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Auto pilot and nose down problem


Raptorx7
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I've noticed that if I don't keep the aircraft trimmed at at least -5dg it will nose down harshly, this is a bit of a problem in the instant action missions where I need to immediately trim it out or crash. Is this intended or a problem on my end? And if it is a problem on my end I can't imagine what it is because none of my other DCS aircraft nose down like this. As for auto pilot it just simply doesn't seem to work, i hold steady at an altitude I want and engage it but the aircraft still goes up and down drastically. I have read the manual on this and I am not sure whats wrong. Thanks guys!


Edited by Raptorx7
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What speed are you seeing this at? :)

 

Keep in mind, that around transonic and supersonic regimes, you will begin to experience mach tuck.

 

Thanks for the quick response! Its definitely not at those speeds, its usually around 500-600 or so. I must be doing something wrong with the trim, but it says in the manual that it becomes automatic when altitude hold is on so I'm very confused. Can you repeat the problem with the instant missions that I mentioned in the OP? Edit: Forgive my negativity here, I love the module overall :)


Edited by Raptorx7
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Not necessarily. For a centerline tank you need a 3deg nose up trim for takeoff, manual says. Pretty close to the five you describe, also Attitude and altitude hold is a must to use on this baby. Recommend mapping it to Hotas, power grid whatever

 

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I've also experienced something along this. After take-off, get up to speed, engage altitude hold. After 3-4 seconds of horizontal flight the aircraft decides to pitch down at a rate of about 5 degrees per second, quickly leading to a fast dive. All while altitude hold stays engaged.

 

Disclaimer: I haven't gone through the manual, there is a risk of user error on my part. Although not sure what it would be.

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Tested again and experienced the same. Confirmed that it wasn't a joystick input commanded dive. I'm aware that as the landing gear comes up, the flaps are retracted and you could have a little dip. But this happens afterwards, when already at speed (550km/h) and engaging altitude hold. It sits perfect for a while, but after a couple of seconds (5-10s) it just starts diving without any other indication.

 

It seems to happen soon after take-off; airborne, gear is up, speed stable around 550km/h and leveled off at 200-300 meters when engaging the altitude hold mode. For some reason it's not consistent, I get it sometimes - sometimes not. I even caught it once, disengaged altitude hold, leveled off manually and re-engaged. Same thing again.

 

However, once having been airborne for a little longer, the problem doesn't occur. So it seems associated with the first minute or so after take-off. Is there any particular procedure here that I might have missed?

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I'm not that familiar with the Viggen yet, but generally with altitude hold: is your altimeter functioning? Is this over flat ground?

 

You should probably post a track.

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I've been running with just a simple generated mission starting from the runway. Nothing special. Doing a few more runs now to see if I can re-create it in a sensible way.

 

I've done another 10 take-offs now, I'm starting to suspect it is/was a controller input issue after all. Noticed odd/random drift possibly related to controller calibration, moving all input devices through their full axis just before take-off seems to have resolved it.

 

My apologies for consuming your time. Will do another 10 runs to confirm. (Rudder is still super-twitchy on the runway though... :-))

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Could this possibly be related?

 

I had the same issue of a non-functional pitch trim. As i tried to investigate, why sometimes it works and sometimes not, I figured out that if once an emergency trim switch was clicked (doesn't matter which one and doesn't matter if you set it back into its initial position), the normal trim system does not work any more. As one is ordered to check whether the switch (Nr. 3 on page 24 in the manual) is centered during the startup instructions, one can get easily tempted to click on the emergency trim switch. As said, this causes the normal system to stop working.

 

However, i had a look into the manual and there is stated as well, that it is intended to work in this way (page 75, Emergency trim section). Furthermore, according to the manual, you have to reset the circuit breaker on the right side of the cockpit in order to reenable the normal trim system.

 

Therefore, it's not a bug but an obstacle as it can easily ruin the mission.

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Don't think so as I don't touch any buttons on an on-runway-from-mission-start take-off. At least I haven't touched any buttons. As per my previous comment, I suspect it was local user (machine) error causing the issue for me, still no issues after plenty more take-offs (maybe I'm just getting better and not pushing things far off the norm to trigger any possible bugs... :joystick:). Thanks anyway! :thumbup:

 

Could this possibly be related?
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Does anyone have as solution for this auto-pilot problem? The plane just goes into a climb when I turn on altitude-hold, all 3 lights are on at this point. If I move the stick at all or take it out of it the trim immediately resets and the nose points straight at the ground.

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Is this at very low altitude?

 

This happens no matter what altitude I am at. The plane just starts nosing up immediately after I turn altitude hold on. It does the same with the attitude control as well, even if the aircraft is at a negative AOA when I turn it on.


Edited by Raptorx7
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Thanks for the suggestions guys, but I figured it out. Heres what I did if anyone else is having this problem. Setting my joy sticks dead zone/curvature to at least 20-25 stopped the strange auto pilot behavior. I'm not entirely sure why though because when flying I could trim it out and it wouldn't behave that way.

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