Crazy Yawing

[Acedy]

Before taking off you need to trim some forward cyclic to prevent that the chopper pitches up.

[msalama]

Anyone care to share some insight on their take off procedure?

 

I favor an aeroplane-type takeoff whenever possible and trim accordingly, i.e. if I'm rolling straight and true ahead with my real controls at neutral I know I'm usually good. But I've also noticed that it's still prudent to visually compare your virtual control positions with your real ones before you go: if they're approximately the same, no problem, but if there's a marked difference, then a correction and a re-trim is often needed after liftoff.

 

As regards hover checks and stationary takeoffs I've found that some slight forward cyclic is usually needed, or your chopper may indeed pitch up too much and even start to move backwards.

[EtherealN]

I usually don't trim before takeoff, but I use a very slight forward cyclic on vertical takeoffs. If I do a rolling takeoff (which almost never happens) I do trim it slightly as I start rolling on the runway.

[LastRifleRound]

Well i noticed something quite disturbing today. I was lifting off for hover check, when, predictably, the helo starting banking and yawing like crazy, as always. I had enabled invlunerability as this was a mission i created in the editor and i wanted to see how everything played out. I was fighting the conrols hard at just 2m AGL, and had not trimmed anything yet. I gave up and let the helo do what it wanted. To my surprise, it yawed hard to the exact heading of my first waypoint and then stabilized there with no control input on my part.

 

I had ctrl-ENTER activated, and double-checked to make sure there was no "a" activated for route following autopilot. Not that it should be on at 2m AGL anyway, but there was no "a" or "h" or anything. I have a feeling the autopilot system is far more bugged than I first thought. There doesn't seem to be a rational explanation for this. I will try taking off with no autopilot channels activated and see if that is much easier and will report back. Whenever I turn off autopilot I tend to have trouble making neutral my bank angle. in fact, even with trim i have this problem, but i will risk a little sideslip if it means i don't have to peg the cyclic and pedals everytime i want to grab some air off the runway.

[Safari Ken]

Anyone care to share some insight on their take off procedure? Do you trim before increasing collective for hover check or after, do you trim rudder, deactivate autopilot, etc etc

 

I like to apply just enough power so that one or two (but not all three) of the wheels lift off the ground a bit, then do a quick cyclic trim, which is usually to pitch it down a bit. Then I give enough power for full lift-off, and it's always very smooth. I like lifting off just a little like that, as it prevents me from tilting too much in any direction before I trim.

[EvilBivol-1]

Well i noticed something quite disturbing today. I was lifting off for hover check, when, predictably, the helo starting banking and yawing like crazy, as always. I had enabled invlunerability as this was a mission i created in the editor and i wanted to see how everything played out. I was fighting the conrols hard at just 2m AGL, and had not trimmed anything yet. I gave up and let the helo do what it wanted. To my surprise, it yawed hard to the exact heading of my first waypoint and then stabilized there with no control input on my part.

 

I had ctrl-ENTER activated, and double-checked to make sure there was no "a" activated for route following autopilot. Not that it should be on at 2m AGL anyway, but there was no "a" or "h" or anything. I have a feeling the autopilot system is far more bugged than I first thought. There doesn't seem to be a rational explanation for this. I will try taking off with no autopilot channels activated and see if that is much easier and will report back. Whenever I turn off autopilot I tend to have trouble making neutral my bank angle. in fact, even with trim i have this problem, but i will risk a little sideslip if it means i don't have to peg the cyclic and pedals everytime i want to grab some air off the runway.

I don't know, my helicoper never does this. Have you considered that you may have undesidred commands mapped in the HOTAS?

[159th_Viper]

Well i noticed something quite disturbing today. I was lifting off for hover check, when, predictably, the helo starting banking and yawing like crazy, as always. I had enabled invlunerability as this was a mission i created in the editor and i wanted to see how everything played out. I was fighting the conrols hard at just 2m AGL, and had not trimmed anything yet. I gave up and let the helo do what it wanted. To my surprise, it yawed hard to the exact heading of my first waypoint and then stabilized there with no control input on my part.

 

I had ctrl-ENTER activated, and double-checked to make sure there was no "a" activated for route following autopilot. Not that it should be on at 2m AGL anyway, but there was no "a" or "h" or anything. I have a feeling the autopilot system is far more bugged than I first thought. There doesn't seem to be a rational explanation for this. I will try taking off with no autopilot channels activated and see if that is much easier and will report back. Whenever I turn off autopilot I tend to have trouble making neutral my bank angle. in fact, even with trim i have this problem, but i will risk a little sideslip if it means i don't have to peg the cyclic and pedals everytime i want to grab some air off the runway.

 

Post a Track.

 

I'm dying to get to grips with/experience the Gremlins that are causing this behaviour.......I hasten to add behaviour which I have never experienced/witnessed before.

[Skydoc]

Try disengaging the yaw dampener when you are not in autohover or route autopilot, I bet that will fix it - I found a similar problem. As a general rule, I do not land with yaw dampener on.

 

Some folks have talked about using FD mode, but I have not played with it that much. Controlling the yaw manually works out fine for me.

 

HTH

[Yskonyn]

I have no problems with the yaw damper and if anything a damper should dampen / soften the input from the control surface.

If you have erratic yaw problems the damper should make things better, not worse. ;) So turning it off in a critical flight phase does not sound like a good idea to me.

[Skypat]

In a turn, the AP yaw channel should try to maintain your turn parameters, not your heading. This logic was presented to ED after code final, so it will be added in the patch.

 

hum...

so are you ok to say that disabling Heading AP is actually more realistic that let it UP (i mean in the actual BS version)

 

what i mean is: i think that AP Heading OFF (pre-patch) is globally closer to the future AP heading ON( post-patch) than AP Heading ON (pre-patch)

 

actual AP heading is very disturbing our flight turn

 

thx in advance for your advice

Edited April 20, 2009 by Skypat

[LastRifleRound]

Well I got this confirmed. To see it for yourself, make sure you have default trim. Make sure there is no waypoint selected on the PVI 800

 

Now look at your HUD. You will see a heading carat there, in the direction where the ME plots dead center runway in the ME.

 

Start taxiing, do not trim the bird. Yaw the bird in a different direction. Stare in amazement as the chopper begins to yaw itself back to that carat. Now, change heading, and mash the trim button. The carat jumps what heading you were facing when you released the button. The autopilot will now force the chopper to this heading.

 

I performed a near-perfect hover now keeping this in mind. It appears that when the 3 recommended channels of the FCS are active, the helo behaves in a manner similar to what the manual describes as "route without task" autopilot mode. You never need to use this mode, as the chopper behaves like this by default with the 3 channels on.

 

Try it out for yourself. I will post a track if desired, but i know with CTRL-ENTER i don't have any control spikes or inadvertant HOTAS activation of any autopilot modes.

[EvilBivol-1]

Nope, I'm not seeing that. Tried it with both runway start and cold start.

[Yskonyn]

Sorry LastRifleRoun, but my carat stays in place just fine when I yaw and trim change heading and trim, hover and trim and whatnot.

I can trim all over the place, change heading what I want, but the carat stays on the waypoint. ;)

[EtherealN]

Yskonyn, it'll move if you have no waypoint programmed in the PVI-800. At least I'm seing that.

 

I'm not seeing any of the maneuvers that LastRifleRound is talking about though, they seem very very strange. I always have full authority even if I have not trimmed. (When I do trim it it does move the carat, but behaviour does not change beyond what comes from the retrimming.)

[Yskonyn]

Whoops I misread the post;

 

You actually said: "Make sure NO waypoint is selected (...)"

I missed the 'no' part. :P

 

Thanks for the header, EtherealN

[LastRifleRound]

I'll get a quick track up here for you tonight to show you. There's got to be something wrong with my setup if no one else has seen this, because it's pretty obvious. Maybe someone can take a look at my pit and tell me if have something set up wrong. How do i post a track here? Should i just link to mediafire, etc.? I'm kind of a forum noob....

[Skydoc]

That yawing is why I disable the yaw dampener/autopilot channel thing - maybe I shouldnt have called it dampener. It the channel for the anitorque.

 

I have noted the caret moving trick as well. Having a play the other day with this function and leaving all trim channels engaged, I did a hands-off cyclic/feet off pedals landing, just collective to cushion the descent. The yaw channel kept me flying right down the center of the runway. You can also do this with the "turn to target" function engaged if there is a convienient target to lock up at the end of the runway. I found this to be a good exercise in understanding the trim capabilities and limits.

 

But LastRR, just try turning off the yaw channel and see if it makes life easier or harder for you. I really "only" leave it on when in route autopilot and "turn to target" during attacks.

 

HTH

[EtherealN]

I really "only" leave it on when in route autopilot and "turn to target" during attacks.

 

Heathen! :P

 

LastRifleRound - to attach a file, like a trk-file, you post a response using the full reply window (not the quick-reply), and above the text box you have a small paperclip. Click that, browse to the file and select "upload".

 

There is a limit to how much you can have uploaded on your account, and file-size limits for each type. I think the limit on a trk file is 5mb, which should be more than enough.

[Distiler]

I'll get a quick track up here for you tonight to show you. There's got to be something wrong with my setup if no one else has seen this, because it's pretty obvious. Maybe someone can take a look at my pit and tell me if have something set up wrong. How do i post a track here? Should i just link to mediafire, etc.? I'm kind of a forum noob....

 

Yes you can use mediafire or any other externar sites, or do the above.

[Yskonyn]

That yawing is why I disable the yaw dampener/autopilot channel thing - maybe I shouldnt have called it dampener. It the channel for the anitorque.

 

That's why it is going to be changed in the patch. It doesn't function correctly.

 

But LastRR, just try turning off the yaw channel and see if it makes life easier or harder for you. I really "only" leave it on when in route autopilot and "turn to target" during attacks.

 

HTH

 

Don't get too comfy using this technique. ;) It's going to be different again after the patch.

[Skydoc]

Don't get too comfy using this technique. ;) It's going to be different again after the patch.

 

 

Oh Joy!

:doh:

But then I will need some new workout program for my legs that have been dancing on the antitorque pedals every night...

[LastRifleRound]

headingholdhurts.trk

 

Well, here it is! This track shows what i mean. Heading hold IS engaged on the runway, regardless of altitude. I first took off from the runway but had to land to disable the waypoint in my PVI to better illustrate what i'm talking about. I hit trim to set the carat, then i begin yawing on the runway. Watch as the heading hold rolls the bird to the carat, even on the ground. I then hover, engage an extreme yawing manuever, and then the FCS actually yaws so hard in the other direction it overshoots the carat and has to re-center.

 

So, there's your proof. The FCS DOES hold specific headings AGAINST pilot input, whether on the runway or in the air.

[EtherealN]

I just ran the track and checked it out, and you are correct in that. However, a few points:

 

The input is very weak - as soon as I got to above 100km/h it couldn't do it anymore.

Also, as soon as I trim the problem goes away. Without any WPs on that's also resets the carat so you get a nice visual queue. With WPs on it doesn't reset the carat but the rest of behaviour is identical.

 

On the runway as well, you get around it through just trimming.

 

The maneuvers do indeed look a bit dramatic when you move a long way from the carat, so I'll have to leave it to the expert to judge whether or not this is correct.

 

But the workaround is - trim often. (It's possible that most people never saw this behaviour because we trim like silly little beavers.)

[LastRifleRound]

LOL yes I trim VERY often now. I just figured this would help some other folks. I was told the AP was non-op on the ramp, and it led to some pretty nasty takeoff scenarios. That's why I was asking about the wind in the OP, as I really thought it was wind doing that to me. I couldn't think of anything else.

[Distiler]

But this has been said lots of times in the forum. The HDG autopilot logic is wrong since the begining and will be corrected in the patch. HDG autopilot logic tries to maintain the heading, real one tries to maintain the turn rate.

To overcome it, trim it or disengange and re-engage HDG autopilot. Or fly in flight director mode.