Crazy Yawing

[LastRifleRound]

Hey all!

 

Noob question here. Why the heck is my shark yawing like a drunken sloth monkey on a banana high right at the moment of take off? I also experience after trying to end a sustained bank turn. I'm sure this sounds like a symptom of "fighting the autopilot". However, I trim constantly, and it's never really been made clear how i can "work with the autopilot" other than repeatedly trimming. Also, not having a FF joystick usually leads to wobbling after trimming, so i can't typically do it when hovering close to the ground.

[EtherealN]

A track file to illustrate would make it easier to see what's actually happening, but it sounds to me simply like too much momentum.

 

When you take off, you leave a state where you had friction between the wheels and ground, which stabilizes the aircraft on the yaw axis. This means you will suddenly lose a lot of stability while at the same time subjecting it to either equal (in the case of absolutely no wind) or greater (if there is wind, wind strength increases very fast with altitude) forces that want to twist the aircraft. Due to the stability you get from having wheels on the ground, while there you can "get away" with slightly erroneous inputs or trims - but the moment you lift off they will start acting and it is very very easy to overcompensate.

 

I usually just let the slight wobbling be, both IRL and in the sim, because it will typically stabilize a little over time and then I can trim to counter it.

 

When exiting a banking turn, you are also quickly changing the moments (or is "torques" the proper english word? I forget.) While turning you have a slight rotation in the yaw axis that you want to loose as you exit the turn. Typically this would be through balancing it with rudder as you roll back to level flight - it's not that easy to get just right though. If you do not balance it or overcompensate, the turning motion will still be there and the aircraft will want to wobble.

 

Also, there is always a slight delay between you giving an input and it resulting in the aircraft "following your orders", which can easily lead to a wobble that would self-cancel with time being accentuated by you.

 

However, it is hard to really know if this is what's happening since it's hard to know what you consider constitutes a "drunken sloth monkey on a banana" without a track to analyze.

 

Also, sloth's aren't monkeys. :(

[drummer]

you will no doubt get a lot of useful and techy help here because it is a good forum. If all that fails let me tell you what my problems were. Firstly the old joystick I was using gave spurious inputs, especially on the twisty rudder axis. I found this out by calling up the onscreen control input [right control and enter] this showed me the extra spikes my jotstick was adding. Having sorted that I found out how to use the auto pilot buttons, otherwise you are fighting the machine constantly and the machine usually wins. Thats what I learnt so far if that helps.

[EtherealN]

To add to that - if you think it might be oversensitive joysticks or you just overcompensating and getting problems from that, try tweaking the strength of the inputs you give through adding some curvature to the axes and giving them a small deadzone. I recently did this for my own controls and feel I have enjoyed much better precision - especially in the slow-speed maneuvers like on takeoff, landing and during hover.

 

That way I have a range of motion close to the centre of the controls where only really small things happen, allowing me to fine-tune things better, whereas once I get to about half the range of motion I'm back to the same strength of input that I used to have on the linear "curve" before. So I effectively maintain the same capability of rapid maneuvers (essential for SAM/AAA evasion) but also get much better ability to compensate for small instabilities without making the problem worse.

[McVittees]

I could be way off point here, but it sounds to me like you have a large rudder input trimmed as your taking off. Do you use the contorl inputs box (R Ctrl+Enter)? I always try to make sure the rudder is centered when I release the trim button, because even if you trim a heading, a large rudder deflection will stop the autopilot holding it and you'll end up yawing all over the place.

[nemises]

Hiya,

I'm not sure why you;d be getting bad yaw on takeoff...check these things:

 

1) make sure the 3 Stabalisers are on (pitch role and yaw, the Blue square buttons on the right hand mid cockpit) , no need for the altitude stabaliser at this stage

 

2) press ctrl-enter , and see where your trim is set..it's possible you have accidentally trimmed your pedals on the roll ... make sure to center their trim all the time! (manually..do not use "reset trim" cheat!)

 

3) when you start travelling forward at more than about 100 kph, you will start to pick up a "lean" to the left, especially if using heading hold stabalisation and / or Route mode...this is normal! .. you "can" trim it out of it bothers you, but it is nothing bad.

[LastRifleRound]

Had no idea not to trim rudder input! Thanks for that tip, it helps a little. The main problem seems to be that I'm "Fighting" the auto pilot, mainly the heading hold channel. Once taken off, i bring the helo to a hover no problem. I then try to pedal turn, and the autopilot fights me the whole way. Bank turning is similar but more gradual.

 

I understand that real KA 50 pilots almost always leave this channel on, and that is not advised to turn it off, but I don't understand the proper procedure for initiating smooth turns with it on. It's never really explained how to properly execute a basic turn in the manual nor in the tutorials. I hear "Trim often" tossed about quite a bit, but this seems like it exacerbates some of the issues. If I'm turning, and I hit "Trim," and heading hold is on, then the helo would be fighting itself to maintain the bank attitude necessary for the turn whilst simultaneously maintaining heading. I compnesate with yaw, because i can't understand why sideslip is occurring, but now i'm just adding fuel to the fire.

 

This problem becomes extremely pronounced when trying to execute a line-up to the runway for landing. If i turn off heading hold, I have a much easier time maneuvering the helicopter in all but straight flight. Any pointers?

[Boulund]

Try pressing and holding(!) trim while you change your flight parameters (i.e. changing flight direction or any other thing than just flying a straight level path).

First after you've reached your new flight attitude, altitude and heading should you release trim.

 

Edit: I thought I might just add to this that I've never (yeah that's right, never) understood how you guys fly without AP channels on. The bird becomes totally unstable and you need to keep fighting with the stick just to keep her up - horrible. With the three APs on she's as smooth as a feather and does exactly what I tell her to.

Edited April 17, 2009 by Boulund

[LastRifleRound]

The manual states not to make a habit of this, so there must be a way that doesn't involve this....

[EvilBivol-1]

The manual states not to make a habit of this, so there must be a way that doesn't involve this....

It appears the "press and hold" method is also used by some pilots in some helicopters. It may depend on the particular helicopter model and maybe even training standards. For simulation purposes, I would recommend you try both methods and use whichever you prefer. I think both can be considered realistic, especially given the already existing limitations of our plastic HOTAS controls and 2D monitors.

If I'm turning, and I hit "Trim," and heading hold is on, then the helo would be fighting itself to maintain the bank attitude necessary for the turn whilst simultaneously maintaining heading.

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. Edited April 17, 2009 by EvilBivol-1

[Boulund]

The manual states not to make a habit of this, so there must be a way that doesn't involve this....

 

I thought the manual stated that we should do this in exactly the way I described, or did I misread?

 

During Flight Director:

"To set a new airspeed and altitude, it is necessary to press and hold the trim button and

change the speed and altitude. Then release the trim button and the current values of

the airspeed and altitude are set as desired."

 

Route without task:

"For changing flight parameters it is necessary to:

1. Press and hold the Trimmer on the cyclic stick.

2. Set new flight input (bearing, pitch and speed).

3. Release the Trimmer button. "

[Esac_mirmidon]

" 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. "

 

Great to read this finally, EB.

 

The yaw behaviour while turning with the Ka-50 was the most strange thing i had found in the Ka-50. Now in a turn i need to press and hold trim button to evade the " fix heading effect " of the AP and execute a correct turn centering the ball.

 

Then you are saying us that with the new patch the AP would not fight your inputs trying to mainting the original heading when you are turning?

 

This is the real behaviour of the AP in this situation?

 

Thanks for your clarifications

[LastRifleRound]

Ahhhhh thank you Evil! I knew I wasn't going nuts! I could see not needing to disable heading hold if the autopilot logic changes during turning maneuvers not to hold a specific heading.

 

For now, I will engage the trimmer button held down when turning and see how that works out. I have some more questions (did alot of forum searching and read stickies, so i think many KA-50 noobs will benefit):

 

1.)Is this the up and coming patch that the new logic would be introduced?

 

2.) What is proper procedure for triming in auto hover? your post on "easiest way to enter hover" (also found in the DCS American DVD release quick start manual) states that auto hover should be engaged, then the trimmer should be activitated. However, the trim function is different in hover mode, and only serves to lock in a new hover position, not a specific control input. The net result is when I turn off auto hover, i have no idea what settings the FCS engaged to acheive hover, and the departure from the hover is wild and upredictable :joystick:.....

 

3.) Anyone know where I can find a more comprehensive guide on lifting off for hover check? It's glossed over in every take-off tutorial I've seen, like I should know it already. I think the key is to acheive "Take off Trim" before increasing collective to perform a hover, but i have no idea what that trim might be. I know ground trim is aft, but compensating forward only servers to taxi the helicopter forward.

 

4.) Finally, the manual states take off should be performed "into the wind." Nowhere in the training missions can i actually find what the wind speed and direction is. I don't see it reported on any gauge or on the ABRIS, and cannot seem to request this info from Tower. How can I take off "into the wind" if I have no idea which way the wind is blowing? :helpsmilie:

 

Bottom line-Wags, work on those tuts man :thumbup:! They're good, but not basic enough. More explanation on just what control inputs your using would help. Knowing the numbers is good, but I can see that in the manual (land in rotor effect 4m AGL at 30-40m/s, etc.). And you are NOT the worst rotary wing pilot in the world! I challenger your position on that after watching the producer's note #3. That was well-coordinated flying :pilotfly:

[msalama]

For now, I will engage the trimmer button held down when turning and see how that works out.

 

As things are implemented now it'll most likely work out much better, unless there's something really weird going on with your controllers (probably isn't).

 

But as regards trimming the bugger I've noticed that you actually _have_ to check where your C/P (i.e. virtual) controllers are positioned compared to your physical ones, and do your corrections based on that. I'm sorry that I really can't explain it any better, but that's how it seems to be nevertheless...

 

It isn't that important when you're, say, flying straight and level at high speed. But being slow, either airborne or on-ground, it really means a lot.

 

I'm sure there's geezers here who can explain it better than me BTW ;)

Edited April 17, 2009 by msalama

[EtherealN]

I'm not sure I can, since I don't really understand what you mean.

 

I change both my general inputs and trimming based entirely on how the helicopter is acting and as soon as I have to give a "big" input to get it to do what I want it to do I trim it to that position and that's that. Only time ever that I have had that controls window thingie up was during a track analysis for a guy that was having some troubles.

 

Time spent looking at instruments, sticks and dials is time that should be spent looking out the windows. If you cannot control the helicopter on visual input you need more practice on doing that - not more practice looking at instruments, since that will only increase your dependence and make it even more difficult to learn properly.

 

When you are trimming and performing all the controls without thinking about what you actually do with your hands, fingers and feet, but rather only decides that you want to do X maneuver and X is then performed - THAT is when you has learned to fly. ;)

 

(There are a few exceptions, I am kinda counscious of my controls when performing barrel rolls and loopings, but that is more because it is very very very easy to meet an untimely death when doing those and as such it'll take a whole lot more practice to get them to be "second nature".)

[EtherealN]

Oh wait, msalama! I think I just now got it like seconds after I pressed post... You mean the fact that a non-force feedback joystick will be centered after trimming, whereas the "real" controls would not centre but rather stay in the position they were as a new "default"?

 

This is an effect that is simulated if you have a Force Feedback stick.

[LastRifleRound]

well i just took a flight and holding that trimmer button while making adjustments did the trick for flight :)

 

Still having epic troubles establishing hover at the 2-4m AGL range. This is a problem both when taking off and landing.

[EtherealN]

Ah, yeah, it's not when you press the trim button that matters, it's when you release it.

[EvilBivol-1]

You can't engage auto-hover below 4 m. altitude. This is a limitation of the AP system, which uses the Doppler Speed and Drift Indicator system (essentially a downward doppler radar) to measure your motion relative to the ground. This system has a minimum altitude limit. Engaging auto-hover outside of the permitted limits (under 4 or above 300 m, I believe) will kick off the AP system (flashing blue lights).

[Skydoc]

 

2.) What is proper procedure for triming in auto hover?

 

4.) Finally, the manual states take off should be performed "into the wind." Nowhere in the training missions can i actually find what the wind speed and direction is.

 

2. This may have been mentioned, but enable your controls indicator to help figure out what you are actually trimmed to (right CNTL-ENTER). I find that the Shark likes a little forward and slight left bank in a hover, but that may depend on your loadout.

 

4. Your PVI-800 nav keyboard has a button in the middle bottom row of keys "d/V" or so, it will give you wind direction/velocity. see manual page 2-63.

 

HTH

[msalama]

You mean the fact that a non-force feedback joystick will be centered after trimming, whereas the "real" controls would not centre but rather stay in the position they were as a new "default"?

 

Exactly :thumbup: And strange things can happen if you don't take that into account, especially when there's a large difference between the real and the virtual control positions...

[msalama]

It isn't that important when you're, say, flying straight and level at high speed. But being slow, either airborne or on-ground, it really means a lot.

 

Ah, OK, let me explain what I _think_ I meant ;) by this a bit better:

 

Let's suppose that you've just executed a successful heavy crosswind landing. You may find that you now have a huge controls deflection trimmed in - and if so, then what you _have_ to do before moving again is to manually trim / reset the controls to neutral or strange and possibly deadly things will happen! This is because the difference between the 2 A/C states, flying and stationary (and thus between the real and the virtual controls too) is really big in this case, whereas it really can't be if you were just, say, flying straight and level and did a small correction only...

 

Or something like that anyway. Folks less thick than me can (and hopefully will) explain it better as needed I'm sure ;)

[Sharkster64]

Awe man that is great news about adding that to the patch. I always thought that was weird that the helicopter would try to maintain its heading. It just didn't seem right. Thanks for bringing that to our attention and fixing it in the patch. Now I really can't wait for the patch.

[Sharkster64]

You can't engage auto-hover below 4 m. altitude. This is a limitation of the AP system, which uses the Doppler Speed and Drift Indicator system (essentially a downward doppler radar) to measure your motion relative to the ground. This system has a minimum altitude limit. Engaging auto-hover outside of the permitted limits (under 4 or above 300 m, I believe) will kick off the AP system (flashing blue lights).

That is why my auto pilot turns off sometimes. I was wondering why it did that occasionally. Thanks for bringing that to my attention as well.

[LastRifleRound]

yes good stuff in this thready thank you everyone :thumbup:

 

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