MiG-29 turn performance

Rakurs table by targe type (bit outdated):

http://www.avijacijabezgranica.com/Tehnika/vtupl17/images/VTUP%20L-17_Page_059.jpg

Target size-distance-o/oo

http://www.avijacijabezgranica.com/Tehnika/vtupl17/images/VTUP%20L-17_Page_060.jpg

Now, what are they? :D

So at 400km/h the mig has a higher sustained rate of turn than instantaneous rate of turn ?????

Where's the sense in that?

If this were the case the two lines would converge...

If I'm right the thick line is the max sustained turn rate (with no limiter) and the thin line is where the flight control system kicks in to limit the AOA for stability reasons,( that would explain why the ingame mig seems to under turn (as the flight control system is activated & is limiting both instantaneous & sustained turn rates by limiting AOA, whereas IRL in demo's & manouvers for testing it's probably over-ridden).

That would also explain why the lines stop rather than continuing for the whole flight envelope. There probably is no artificial AOA limiter at 800km/h as you can't get the plane to that angle without blacking out or tearing it apart anyway.

Yeah, that bit's a puzzler . . . .

To be honest, I'm not sure what that's about either - I don't think it's got anything to do with the alpha limiter, mostly because the MiG's FCS doesn't actually limit the angle of attack.

Interestingly:

It's from the SimHQ article "How to be a good stick in Lomac" (http://www.simhq.com/_air/air_097a.html), which is well worth a look - again, for some reason it shows sustained turn rate to be above instantaneous for the MiG29, although in a different part of the flight envelope.

There's something funny going on here . . . . . grin.

I guess the different shapes are because this graph is for all altitudes & the others are at fixed altitudes (?)

If the ACS in a mig really doesn't have anything to limit AOA (I'm sure I've read it had to be turned off before executing a cobra?) then yes - something funny is going on :-)

However - in this diagram the instantaneous & sustained curves DO converge at low speed - at a line which has an abrupt break from the sustained curve

If you look at the shape of the sustained curves for all these diagrams they are obviously derived from observed figure - a bit bumpy, not consistant curves.

The instantaneous curves are obviously "imposed" figures - which is why the exactly follow the 9G line.

At Mach 1.25 in the mig you can have a maximum sustained turn rate of ~ 3 degrees/sec without loosing speed, but haul the stick back & you'll get to exactly 9G & lose speed - I think it unlikely that the plane won't physicaly go beyond exactly 9G when the sustained curve figures go beyond this earlier in the curve. Maybe the left curve is defined by where you still have laminar flow over the wings: The instantaneous ROT for a Flanker or Fulcrum at whatever speed a Cobra is performed at must be 90 degrees over however long it takes to perform the manouver in seconds ~ > 180 degrees/sec, but can you count this as part of the "normal" operating envelope as the airflow is anything but laminar? I think this is what the instantaneous line is - not the absolute maximum instantaneous turn rate, but the maximum turn rate while staying inside the normal operating range - ie not exceeding a certain AOA or G.

I read in a post on this forum in the last couple of days that the Russian planes had some sort of phsical limiter which kicked in to limit stick travel at high G & "advise" you that the design limits had been reached, but that as it is in the form of a pnumatically operated bumper it could just be over-ridden by a bit of extra force.

Well there's limiters and there's limiters - as long as you can continue increasing the angle of attack beyond stall (even if this has a detrimental effect on the flight characteristics), I'd say there is no limiter.

There is a limit at which the stick hits a buffer in the MiG, but apply more force and the stick continues moving - to all intents and purposes there is no limiter.

The Cobra is an interesting move, but what disqualifies it from rate of turn analysis is that the velocity vector hardly changes - you continue moving forward in a straight line. Cobra is about instantaneous pitch rate, which is something different yet again.

Will look a bit further into what happens with the Cobra and limiters - there's a very big initial pitching moment resulting from a large elevator deflection that you wouldn't normally be able to get, so clearly SOMETHING has to be disabled. Really it's the initial shove that causes the rotation - logically considered, it has to be:

To pitch up you need to deflect the elevator downwards - creates lift downwards on the tail, rotates the aircraft around the CG.

Now, once you're beyond about fifteen degrees nose up, a flat plate aerofoil will stall - assuming a maximum elevator deflection of fifteen degrees, at fifteen degrees nose up the elevator is at zero alpha, no further downward lift is being generated, and hence no rotational force can be applied. At thirty degrees nose up the elevator is pointing upwards AND stalled in that direction, and you've only just gone through the alpha limiter.

So the problem is the big initial deflection. How you'd get that . . . well that gets into FCS programming. I think you disable the FCS - normally the FCS will adjust how much it moves the control surfaces based on a number of variables (don't know variables which and by what logic, didn't write the MiG software), but IIRC the MiG's backup control system is a direct-link system . . . i.e. 50% stick travel = 50% control surface deflection, 100% stick travel = 100% control surface deflection.

Yeah . . . . that sounds about right.

I need to sit down in the morning with a large mug of coffee and delve into this stuff a bit more deeply - I'm still not sure what the bottom end of those curves is all about.

Maybe that's the curve at which Betty starts her "Angle of attack over limits" song.

If you were in Wellington I'd bet you a beer the left curve is about AOA - maybe -as you mention - the point at which the plane is officially considered stalled (which is what I was getting at with the "laminar" flow thing) even though still controllable and capable of a faster rate of turn at that increased AOA.

Yeah, that bit's a puzzler . . . .

 

 

Interestingly:

 

 

It's from the SimHQ article "How to be a good stick in Lomac" (http://www.simhq.com/_air/air_097a.html), which is well worth a look - again, for some reason it shows sustained turn rate to be above instantaneous for the MiG29, although in a different part of the flight envelope.

 

 

There's something funny going on here . . . . . grin.

Suatained turn rate being faster than instantaneous is nothing strange, at least not if you take the accelerated motion law perspective. It only means the aircrat takes time to accelerate from an initial turn rate (slower ) to the sustaind turn rate (faster).

unless Im missing something here.

Additionaly these graps have probably different sources with different parameters of censorship. After all some of this data is still classified.

Except that if talking acceleration the scale would then be in degrees per second per second, not degrees per second, & if merely saying that rate of turn takes time to build up & that it's being measured at some (arbitrarily defined) point before it reaches maximum, you would have to define the point at which you were making the measurement - say - degrees per second one second after starting the turn... Which isn't given.

The expression itself points to the transient PEAK turning rate attainable at a given speed & I think your idea this wouldn't fit the curves anyway. If it weren then the instantaneous turn rate would simply continue to rise as the speed went up - the mass (or rotational inertia if you like) remain the same, but the forces exerted by the air for a given deflection of the control surfaces go up, so the initial "turn in" (angular acceleration) goes up.

These figures go up then down in what I think is obviously a calculated or "limited" rather than emperically derived way.

It would be real neat if ED did a turn rate indicator (deg/sec) on the external status bar ... just for practice. I now there is a great little util that lets you do it with lua, but given it is sooo critical in A2A, it would be better to have it built-in.