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Why are there two red lines on the G-meter on the MiG-29 aircraft? One at 7.5G, another one is at 9G. Also on the AOA scale the red line is at only 15 degrees. That is max AOA. It looks very low to me. Or the max G must not have more than the 15AOA? Now it's about the 7.5 G at 15AOA or the 9G at only 15AOA?

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    $\begingroup$ Take this with a grain of salt as I don't have a source, but 7.5 might be the G limit in air-to-ground configuration, and 9G is the limit in clean or air-to-air configuarion $\endgroup$
    – DeepSpace
    Commented Mar 27, 2020 at 11:56
  • $\begingroup$ The Mig will be like any other jet limit only 5.5 in air to ground because of the pylons $\endgroup$
    – George Geo
    Commented Mar 27, 2020 at 11:59
  • $\begingroup$ There is 7.5rated but could go 9G if you want occasionally. $\endgroup$
    – George Geo
    Commented Mar 27, 2020 at 12:00
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    $\begingroup$ 15 degrees is a typical stalling AOA for an airfoil (generally 13 - 16 degrees), so that's not unusual at all. The G meter, hard so say why there are two marks beyond something like an operational limit and ultimate limit. You will exceed stalling AOA at max G if are at or below Maneuvering Speed. If you're going at top speed and you pull, you will hit max G long before AOA gets to 15 deg. $\endgroup$
    – John K
    Commented Mar 27, 2020 at 13:42
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    $\begingroup$ @CarloFelicione yes I agree with that. I would bet the small tick mark is a limit with stores and the fat one without. $\endgroup$
    – John K
    Commented Mar 27, 2020 at 16:26

3 Answers 3

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@George already gave a correct answer, but I'll expand it a bit and show the source.

Indeed, the lower load limit is for trans- and supersonic flight (formally M > 0.85) and the higher limit is for subsonic conditions.

The AoA redline at 15° also relates to M > 0.85. At subsonic speeds, the max AoA is 26°. I can only speculate why it is not shown on the gauge. Normally, the control system will enforce these (AoA) limits automatically.

Here are the load and AoA graphs from the MiG-29 flight manual (or more precisely, its 'Practical aerodynamics' part).

MiG-29 limits

One might notice that the official supersonic load limit is 7 rather than 7.5. I'm not sure why is the gauge showing 7.5.

The curves indicate loads and AoA that are actually achievable at different altitudes (in km). The boundaries are labelled 'structural limits' (on the top) and 'control system limiter settings' (for alpha).

The text explains:

  • The load applies to the mass 14200 kg, whether with or without missiles. For higher mass, the load limit is reduced by 1 g.
  • The lower supersonic limit is explained by the lift losses for trim. (MiG-29 is marginally stable at low speed, but (like nearly any aircraft) is highly stable at supersonic speeds, and part of the wing lift must be used to counteract the strong tail downforce).
  • At M > 0.85, the leading edge droop flaps are stowed, which limits AoA at 15°. At lower speeds, the flaps expand the AoA limit significantly. (There may be further limits; e.g. 13° with a failed SAS (stability augmentation system)).
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  • $\begingroup$ You are correct about only 7G's red line, but incorect about you said 7G being lower load limit is for trans- and supersonic flight (formally M > 0.85)" that is for 9G's and" the higher limit is for subsonic conditions".There's a contradiction in terms. Please read first passage of your post $\endgroup$
    – George Geo
    Commented Apr 1, 2020 at 4:07
  • $\begingroup$ I don't understand. 7G is a lower load than 9G, isn't it? And it applies to M > 0.85. What's wrong with it? $\endgroup$
    – Zeus
    Commented Apr 1, 2020 at 4:17
  • $\begingroup$ Read this,and you will understand "Indeed, the lower load limit is for trans- and supersonic flight (formally M > 0.85) and the higher limit is for subsonic conditions."Graphics show 9G until 0.85Mach. Only modify the 7G with the 9 and that correct from the first graph $\endgroup$
    – George Geo
    Commented Apr 1, 2020 at 4:37
  • $\begingroup$ Yes, and that's what I'm saying. Lower load limit (i.e. 7G) is for supersonic. What is not clear here? $\endgroup$
    – Zeus
    Commented Apr 1, 2020 at 4:44
  • $\begingroup$ I draw brown lines for you to see that the 9G's is only in subsonic flight Not Supersonic and 7G is above 0.85 Mach. It is your graphic, not mine $\endgroup$
    – George Geo
    Commented Apr 1, 2020 at 7:06
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The line that is at the 9 G's is limit of maximum amount of G's( 9) until 0.85Mach (that is subsonic speed) and the lower [email protected] is the limit for supersonic flight.

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I can’t comment on the MiG exactly, but most fighter aircraft have maneuvering limitations when heavily loaded with external stores. If I recall correctly, the F-16 is limited to ~7Gs with a loadout. A good guess is that the MiG has similar limitations; this would be verified by looking at a MiG-29 flight manual under operational limitations listed therein.

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  • $\begingroup$ F-16 is 9G( at 15 degrees AOA) capable but only in CAT1( Max AOA is 25degrees) that is his AtoAir load. For A to Ground the stores limit is done by pylons and weight of all bombs. This is CAT3 limit. Angle of Attack is only 18 degrees max. $\endgroup$
    – George Geo
    Commented Mar 27, 2020 at 15:34
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    $\begingroup$ The F-16 is limited to 9Gs w/o heavy stores on the pylons; the aircraft, or its sub components, are not designed to withstand more than 6.5-7Gs with a full loadout. You will have to consult the operating handbook on that aircraft under performance limitations. $\endgroup$
    – Romeo_4808N
    Commented Mar 27, 2020 at 16:44

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