BUG REPORT: V/S indication mismatch HUD and VVI

[Hydrox]

Nice video, so yea turn indicator indeed. Always good to get to know my gf better.

[Ironhand]

Interesting video, thanks for posting it.

 

Not sure what the value of such an indicator is on a modern aircraft that essentially takes care of coordinated turns automatically (i.e. flight control system). Setting rudder trim for asymmetric loads maybe?

Or making standard turns--something we don't do as we hot dog through the sky...even in the landing pattern. :)

[Ironhand]

...What in the Flanker is called the VVI is in other aircraft normally called the turn & slip indicator...

Just noticed this. That dial is actually two instruments combined. It's a VVI (Vertical Velocity Indicator) as well as turn and slip indicator (sometimes shortened to "turn indicator").

[Bourrinopathe]

Very interesting video and tests. Thanks!

 

If it can fuel the thought and hopefully shade some light on this instrument, I found some descriptions about a very similar instrument, also using 45° max value for a reference speed of 500 km/h. The ЭУП-53 could be somewhat different from the one we have in the Flanker though.

 

>>> ЭУП-53 @ Avsim.su (Brootle translate)

(it describes it as a bank angle indicator (up to 45°) (угол крена до 45°))

 

>>> a bit more technical @ studopedia.ru (with a gyroscope diagram)

 

>>> [ame=https://www.youtube.com/watch?v=Emcz-o2Xydg]and a sloppy video demonstration[/ame] (difficult to see how it behaves with roll input)

 

I was confused about the numbers on the instruments and the weird behavior, but a 45° turn rate would be unreachable with a Flanker. (thanks Rich ;) )

Edited March 3, 2016 by Bourrinopathe

[Ironhand]

...

 

>>>

 

and a sloppy video demonstration(difficult to see how it behaves with roll input)

 

...

Interesting. It is a sloppy demonstration but I think I see it responding to roll. That would make this a turn coordinator rather than the turn/slip indicator shown in the video I linked. Now we just have to figure out which one is in our cockpit and, then, how to use it. :)

 

Rich

[DarkFire]

From watching both those videos I think what we have is probably a not particularly accurate & not particularly linear turn & slip indicator.

 

Good point on it being theoretically useful for standard turns. The other thing I thought of was that were it accurate & sensitive it would presumably show the effects of wind drift while flying straight & level.

[Ironhand]

From watching both those videos I think what we have is probably a not particularly accurate & not particularly linear turn & slip indicator.

 

Good point on it being theoretically useful for standard turns. The other thing I thought of was that were it accurate & sensitive it would presumably show the effects of wind drift while flying straight & level.

I spent about 1/2 hour this morning with it making level turns and was surprised at how steady it was. I had gotten the impression from this thread that it was all over the map and that's really not the case. The first and 2nd tick marks were easy to maintain assuming a steady speed. The third was decidedly more difficult. Perhaps it's just a matter of figuring out the ratios involved.

 

As far as drift is concerned, would it indicate that? I suppose it would as long as the wind was inducing a yaw effect.

[DarkFire]

With respect to my earlier post: or possibly not a turn & slip.

 

Some testing I've just done:

 

I was doing roll tests by banking and then maintaining bank without pulling back on the stick. The yellow needle showed a given deflection. When I then pulled back on the stick, effectively increasing turn rate, the yellow needle did not move further.

 

Even when performing a near-max rate turn the needle didn't appreciably go beyond what I'd experienced while conducting the turn tests at ~60 degree bank.

 

Maybe it is supposed to be a turn co-ordinator and just not a very accurate one.

[Ironhand]

With respect to my earlier post: or possibly not a turn & slip.

 

Some testing I've just done:

 

I was doing roll tests by banking and then maintaining bank without pulling back on the stick. The yellow needle showed a given deflection. When I then pulled back on the stick, effectively increasing turn rate, the yellow needle did not move further.

 

Even when performing a near-max rate turn the needle didn't appreciably go beyond what I'd experienced while conducting the turn tests at ~60 degree bank.

 

Maybe it is supposed to be a turn co-ordinator and just not a very accurate one.

 

Hmmm...it's a puzzlement. :) Looking forward to seeing your track. It sounds like you weren't making level turns, though. Or were you?

[DarkFire]

Hmmm...it's a puzzlement. :) Looking forward to seeing your track. It sounds like you weren't making level turns, though. Or were you?

 

The turns started out level but with bank and no initial pitch inputs the side slip quickly introduced a negative vertical velocity component, if that makes sense. I then applied pitch in order to increase the turn rate which also had the effect of bringing the nose above the horizon.

 

Didn't notice any appreciable change in the yellow needle throughout.

 

The max rate turns were level-ish :)

 

I'm actually confused at this point as to what the turn/bank/slip/yaw indicator actually does. I'm leaning towards thinking that it's a turn co-ordinator, but possibly only up to a fairly mild maximum turn rate, after which piling on more turn rate has no effect. Instrument gyro limit possibly...?

[Ironhand]

 

I'm actually confused at this point as to what the turn/bank/slip/yaw indicator actually does. I'm leaning towards thinking that it's a turn co-ordinator, but possibly only up to a fairly mild maximum turn rate, after which piling on more turn rate has no effect. Instrument gyro limit possibly...?

Watched your track and did some experimenting myself this morning. As far as I can tell, this thing only shows direction of turn right now. The rest of that part is either measuring something that we're not considering. OR is broken. I doubt, if it's the latter, that we'll see any fix until we get a fully developed module. I still think it should be showing turn rate but it currently isn't.

[DarkFire]

Watched your track and did some experimenting myself this morning. As far as I can tell, this thing only shows direction of turn right now. The rest of that part is either measuring something that we're not considering. OR is broken. I doubt, if it's the latter, that we'll see any fix until we get a fully developed module. I still think it should be showing turn rate but it currently isn't.

 

Having viewed my track again, I think that the yellow needle should be a turn indicator. If we assume that the black dot in the tube is nothing more than a glorified spirit level then it should be the bank indicator, whereas the yellow needle should be the turn indicator.

 

Watching how the black dot behaved, I think the entire instrument is bugged.

 

Here's hoping for a DCS: Su-27 (and the Eagle for our NATO aircraft fans).

Edited March 4, 2016 by DarkFire

[Ironhand]

Having viewed my track again, I think that the yellow needle should be a turn indicator. If we assume that the black dot in the tube is nothing more than a glorified spirit level then it should be the bank indicator, whereas the yellow needle should be the turn indicator.

 

Watching how the black dot behaved, I think the entire instrument is bugged.

 

Here's hoping for a DCS: Su-27 (and the Eagle for our NATO aircraft fans).

I think we more or less agree. The top part indicates direction of turn and those tick marks should indicate standard turn rates as defined by Russian aviation. When you are at the correct bank and airspeed for a predefined turn rate, the needle should sit on the corresponding mark. I doubt it's a bank indicator. If it was, it'd be the 3rd one in the cockpit. One on the HUD and one on the ADI along with this one sitting right next to it.

 

The bottom part is an inclinometer. Basically, it's no different than hanging a small smurf ball on a string in the cockpit (which I've seen done in some bush planes). At rest, it indicates whether or not you're level with the horizon as defined by gravity. In a turn, gravity and centripetal acceleration are what effect it. It's behavior hasn't seemed strange to my eye. But, then again, in the sim you don't have the seat of the pants feel that a skidding or slipping aircraft would provide.

[Hydrox]

I think it's the device, which is seen in the videos, just that it's not working as it should. When the autopilot is faulty, planes speeds are bugged, wouldn't be surprising if the indicator was too.

[DarkFire]

I think we more or less agree. The top part indicates direction of turn and those tick marks should indicate standard turn rates as defined by Russian aviation. When you are at the correct bank and airspeed for a predefined turn rate, the needle should sit on the corresponding mark. I doubt it's a bank indicator. If it was, it'd be the 3rd one in the cockpit. One on the HUD and one on the ADI along with this one sitting right next to it.

 

The bottom part is an inclinometer. Basically, it's no different than hanging a small smurf ball on a string in the cockpit (which I've seen done in some bush planes). At rest, it indicates whether or not you're level with the horizon as defined by gravity. In a turn, gravity and centripetal acceleration are what effect it. It's behavior hasn't seemed strange to my eye. But, then again, in the sim you don't have the seat of the pants feel that a skidding or slipping aircraft would provide.

 

I think it's the device, which is seen in the videos, just that it's not working as it should. When the autopilot is faulty, planes speeds are bugged, wouldn't be surprising if the indicator was too.

 

Agreed. I also think that it would be logical for the tick marks on the yellow scale to be calibrated to the roll markers on the HUD: 15, 30 & 60 degrees. So, setting a given bank angle at a given speed would produce a 'standard' turn as indicated by the turn indicator.

 

If that is the case then it would also make sense for the instrument to be doing that to help with navigation under IFR conditions, e.g. a flight plan could call for navigating to waypoint 4 then carrying out standard turn no. 2 (lets say a 60 degree bank turn) in order to put yourself on the desired track for waypoint 5. Etc. etc.

 

Looks like the intended function is as we're agreed on, but that it isn't working correctly at the moment.

 

I think we can call this case solved :detective: :)

 

Slightly off topic, it'd be fascinating to see a real RuAF flight plan document, though I can't imagine that will happen any time soon... :(

Edited March 4, 2016 by DarkFire

[Ironhand]

Agreed. I also think that it would be logical for the tick marks on the yellow scale to be calibrated to the roll markers on the HUD: 15, 30 & 60 degrees. So, setting a given bank angle at a given speed would produce a 'standard' turn as indicated by the turn indicator.

!5, 30, 60? I only have 30, 60 on the HUD. ???

 

Unless I'm completely out to lunch, a given bank angle at a given speed, assuming a level turn, will always yield the same turn rate. There'd be no need for a gauge to tell you that you've arrived.

 

If that is the case then it would also make sense for the instrument to be doing that to help with navigation under IFR conditions, e.g. a flight plan could call for navigating to waypoint 4 then carrying out standard turn no. 2 (lets say a 60 degree bank turn) in order to put yourself on the desired track for waypoint 5. Etc. etc.

Standard turns are usually used in poor weather conditions. ATC would tell you to make a rate one turn, etc.

 

Looks like the intended function is as we're agreed on, but that it isn't working correctly at the moment.

 

I think we can call this case solved :detective: :) ...

Yes. I think we have a malfunctioning instrument. :)

[Bourrinopathe]

I had a response from ED about the instrument. Apparently, it's a "classic" turn coordinator with a 2-axis gyro showing an angular turn rate. They confirmed it should display the real bank angle at a TAS=500 km/h (sustained turn).

 

Is there a way to display the TAS in the sim (I didn't check the F10/map view)?

I'll try to test the instrument @ 500 km/h TAS using reference IAS and Tacview but it would be neat to have access to an ingame TAS.

[DarkFire]

I had a response from ED about the instrument. Apparently, it's a "classic" turn coordinator with a 2-axis gyro showing an angular turn rate. They confirmed it should display the real bank angle at a TAS=500 km/h (sustained turn).

 

Is there a way to display the TAS in the sim (I didn't check the F10/map view)?

I'll try to test the instrument @ 500 km/h TAS using reference IAS and Tacview but it would be neat to have access to an ingame TAS.

 

Good effort! How did you get an official response?

 

Surprising that it's based on a TAS of 500 Km/h as that's about half of what the Flanker flies at, even at a nominal 85% cruise RPM. No wonder we can't get it to work properly.

 

As for TAS: when in nav mode, or pretty much any mode, the number shown on the bottom right hand side of the HDD is your TAS. IAS is of course shown on the HUD and your TAS is shown on the HDD. F2 view will also give you the TAS.

[Bourrinopathe]

I should have missed that F2 TAS (also for the HDD - I forgot that). Thanks a lot. That will ease the tests.

 

Maybe it's supposed to be useful (as a backup) for landing approaches or some similar low speed maneuvers ? Unless it's a mechanical/design precision limitation.

Also I'm not sure about the emergency procedures. Maybe it's required to keep the speed below a specific value if the main navigation systems fail. (The Su-27SK flight manual should have some specific info about that)

 

About ED: I asked kindly ;) but more importantly, they were kind enough to answer.

[Ironhand]

I had a response from ED about the instrument. Apparently, it's a "classic" turn coordinator with a 2-axis gyro showing an angular turn rate. They confirmed it should display the real bank angle at a TAS=500 km/h (sustained turn).

 

Is there a way to display the TAS in the sim (I didn't check the F10/map view)?

I'll try to test the instrument @ 500 km/h TAS using reference IAS and Tacview but it would be neat to have access to an ingame TAS.

Excellent.

 

After a quick test at TAS 500 k/h, it seems valid for 15 and 30 degree bank but not 45. Interestingly, in the process of testing something else in the same flight, I had slowed to 430 k/h (TAS) making level turns and noticed that everything worked exactly as advertised including 45* bank.

 

So it might be that 500 TAS is the top speed limit after which the measurement error become too large? It'll be interesting to see what you find.

Edited March 5, 2016 by Ironhand

[DarkFire]

!5, 30, 60? I only have 30, 60 on the HUD. ???

 

Huge derp on my part. No idea what fantasy land I imagined that from but you're right of course, 30 and 60 degree bank marks only :)

 

Ironhand I think you're right: it appears to work at pretty much all speeds at or beneath 500 Km/h TAS. Makes it a useful instrument for flying IFR patterns but not much else.

[Ironhand]

Huge derp on my part. No idea what fantasy land I imagined that from but you're right of course, 30 and 60 degree bank marks only...

:) A one point in this aircraft's modeling FC 1.5?), there was a 15* mark. But it was removed somewhere along the line. There are still times when I think I know something and realize that I"m remembering past details that no longer exist (or have validity) in the current sim. You and I both go back a ways...

[DarkFire]

:) A one point in this aircraft's modeling FC 1.5?), there was a 15* mark. But it was removed somewhere along the line. There are still times when I think I know something and realize that I"m remembering past details that no longer exist (or have validity) in the current sim. You and I both go back a ways...

 

He he yes, we've come a long way since Su-27: Squadron Commanders Edition!

 

Looking at various screen shots it looks like Flanker 1.0 all the way up to FC2 had bank marks at 5, 10, 15, 30 and 60 degrees. I'd forgotten or simply not noticed that everything up to 30 degrees was removed for FC3 :D

[Ironhand]

...I'd forgotten or simply not noticed that everything up to 30 degrees was removed for FC3 :D

:) We see what we expect to see...

[esb77]

Huge derp on my part. No idea what fantasy land I imagined that from but you're right of course, 30 and 60 degree bank marks only :)

 

Ironhand I think you're right: it appears to work at pretty much all speeds at or beneath 500 Km/h TAS. Makes it a useful instrument for flying IFR patterns but not much else.

 

If you're in a plane that's short on fuel in low vis conditions an instrument useful for flying IFR patterns is about as useful as aircraft avionics can ever get.

 

Or to put it another way, since our lives and our hardware aren't on the line, we virtual pilots have some serious distortions when it comes to evaluating importance in aircraft features and flight procedures. ;)