RagnarDa

DCS: AJS-37 Viggen Discussion I can't remember reading that low-alpha landings was a design criterion for Viggen? I might misremember or missed it but all I can remember reading is the short-field requirements (<500m), and that the design should be mechanically simple (ruling out variable wings), "good maneuverability" and then nothing else. Don't know what is considered low alpha while landing and if 12 or 15,5 degrees qualify as low or high but a short Google-search for comparison gives the F-4 at about 10 degrees and the F-18 at 8 degrees when landing at a carrier. Since this has come up before I think it's important to get the right expectation of how the Viggen flies and understand the trade-off of the severe induced drag that is inherent in its design. I suggest reading more on Wikipedia on the topics of induced drag or aspect ratio or searching for "Aerodynamics of the Viggen 37 aircraft". If nothing else you might want to read this interview with a Viggen pilot: http://www.warbirdsnews.com/warbird-articles/swedish-air-force-historic-flight-cockpit.html

One important difference between Viggen and other planes like F-4 and F-16 is aspect ratio: the ratio of the length vs width of the wing. Hold your hand flat with the thumb facing your eyes. Imaging what you see is what the wind racing against the wing is "seeing" and interacting with. If you angle your hand so your thumb points to the ceiling you will see a little more of your hand and by analogy the wind will interact with. This represent a high-aspect wing. If you on the other hand hold your hand flat and so the tips of your fingers are pointing towards your eye you will see less of your hand than in the first case, and therefore the wind which is flowing on the wing will have less wing to generate lift with. If you angle your hand now so the tips of your hand is pointing towards the ceiling your will again see most of your hand-wing. This represent a low aspect wing. A low-aspect wing with short wings are good if you want to cram as much wing-area you can behind the shock-wave that is generated by the nose during supersonic flight. A high-aspect ratio wing on the other hand don't need to be angled so much (alpha or angle of attack) to expose a large part of the wing and is therefore more efficient (on for example sail-planes) because if you need to angle your wing a lot to generate the needed lift more of the lift is pointed in the opposite direction of your travel direction (now called "induced drag"). So compared to a high-aspect fighter like the F-16 the Viggen can generate the same lift or more in a turn = acceleration into another direction or G's. But, it can't do it without loosing a lot of its speed in the process because it has to hold a higher alpha. This problem is also apparent when for example landing as it is difficult to maintain a specific airspeed, hence the implementation of the landing-autothrust called AFK in the Viggen.

1) The max distance displayed on the radar screen is 120km. The altitude of the airplane hasn't any effect except for larger parts of the scan area might be "in radar-shade" when flying low so you of course have a better and larger view high up. The picture is aligned with the ground so the attitude of the aircraft matters as the gimbal-range of the radar dish would restrict you from viewing terrain that is close (when pitching up) or far away (when pitching down). 2) Other aircrafts within the scan zone would get a beep on their RWR even though you are in air-to-ground mode. There is also the possibility you might pick out low flying aircrafts while in terrain-mapping mode.

Yes the Rb75/DWS39(="Bk90" in Sweden) is one of those combinations that could be enabled if less realistic options was added. When using the Bk90/DWS39 there is no indication on the HUD where on the ground the target is, only the direction where to fly to (and when to release the munition). Other attack-modes does show where the target is on the ground (like for rockets for example). The reason they don't show it is because while using the Bk90 the velocity vector indicator/flight path marker is displayed and it's the same symbol as the target-marker (!) - a ring. The HUD in the Viggen is very different to what we are used to, especially that it uses a small number of symbols (a ring and 14 lines in different lengths) which all have different meanings in different modes. For example, the tailfin of the velocity vector indicator indicates the error in time-to-waypoint when navigating and it also indicates that the radar is used to measure distance to the ground when attacking.

Yes the options for different armament combinations are very limited. There is a rotary-switch where the ground crew selects what armament is carried and it only allows one type of air-to-ground type except for the Rb05/AKAN-combo (and possibly AGM65/AKAN, not sure). I am considering expanding the list of possible combinations but the ultimate restriction is the weapon selector in the cockpit (for example the same switch position selects the bombs in dive aiming as well as the Rb05 in anti ship configuration iirc).

I löve how the Blackbird-pilots helmet covers his whole body :D

In short, you aim the Rb04 with a wind-corrected line on the radar (straight ahead) or just visually. When released it dives to sea-skimming height using the radar altimeter and start searching for targets. If you have selected the single-target mode it will target the first contact it sees. If you selected the group-mode it will search for three targets that is in a straight line from the POV of the seeker (themselves not more that 2,7km from each other). Then it selects one of these three targets depending on a switch selected by ground crew. This way, if you for example launch two missiles one could target the first ship and the other missile target the third ship. The Rb15 is different. It can be launched "straight ahead" like the Rb04 but usually you'll use waypoints for it. It uses up to 4 waypoints: one is where the target is (or search area), one is a turning point, one where it is to dive to sea-skimming altitude (or rather the distance to turning-point) and the last is a auto-destruct point. You can set them up by inputting coordinates in the computer, or moving a cursor on the radar screen. There are many different search modes and options for for example how the targets would be selected in a group (randomly or depending on closeness to target-waypoint for example) or the size of the search area. The navigation computer in the aircraft can use a set "missile-in-target" target time so you can coordinate an attack from different directions and all missiles will arrive at the same time.

DCS: AJS-37 Viggen Discussion The terrnav has the whole region of operation (at least that what's what we think). They probably loaded the map of where they where supposed to be flying, as opposed to all of Sweden for example. I don't have info about the resolution (at least from memory, do you Jedi?) but the current guesstimation is 100m based on the fact that that's the resolution of the estimated navigational error presented to the pilot (it is reset to 0, or below 100m when the TERRNAV performs a "fix"). Edit: some quick calculations: Georgia is ~70 000 square kilometers so a 16-bit height map with resolution 100m is roughly 1.4 megabytes of data. Wikipedia tells me they have been making 2mb SSDs since middle of the 70's and tape-drives are of course even larger...

The radar in the attack-Viggens doesn't do any processing or interpretation of the radar-signal, it just shows you the raw input from the receiver (except for scaling of course and a anti-jamming filter). It is up to the pilot to figure out what everything is. Air-to-air mode is same as terrain-mapping mode except the antenna is pointed upward. Air contacts is shown as "blimps". Symbols on the radar-screen are fed from the navigation computer and shows where for example the current waypoint is believed to be. It might or it might not match with the real location as shown by the radar picture. As for comparison with the MiG-21 I unfortunately haven't had enough time to compare the two in-game but I wouldn't be surprised if the detection-ranges of air-targets is similar.

The AJ and AJS radar has a air to air mode, just not like the ones you are used to ;) Not sure about A/G on the fighter-Viggen but I don't think so.

DCS: AJS-37 Viggen Discussion Remember the AJ/S radar is somewhat low resolution. It has low PRF optimal for detecting high contrast objects in the sea or large terrain features (for navigation) at long ranges. I've calculated the resolution at max range (120km) to be in the ballpark of 500m. A pilot described it as you can possibly make out large buildings like the Globen-building (diameter 110m) but anything smaller is blurry. You won't normally detect a fighter-size target unless really close. Edit: So lower PRF = longer range but lower resolution Edit2: No link-system in the AJ or AJS.

DCS: AJS-37 Viggen Discussion 3 degrees is 5% (or 5,24%) so to get distance to start descending just check your height and multiply that with 20. To get correct descent rate divide your ground speed with 20. Edit: I realized the sink rate indicator is scaled in m/s so uh... divide your ground speed with 3,6 then 20...

DCS: AJS-37 Viggen Discussion The Bk90 INS is only active from launch, or at least I think it is from what I can tell. To minimize the effect of accumulated navigational error the pilot are supposed to correct the airplanes indicated own position before launch by either doing a visual overfly over a predefined point and pressing a button or marking that point with radar. There is also a system in the AJS that is called TERRNAV that reads the radar altimeter and tries to figure out the position of the jet from that. And lastly, the Bk90s submunitions covers a pretty big area which helps. They are mostly launched in pairs to maximize this effect too. Apart from that, you are correct in that the Bk90 could be quite inaccurate if you are not careful.

Yes everything above is modeled. The indicated own position will drift (especially at height or when flying over sea or flat terrain, or upside down); gyroscopes will drift and the headings will need to be reset; everything has latencies modeled; and also all presentation aswell as ballistic calculations uses the proper simulated sources so you will have to for example make sure the altimeter is correct for your bombs to hit where you are aiming.

DCS: AJS-37 Viggen Discussion It has a early "kind-of" INS that instead of accelerometers uses indicated airspeed (from the pitot) and the gyrocompass to determine the route traveled over the ground. It has drawbacks so the pilot is required to constantly monitor the system giving it updates of the airplanes known position, inputting the wind speed at height, setting correct altimeter setting etc. There are support-systems like a Doppler-system and a system that determines the planes position by using the radar altimeter and comparing it with a stored height-map. You can input new waypoints at any time using a keypad by the pilots right knee.

It already is.

There are 5 bombing-modes IIRC (I'll have to check) and most of them share the same general visual layout of the rocket/guns sights but function differently. There are 4 different general layouts of the HUD symbology and they all share the same individual symbology but these shift meaning in different modes (for example a ring shows where the plane is heading when in NAV-mode, the same ring shows where the target is when in rocket-attack mode and when using bombs it sometimes show where to steer to avoid shrapnel, another example is two lines that shows time to pull-up point and also the wing-span of the target).

Yes I meant that not only the symbology is different.

DCS: AJS-37 Viggen Discussion It's good in that it's accurate and also good if you hate that target in particular you can provide a excessive amount of explosives in a very tight spot. What is bad about it is if the target fires back... ;) It is also just different with some outside-of-the-box-thinking by SAAB (or whoever designed it).

No it didn't have this option IRL. It was a requested feature here on the forum so I added it in. The salvo length is 0.6 seconds IIRC (0.1 sec per rocket "wave"). You might also be interested to know that the standard rocket and a/g guns sight in the Viggen is quite different to anything you (or at least I) have tried before.

What I did was I used a switch that has no function for rockets (Prepared/Standard) and if you flip it the rockets will fire one from each pod in 0.1 seconds. Also changed the sight so it changes according to the position of the switch. The way you suggested you would lose potential accuracy because the sight considers the salvo-length of the rockets so either it's a on/off switch/setting or I have to add a short delay (0.3 seconds) after pulling the trigger before the rockets launch. I did a very quick test of my implementation and I wasn't able to hit anything :P so I'm not sure it's a advantage or even very useful...

Ok it's implemented now.

The manual states that the Maverick display shows a 5 degree picture, and compared with other modules in DCS that's pretty zoomed out making it slightly difficult to use (it's almost no zoom at all). In a simulator it's even more difficult to use than IRL I believe. Not sure if the B-version was ever purchased or carried but it might have been at least plausible that it could have been carried. So it would be included for playability reasons.

+1

You'll hear a tone which frequency is the pulse repetition frequency (PRF) of the radar signal. There is no database in the rwr that identifies the emitter so it's up to the pilot to guess what it is. Generally, a higher pitch means it's a radar with shorter range; and frequent beeps could indicate it is tracking you. There are also two extra sounds: one for PRFs that are so high-frequency that the human ear can't hear them, and one for continuous waveforms (if carrying the U22/A pod).