AJS37 poor flight controls, unstable and no engine thrust

[Aero_105]

I am running a 2 week trial on the AJS37 and find the flight characteristics poor and unstable.  I also notice their isn't much engine thrust.  A F-15 is on my back in no time.  Am I missing something I adjusted the control axis tune and nothing has changed.  I have SPAK enabled.  I am coming from flying a F-18, F-16, F-15 and M2000.  The performance of this aircraft is worse than a Mig 21.  Growling Sidewinder https://www.youtube.com/watch?v=sVKjFG_suOI demostration flight model does not compare to my current one with the AJS37.

 

[razo+r]

What you describe does not sound right, but we need more informations from you.

Make sure you follow the stadard troubleshooting steps, like checking your controls, turn off arcade/game flight mode, if necessary remove all mods, run a repair etc.

Also, upload a short track. That will help a lot more.

[Aero_105]

I made sure arcade/game flight mode is off.  I did not have any mods.  I ran a repair still no change.  Here is a trk file.  The AJS37 flys like a rocking boat.  If the airspeed goes below the 4 mark the aircraft is very unstable.

AJS37TestRun2.trk

[Machalot]

Did you notice that starting a few seconds into the track, you are inputting opposing rudder and stick?  You input left rudder along with strong right stick -- a recipe for unpredictable flight.  There's no reason to use the rudder in flight.  For most of the track your stick was hard to the right.  Let go of both controls and let the aircraft settle.

As for the airspeed, note that the 4 mark on the airspeed indicator is 400 km/h, which is only 216 knots.  That is not a good speed for maneuvering, and a delta-wing aircraft like the Viggen has high drag when flying at low speed and high angle of attack.  You also exceeded 20 deg angle of attack many times during this flight, which is prohibited and will cause big problems (shown on the gauge just left and below the HUD).  Anything above 17 deg comes with a high chance of compressor stall, which also happened in your flight (sounds like a hammer accompanied with flashing Master Warning and tones ["HUVUDVARNING"]).  Compressor stalls drastically reduce engine power and are deadly at low altitude.

My advice to you is to lay off the rudder, keep your airspeed above 550 km/h except when approaching an airfield to land, and take it easy on the stick inputs.  Spend some time doing gentle maneuvers with simple, single-axis inputs (pitch only, roll only, etc.), and get a sense of how to fly without pegging the angle of attack so hard.  If you experience a compressor stall, reduce the angle of attack below 10 deg by letting go of the pull or gently pushing forward on the stick, throttle back to clear the stall, and then go to max power, wait for thrust to come back, and gently pull up.

Edited November 19, 2024 by Machalot

[Machalot]

One last thing.  In a Viggen you will lose dogfights against the F-15C.  Just to set expectations.  The Viggen is a low level attack jet, and the Eagle was the king of the sky for almost the entire service life of the Viggen.  The Eagle is faster, can pull more instantaneous and sustained G's, climbs better, accelerates better, has better cockpit visibility, a better radar, and better missiles.

Edited November 19, 2024 by Machalot

[Aero_105]

13 hours ago, Machalot said:

 There's no reason to use the rudder in flight.

 

I ended up setting a 15 deadzone on JOY_RZ to reduce unintentional rudder.  I tend to use rudder to make small corrections in flight.  When should you use rudder then, taxi, take off and landing at low speeds?  The  AJS37 does have a low angle of attack 20 degrees or less just as the Mig 21.  The AJS37 flys just not near as aggressive as a F-15.

[razo+r]

2 minutes ago, Aero_105 said:

I ended up setting a 15 deadzone on JOY_RZ to reduce unintentional rudder.  I tend to use rudder to make small corrections in flight.  When should you use rudder then, taxi, take off and landing at low speeds?  The  AJS37 does have a low angle of attack 20 degrees or less just as the Mig 21.  The AJS37 flys just not near as aggressive as a F-15.

You should only have to use rudder on the ground, in the air pretty much not at all, unless you have SPAK disabled. Only then you have to apply a bit of rudder for coordinated rolls/turns.

The Viggen can fly as aggressive as an F-15, but only once. After that all your speed is depleted and you'lll be a sitting duck.

So, different airframe, different way to fly. It's the ground attack version after all. If you get into a dogfight with an F-15, many things went wrong. Not saying you cannot try that, but it's definitly a bad idea with a predictable result.

[MAXsenna]

I ended up setting a 15 deadzone on JOY_RZ to reduce unintentional rudder.  I tend to use rudder to make small corrections in flight.  When should you use rudder then, taxi, take off and landing at low speeds?  The  AJS37 does have a low angle of attack 20 degrees or less just as the Mig 21.  The AJS37 flys just not near as aggressive as a F-15.

When taking off. Use the stick instead of pedals to correct. It's a real feature.

Sent from my SM-A536B using Tapatalk

[Snappy]

13 hours ago, MAXsenna said:

When taking off. Use the stick instead of pedals to correct. It's a real feature.

Sent from my SM-A536B using Tapatalk
 

Not sure where you got this idea from. The real manual says to use the pedals. If you want to look it up, its in the AJS 37 DEL 2 Kap II manual, page 17 in the manual (page 23 of the pdf) where the take-off procedure is outlined. Clearly says after brake release "Styr med pedalerna."

 

 

Edited November 20, 2024 by Snappy

[Snappy]

 

14 hours ago, Aero_105 said:

I ended up setting a 15 deadzone on JOY_RZ to reduce unintentional rudder.  I tend to use rudder to make small corrections in flight.  When should you use rudder then, taxi, take off and landing at low speeds?  The  AJS37 does have a low angle of attack 20 degrees or less just as the Mig 21.  The AJS37 flys just not near as aggressive as a F-15.

A few more things to consider:

A) The AJS 37 is not a dedicated air to air platform, unlike the F-15.

B) The F-15,16,18 and Mirage you came from, where all designed with a high amount of manouverability and high thrust to weight ratio.

C) In regards to the GS video, the video is from 3 years ago and I think there was a significant revision of the Viggen flight model in the meantime if I remember correctly, because it originally performed to well. 

Doesn't mean you can't fly air to air with the Viggen, it isn't too bad actually, you just need to be aware of its limitations and where the strength and  weaknesses lie. It fares better against contemporary aircraft of its era. Unfortunately the AI Mig-21 is not very realistic in its flight model and overperforming a lot ,last time I checked.

 

Edited November 20, 2024 by Snappy

[MAXsenna]

1 hour ago, Snappy said:

Not sure where you got this idea from.

I got the idea from this forum. I take it you trust @MYSE1234

 

[Ramius007]

IIRC, current Viggen FM follow charts, issues were few years ago, when Viggen was capable of mach 1.3 on the deck, it was very optimistic, rn it's great FM, but definitely, not near as easy to fly like any 4th gen, even ones without FBW

[Snappy]

8 hours ago, MAXsenna said:

I got the idea from this forum. I take it you trust @MYSE1234

 

I don’t doubt it’s possible to do it technically  , but I also think there are reasons why the real world manual explicitly says use the pedals.

Probably amongst other things because at low speeds you get no response, since stick movement does not actuate nosewheel steering contrary to the pedals, and the rudder is not effective at low speeds because of insufficient airflow.

And in the opposite way using stick to control yaw during take off roll gives you uneven lift and drag distribution because the elevons deflect which is also not desirable.

Edited November 20, 2024 by Snappy