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Artificial Horizon gyro


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Just wondering 'cause I've had this problem with the P-51 since day 1:

I uncage the AI when I'm on the runway, checking that the vacuum gauge is in the green. Soon after I take off, the AI is all wrong and slacking off big time, even though the vacuum was always in the green. It's like the gyro isn't spun up properly, but I haven't seen this happen on any aircraft (in RL) unless there is a drop in vacuum pressure.

 

Any thoughts?

Windows 10 - Intel i7 7700K 4.2 Ghz (no OC) - Asus Strix GTX 1080 8Gb - 16GB DDR4 (3000 MHz) - SSD 500GB + WD Black FZEX 1TB 6Gb/s

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I've noticed this too. It's gotten to the point where I don't even bother uncaging it until after I am airborne which is less than ideal.
same here. I find it invaluable for rocket and bomb attacks so it's important that it be pretty aligned.
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I *think* it is correct behavior: say you uncage on the ground, pointing north. The artificial horizon gyro "thinks" that it is level, but it is in fact tilted up (in the north) some 15-20 degrees, because the airplane is not at a level stance on the ground. If you then take off and turn to the east, the gyro will be tilted some 15-20 degrees to the right.

 

As best I can tell, the artificial horizon is a ball with a slightly weighted bottom (to force it to level), and the gyro is just there to steady it and prevent it from tumbling. This means that if you continue to fly generally level, it will slowly settle into level. It also means that violent maneuvering will cause it to drift out of level. Both appear to be reflected in how the simulation seems to do it.

 

If you're impatient, just go wings level and momentarily cage it, and it'll be good to go.

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If you're impatient, just go wings level and momentarily cage it, and it'll be good to go.

 

But if the Artificial Horizon is incorrect how do you know you are level??? :D


Edited by Mike Busutil
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I don't recall this happening on the dora, which I'm going to guess is a very similar system.

 

I also find it to be a pain on the 51. But at least it holds its calibration consistently. I'd crash if I was in a cloud having to rely on the ka50 backup horizon

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I *think* it is correct behavior: say you uncage on the ground, pointing north. The artificial horizon gyro "thinks" that it is level, but it is in fact tilted up (in the north) some 15-20 degrees, because the airplane is not at a level stance on the ground. If you then take off and turn to the east, the gyro will be tilted some 15-20 degrees to the right.

 

As best I can tell, the artificial horizon is a ball with a slightly weighted bottom (to force it to level), and the gyro is just there to steady it and prevent it from tumbling. This means that if you continue to fly generally level, it will slowly settle into level. It also means that violent maneuvering will cause it to drift out of level. Both appear to be reflected in how the simulation seems to do it.

 

If you're impatient, just go wings level and momentarily cage it, and it'll be good to go.

 

I don't mean to sound harsh or anything, but you actually got it all wrong.

Nice read here: http://www.pilotfriend.com/training/flight_training/fxd_wing/attitude.htm

Windows 10 - Intel i7 7700K 4.2 Ghz (no OC) - Asus Strix GTX 1080 8Gb - 16GB DDR4 (3000 MHz) - SSD 500GB + WD Black FZEX 1TB 6Gb/s

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Well that topic only goes to prove my point (and yours maybe): it is WAY overdone.

As others have stated, I have never ever seen that effect in RL, certainly not after 30 seconds from gear up, flying straight.....

What I noticed the other day is actually the opposite of the gyro precession described in that topic, that is, the AI drifted down and right as I was in a slight right turn, according to the topic it should have done the opposite.

 

To me the problem looks like bad vacuum pressure / worn out gimbals. The pressure gauge was steadily in the green though, and I'm not sure they simulated worn out gimbals, especially after a 1 minute flight...

Windows 10 - Intel i7 7700K 4.2 Ghz (no OC) - Asus Strix GTX 1080 8Gb - 16GB DDR4 (3000 MHz) - SSD 500GB + WD Black FZEX 1TB 6Gb/s

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  • 6 months later...

I don't understand how I'm supposed to use this for IFR flying. It accumulates more and more error at a rapid rate, even when I'm flying more or less straight & level and more or less coordinated. If I were trying to fly in clouds, I'd lose use of this thing within a couple of minutes, and have no way to realign it ('coz I have no good way to know when I'm actually level, if horizon isn't visible and the gyro horizon isn't reliable).

 

I know I could technically use the turn & bank indicator to more-or-less align it, but if I'm constantly (every few minutes) having to us the turn & bank indicator because the gyro horizon is off again by as much as 20 degrees, then I might as well be stuck with just the turn & bank indicator.

 

I know I never experienced this effect (that is, of the gyro horizon gaining ~20% error within 15 minutes of normal flying) in the Cessnas I flew IRL. Hour-long flights with circles-around-a-point and S-turns over a line didn't result in any noticeable errors. I must question if this effect isn't overdone in DCS, since I can't think of a reason why the P-51's gyro horizon would behave differently than a modern one.

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Same here. I leave it caged from engine startup to engine shutdown. I find it difficult to believe that the instrument would have been included if it were unreliable to this extreme.

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Color me weird, but it seems that if you reset the AH by pressing & momentarily holding the caging knob 2 or 3 times within, say, 30 minutes from startup, it'll eventually start to behave itself. Maybe the gyro just needs time to spinup / stabilize properly?

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What would happen if you were to adjust the pitch knob to match the ACTUAL pitch up of the plane while sitting on the ground? Could it be that the errors are accumulating so radically from the original 5 - 10 degree pitch error of a taildragger to ground "level"?

 

Haven't tried it myself... Just spitballing...

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Another thing that occurred to me--maybe, just maybe, something's happening with the vibration of the aircraft on the ground? My accelerometer always shows +-0.5G before I even get to the runway, even when I reset it several times (after startup, after warmup, and before takeoff). I wonder if the gyro is being effected by this heavy vibration. Just a shot in the dark.

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Color me weird, but it seems that if you reset the AH by pressing & momentarily holding the caging knob 2 or 3 times within, say, 30 minutes from startup, it'll eventually start to behave itself. Maybe the gyro just needs time to spinup / stabilize properly?

 

This is my solution as well. Seems to work.

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Well, i think this video is great for P-51 flyers! Always a pleasure to watch and the checklist he follows is pretty similar to D model.

 

You can see the moment he uncage the A.H. and when he resets it.

 

335th_GREros

 

[sIGPIC][/sIGPIC]

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I also think that he resets it again when the clip has been cut too. Just check out the position of the AH when the clip jumps forwards during the warm up phase.

 

I personally have absolutely no doubt that during the engine warm up phase, variation in vaccuum will cause progression, as would any bumps and G variation during the take off roll. These are highly sensitive instruments, and although they are useful, they're only useful when used in combination with ALL the other flight instruments.

 

I for one think the P-51D is a work of art. The fact that giro progression is modelled is why we're having this debate. Welcome to reality!

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