renhanxue

Well, remember that the original CK37 was a dawn-of-the-digital-era design from the late 60's. The 80286 solution in the AJS 37 was kind of a kludge, really - they upgraded the core of the computer with 80's off-the-shelf components, new memory etc, but kept most of the old interfaces the same while adding a few new ones (such as the MIL-STD-1553B serial bus). The Gripen A and B's computer was a completely new, modern (for the 90's) design and while I know very little about it I believe it was based on the PowerPC architecture (also popular in 90's Macintoshes), with CPU's made by Ericsson. There's a little information about it here: http://www.x-plane.org/home/urf/aviation/gripen/gripen-network.html

TIL that when they updated CK37 (the central computer aboard the AJS 37) from its original 60's incarnation to 80's technology, the CPU they chose was a 80286 together with the 80287 math coprocessor. If you had an IBM PC or PC clone in the mid-80's, you probably had a very similar CPU. (I'm on vacation, that's why I'm posting so much)

The SFI says you're allowed up to 10 seconds of flying with negative G load, but unless you're in full AB it's actually limited by the engine lubrication system, not by the fuel feed. The central feed tank has two compartments designed for keeping the fuel feed working while under negative load, with a total volume of about 2% of the internal fuel. This volume was deliberately chosen to provide sufficient fuel for those 10 seconds mentioned above assuming full AB at sea level. If you're using less thrust you're going to get the OLJETRYCK (oil pressure) warning way before the engine flames out from fuel starvation. Very nice! I've been thinking I should go there since forever. I think it's time I get off my butt and call up my brother (who lives in Gothenburg) and ask him if I can come over and visit sometime. Like JanTelefon says, the landing gear lever is to the left side of the pilot, it's just really far back and pretty low. I've marked it in red:

Anvisningar för typinflygning fpl 37, 1985 års utgåva I haven't really proofed this PDF at all so yell if something's weird and I'll get you the original photos.

From around M 0.6 at sea level (increasing with altitude) and up there are also ample opportunities to exceed the load factor limit (8 G), and there is nothing to stop you from doing it :) It is also very easily possible to overspeed a clean aircraft in level flight at low altitude. At low altitudes, the thrust-to-drag ratio at max AB reaches 1:1 well above Vmo (which is M 1.1 at sea level), and if you're lightly loaded it takes only 12 seconds from M 0.9 to M 1.1 at max AB.

There's a stick shaker, that's it. It has a few different modes of operation, so it can activate at different points - IIRC it activates earlier in more critical flight phases such as landing and low altitude flying etc.

It's mostly manual, but there is a function called "serietrim" which automatically compensates for most of the big pitch trim changes in the transonic and supersonic regimes.

Well, I'm sure they did it occasionally, the question is how often and whether it was sanctioned by the higher ups. What I do know as a verifiable fact is during the basic type rating for any Viggen model (that is, conversion from the Sk 60 subsonic trainer), you would have to fly at least two lessons in the Sk 37 (the two-seater Viggen) involving navigation at 50 m AGL and M 0.8. From there, there is of course a long way to 10 meters and M 0.9, but that's the baseline that got taught to pretty fresh cadets as a part of their introduction to the aircraft within their first ~45 flight hours on the type, before you even started training them in tactical flying. The source for the above is anvisningar för typinflygning fpl 37 (ATIS 37); I have the entire thing photographed and I could turn it into a PDF if anyone's interested, but here are the pages that describe the lesson in question.

Page 21 in this PDF.

It's not at all surprising to me that someone who's only really flown the Jaguar might be very impressed with the Viggen's performance.

tall tales, I told you :V Pilots tend to love good stories just a bit too much.

Okay I'm sorry for killing the thread. Have some funnies and tall tales instead (Viggen stuff starts at the bottom of page 3): [ame]http://www.collectair.co.uk/pdf/interview-hr.pdf[/ame]

To make the thread boring again after all this excitement, here are some numbers/talking about the flight envelope limitations, extracted from Aerodynamik III for those who either don't speak ärans och hjältarnas språk or don't feel like reading obscure technical texts from the 1980's in their spare time. For the AJ(S) 37, max permitted alpha is 18° (JA 37: 23°). You will start getting engine surges at around 20° (JA 37: 25°, be jealous of that RM8B) and pitch-up tendencies followed by spin or superstall at around 28-30°. The pitch stability is described as "okay" or "basically undisturbed" up to around 25° for a clean aircraft; payload on the wing pylons worsens this stability somewhat. When it comes to sustained turn performance, the AJ(S) 37 unsurprisingly isn't exactly stellar. At sea level with a clean, light aircraft, you can barely maintain a 3 G turn at 7-800 km/h IAS at military power. With full afterburner, you can reach 6 G's in a pretty narrow band of speeds above 800 km/h IAS. See this graph: On the Y axis, drag (D) and thrust (T) in kiloponds. On the X axis, IAS in km/h. The solid lines in the chart that start at the far left are, from bottom and up: D PLANFLYKT - drag in level flight T, MAX SLÄCKT - thrust at military power T, MAX TÄND EBK - thrust at full AB Then there are three solid curved lines starting at around 400 km/h IAS from the top, indicating the drag at G loads of 6, 4 and 3 G's respectively from the top (marked with n(z) in the right margin). The shaded areas show where there's a significant lack of thrust to maintain the desired turn.

The JA 37's radar was a medium PRF monopulse doppler, the AJ(S) 37's a low PRF monopulse with no doppler function. They had completely different purposes. In the JA 37 avionics seminar they mentioned that choosing medium PRF was a compromise, since they figured it was too complex to support multiple PRF's at the time - but they added it on later JA 37 edits, I believe. Consider though that the JA 37 had datalinks that let it get radar images both from the ground and from other JA 37's and the need for a very long range radar on each aircraft becomes much less pressing. The Swedish air defense kind of assumed that Stril would be available to guide the fighters to intercept - autonomous operation was a last resort. Yep, provides emergency power in case of generator failure or somesuch. Said reserve power will also feed an emergency hydraulic pump to provide pressure to system 2 if that also fails. There's a whole bunch of reasons for those - off the top of my head I seem to recall lack of space in the wing for a conventional gear and helping yaw stability when landing.

RBS 15 yes, as far as I know it can be programmed to fly a route with multiple waypoints. The rb 04E is a lot more primitive - as far as I can tell from the manual the only setting you can select in the air is the targeting mode, ENKEL or GRUPP (single target mode or group of targets mode). Everything else is programmed on the missile itself by the preflight mechanic, including (as far as I know) if the fallback home-on-jam is enabled or not. Other than that, the only thing you do is find a likely target on your radar B-scope, point your plane thataway, hit weapons release and off it goes, in a straight line. It's completely fire and forget, you can't do anything to influence its targeting really so just turn away and hope for the best. edit: beaten twice over

Soooo, who wants to revive that old split S debate again? Nobody? Well, too bad, because I'm doing it anyway, if only to lay down the facts! This is based on pages 50-52 in Fpl 37 aerodynamik III (pages 51-53 in the PDF since it counts the cover as page 1). First, the scenario. The document states that ordinary split S technique is to start applying G load during the roll and reach max permitted load (8 G's) about at the same time as reaching a fully inverted state. If you disregard the time it takes to reach max G load, you arrive at the thick dashed line marked "Lägsta ing. höjd för halvroll" in this diagram: On the Y axis, lowest possible entry altitude for a split S, with a clean AJ 37 at flight idle, and an exit altitude of 500 meters. The solid line is the same but for entry at the least optimal dive angle (steeper dive = split S exits at lower altitude, assuming the entry speed exceeds M 0.8 or so). On the X axis, entry speed (Mach number). The thin, numbered (barely legible) s-formed curves connect the entry point with the exit point and thus show the speed loss over altitude. All split S maneuvers exit subsonic regardless of the entry speed. So, yeah, you'll need about a thousand meters of altitude (well, ish) to do a split S in an AJS 37. And that's that. The margins are really small, too and you risk superstall by exceeding max alpha, engine compressor stalls, flying into the ground because you didn't pull the stick hard enough, etc etc. There's also this though, which shows the minimum altitude required to recover from a dive with 500 meters to spare, also at flight idle: So you can recover from a vertical dive if you have about 500 meters. Maybe. The diagram hasn't been corrected for the time it takes to reach max permitted G loading.

I don't know! I'm going to the archives tomorrow to see if I can get something out of Publikationsförteckning fpl 37.

It was cleared for operational use so there's got to have been live fire tests. Test flights started in fall 1997. The photo mattebubben posted is from 1999.

Yes. The AIM-120 was procured with the intention of using it on the Gripen, but it was also integrated on the JA 37D(i?) very late in its life. In the late 90's they were still figuring they'd be running the JA 37 in parallel with the Gripens for many years to come, like the Draken had been kept in parallel with the Viggen, and they wanted to keep it "operationally relevant". It never turned out that way because a ton of air wings got disbanded after 2000, but it wasn't a bad idea.

Fpl 37 aerodynamik III : Manöverprestandabegränsningar : Halvroll : Kompendium So I heard you guys were interested in the Viggen's split S performance...? Well, here you go, read 50 pages about it, (tl;dr: no I'm pretty sure you can't do it from 500m) and remember to eat your spinach: If anything happens after you've reached 60° dive angle, continue the maneuver but exert yourself (on the stick) (eat twice as many slices of bread + spinach) and reduce throttle to flight idle. Also, gonna quote myself for the previous part because nobody reads the last post on a page when the next page has a Cobra post on top:

Added Aerodynamik fpl 37: kompendium. edit: and Fpl 37 aerodynamik III: Manöverprestandabegränsningar, halvroll: kompendium

Aerodynamik fpl 37: kompendium Discovered yesterday that this was declassified and received photos of it from an acquaintance. There's another part forthcoming too that may solve the silly split S debate forever. Lots of cool illustrations too, my favorite might be this one: Use the afterburner, fool!

Added checklists/memory items.

Here's something on topic, then! I mentioned last week that I didn't have any checklists for the AJS 37. Well, I was at the national archives today and now I do! Or, rather, I think these are memory items but I'm not sure if pilots were required to learn they all by heart. Something for your kneeboard? Either way, here you go, regular and emergency: Minneslista för ff i fpl AJS37 Minneslista för ff i fpl 37 NÖD

Great post, thanks! We have the open description part 1 chapter 1 as well as the formerly secret parts 2 and 3 for the AJ 37 (the orginal edition from the early-mid 70's). The rest of the parts I haven't gotten around to photographing. It'd be great if you could, though!