INU alignment coordinate versus orientation question

[ChromeWasp]

hi

 

i read the manual and searched about for this

 

the inu alignment in the manual uses a single reference point

which I think means it only fixes lateral coordinate drift

 

every flight i have ends up with the aircraft flying sideways

even in route + hdg hold mode etc.

plus it won't hold its autohover heading either

 

is this caused by inu misalignment?

 

and if so how can a single reference point realign it completely?

 

ps oh yes - and is it a laser gyro or an actual spinning gyro?

[Dash]

If you use a point feature, like a bridge or a road junction to perform an INU fix, both latitude and longitude will be corrected. If you use a linear feature, like a road or stream that crosses your path, then only the components of latitude and longitude perpendicular to the feature will be corrected.

 

The peculiarities that you describe are not caused by INU drift. There are many things that can cause your heading to drift while in hover or in route mode, but having an erroneous position fix is not one of them.

[sweinhart3]

The aircraft flies sideways because thats how it was designed. It has a natural tendancy to bank during forward flight and so the autopilot uses yaw to counteract. Forward flight wont be straight and level like in other aircraft.

[slug88]

The aircraft flies sideways because thats how it was designed. It has a natural tendancy to bank during forward flight and so the autopilot uses yaw to counteract. Forward flight wont be straight and level like in other aircraft.

 

Exactly. You can either fly wings horizontal while slipping, or you can fly straight and without slipping but at a constant bank angle to the right. The necessary bank angle to avoid slippage increase with forward airspeed. Ultimately it's due to the fact that the coaxial rotor system can't be perfectly symmetric: the upper rotor is farther from the CG, and so it has more leverage. There are much more detailed explanations with force diagrams and everything in this forum, shouldn't be too difficult to find with a search.

 

So, just to be as clear as possible: flying with a bank/slippage has nothing to due with the INU alignment.

Edited August 12, 2010 by slug88

[nemises]

(and infact INU alignment is not necessary at all, as the INU does not currently accumulate error!)

[Iron]

(and infact INU alignment is not necessary at all, as the INU does not currently accumulate error!)

 

OMG...oh well at least I have learn't to do it.

[MTFDarkEagle]

plus it won't hold its autohover heading either

If you have your heading stability channel engaged, it's a trimming issue. In hover, apply rudder to head to your desired heading and trim the aircraft, and you should see the diamond on the desired heading on the compass on the hud.

Edited August 12, 2010 by MTFDarkEagle
typo

[topdog]

Would this explain why when I'm trying to fly straight and level, my cyclic is always banked a few degrees to the left (and I tend to fly in a slight slip) whilst rudders are centered? I did mean to figure out the reason for it as I couldn't be entirely sure it wasn't just me flying with a wonky controller.

 

So I'm not sure I understood the normal tendency of the craft, whether you have to correct it by banking right (as I read it), or if it banks right by itself and you (optionally) correct it with counter-banking left.

[MTFDarkEagle]

Yes it does topdog, it's because of the torque of the engines that the plane flies slightly banked. Put a bit of counter cyclic and rudder up, and you'll be fine.

[ChromeWasp]

what I mean is at the beginning of the flight things work normally

but after 30 minutes or so things change so the helicopter

will only fly with about 45 degrees of sideslip

 

even if I reset trim - etc.

 

it isn't a damage issue as I am IMMORTAL

 

I think it is related to a hard landing

 

the only explanation I can think of is inertial navigation error

[takamba]

Please post a track of this issue.

[PhoenixBvo]

Related to a hard landing?

 

Well maybe if you'd normally have crashed (without the immortality (please turn that off!!)) the INU might get an offset. This would be a numerical simulation related issue due to the enormous accelerations of an impact. The INU has to integrate accelerations and rotational rates to get attitude. The numerical algorithm to this will be inaccurate for very large integration steps.

Again, please turn immortality off and just crash like everyone else ;).

[MTFDarkEagle]

Post a track

[ChromeWasp]

I will post track next time it happens

is it possible to realign the inu in this case without landing and powering down?

[sweinhart3]

45degrees is way too much. Are you sure you dont have something like a target/waypoint selected on the PVI? If you have a waypoint selected and enroute mode on that is north and you try to fly west, itll let you fly west but still attempt hold the heading north. Trying to trim the aircraft in another heading will just fight the autopilot. INU drift wasnt implemented in BS.

[Slayer]

Are you using DT or DH mode for your autopilots? (Desired track/Desired Heading) Sounds to me like you are in the DT mode to me... its the switch on the autopilots panel.

 

Edit : DH/DT switch defaults to a neutral position . Also you can try auto turn on target it works with the APs in all modes including enroute.

Edited August 13, 2010 by Slayer

[ChromeWasp]

Each AP mode responds to TRIM in a different way

 

I had assumed during HOVER mode that TRIM was setting HEADING only but it also sets RUDDER trim

 

So when you exit a HOVER that required rudder to hold a heading you will have some hidden rudder trim

 

IRL you would feel this in the pedals - if the RCTRL+ENTER red box control display would indicate rudder trim that would help alot - as this information would be available to a real pilot - but isn't available to us

[ZaltysZ]

Each AP mode responds to TRIM in a different way

 

I had assumed during HOVER mode that TRIM was setting HEADING only but it also sets RUDDER trim

 

So when you exit a HOVER that required rudder to hold a heading you will have some hidden rudder trim

 

You must break trim button effect into 2 parts: force trim and AP commands. Force trim always works on all 3 axis and is not affected by which AP mode is chosen. However, commands sent by trim button to AP do depend on AP mode. In hover mode, trim button designates new hover point and direction. In route mode it designates speed and direction (if no waypoint is chosen).

 

IRL you would feel this in the pedals - if the RCTRL+ENTER red box control display would indicate rudder trim that would help alot - as this information would be available to a real pilot - but isn't available to us

 

Pedals position is shown under red box.

[Lobrau]

Again, please turn immortality off and just crash like everyone else ;).

 

Quite right, the Shark bounces incredibly well as it happens! I was flying on the 104th server yesterday, cracking along at 250km/h at 4m and didn't notice a slight undulation. Suffice to say the shark got a dirty belly and I left a gouge in some poor farmers fields but nothing was broken!

 

As to the side-slip issue I don't think it's anything to worry about. I'm always flying with a slight yaw, especially at high speeds and I always get to where I'm going. The effect is amplified the greater the speed but I hardly notice it at speeds below 160

[ChromeWasp]

Force trim always works on all 3 axis and is not affected by which AP mode is chosen

 

and that makes sense now I think about it

 

Pedals position is shown under red box.

 

I am sure it shows the current control input - not the rudder position

because it will show 0 when I have full left rudder trim

 

[EDIT] hmm it does normally show rudder position - now I am confused because sometimes I definitely have full left rudder trim but red box shows center - and it takes 3 or 4 attempts before I can pull the trim back to center ...

 

The only way to fix the accidental trim is to apply right rudder - retrim

test - repeat, until you manage to drag the hidden rudder trim back to zero

 

Either that or hold cyclic well forward and click Reset Trim ... and then ride the rodeo for a few seconds

 

There are 3 things I keep in my mind:

 

a) Control Position (the joystick physical position)

b) Trim Position (by feel / attitude / angular velocity)

c) AutoPilot control signal (within 20% authority band) (by deduction)

 

but (b) can be a big surprise when you disengage an AP mode - which is why we need that information in the red box

Edited August 16, 2010 by ChromeWasp

[ChromeWasp]

Quite right, the Shark bounces incredibly well as it happens! I was flying on the 104th server yesterday, cracking along at 250km/h at 4m and didn't notice a slight undulation. Suffice to say the shark got a dirty belly and I left a gouge in some poor farmers fields but nothing was broken!

 

I appreciate the sentiment but it isn't possible to learn when you are constantly restarting the mission - I will turn off immortal when I have a hope in hell's chance of surviving for more than 30 seconds

[ZaltysZ]

I am sure it shows the current control input - not the rudder position

because it will show 0 when I have full left rudder trim

 

[EDIT] hmm it does normally show rudder position - now I am confused because sometimes I definitely have full left rudder trim but red box shows center - and it takes 3 or 4 attempts before I can pull the trim back to center ...

 

Red box does not show position of rudder (control surface), but it shows position of pedals (control device). Keep in mind that it does only show position of virtual controls (in game collective, cyclic, pedals), but not position of your game controllers (i.e. joysticks). I.e., if right pedal is pressed fully in game, red box will show pedals mark fully to right.

 

I suspect that you and AP may still not live in peace. Remember, that AI has 20% authority and if it is told to do something, it may wrestle you by using those 20%. Pedals might be centered, by aircraft might still turn around, just because AP makes it do so. AP does not move your controls, so red box won't help you tracking what AP does.

[Sarge55]

Just a quick tip to recenter your rudders, double tap the "Z" or "X" key while you have your pedals or stick physically centered and the in game rudder will center automatically.

 

Saves having to move the pedals or stick so the red control box shows your rudder centered then retrimming.

 

It's kind of like a rudder only trim reset.

 

________________________________________________________________________________________________

 

I just remembered reading a thread about fellow who set up a script to do that automatically. A search should turn it up.

Edited August 16, 2010 by Sarge55
update

[topdog]

Yep, and with that tip (to use Z or X) to fix a crazy rudder situation, I'd forget from there that Reset Trim even exists (I'm told it doesn't in the real heli anyway), and you'll be able to avoid the violent kickbacks it gives.

 

Resetting Trim isn't even that useful on the ground, which is where I expect it gets its most use upon a touchdown.

[Slayer]

There are certain situations where you trim and center the pedals but the in game pedals (what you see in the cockpit) continue to travel in the last direction you pushed until they hit the virtual "stop" This results in uncontrolled spin. Pressing X or Z stops this ghost pedals movement. Also trim reset will correct it BUT from what I see in game if I only do a short press of the trim reset button the peddals do NOT move back to the neutral position, you need to press and hold the trim reset then the pedals will slowly move back to neutral position.

 

In my case I suspect the G940 rudder pedals use a very sensitive hall sensor and even the slightest movement while pressing trim will cause this problem( think of it in the same way as trimming then not returning stick to center and its the same effect if you don't have a FFB stick)

 

In the game specific settings for Blackshark in my G940 profiler I added an 8% deadzone and it seems to help but it is not a 100% solution.

 

rudder and trim issues have been beat to death in the input section of the forum. Do a search there for more info.