MiG-29's BFM characteristics / doubts

[HDpilot]

The negative and biased opinion is not from my point of view but from the point of objective and scientific based investigation. Are you an engineer or MiG-29 test pilot to have your own professional based point of view? No. You act here as an amplifier and loudspeaker of only one man's who flew the aircraft in RL. But you are trying to use the language barrier and spread here the part of his opinion beneficial to your.

Though fighter29 finally agreed that the difference in his perception is actually due to the lack of acceleration feedback and very different stick forces and travel, you keep claiming here "FM is wrong" and demanding "FM correction".

You intentionally ignore our SME's opinion who wrote a big post about the landing technics of MiG-29. By the way, he mentioned very typical imperfection at landing in RL - small lifting-off due to prolonged stick pulling after touchdown - that is common in DCS.

So, please understand that such activity either on Russian or English forum are not constructive - it steals our time, resources to make, for example, very interesting CFD investigation to prove the things WE ALREADY KNEW. And it's very sad that engineering approach has less sense for some people now than a blind faith in somebody's words.

 

That i'm not a pilot or an engineer doesn't mean that i'm stupid and and have no technical understanding, although technical math + cnc programming are a long time ago in my life. Your scientific investigation not contain the answers to my questions since a long time, so I was very grateful for Fighter29´s factual explanations and i dare to say, that other russian forum members felt the same.

Fact is: I didn't post Fighter29's comment here, i just trying to explain the reason for his comment from russian part, wich being linked here by another member, i can't remember claiming "fm is wrong", didn´t rate the FM here and don't understand why you're attacking me. I just wished a little more pitch stability, that´s all.

If you need a victim, please here:

Anyone thinking the FC3 "PFM" flight models are anywhere close to the real thing are kidding themselves. They are good for producing certain numbers like turn rate, radius and thrust to weight ratio but that's mostly it.

or better here:

Я бы скорее сказал, что проблема продольного канала в DCS - центровка/эффективность стабилизатора.

or many others too...

I see your reaction to me as pure demagogy. Its my opinion, if its OK for you. Thanks

Edited August 12, 2020 by HDpilot

[Ironhand]

First post by Cmptohocah:

...it turns out that in a coordinated turn (no side slips), that has no altitude changes and with constant speed the aircraft...The slower you fly the tighter the turn and there fore the higher the turn rate.

 

Second post:

...[T]hese are two different things (turn rate and turn radius). Former is the angular change of direction expressed as degrees/s and the latter is the radius of an inscribed circle in a turn. However, they are (due to geometry, or rather kinematics) in direct relation to one another. Increase in turn rate leads to decrease in radius of turn and vice versa.

Yes, they are inversely related. My difficulty was with your original statement(s).

[Yo-Yo]

Originally Posted by ФрогФут View Post

Я бы скорее сказал, что проблема продольного канала в DCS - центровка/эффективность стабилизатора.

 

(I'd rather say that the problem of the longitudinal channel in DCS is balance /stabiliser effectiveness)

 

 

 

That's another example of unprofessional and biased opinion, I hope that the English forum members with aero-engineering background can explain you the graph below (MiG-29 AB trim at low altitude from our newsletter) if you can not understand it yourself and prefer to amplify somebody's statement...

[NineLine]

[BlackPixxel]

In this video you can see very often how he is unable to keep the nose in a straight line, it is always pumping up and down.

 

What makes it so difficult to fly precisely is that it feels like 95% of the stick travel is for trim, and 5% are actually used for the full maneuvering around the trim center.

 

When landing, tiny movements of the stick make the plane go up and down by alot, which makes it harder to touch down smoothly than with any another plane.

 

 

Not sure if this is correct or not, but this is the simple reason why the MiG is so weird to fly in DCS.

[NineLine]

In this video you can see very often how he is unable to keep the nose in a straight line, it is always pumping up and down.

 

What makes it so difficult to fly precisely is that it feels like 95% of the stick travel is for trim, and 5% are actually used for the full maneuvering around the trim center.

 

When landing, tiny movements of the stick make the plane go up and down by alot, which makes it harder to touch down smoothly than with any another plane.

 

 

Not sure if this is correct or not, but this is the simple reason why the MiG is so weird to fly in DCS.

 

Well, that may be just tuning the controls to your liking, this is why warbird pilots swear by extensions, etc. the controls on our desktop will never match the real thing, but the FMs were built with real controls in mind, it's our job as virtual pilots to get it to where we want it. It's like that for every module, but more or less depending on the aircraft.

[Yo-Yo]

In this video you can see very often how he is unable to keep the nose in a straight line, it is always pumping up and down.

 

What makes it so difficult to fly precisely is that it feels like 95% of the stick travel is for trim, and 5% are actually used for the full maneuvering around the trim center.

 

When landing, tiny movements of the stick make the plane go up and down by alot, which makes it harder to touch down smoothly than with any another plane.

 

 

Not sure if this is correct or not, but this is the simple reason why the MiG is so weird to fly in DCS.

 

No, it's not right. If you take a look at the trim chart, you can see that in subsonic range very small (but reverse - pulling with increased IAS) stick movement required.

https://forums.eagle.ru/showpost.php?p=4441575&postcount=4235

[bbrz]

This very instinct is one of the main stall/spin factors in general aviation. People with inadequate training tend to develop bad habits and do stupid things. Especially when coupled with spacial disorientation and vestibular illusions.

Instinct and intuition are different things and are causing different reactions.

Especially considering the startle and surprise effect when entering an unintentional spin at very low altitude and the danger of immediate death.

This has very little to do with stupidity etc.

Edited August 13, 2020 by bbrz

[Cmptohocah]

In this video you can see very often how he is unable to keep the nose in a straight line, it is always pumping up and down.

 

What makes it so difficult to fly precisely is that it feels like 95% of the stick travel is for trim, and 5% are actually used for the full maneuvering around the trim center.

 

When landing, tiny movements of the stick make the plane go up and down by alot, which makes it harder to touch down smoothly than with any another plane.

 

 

Not sure if this is correct or not, but this is the simple reason why the MiG is so weird to fly in DCS.

 

I can confirm this. There seems to be a certain amount of pitch instability especially when getting close to the max AoA.

I've also noticed it when trying to determine a stall speed for a certain weight and at one point, just before the stall, the nose just started wobbling. The conclusion of my test was that the maximum angle of attack for that certain weight was between 20 and 25 degrees :D - that's 5 degrees uncertainty.

 

 

The same effect can be experienced when trying to get into max sustained turn in a level flight. Even with small inputs on the stick, the pitch runs away from you and you suddenly end up loosing a lot of airspeed.

 

It can be, to a certain extend, mitigated by wobbling the joystick (up-down) which seems to calm the "beast" down a bit. I know it sounds silly, but it works.

Edited August 13, 2020 by Cmptohocah

[Cmptohocah]

Yes, they are inversely related. My difficulty was with your original statement(s).

 

So the original statement was:

In a constant speed, altitude and coordinated turn the slower the aircraft flies (the lower the TAS - true air speed), the tighter the turn - highest turn rate (TR) / lowest radius of turn (RT).

 

 

A simplified explanation of this could be something like this:

In order for an airplane to turn, two things are needed:

1. "pulling" force that tends to bring the airplane to the center of the turn circle

2. forward motion

 

"Pulling" force is provided by a component of lift and this is what we popularly call "G", or rather "G-load". We all know that lift in aircraft is produced by the airflow over the lift surfaces, but let's briefly substitute this force with a string. So imagine that the airplane is suspended by cables (one making sure that the airplane stays in the air, ie. counters the weight; one providing the "pulling" force needed to turn), but there is no forward motion, ie. engines are turned off. What would happen is that the airplane would just move in a straight line in the direction of the "pulling" force (towards the banked side) - it would move like a helicopter, just "slewing" to the side. So we can think of the G-load as a sort of "turning potential". The more G you pull, the higher the potential to turn, but without the forward motion there is no turning (no circle is being described, no heading change occurs). I think a good analogy would be the amount of steering wheel turn in a car.

 

This is where forward motion comes into play. You can think of it as the "time" that the airplane has in order to use that "turning potential" and convert it into a turn - the lower the speed the less time an airplane has to use the available G's, the higher the turn rate (TR) and lower the radius of turn (RT). Note that TAS is the one that is important here and not the IAS.

 

You can test this in DCS by making a turn at a certain constant bank angle, let's say 60 degrees, for example, and varying the airplane speed. Let's say in the first test you are doing 1000km/h TAS and in the second you are doing 500km/h. A 60deg of bank will yield 2G of force, so your load in both cases is exactly the same, but since you are doing half the forward speed in the second case you will "draw" a smaller circle. In order to go around a smaller circle you need to change the heading quicker, hence where the higher TR comes from. :smartass:

[bbrz]

So the original statement was:

In a constant speed, altitude and coordinated turn the slower the aircraft flies (the lower the TAS - true air speed), the tighter the turn - highest turn rate (TR) / lowest radius of turn (RT).

 

No, the highest turn rate does not occur at the lowest speed.

 

E.g. F-16 @ S.L. at MIL thrust.

 

Tightest turn radius at M0.3. and 2.6G (68° AOB) > Turn rate = 14deg/sec

 

Quickest turn at M0.6. and 8.0G. (83° AOB) > Turn rate = 22deg/sec

Edited August 15, 2020 by bbrz

[Cmptohocah]

No, the highest turn rate does not occur at the lowest speed.

 

E.g. F-16 @ S.L. at MIL thrust.

 

Tightest turn radius at M0.3. and 2.6G (68° AOB) > Turn rate = 14deg/sec

 

Quickest turn at M0.6. and 8.0G. (83° AOB) > Turn rate = 22deg/sec

 

Did you read what I wrote above?

 

Of course that a 2.6G turn, will not have the same turn rate as an 8G turn. The bank angles are completely different and so are the loads.

 

Now, why the F-16 can't pull more than 2.6G at M0.3 is a different thing.

Let's say you are happily flying the "tightest turn radius" in your F-16 and I come along with my MiG-29 in full AB pulling some 6G or so at 450km/h (M0.36). Do you think we would have the same turn performance?

Edited August 15, 2020 by Cmptohocah
Typo

[bbrz]

1. Did you read what I wrote above?

2. I come along with my MiG-29 in full AB pulling some 6G or so at 450km/h (M0.36). Do you think we would have the same turn performance?

1. Yes and I do have the impression that there is a language barrier and/or a lack of understanding.

You wrote: the lower the TAS, the tighter the turn - highest turn rate (TR)/lowest radius of turn(RT).

 

2. That's a weird question. Can you show me an official performance chart where a MiG-29 can pull 6G at M.36?

I don't understand what you consider turn performance. Turn rate or turn radius?

Edited August 15, 2020 by bbrz

[Ironhand]

So the original statement was:

In a constant speed, altitude and coordinated turn the slower the aircraft flies (the lower the TAS - true air speed), the tighter the turn - highest turn rate (TR) / lowest radius of turn (RT).

 

 

A simplified explanation of this could be something like this:

In order for an airplane to turn, two things are needed:

1. "pulling" force that tends to bring the airplane to the center of the turn circle

2. forward motion

 

"Pulling" force is provided by a component of lift and this is what we popularly call "G", or rather "G-load". We all know that lift in aircraft is produced by the airflow over the lift surfaces, but let's briefly substitute this force with a string. So imagine that the airplane is suspended by cables (one making sure that the airplane stays in the air, ie. counters the weight; one providing the "pulling" force needed to turn), but there is no forward motion, ie. engines are turned off. What would happen is that the airplane would just move in a straight line in the direction of the "pulling" force (towards the banked side) - it would move like a helicopter, just "slewing" to the side. So we can think of the G-load as a sort of "turning potential". The more G you pull, the higher the potential to turn, but without the forward motion there is no turning (no circle is being described, no heading change occurs). I think a good analogy would be the amount of steering wheel turn in a car.

 

This is where forward motion comes into play. You can think of it as the "time" that the airplane has in order to use that "turning potential" and convert it into a turn - the lower the speed the less time an airplane has to use the available G's, the higher the turn rate (TR) and lower the radius of turn (RT). Note that TAS is the one that is important here and not the IAS.

 

You can test this in DCS by making a turn at a certain constant bank angle, let's say 60 degrees, for example, and varying the airplane speed. Let's say in the first test you are doing 1000km/h TAS and in the second you are doing 500km/h. A 60deg of bank will yield 2G of force, so your load in both cases is exactly the same, but since you are doing half the forward speed in the second case you will "draw" a smaller circle. In order to go around a smaller circle you need to change the heading quicker, hence where the higher TR comes from. :smartass:

OK. I see where you're coming from and it's no different than what everyone else is saying. The confusion stems from your use of 2Gs, when the conversion was about the fastest rates possible. In the case of maximum turn rate, that would occur at the lowest speed that puts maximum Gs on the airframe.

[Top Jockey]

A small doubt :

 

From the diagrams below, one can conclude that the maximum sustained turn rates, for those circumstances, are attained respectively at the speeds:

 

MiG-29: ~ 900 kph

Su-27: ~ 970 kph

 

Correct ?

[Cmptohocah]

1. Yes and I do have the impression that there is a language barrier and/or a lack of understanding.

You wrote: the lower the TAS, the tighter the turn - highest turn rate (TR)/lowest radius of turn(RT).

 

2. That's a weird question. Can you show me an official performance chart where a MiG-29 can pull 6G at M.36?

I don't understand what you consider turn performance. Turn rate or turn radius?

 

Well that's a bit disappointing :(. I never considered my self an English native speaker, but I also didn't expect for people not to understand me. :D

Anyway to put it in very simple terms:

 

highest possible angle of attack (AoA) = highest possible lift

highest possible lift = highest possible G load

highest possible G load + slowest possible speed = smallest turn radius and highest possible rate of turn

 

Load only depends on the bank angle:

 

Both turn rate and turn radius depend on load + true airspeed (TAS).

 

When it comes to the MiG-29 turn performance, I will make a video once I am back from my holidays to demonstrate what I mean and post it here.

 

...In the case of maximum turn rate, that would occur at the lowest speed that puts maximum Gs on the airframe.

 

And also the minimum turn radius. Max turn rate and min turn radius are intrinsically coupled.

[Cmptohocah]

A small doubt :

 

From the diagrams below, one can conclude that the maximum sustained turn rates, for those circumstances, are attained respectively at the speeds:

 

MiG-29: ~ 900 kph

Su-27: ~ 970 kph

 

Correct ?

 

Yes, those V-n diagrams are a bit difficult tricky to analyze, I must admit. For example, when it comes to the sustained turn rates: what are the Gs being pulled in this particular case?

 

 

For the "instantaneous turn performance" it is quite clear: the highest attainable G and the lowest airspeed give the highest turn rate (omega), which in this case is 10G, 580km/h and (I am guessing, as it doesn't really say on the diagram) around 400m turn radius.

[Top Jockey]

Yes, those V-n diagrams are a bit difficult tricky to analyze, I must admit. For example, when it comes to the sustained turn rates: what are the Gs being pulled in this particular case?

 

 

For the "instantaneous turn performance" it is quite clear: the highest attainable G and the lowest airspeed give the highest turn rate (omega), which in this case is 10G, 580km/h and (I am guessing, as it doesn't really say on the diagram) around 400m turn radius.

 

Thank you for the insight Cmptohocah.

Regarding Sustained turn rate, I'm asking about the absolute maximum ...

 

So the Su-27's minimum Turn Radius, is bigger than the MiG-29's one after all ?

 

edit:

 

By the way, using Tacview, in DCS I can do a 300m minimum turn radius without much problem with the Su-27, so my doubts still persist...

Edited August 15, 2020 by Top Jockey

[Yo-Yo]

Well that's a bit disappointing :(. I never considered my self an English native speaker, but I also didn't expect for people not to understand me. :D

Anyway to put it in very simple terms:

 

highest possible angle of attack (AoA) = highest possible lift

highest possible lift = highest possible G load

highest possible G load + slowest possible speed = smallest turn radius and highest possible rate of turn

 

Load only depends on the bank angle:

 

Both turn rate and turn radius depend on load + true airspeed (TAS).

 

When it comes to the MiG-29 turn performance, I will make a video once I am back from my holidays to demonstrate what I mean and post it here.

 

 

 

And also the minimum turn radius. Max turn rate and min turn radius are intrinsically coupled.

 

This diagram represents only one LEVEL TURN condition - the coupling between normal g-load and its projection to vertical =1. This diagram is absolutely useless regarding the certain aircraft.

 

If you want to calculate instantenious turn rate vs speed you need to calculate n = Lift/mg normal g-load using CL_max for the plane or CL_max (M) as S*q*CL_max.

Then, you need to find a = g * sqrt(n^2 - 1) (this sqrt is represented at your graph, by the way)

 

And only then you can get w = a/TAS.

 

Sustained turn is more complicated to calculate because it depends on CD = f(CL) and thrust P = f(M) and the point of n_sust is found as a point of equilibrum of thrust and drag.

 

And finally I have to mention that for the planes with high thrust/weight ratio you need to take in account the normal part of thrust vector at high AoA and add it to the lift.

[Top Jockey]

Hello again everyone,

 

I've been posting my doubts at the russian forum also, which indeed helped to clarify some aspects, but still, some doubts do persist.

So I'm asking your opinion on my comment below, if you will - which is:

 

If the Su-27 supposedly does have the advantages I've writen in 4 points, how come are the MiG-29's close combat capabilities frequently praised in several places ?

 

Thank you.

 

Hello again, comrades who know the MiG-29 and Su-27,

 

I am here again, with additional questions about the maneuvers of the MiG-29 and Su-27.

I watched my past computer games and ... I found interesting things again.

I'm sure you remember the images.

 

According to the text on page 76 of the Flanker 2.0 instruction manual, the red underline in the image reads:

 

“ The Su-27 is far from invincible (as evidenced by the repeated aerial combat with the MiG-29 from West Germany equipped with a helmet system). ”

 

As you already know, , these two planes are very interesting to me.

Then help me understand please:

Also in commentary no. 25, published by colleague Tory, it is reported that the MiG-29 has shown advantages in aerial combat.

 

However, considering that the Su-27 :

1 - has a higher instantaneous rotation speed (30 degrees / sec);

2 - can pull more G-forces at low speeds than the MiG-29;

3 - does not lose speed as quickly when cornering as the MiG-29, due to the fact that it is "Fly By Wire" and has "unstable" aerodynamics ";

4 - presumably has a smaller radius of curvature;

 

So, how is it possible, after reading on several sites, that the MiG-29 has an advantage in aerial combat ?

 

Thank.

 

https://forums.eagle.ru/showpost.php?p=4455236&postcount=80

[Cmptohocah]

No, the highest turn rate does not occur at the lowest speed.

 

E.g. F-16 @ S.L. at MIL thrust.

 

Tightest turn radius at M0.3. and 2.6G (68° AOB) > Turn rate = 14deg/sec

 

Quickest turn at M0.6. and 8.0G. (83° AOB) > Turn rate = 22deg/sec

 

Well, looks like you are right. I did some flight testing in DCS and a MiG-29S @ full AB does:

 

M0.36 (420km/h) 4G (80°) > Turn rate = 16.6 °/s

 

The turn radius was around 900m.

 

Now there is a question of: why is that?

 

I am yet to understand how 80° bank and constant airspeed and altitude yield such low Gs. :huh:

 

Here is the video:

 

Edited August 16, 2020 by Cmptohocah

[Top Jockey]

No, the highest turn rate does not occur at the lowest speed.

 

E.g. F-16 @ S.L. at MIL thrust.

 

Tightest turn radius at M0.3. and 2.6G (68° AOB) > Turn rate = 14deg/sec

 

Quickest turn at M0.6. and 8.0G. (83° AOB) > Turn rate = 22deg/sec

 

Well, looks like you are right. I did some flight testing in DCS and a MiG-29S @ full AB does:

 

M0.36 (420km/h) 4G (80°) > Turn rate = 16.6 °/s

 

Now there is a question of: why is that?

 

I am yet to understand how 80° bank and constant airspeed and altitude yield such low Gs. :huh:

 

From the diagram I posted above, I believe that for the MiG-29:

 

- maximum Sustained Turn Rate, would be at 900 kph (at the least at 5000 ft), at sea level I believe it should be a t a lower speed;

- maximum STR should be roughly 22º / sec.

- corner speed is probably around 685 kph - both from the diagram above, and from other people here at the forum;

- using Tacview, managed to get a minimum Turn Radius of: 300m at a 330 kph speed.

[Yo-Yo]

If the formulas are not obvious.

 

So, few rules consequent from the math:

instant turn radius is CONSTANT within useful speed range until g-limit is reached;

AB and MIL sustained turn rate generally increases with speed up to transsonic range with higher drag losses;

sustained turn radius generally increases with speed for AB though low speed MIL turn can have almost constant radius at low speed.

Edited August 17, 2020 by Yo-Yo

[Top Jockey]

If the formulas are not obvious.

 

So, few rules consequent from the math:

instant turn radius is CONSTANT within useful speed range until g-limit is reached;

AB and MIL sustained turn rate generally increases with speed up to transsonic range with higher drag losses;

sustained turn radius generally increases with speed for AB though low speed MIL turn can have almost constant radius at low speed.

 

Hello,

 

Just to be sure, this diagram is for the MiG-29 or Su-27 ?

[Yo-Yo]

Hello,

 

Just to be sure, this diagram is for the MiG-29 or Su-27 ?

 

It is not a certain plane and certain weight diagram, it is a general diagram showing the main general laws for any modern fighter. It can be derived from Su-27, MiG-29, F-15, F-18, whatever, but the main dependancies will be the same. Only the certain numbers can vary a bit.