Afternoon all,In FSX, I'm sure many of us are accustomed to seeing the attitude indicator (AI) pitched way up and banked one way or another when the cockpit is cold and dark. (Don't know whether that's the case in real life, but it's a pointer in the right direction).That's sometimes, but not always the case in X-Plane (in particular my plane of choice - the Beechcraft Baron), and I'm wandering what the realistic cold dark state for this device should be.So I've got a question: How shoud the function and behaviour of the attitude indicators vary between aircraft? (especially when systems are off). I've been doing some wikipediaing and it describes the following:http://en.wikipedia....itude_indicatorAI's are either derived from Vacuum Powered or Electrically Powered gyros. But there's a third methodology in the form of the AHRS (Attitude Heading & Reference System).So in the case of the Baron it's got a vacuum system onboard, but it seems like when the engines are cut, or the vacum system fails, then the attitude indicator is still working properly. So I'm wandering if this indicator is electrically powered..... or .... have I found another bug to report?Anthony

Edited February 1, 201214 yr by anthony_d

As you said, this should depend on the way the AI works. From my personal experience as a private pilot, I can tell you the behavior you see in FSX is realistic for vacuum AI. In the Cessna 152 and 172 I used to fly, the AI used to fall down and left when the engine was turned off.Eric

One of my flatmates had a PPL, and I remember getting a free ride from him in a Piper Warrier. The AI would go through a quick wobbly phase before settling down on engine start. Like watching a spinning top eventually collapse - but in reverse!On the subject of Gyros I'm having a thought right now. With the gyro compass, I should get gyro drift on account of the earth's rotation shouldn't I? If I leave a plane parked with engines on, would I expect to see the gyro compass rotate a full 360 degrees in 24 hours if parked on the equator? Or are gyro compasses in GA craft auto correcting?Not sure if gyro drift is simulated in x-plane..... need to test.

Your heading indicator will drift over time, so you're supposed to adjust it perodically by comparing it to the whiskey compass. Just make sure you do this when you are flying straight and level and your airspeed is constant (not accelerating or deaccelerating). Otherwise you'll be reading induced errors off your whiskey compass. In the 172R and 172S birds that I fly, the heading indicator (gyro) drifted only slightly after about an hour of flying. I do most of my flying around Chicago and southern Wisconsin. Keep in mind that a gyro compass requires either AC power or vacuum power... When you shut down the plane, it may not stay in the same heading. Once the gyro has spun down, it is not likely to drift at all without power or vacuum. 24 hours parked would be a lot of wasted fuel! I do not know whether X-Plane simulates gyro drift.

Edited February 1, 201214 yr by Xpendable

Attitude indicator or directional gyro, both rely on a fast spinning rotational gyro that spins in excess of 20000rpm. When shutting down the aircraft, as the gyro slows, it will drift and droop. The DG, being vertically mounted usually will not drift at normal latitudes, but the horizontally mounted AI will tilt in one direction as it slows. Gyroscopic procession means that any weight/force applied to a spinning object will be applied 90 degrees in the direction of rotation. If the AI gyro spins clockwise and is mounted at the 3/9 o'clock positions, the force of gravity would be applied at the 12/6 o'clock positions. Procession would mean the weight is applied at the edges, causing the pitch/bank to apply at angles other than straight forward.The end result is as the AI spins down, it will indicate pitch and bank other than actual. This is also caused due to a vacuum pump putting out less than 100% suction or a electric gyro not putting out required voltage to the motor will cause less-than-normal RPM, which could result in inaccurate or sluggish responses.The gyros have a series of flaps on the outside of the gyro called pendulous vanes that are V shaped and open as the gyro tilts. This allows pressured air to be expelled from the opening, pushing the gyro back to the erect state. That is the reason for the bouncing AI on startup. As the AI gyro spins up, it suddenly erects itself and overcorrects, then re-corrects and corrects again until it is up to speed and upright.