a bit far, I think. edit: hm, checked the old countermeasures PDF and maybe you're right after all. App 27 does have a bunch of filters for uninteresting signals but there's nothing that indicates that it's more complex than that. Really not sure though. The JA 37's app 27 variant only has synthetic tones though.

With a constant M 0.9 climb profile even a clean aircraft should top out at around 15500m. To get higher than that you need to zoom climb. The climb performance is very good below 10km but falls off quickly after that.

Interesting, thank you! Does "+VT" in the first image mean it's including a (full) ventral tank? That Draken chart isn't really representative for the aircraft though. The Danish Drakens were significantly different from all other Draken variants since they were primarily intended as strike aircraft, not interceptors - they didn't even have radar originally. The 35XD/TF-35 was significantly heavier than any other variant because it had a redesigned wing with space for more internal fuel, a stronger undercarriage, more hardpoints, etc. Even with that said though I wonder if that chart might be with a drop tank included, because it's significantly worse than even a J 35F with a combat loadout (two rb28 and two drop tanks) 3000 ft lower. In SFI J 35F, part 3, page 112, there's an acceleration chart for that loadout in the bottom right. The upper half of the diagram plots Mach number on the horizontal axis vs time in minutes on the vertical axis at 10 km MSL (~33000 ft) - ICAO standard atmospheric conditions in black. An identical chart but with just the two drop tanks can be found on page 100, and for a clean aircraft on page 94. It's easy to see that the J 35F definitely accelerates significantly slower than any Lightning variant (after two minutes it's up to only M 1.22, from M 0.9), but it's not nearly as bad as that TF-35 chart makes it out to be. Climbing charts for a clean aircraft can be found on page 9, by the way (with drop tanks on page 22, then there's a whole bunch of various loadout configurations covered further on). All four charts have altitude in km MSL on the vertical axis. Top left chart plots it against against time from brakes release on the runway in minutes, top right against fuel consumption as percentage of internal fuel, bottom left against distance over ground in km, bottom right against rate of climb in m/s. Would be interesting to see similar charts for the Lightning, if you have them. The Lightning completely outclasses the Viggen in acceleration at altitude as well, of course, but that's hardly surprising - the Viggen climbs pretty well (for its time) but is pretty terrible at actually doing anything at high altitude (a trait shared by many other early afterburning turbofans, which probably contributed to the legends of the turbojet interceptors). e: again though the real king of these contests is the F-4, which - if I'm reading the charts right (p. 382) - can keep pace with the earlier Lightnings even with 4xAIM-7's on the pylons. Once it's burned some fuel, at least.

Everything I've seen indicates that the Lightning was rather unremarkable for its time as far as climb rate and acceleration goes. Remember that it's roughly contemporary with the F-4, which held all of the time-to-altitude records for turbojet powered aircraft until the Streak Eagle came around in the 1970's. The numbers I've seen for its rate of climb makes it roughly on par with the J 35 Draken, which is actually really weird because the Draken uses the same engine, except it's only got one instead of two. As far as acceleration goes, if it's on the deck I'd bet on the AJ 37 over almost any aircraft that came before it. If anyone has some real charts with actual data though please post them, I'd be very interested and I could very well be wrong.

Does it, now? Where might I find that information? Seriously, I think the only bit of the flight manual for the 39A/B that I've actually confirmed to be unclassified and available at the national archives library is the list of pilot memory items. Like, just think for like three seconds about it. The aerodynamical performance for the 39A/B is almost identical to the 39C/D. I can all but assure you that those performance charts are classified.

That is possible on the later variants of the RBS15 AFAIK, but not on the variant the AJS 37 could carry.

Well, the 90+ degree turns in the upper left corner don't seem to jive with what's in the flight manual, no. The rest looks at least sorta plausible considering it's a rough sketch.

There's a targeting envelope diagram for it in the manual somewhere. You can launch it a bit off-axis, but not much more than that. It is definitely not capable of a 180 degree turn. e: from the SFI:

Swedish standard term of expiry for classification is 40 years. You can get stuff declassified before that, but it's a pain and takes forever (especially since that debacle with the accidental release of some RBS 15 info a few years back - they've tightened up their procedures since). I know a small part of the JA 37 flight manual has been declassified (the part containing aerodynamic performance charts) but I wouldn't be surprised if someone goes for requesting declassification of the entire manual around 2021 or so (I think the original was published in 1981). The part of the JA 37 that might be still classified is the data link, because as I understand it, it got adapted and improved and carried over to the Gripen, where it is a fighter-to-fighter link in addition to Link 16 even to this day. This is me speculating though.

The F-14A is needed so you can compare it to the Viggen and see two aircraft that entered operational service within about a year of each other, but are almost polar opposites. Aside from the fact that one of them is for killing ships and the other is for preventing just that, they make for a very interesting contrast in how the designers approached certain problems that the two had in common. For example: - Both aircraft needed good supersonic performance but neither could accept an excessively high approach speed. The F-14 got swing wings, and while that solution was also considered for the Viggen, it was rejected in favor of the close-coupled canard configuration. - Both aircraft faced challenges with a significant increase in weapon system complexity and an unacceptably high pilot workload. The F-14 chose a second crew member, while the Viggen made the (quite controversial at the time) decision to go with limited complexity, more assistance from the new and unproven onboard computer and therefore also full integration of basically all onboard systems with that computer. - Both aircraft faced challenges with regards to the reliability of first generation afterburning turbofans, and especially when it came to compressor stalls. For the Viggen this was less of a problem due to its role as a strike aircraft, but it was still considered a problem and the engine was only considered "acceptable with hesitation". Of course, the Viggen could get away with cutting a lot of corners because its mission scope was extremely tightly focused - it was made for one type of mission in a very specific operational area, and so (for example) it was possible to omit a real INS system in exchange for faster cold starts (because you don't need to wait for alignment).

No, there is nothing in the aircraft that enforces a set G limit. There are limits to the max attainable load factor, but they're mostly related to practical limitations of the control surfaces and the related systems - maximum force the hydraulics are capable of exerting on the elevons, max elevon deflection angle, that sort of thing. That means it varies a lot with airspeed and altitude, of course. See here for an old post of mine with more details. As per the diagram in that post, the theoretical max possible load factor is 12 G (if the wings don't rip off before that), around Mach 0.8 and below ~1000 m MSL.

For clarity: it does have gyros, but only for attitude sensing. The nav system is just dead reckoning based on initial position, attitude, course, airspeed and wind speed. The position is calculated cumulatively every 110 milliseconds or something like that. What you're doing when pressing the reference button on the stick has more to do with getting an accurate initial position than anything else, AFAIU. It's kind of an oddball solution, but it did have some advantages in the 1960's. Just like true INS (but unlike radio beacon-based systems like TACAN that were common at the time) it can't be jammed and isn't reliant on infrastructure that can be destroyed, while offering far faster cold starts than INS, and avoids an additional complicated and expensive gyro installation. The downsides were considered to be possible to live with in the tactical context the Viggen was designed to operate in.

The manual matches what's in the flight manual for the real aircraft, which states (in my translation) This course hold is not supposed to level the plane in pitch, though.

Nah, the design is completely bulletproof, since the highest mountain in Sweden (Kebnekaise) tops out at just under 2100 meters. Saab left plenty of margin of error, don't worry. :V Seriously though, the reality is that the Viggen was very tightly coupled to its intended operational niche and area. This was most definitely not an expeditionary aircraft. In reality, you would not be able to use the navigational computer at all in most of the areas on the maps currently available or announced for DCS (the exceptions being the western half of Caucasus and the small part of Normandy that lies east of Greenwich). The reason for this is that on the real nav computer, you can enter the longitude and latitude in any order, and it'll autodetect which is which. It can do this because it comes programmed with the restriction that longitude must be greater than 0° but smaller than 40°, while latitude must be greater than 40° but smaller than 90°. If you're east of Sochi-Adler, west of Greenwhich or south of Madrid, you better have brought a paper map and your dead reckoning A-game, because the computer is completely useless to you. Not that you would have been entering latitude/longitude manually all that often in reality though, the computer came preprogrammed with plenty of common Swedish landmarks and airfields accessed via the REF codes. They're input via the same entry mode on the data panel as the lat/lon coordinates (REF/LOLA, remember?) so that's why the seemingly pointless latitude restriction of 90° is there - the computer knows you're inputting a REF code rather than a coordinate if the first digit is a 9. On the JA 37 I think they reduced the max latitude to 85° to make room for more preprogrammed points, though.

Times New Roman is, uh... extremely common, to say the least, so if you've got problems with that typeface in particular you've got some pretty big problems. I'm not trying to dispute that the manual is hard to read for you, but I've got to say it's probably something other than the typeface that's causing it.

You are a great and a generous man and I will try to spread the word of your work. Will see about linguistic feedback as well.

Exactly like it does in the AJS 37 when you disable TERNAV. The nav system just drifts a bit more noticeably because the TERNAV isn't there to take fixes for you automatically. Here's an anecdote for you, though: when the original AJ 37 was complete and Saab started working on the updated and modified JA 37, they figured they wanted a better navigation system, so they went off and bought a fancy new Kearfott inertial navigation unit from the US, complete with an integrated computer. That was nice, because they could then move over all the nav calculations from the central computer to the inertial unit's own computer and just not worry about that - or so they thought. In the test aircraft they still had the logic in the central computer, so to get things working for the moment, they hacked up some bits of programming that let the computer in the inertial navigation unit emulate the analog interface the old AJ 37's unit had used and kept the calculations in the central computer. And it worked, the test aircraft flew with this hack, and then it just sorta lived on (since it worked, after all) and it got into production and in the end all JA 37's flew that way until retirement. The fancy computerized nav unit pretended to be the AJ 37's old analog one for compatibility reasons for the entire career of the aircraft.

Green munitions in the Swedish Air Force means “inert”. The live ones were mainly white. Photos of Viggens in the air with live weapons on the stations are exceptionally rare though. Live weapons were essentially never used in publicity shoots and were rarely carried of live fire training.

The outermost wing stations were originally intended for the rb 28 (AIM-4C, an early IR missile) but they were found to cause flutter and fatigue issues and were never used in service. The pylons therefore went unused for most of the aircraft's service life, until the AJS mod came around.

Yes, the IFF and the transponder are separate systems. What you've marked in red is a completely bog standard civilian SSR transponder. It has nothing to do with the IFF system at all - it's exclusively used for the benefit of civilian ATC. What you've marked in blue is a simple indicator light (actually not sure if the thing in blue is the light or if it's actually the green circle below it). It lights up when the IFF system is responding to a query, or blinks in a certain pattern if the IFF self-test fails. The actual controls for the IFF system are two knobs below the external lightning controls (far back on the right side) - there's one FRÅN/TILL knob that turns the IFF system on and off, and one knob with 11 numbered positions that sets the query/response code. That's pretty much all I know. Hope it helps.