Pitch Instability on Takeoff Rotation

[Hawkeye91]

So I've noticed on takeoffs that when I rotate the aircraft once the timer bar touches the markers and I pull back slightly to rotate, the airplane rips off the ground and I get the stall warning. It seems that as I pitch the aircraft back, it continues to rotate up even if I relax the back pressure on the stick to try to prevent over rotating. This instability seems rather dubious. Perhaps it is accurate, but when I watch videos of Viggens doing take offs at airshows, they all seem to have a nice gentle consistent rotation, not the drastic pitch up craziness I see. Now I know that these aircraft at the airshows are probably sitting on like 50% fuel with no stores, but I would think that more weight would have the opposite and make the aircraft more stable as you would need greater control deflections to achieve the same rotation rate on take off. Maybe this is accurate to the real aircraft, but it feels very unstable to me, regardless of how gentle I try to rotate. Also if I wait a little longer to get a good rotation, I end up overspeed the tires and blowing them. 

 

Any suggestions?

 

Also I do have a modest curve of 10 set with a 10mm extension on my stick.

 

Edited August 24, 2021 by Hawkeye91

[Skyracer]

Adjust the trim. IRL you were sopose to set the trim -2.5. But in the game i find it -1 or 0 the best

[Machalot]

7 hours ago, Skyracer said:

Adjust the trim. IRL you were sopose to set the trim -2.5. But in the game i find it -1 or 0 the best

Is that pitch down trim? 

[Skyracer]

Nose up!

[Machalot]

1 hour ago, Skyracer said:

Nose up!

Thought so, I was just confused by the minus sign. 

[TOViper]

I flew ~1.000.000 sorties with the DCS Viggen (at least!) until yesterday

During a longer discussion with other members (including @RagnarDa ) and testing a lot, I finally found out that waiting for the timeline to overlap the markers (not just touching them) is currently "my" key for a "solid & round & smooth" lift-off. It seems to me that lift-off at approx 310-315 km/h is what the DCS module currently needs.

I know that @320 the tires should burst, and yes ... they do!

 

The discussion can be found here:

https://forums.eagle.ru/topic/220737-ajs37-and-acceleration/page/2/

 

Another discussion related to this topic might be interesting as well:

https://forums.eagle.ru/topic/153817-nose-heavy-on-rotation

 

There is also a difference in having the X-tank mounted or not.

X-tank mounted needs according to manual approx 2.5 to 3 nos upp, while no X-tank requires ~0.

 

I add a few tracks I did today morning:
You can see that in the DCS module there is even no stick necessary for a nice & smooth lift-off, when using good "nos upp" values.

The trim values depend on which stations the load-out is mounted, but as a general guide 5° to 5.5° nos upp are just fine.

No pitch movement on the stick, just trim *LOL*

 

So the over-rotation other users report must have to do with stick input, does it?

 

 

 

2021-08-26_Viggen_Take-Offs_Focus_on_trim_settings.zip

Edited August 27, 2021 by TOViper
removed unnecessary infos