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Is the attitude gyro (artificial horizon) equipment on our DA40NG aircraft powered by electricity?

While reading the flight manual of the plane, I saw an article about the emergency switch:
"by switching the EMERGENCY switch ON, if installed, the emergency battery, if installed will supply power to the attitude gyro (artificial horizon) and the flood light"

This article confused me because I thought attitude gyro (artificial horizon) equipment was backup equipment that works with "gyro" without electricity. Then I thought that the intended attitude gyro (artificial horizon) equipment could be the digital attitude gyro on the PFD, but with the image I shared below, I understood that it was not meant.

So my question is, is this attitude gyro (artificial horizon) equipment powered by electricity? Also, wouldn't it be more reasonable and logical for the emergency battery to support the digital display in the PFD instead of feeding this equipment with electricity? (Also, in my opinion, it would make more sense to feed instrument light instead of flood light.)

enter image description here enter image description here

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  • $\begingroup$ Do the three backup instruments on top of the panel even have instrument lights at all? Just wondering. $\endgroup$ Mar 21, 2023 at 11:59
  • $\begingroup$ Except for the attitude gyro (artificial horizon) I guess... This makes it logical to prefer flood light instead of instrument light. Thanks... $\endgroup$
    – pilot162
    Mar 21, 2023 at 12:03

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That attitude gyro is electric, and having a standalone emergency battery power supply, is your last resort to get to VFR conditions if you have a primary flight display failure and/or total electrical failure.

The little emergency battery that powers it is an odd way to do things (and one hour seems a bit short to me, but whatever). I would expect to see an emergency electrical bus operating directly off the main battery to power that gyro, because to lose all power, you would need both the engine's generator and the battery to fail and you normally don't cater to simultaneous failures of separate components.

Perhaps the emergency battery is to save yourself if you have an electrical failure, and the main battery runs down. This system does seem to be a little over-engineered for a single engine airplane.

Electric gyros need motors that run on 3 phase AC power for precise and efficient control of the gyro, so if they need to run off a DC power source as in this case, they will have an internal inverter to provide the AC power to the gyro's motor from the DC input. Mechanical turn coordinators you see on most small airplanes are like that.

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  • $\begingroup$ Thank you for your detailed explanation. I think "Emergency Switch" is a model designed so that we can use electricity even though the engine is running when there is a total loss of electrical power. $\endgroup$
    – pilot162
    Mar 21, 2023 at 13:28
  • $\begingroup$ I'd have to see a schematic, but I can't believe the standby att doesn't also run directly off the aircraft battery, with the Emer battery there as a last ditch to keep the thing running if the a/c battery runs flat, following extended flight after a generator failure. A lot of stuff has to go wrong. $\endgroup$
    – John K
    Mar 21, 2023 at 17:12
  • $\begingroup$ I'm not sure on the exact attitude instrument installed in the D40 NG (I have my suspicions) , but I'd be almost certain the standby attitude instrument runs off the DC bus during normal flight $\endgroup$ Mar 21, 2023 at 20:39
  • $\begingroup$ @selectstriker2 there is likely a dedicated battery bus, or emergency bus for powering an instrument like that, as opposed to the main DC bus, unless it's a cruder system than I think it is. $\endgroup$
    – John K
    Mar 22, 2023 at 5:00
  • $\begingroup$ looking through the Diamond forums, it appears the backup battery for the AI is a primary cell pack that the Emergency switch is used to connect to the power on the AI $\endgroup$ Mar 22, 2023 at 18:11
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Is the attitude gyro (artificial horizon) equipment on our DA40NG aircraft powered by electricity?

While reading the flight manual of the plane, I saw an article about the emergency switch: "by switching the EMERGENCY switch ON, if installed, the emergency battery, if installed will supply power to the attitude gyro (artificial horizon) and the flood light"

If the sentence you've quoted from the manual refers to anything other than the traditional "attitude indicator" at the top of panel, then it's a poorly-written manual-- so I think you've answered your own question: "yes".

This article confused me because I thought attitude gyro (artificial horizon) equipment was backup equipment that works with "gyro" without electricity.

Any gyro instrument needs some source of power, which (depending on the design of the specific instrument) would be either a vacuum system, or electricity. It appears that the DA40NG has dispensed with the vacuum system entirely, so the artificial horizon is of a design that is powered by electricity rather than by the more traditional vacuum system.

Note that the more traditional solution in aircraft with "steam gauge"-type instrument panels to provide a way for the pilot to maintain orientation in cloud case or total darkness in case of failure of the vacuum system (including due to failure of the engine) is to have an electrically powered turn coordinator or turn rate indicator. But, the DA40NG doesn't have one of those.

Also, wouldn't it be more reasonable and logical for the emergency battery >to support the digital display in the PFD instead of feeding this equipment with electricity?

The PFD and the associated systems are fairly power-hungry so the battery would not last very long. Also this solution would not provide redundancy against a failure of the PFD itself, and the associated systems.

(Also, in my opinion, it would make more sense to feed instrument light instead of flood light.)

The flood light will light all three of the backup instruments on top of the panel, as well as give the pilot some way to read a map, etc. Seems fairly logical.

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  • $\begingroup$ If I understood correctly, the attitude gyro (artificial horizon) is an instrument that needs electricity indirectly (a vacuum system) to operate, even if it is not directly powered by electricity. Also, according to the image in the reference manual, what is meant is this attitude gyro (artificial horizon), which is a standby indicator. When I evaluate these two expressions correctly, there is no question mark in my mind. $\endgroup$
    – pilot162
    Mar 21, 2023 at 12:09
  • $\begingroup$ In most aircraft (at least piston-engine aircraft) the vacuum system has nothing to do with electricity-- see for example provac.com/blogs/news/…. $\endgroup$ Mar 21, 2023 at 12:14
  • $\begingroup$ So why is the emergency battery feeding the attitude gyro (artificial horizon)? For what purpose does this instrument use electricity? $\endgroup$
    – pilot162
    Mar 21, 2023 at 12:17
  • $\begingroup$ Well, it's a different design of artificial horizon that runs on electricity rather than a vacuum system. Still has a mechanical gyro inside, just powered differently. Not terribly uncommon these days. Traditionally though all the gyro instruments except the turn rate indicator or turn coordinator were usually vacuum driven. I'm guessing this aircraft has no vacuum pump or vacuum system at all, right? $\endgroup$ Mar 21, 2023 at 12:22
  • $\begingroup$ @pilot162 -- perhaps my answer was unclear, didn't mean to imply that the specific attitude indicator installed in the DA40NG could run either on electricity or vacuum. Edited to clarify-- $\endgroup$ Mar 21, 2023 at 12:34
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This description is found in the airplane maintenance manual of the DA40NG aircraft.

enter image description here

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    $\begingroup$ Re "incorporating a special air erection mechanism"-- fascinating. I wonder how it works, in the context of an electrically-driven instrument. New ASE question perhaps-- $\endgroup$ Mar 21, 2023 at 13:46
  • $\begingroup$ It's electrically after all.. But it's like they don't want us to know something lol. $\endgroup$
    – pilot162
    Mar 21, 2023 at 13:56

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