Artificial horizon

[jef32]

It's a question that I have, since I've bought P-51, years ago:

 

 

The succion is OK and despite that, the horizon loose its good position very often. Just when I'm taxying in exemple, even if I've uncaged it before moving, the instrument loose the horizon with the first turn.

 

 

 

And in flight it's the same: Very often I must stabilize my flight Vz=0 and with my sight i must cage/uncage again to have an approximate horizon ( more difficult in a mountain zone with the false appreciation of the horizon by the human sight )

[saburo_cz]

Do not taxi with unceged horizon!

Uncege it before take-off after you line up with RWY.

 

During flight, just fly with ball in the middle.

 

These will help to keep horizon works properly.

 

This instrument is old technology without correction of errors caused by turns. (means rotation around the vertical axis - Yaw)

[jef32]

Ok for uncaging just before take-off. But do you think that uncaging before moving can damage the artificial horizon ? And that's why after, it loose its good behaviour during flight ?

[saburo_cz]

But do you think that uncaging before moving can damage the artificial horizon ?

No, it will not damage horizon.

It will cause horizon misalignment due to plane movement in third axis, Yaw.

Horizon measures and shows only Pitch and Roll movement, but Yaw movement have effect on horizon gyroscope too.

 

And that's why after, it loose its good behaviour during flight ?

Align plane, just try to fly straight without any roll, pitch and yaw movement, and then align horizon, there is no another advice or help..

[Andy1966]

Ok for uncaging just before take-off. But do you think that uncaging before moving can damage the artificial horizon ? And that's why after, it loose its good behaviour during flight ?

 

yes, never taxi uncaged. every time you change direction, it throws it further out of alignment, I usually leave mine caged until after take off then get well trimmed straight and level then uncage it. during violent maneuvers, it can get out of alignment, and just get straight and level and cage and uncage it will correct it.

[-0303-]

On 3/2/2019 at 4:42 PM, saburo_cz said:

This instrument is old technology without correction of errors caused by turns. (means rotation around the vertical axis - Yaw)

To unbury the lede the DCS AH does not work correctly in any old plane up to and including the F-86. This because a key modelling of Artificial Horizon (AH) self correction is completely missing rendering the DCS AH useless for any real world simulation. It drifts and it shouldn't.

~

It is not true that WW2 Artificial Horizon (AH) technology lacks correction. The correction mechanism is the pendulous vanes that continuously self correct toward the gravity vector.

Bench example of actual P-51 AH self correction. Un-mute.

It's true that small momentary errors are induced by a 180 degree turn (for example). But adding an additional 180, ie doing a full 360, the opposite error will cancel the first error out. So forever turning will not skew the AH erroneously. The actual error is caused by the centrifugal force acting on the inertia of the free-hanging pendulous vanes.

If one performs a 180 turn and then flies straight and level, the small AH error will quickly self-correct by the pendulous vanes. Actually it's wrong to think of it as having to fly straight and level  to self correct. The pendulous vanes works continuously at all times though they can be momentarily overcome by violent maneuvers. It's obviously insane to have to fly perfectly straight and  level for AH self-correction.

An additional important limitation applies to WW2 era AH (and in to the 50's). For mechanical protection the AH has built in mechanical stops at +-60 pitch and 110 roll. In practical terms the AH will go bananas, coco-for cocopuffs at every roll or looping. DCS AH doesn't do this. It should.

This real life Spitfire video shows this. Roll at 17:01, 27:15, 31:40, 32:40, 37:50, 38:47, 39:08, 39:40. Also note self-correction (full 90 degrees) over 9 minutes from 18:05 - 27:00.

 

This video training video explains much of this. How it works, momentary errors caused by turns  (180, 270, 360), by acceleration or deceleration. Also mentions the  60 and 110 degree mechanical stops. First 11:25 minutes covers vacuum driven (WW2) AH.

 

This bug is more than 10 years old (in that thread read kablamoman).

Not just P-51 as mentioned, every old old plane up to and including F-86. Testing this is easy in a plane  with a cageable AH:

Cage AH, roll 30, 60, 90  whatever, uncage, roll level. Fly straight and level for some minutes (10 min should be enough). If it doesn't self correct it's wrong. Tested P-51, Spitfire, Bf109, F-86 myself. All fail.

Edited February 26 by -0303-

[kablamoman]

@NineLine As -303- mentioned, it's been over a decade. Any chance we can actually get a fix for this long-standing problem?

[grafspee]

This issue always got me feeling that it is something very wrong in modeling, i had no proof for this. But when i flew in clouds even if i stayed very gentle artificial horizon could not provide me enough stability to go through cloud layer. Fact that this issue is decade old is jut straight forward outrages. And i put all my money that ED team knew this.

Edited February 26 by grafspee

[=475FG= Dawger]

I know that it being buggy sucks but you dont really need it to fly through the clouds for short periods. 
 

Other instruments provide all the information you need to fly blind. 

[-0303-]

22 hours ago, grafspee said:

This issue always got me feeling that it is something very wrong in modeling, i had no proof for this. But when i flew in clouds even if i stayed very gentle artificial horizon could not provide me enough stability to go through cloud layer. Fact that this issue is decade old is jut straight forward outrages. And i put all my money that ED team knew this.

Though all documentation supports DCS AH being erroneously modeled, all the proof one needs is simple common sense. The DCS AH lacks self correction, it drifts and therefore it's useless.

Doesn't matter if it's cageable or not (manually correctable in clear skies). In zero visibility neither is correctable.

Unless doing acrobatics one never  need to correct the AH because it self corrects. Even after acrobatics it'll correct itself, it might just take a few minutes.

I think the vast majority of DCS users fly in clear skies and ignore the AH because they never need it.

The AH behavior annoyed me from the very beginning but for the longest time I thought I was missing something, that I just didn't "get it". I couldn't, didn't want to believe DCS had modeled it wrong. Until I thought about it and realized this behavior is stupid on it's face and can't possibly be correct.

ED team can not not know this, the AH function must be 101 elementary for any professional or serious pilot because the AH is one of the six basic flight instruments.

I'd prioritize this bug over hundreds of minor graphic flaws.