DCS: AJS-37 Viggen Discussion

[shaggy]

[mambo]

[QuiGon]

Quick question: Can the radar lock onto ground targets (e.g. ships)?

[Pocket Sized]

I've heard that the Viggen becomes unstable in the transonic region, (to the point of there being a dedicated warning light) can anyone elaborate on this?

 

Seeing as we're probably going to spend a lot of time at low altitude + full mil, this kinda concerns me :(

[BlackLion213]

I've heard that the Viggen becomes unstable in the transonic region, (to the point of there being a dedicated warning light) can anyone elaborate on this?

 

Seeing as we're probably going to spend a lot of time at low altitude + full mil, this kinda concerns me :(

 

I'm not that well informed, but judging from yesterdays Grudge Match where Viggens were seen reaching ~797 KIAS on the deck (with rockets loaded)!!....I'm pretty sure that it will be flyable straight and level at very high speeds.

 

However, the Viggen gameplay video does show some less than elegant pitch response at transonic speeds (section while firing rockets). My guess is that it will fly beautifully straight and level, but fight back a bit as you load up the airframe in the transonic region.

 

Just I guess from what I've seen thus far.

 

-Nick

[renhanxue]

It's not unstable in the transonic region, but there are trim changes and that's what the light is calling your attention to. The SFI (del 2 kap II) says:

 

24.2 Characteristics in the transonic region and at high Mach numbers

 

The aircraft has good handling characteristics at high Mach numbers.

 

[...]

 

With the autopilot's standard mode SPAK active, a weak nose down trim change appears at M = 0.95, but it becomes negligible at M ≈ 1.03. At high Mach (depending on altitude), there is a moderate nose down trim change that is caused by exceeding the series trim authority.

 

Elevon authority is somewhat reduced at supersonic seeds. Stick movements hence become somewhat larger, which leads to increased stick forces.

The issues start if the autopilot has failed somehow so you don't have the oscillation dampening and trim help etc that SPAK mode provides. In the fallback mode (GSA) the aircraft starts having weak pitch down tendencies at M ≈ 0.85, changing to pitch up at M ≈ 0.95, and then changing back to pitch down at M > 1.03 and increasing in force as M increases.

 

Additionally:

24.3 High alpha

[...]

24.3.2 Load factor > 1

[...]

Drag increases heavily as alpha rises. The aircraft therefore loses speed rapidly in turns with high load factor, if the speed loss is not offset by increased throttle and/or a reduction in altitude. The aircraft is capable of very tight turns, but these require high throttle (lit AB in most cases) in order to avoid losing speed rapidly. When rapidly applying large pitch inputs, there is a risk of load factor overshoot resulting in exceeding maximum permitted load factor. The pilot should therefore avoid harsh stick movements that give rapid load factor increases. In order to avoid quick retardation when flying with high load factor, the pilot should apply throttle increase before the stick command, so that the power comes at the same time as the load factor increase.

 

Light buffeting starts appearing at ɑ 4-5°. The buffeting grows somewhat in strength with increasing alpha, and is more or less constant at ɑ > 12°. The buffeting level does not limit maneuverability or the ability to aim. At supersonic speeds there is no buffeting at any load factor.

 

In turns with quick retardation from M = 1.0 down to M ≈ 0.9 pitch-up tendencies appear, the strength of which depend on the aircraft's load factor when entering the transonic region. The reason for this is the normal change of the longitudinal stability and control surface authority in this speed regime. External loads only have a moderate effect on these characteristics. Care shall be taken when retarding from M ≈ 1.0 to M ≈ 0.9 so no unacceptable increases of load factor and/or alpha are encountered.

 

 

e: the aerodynamics compendium has more to say about this though, namely that certain types of underwing loads (ARAK and countermeasure pods mentioned) make the available pitch authority quite low in transonic and supersonic regimes.

Edited December 11, 2016 by renhanxue

[probad]

I've heard that the Viggen becomes unstable in the transonic region, (to the point of there being a dedicated warning light) can anyone elaborate on this?

 

Seeing as we're probably going to spend a lot of time at low altitude + full mil, this kinda concerns me :(

 

who are you hearing these things from? that's what concerns me.

[Goblin]

who are you hearing these things from? that's what concerns me.

 

Cobra said so himself, in a post here, somewhere :)

[probad]

i dont recall cobra's description of it to be too alarming, which was why i was curious to know if he heard it from somewhere else.

[Cobra847]

Mach tuck is quite noticeable, and the aircraft does vibrate in the transonic region.

 

Additionally, the control scheme changes significantly between sub-sonic and supersonic flight regimes, so there is a noticeably "sharp" change in control deflection.

[Goblin]

The Viggen had pitch stability problems in the transpnic speed region. This was partly solved by area ruling the fuselage by adding a hump on the fuselage spine.

 

I wrote about it in the "Can you make it over the hump" thread... :)

 

https://forums.eagle.ru/showpost.php?p=2811750&postcount=54

 

Come to think of it, I don't believe we ever got an answer to the question in that thread... ;)

[Hummingbird]

Mach tuck is quite noticeable, and the aircraft does vibrate in the transonic region.

 

Additionally, the control scheme changes significantly between sub-sonic and supersonic flight regimes, so there is a noticeably "sharp" change in control deflection.

 

The bobbing up and down in pitch as if bouncing on a spring, that I've noticed in a couple of videos now, looks abit weird though.

[Cobra847]

The bobbing up and down in pitch as if bouncing on a spring, that I've noticed in a couple of videos now, looks abit weird though.

 

That's just me flying poorly. Pilot induced oscillations, as it were.

 

Not something that happens with a neutral stick.

[Hummingbird]

That's just me flying poorly. Pilot induced oscillations, as it were.

 

Not something that happens with a neutral stick.

 

Ok, so it does not happen after centering the stick following a pull or push?

 

I'm asking because I noticed it in a couple of videos now so I became abit worried.

Edited December 13, 2016 by Hummingbird

[Pikey]

I cannot see anything to worry about, the close formations at that speed were retained during the grudge match stream. That's all you need to know.

[Pikey]

Oh and you can sucker the LNS dev pilots into a sharp climbing turn at the merge and demolish their energy...but thats another story... :P

I cannot see anything to worry about, the close formations at that speed were retained during the grudge match stream. That's all you need to know.

[Agremont]

Just a quick question. I know this is an SF37 but I'm curious about the two pods around the external fuel tank in this photo. What are they? Camera pods?

 

[mattebubben]

Just a quick question. I know this is an SF37 but I'm curious about the two pods around the external fuel tank in this photo. What are they? Camera pods?

 

 

Yes they are Recce pods

they are named MSK Vänster (Vänster = Left) and MSK Höger (Höger = Right)

they are used for Night Recce.

MSK Vänster (left Pod) has 3 Cameras with 76mm optic + a Flash Unit,

The cameras are mounted to cover a 120 degree area.

 

The Flash unit on the Left pod only lights up the 60 degrees to the left inside the area covered by the cameras but the second pod (MSK Höger) contains only a flash unit in order to cover the 60 degrees to the right so together they cover the entire 120 degree area covered by the Cameras.

 

The Cameras/Flash Units work in the shortwave IR range that is immediately outside the visible spectrum so the flash from the flash units is not visible to the human eye.

This System was used for Photography from a low altitude.

 

 

 

the SH-37 also carried camera pods of different types including those just mentioned

as it lacked the nose camera set as it was equipped with a radar instead.

 

Here are Examples of a SH 37 with Camera Pods.

 

 

 

 

The SH 37 could carry the same MSK Vänster / MSK Höger pods as the SF 37 but also had a dedicated camera pod fixed to the right side of the body named KaK with a 600 mm focal length that was designed for long range photography against targets such as Ships and harbors the.

 

That Camera had to be removed in order to Carry the Night Recce pods.

 

On the Second Picture it looks like its mounted with both the KAK Camera as well as the MSK Vänster Pod but im not sure if that was an operational loadout

(since only have of the area covered by the Cameras in the MSK Pod would be correctly lit without the other MSK Pod)

or if its simply that they mounted it for Display purposes.

 

On a side note.

These two pictures surprised me at first as i did not know that F 15 had operated the SH 37 but it seems that during the 90s when the second division was reformed and brought up to full combat strenght it included both attack and Recce aircraft (from other Wings had had been retired) and not with just AJ/AJS aircraft as i had assumed earlier

but looking into Viggen Serial number lists confirms that F 15 did indeed fly some SH 37 and SF 37s

 

And if that list is correct then the aircraft on these two picture (15-81) crashed in an accident a few months after these pictures were taken.

(The second picture was taken at RIAT on 21 July 1996 and it crashed in October 16 1996 with the pilot dying in the accident)

Edited December 13, 2016 by mattebubben

[AdurianJ]

Just a quick question. I know this is an SF37 but I'm curious about the two pods around the external fuel tank in this photo. What are they? Camera pods?

 

 

It should be a Night photography pod on the left which contained IR film cameras while the one on the right side (from the aircraft POV) is a flash pod for low light photography illumination.

[Agremont]

Thanks for the replies.

[Quip]

What was the Viggen Selfie-pod called?

[EasyEB]

That would be the Självporträttskapsel.

[drPhibes]

I think roadside speed cameras would work well for that purpose (at least if they were radar based and not based on sensors in the road as is the norm these days).

[RaXha]

I think roadside speed cameras would work well for that purpose (at least if they were radar based and not based on sensors in the road as is the norm these days).

 

I'm faily sure swedish speed cameras are radar based. :P

[Quip]

That (Speed trap) has been done... I doubt this is true though