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Why are the colors of the MiG-15's attitude indicator inverted (blue on the ground side, brown on the sky side)?

enter image description here
Source: http://www.warbirdalley.com/mig17.htm

George Geo
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2 Answers2

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That attitude gyro reacts in the opposite manner to pitch movement (pitch down = horizon line rolls DOWN) compared to the "conventional" manner (pitch down, horizon line rolls UP). This is sufficiently confusing that on similar gyros of American manufacture, the words CLIMB and DIVE are printed on the "ball" inside the gyro case to remind the pilot what the instrument is telling him or her.

The "opposite" reading gyro horizons were commonly used in American fighter aircraft because their construction made them more resistant to tumbling than were the "conventional" reading instruments, which were used in civilian aircraft.

After WWII, those opposite-reading gyros wound up on the surplus market and a number of them were installed in civilian aircraft, including the Beech Bonanza that was carrying Buddy Holly, Ritchie Valens and the Big Bopper on the night of their crash. The pilot had trained in a plane with a conventionally-reading instrument in its panel and the accident report claimed that he was confused by that opposite-reading gyro in the dark, thinking he was trimming for an 800FPM climb when what he was really doing was trimming for a descent- and minutes after takeoff, the plane flew smoothly into the ground and everyone aboard was killed.

I have an example of both types of gyro horizon in my collection, and even when they are not spinning, simply tilting their cases in unison demonstrates the difference: one rolls up, the other rolls down when you pitch them both down.

niels nielsen
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    My God, that is confusing / amazing. That's like Nintendo famously have the Y axis the wrong way; so anyone who's a pilot or has even just played any plane game gets stunningly confused - you push the stick forwards in Splatoon and you .. point upwards. (Fortunately you can change it in the settings.) Conversely kids who got a Switch and have never, you know, flown a plane *have their minds wired the wrong way now* - and hopefully they will never become pilots :O – Fattie Jan 27 '20 at 11:34
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    @Fattie Apparently it was Quake that's ultimately responsible for screwing this one up for everyone. – Mason Wheeler Jan 27 '20 at 17:23
  • fascinating @MasonWheeler , thanks for that ! – Fattie Jan 27 '20 at 17:38
  • @Fattie I'll note that for an FPS, up=up, down=down makes sense. As soon as you're in a vehicle though, that had better switch so that up=push nose and down=pull nose – Baldrickk Jan 28 '20 at 13:11
  • it's definitely an issue, @Baldrickk ! Example my kids use "Nintendo style" when blasting around in Splatoon and it gives me a migraine to even watch their fingers while! :) Humorously, from time to time I'll forget to swap it to what I consider "normal", if they've been using their machine, when I play :) – Fattie Jan 28 '20 at 13:23
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This is interesting! The only lead I was able to find (so far) is this discussion thread, with a comment:

The colour becomes logical, if you see it moving. Climbing the plane which shows the sky in blue on the artificial horizon. Ground being brown/earth, if you see this, the nose of the plane is pointing downwards

And the explanation for arranging the colours in this way is, plausibly (same discussion):

It makes the instrument less complex. The way it is built means you do not have to invert the pitch axis movement of the gyro, which is the case for "conventional" artificial horizons.

If you want to build the simpliest possible attitude indicator, you take a gimballed gyro and attach a sphere with horizon line and some kind of metering lineage on it. This sphere will maintain its position in relation to earths surface. With roll it is self explanatory, it will indicate the tilt of the horizon as it will appear if you look outside. Indicating pitch is not as simple. As you pitch up, the horizon line will move up on this simple AI. Now that's not very intuitive. Pitching down, the line goes down. Again, not that intuitive!

enter image description here
Note how the pilot would see the bottom of the sphere: more blue (source; edited)

So, to keep the mechanism simple, they fixed this with colours: bottom part is blue, because when you pitch up, the bottom part will become more visible, thus indicating you are heading towards the blue sky. Pitch down, and the indicator will show more of its top, which is painted brown, indicating you are headed towards dirt.

You can see the "reversed" AI rolling as described above in the youtube video embedded in the question, approximately 19:10 onwards, as the pilot is doing some maneuvering.

Jpe61
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  • So by the way you explain the difference between percentage of this ttwo colour is the direction of the aircraft travel , meaning more blue on bottom of the sfere then the nose is pointed up – George Geo Jan 25 '20 at 20:35
  • Like the idea of Humpty Dumpty – George Geo Jan 25 '20 at 20:40
  • @GeorgeGeo yes, the way the colors are painted is supposed to signal the direction of flight: blue is up, brown is down. When all you see is brown on you AI, you'd better do something quick :) – Jpe61 Jan 25 '20 at 21:18
  • What am I missing here? If the globe of the attitude indicator represents the earth, then when you pitch up the horizon line will go down. This will show more blue on a conventionally colored instrument, and more brown on the Mig 15. Unless I am misinterpreting your answer, I think you have it backwards. – Michael Hall Jan 25 '20 at 21:42
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    It is like an glass of red wine half empty. – George Geo Jan 25 '20 at 21:51
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    Alright, I see what I missed before. The Russian attitude display works opposite to what the west is used to, so they inverted the colors to compensate. – Michael Hall Jan 25 '20 at 22:33
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    @MichaelHall It's not necessarily opposite to western display but opposite to civilian display considering western fighter planes also sometimes use this opposite type of indicator simply due to their robustness – slebetman Jan 26 '20 at 13:30
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    Thanks @ymb1 for the picture, as always, worth a thousand words. – Jpe61 Jan 26 '20 at 14:01
  • @slebetman, got a recent example to back your assertion? – Michael Hall Jan 26 '20 at 18:32
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    @MichaelHall Why would it have to be recent for the assertion to be true? Mig-15 is old as well. Very old in fact. More recent Russian attitude indicators were also different from it, with a small symbol of a plane moving on a fixed background https://i.stack.imgur.com/BoTMI.jpg The design discussed here is old both for the West and for the East. A Sabre is the same age as Mig-15 https://books.google.cz/books?id=Fdeo9ZVg6dAC&pg=SA1-PA42&lpg=SA1-PA42 – Vladimir F Героям слава Jan 27 '20 at 09:25
  • @GeorgeGeo Yes, but only if it's the bottom half of the glass that's empty... – Darrel Hoffman Jan 27 '20 at 15:37
  • @Vladimir, because the assertion used present tense, not past tense. – Michael Hall Jan 27 '20 at 16:07
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    I had really time hard time wrapping my head around why, with the "simplest possible attitude indicator" described in this answer, pitch indications would be "backwards" from what the pilot would actually see looking at the horizon, while roll indications would not be "reversed". I could see that it was so, yet there seemed to be a paradox here. Finally I realized that if a gimballed gyro was used to stabilize a transparent sphere and the horizon line was painted on the back side of the sphere rather than the front side, everything would work "normally". – quiet flyer Nov 13 '21 at 11:41
  • The situation is not unlike the simplest type of "wet" magnetic compass used in light aircraft. The compass card swings in the "wrong" direction, opposite to the movement of the actual horizon, as the aircraft turns. That's because the heading indications are printed on the front side of the disk that comprises the compass card. Compare and contrast to this type of sailing compass (for example google "LC760 compass") where the heading indications are printed on the back side of the compass card as well as the front side. – quiet flyer Nov 13 '21 at 11:47
  • If you only pay attention to the back side, the sense of "wrong way" movement is eliminated. I actually once purchased a similar compass to use for some experiments with partial-panel blind flying (turn rate indicator but no other gyro instruments) and found it to be much more intuitive to use than the more common kind. (And for more food for thought, google "Bohli compass"-- !!) – quiet flyer Nov 13 '21 at 12:03