Erratic behaviour, could wind speed be the cause?

[Spacehamster]

Getting very weird behaviour from my KA-50, but only on the Virtual Aerobatics server. After take-off it immediately tries to align itself in a certain direction. The server briefing shows a wind speed of 9 meters per second towards 276 degrees.

 

1. The degree number, does it tell the direction the wind is heading towards or from?

 

2. Could a 9 meter per second wind cause the KA-50 to refuse to fly straight, even with the appropriate autopilot systems on? For comparison it does exactly what I want it to do on a default cold start mission.

 

3. Could a preprogrammed flight plan cause the autopilot to rotate the helicopter in a certain direction?

[JG14_Smil]

Yes, it could, but it could be caused by the gyros for the navigation system not being ready.

 

I forget the exact terms, but the wind direction in DCS is the opposite of what we use here in forecasts (wind from).

 

Are you using the Control Indicator? I move mine to the center of my screen. It is quite important to see it when flying the Ka-50. Your Heading Hold blue AP light should always be on.

[Spacehamster]

How do you check for the gyros being ready?

[Frederf]

The gyros are ready instantly as the INU alignment isn't modeled. The Doppler system however does take a few minutes (part of K-041). The Doppler system can be noted by a valid ground speed appearing in the HUD. If you've ever taken off and engaged auto-hover only to have a few stability channels disconnect that is because the Doppler system wasn't ready.

 

I believe the automatically-generated briefing is in "ME language" which is true heading to and m/s. ATC should be in "flying language" which is magnetic heading from but I'm not 100% certain on that.

 

9m/s is almost 18 knots, a firm but manageable wind. The AP channels have 20% of the pilot's control authority from trim center so it's important to trim properly or the AP won't have enough control. The AP, properly trimmed, should be able to hold parameters just as well as the pilot with AP off.

 

The AP can interact with a preprogrammed route but it's unlikely to happen by accident. If you choose a waypoint task, number, and engage route mode then it will.

 

Really a helicopter won't fly straight even without wind due to asymmetry of lift. A crosswind can either be corrected for by a heading correction or a bank (side motion). A route flown in a crosswind will look different than one without a cross wind.

[JG14_Smil]

The gyros are ready instantly as the INU alignment isn't modeled. The Doppler system however does take a few minutes (part of K-041). The Doppler system can be noted by a valid ground speed appearing in the HUD. If you've ever taken off and engaged auto-hover only to have a few stability channels disconnect that is because the Doppler system wasn't ready.

 

 

Thanks Fred, That's what I was thinking of and I can see I had it wrong.

 

I do note I was in the aerobatics server last night. It did feel a bit strange in flight but there was no wind at all and I saw no failures in the pit either.

 

I wonder if a random failure might have happened when you were wind-vanning? Just a thought...

[codefox]

The VA server has dynamic weather enabled (1.5 only at this point), so the wind value shown in the briefing might not be correct for your position.

So, wind speed and direction will vary from time to time.

 

I did notice the wind effect when flying the Ka-50 on there but it was very manageable. Check the windsocks and smoke from houses to get an idea about where the wind comes from.

Random failures are turned off on the server so this won't be the cause of your trouble.

[JG14_Smil]

Thanks, I've been in the 2.0 as the Ka-50 are not cold start in the 1.5. server.

[Spacehamster]

I have added a replay track. On the VA server my copter gets blown off towards the left on take-off. And that does not happen on regular single player missions.

 

I would like to know if wind is causing this or somethin broke on start-up. I can only control it with strong rudder input. And a helicopter with considerable weight and stabilizing systems should not be this hard fly straight even in wind. I can much more easily fly the Huey or Gazelle on the same server.

Virtual Aerobatics public server v1.5.4u4k-20160921-184122.trk

Edited September 21, 2016 by Spacehamster

[probad]

you seem to be having control trouble across a bunch of modules.

 

the first joystick i started out with displayed that it was centered correctly but it nevertheless created undesired inputs in one axis, in my case, right roll.

replaced my joystick and it went away.

[JG14_Smil]

Hello,

 

Heading Hold was not turned on until after you took off. Turn t on and leave it on in your start up checklist.

 

I don't see any rudder inputs on your control indicator. Might be because of different hardware. Anyone else see the rudder pipper move?

 

Cold helo at Anapa?... hope so!

[Spacehamster]

Hello,

 

Heading Hold was not turned on until after you took off. Turn t on and leave it on in your start up checklist.

 

I don't see any rudder inputs on your control indicator. Might be because of different hardware. Anyone else see the rudder pipper move?

 

Cold helo at Anapa?... hope so!

 

I did not use rudder on purpose to see where it will rotate towards. On a regular cold start it will take of straight. It is the wind speed then? There is a windsock on the airfield that indicates a strong wind. However the KA50 should not be that susceptible to it. It has no engine torque that has to be countered with a tailrotor and it is a heavy helicopter.

[Weta43]

Heavy only influences how fast it will turn, not how much it will want to turn.

[JG14_Smil]

I did not use rudder on purpose to see where it will rotate towards. On a regular cold start it will take of straight. It is the wind speed then? There is a windsock on the airfield that indicates a strong wind. However the KA50 should not be that susceptible to it. It has no engine torque that has to be countered with a tailrotor and it is a heavy helicopter.

 

 

I flew on the server you're asking about, no problems. I used my rudders. :)

[JG14_Smil]

Thanks for this thread, I learned a lot from it. I just finished a flight on the 1.5 server and it was very nice. Great to see some of the differences from 2.0. Yes, wind blows there and it is a great feature.

[Spacehamster]

I mean it just feels wrong that the KA50 gets thrown around by the wind so much on that server.

Do you fly with rudder trim on or off? I fly with OFF, because the real helicopter does not have rudder trim I think.

[Yurgon]

I mean it just feels wrong that the KA50 gets thrown around by the wind so much on that server.

Do you fly with rudder trim on or off? I fly with OFF, because the real helicopter does not have rudder trim I think.

 

What's so weird about it? I watched your track yesterday and the wind was really strong. It would be weirder if the wind didn't affect the Ka-50. ;)

 

I mean, just set up a mission in the ME with strong wind and observe how the chopper reacts. It'll probably be a lot like what happened on the VA server.

 

Speaking of VA, a couple of days ago I carried cargos with the Huey and flew some aerobatics with the Ka-50 out of Sukhumi on that server and the winds were a lot less strong. I guess that's why it's called dynamic weather. ;)

 

As for rudder trim, thank goodness we can switch it off! (Earlier releases of DCS Black Shark had it on, and didn't include a way to switch it off). I always fly with rudder trim off.

[Spacehamster]

As for rudder trim, thank goodness we can switch it off! (Earlier releases of DCS Black Shark had it on, and didn't include a way to switch it off). I always fly with rudder trim off.

 

I always want to fly it with the most realistic options. So if the real helicopter has no rudder trim I keep that off

[JG14_Smil]

Hello,

 

The trim feature in BS is a compromise for self-centering controllers. You set the trim and return controls to center. The real Ka-50 controls do not return to center, but stay where the real trim systems sets them. My rudder pedals don't return to center, so I disable the trim in options. I truly hated having the rudder trimmer on and I'm glad it's gone. As most are!

 

The real Ka-50 has rudder (yaw) trim. Use what is best for you though. :)

[Pocket Sized]

I did not use rudder on purpose to see where it will rotate towards. On a regular cold start it will take of straight. It is the wind speed then? There is a windsock on the airfield that indicates a strong wind. However the KA50 should not be that susceptible to it. It has no engine torque that has to be countered with a tailrotor and it is a heavy helicopter.

 

However it does have a giant vertical stabilizer that will try to swing your nose into the wind.

 

Combine that with the absolutely abysmal yaw authority (easily 1/3rd that of the Huey) in a hover and strong wind.

[Weta43]

You need a greater force to move a steel box than a wooden box, but they can both be moved at the same rate if given enough force (force needed will be higher for heavier object).

 

Sorry - this is just so wrong.

It's like saying gravity works more strongly on hammers than feathers.

 

A 5 km/h wind on a rudder 8 m from the mast of a helicopter will put the same amount of torque on the helicopter, regardless of the mass of the helicopter.

All other things being equal, the heavy helicopter will accelerate more slowly for the same torque, so after a given amount of time will be turning more slowly & the pilot will have more time to react, but the actual amount of force that has to be applied to hold the helicopter steady against the torque induced by the rudder has nothing to do with the mass of the helicopter.

[Frederf]

I watched the track.

 

1. The wind brief automatically included in the briefing is only valid if the mission is using static weather. If the server is using dynamic weather then the numbers indicated automatically in the briefing are 100% meaningless.

 

2. In the case of static weather the following is an example of how the ME setting and automatic brief text correlate:

at 10m: 9m/s 180°

at 500m: 19m/s 180° (passive display set from 10m line)

 

briefing text:

At GRND 9m/s, 179°

 

The 1° error aside the briefing is showing the 10m values for direction (true heading not magnetic, blowing to not blowing from) and speed. The wind speed will more than double by 500m presumably in a linear blend between 10m and 500m.

 

2. I assume the odd behavior is the nearly 360 left rotation. The AP channel having limited authority does produce seemingly "on off" behavior as the authority is either exceeded or not exceeded.

 

You used a rather confusing sequence of heading channel off and "Director" mode both on and off. At a hover of less than 10km/h the weathervaning tendency is quite strong but 50-60km/h of sideways movement (as is common in such a wind) with change the direction the nose gravitates to quite severely.

 

The autopilot's limited authority may also swap directional input 180 degrees away from the hold heading.

 

All of these effects combined may result in a helicopter that seemingly can't decide which direction to point. I don't find anything particularly weird about the Ka-50 in wind and can't see clearly wrong with the track (can't take control).

[JG14_Smil]

Frederf:

 

I note that in that server, I hit my PVi-800 Wind button and it showed wind coming from the west. I forget the exact number and it is definitely "wind from" as the helo acted as it should with a westerly wind. Will this button always reflect the briefing weather and not dynamic conditions? I guess I'll learn more about it as I fly more.

 

If I remember correctly now, it is in the ME that the wind is "wind to" direction(?).

 

thanks for all your help.

Edited September 26, 2016 by JG14_Smil

[Weta43]

You're either explaining yourself in a wrong way (talking about how fast in terms of speed rather than acceleration)

Fast is a measure of speed, not acceleration :

fast1

adjective

adjective: fast; comparative adjective: faster; superlative adjective: fastest; adjective: farse

1.

moving or capable of moving at high speed.

 

No contradiction at all.

"a heavy helicopter will accelerate more slowly for the same torque, so after a given amount of time will be turning more slowly" means that "for the same torque : Heavy only influences how fast it will turn" (at a given elapsed time)

 

...

 

If you have a given helicopter with a gross weight of 10 tonne hovering at 90 degrees to a 5m/s wind the torque around the rotor generated by the net effect of the wind will be exactly the same as for the same helicopter with more load and a gross weight of 15 tonne.

It may accelerate around the rotor more slowly, but it will require the same force to hold it steady, and if you let it start moving it will take more force to stop it and get it back to where it started from in the same amount of time as a lighter helicopter.

 

That makes this statement true:

Heavy only influences how fast it will turn, not how much it will want to turn

particularly when read in context as a reply to this statement:

There is a windsock on the airfield that indicates a strong wind. However the KA50 should not be that susceptible to it. It has no engine torque that has to be countered with a tailrotor and it is a heavy helicopter.

 

Also

 

Heavier objects have a stronger gravitational pull AND at the same time a lower acceleration.

Actually, in the absence of any other factors (air resistance etc.) heavy objects and light objects have exactly the same acceleration due to gravity.

[Weta43]

Oh and yeah, you need more force to contrast a heavier weight. I hope that's pretty simple to understand

Sorry - Maybe English isn't your first language, but I have no idea what you mean by contrast a heavier weight.

 

This proves that you actually haven't understood a single thing of what I said

 

We both seem to be in the same boat then :)

 

I agree though, we aren't adding anything to the conversation any more.

I think the O.P. understood what I meant, so I'll leave it at that...

 

Best regards to you too :-)

Edited September 28, 2016 by Weta43

[Spacehamster]

How accurate is the windsock in DCS? Like, visually. If it is flapping in the wind at nearly 90 degrees from the ground plane, does that equal very strong wind? How fine is the animation stepping for it?