MiG-21 turn performance

[Hummingbird]

Been testing the MiG-21's turning performance ingame for abit, and I've found that atm it can hold around 7.1 G's in sustained turns at SL. To me this seems abit high if the wing loading of 78 psf is correct.

 

The much lighter F-13 was capable of ~7.1 G's at SL, but at 50 psf its wing loading is also 28 psf lower than that of the Bis.

 

When it comes to STR an increase in thrust can ofcourse make up for an increase in wing loading, but question is wether the Bis features THAT much extra thrust. A 50+% in wing loading requires A LOT of thrust to negate.

[HugePanic]

one short search reveals that EM chart:

 

According to that, the highest sustainable g-loading should be slighlty lower than 7G.

Gut there is no exact MIG-21 model given, so you never know if this is the correct engine.

 

According to this the BIS has some kN more thrust than the other 21 types...

 

From a 5minute google search basis I find the 7.1G "ok".

[1.JaVA_Platypus]

one short search reveals that EM chart:

 

According to that, the highest sustainable g-loading should be slighlty lower than 7G.

Gut there is no exact MIG-21 model given, so you never know if this is the correct engine.

 

According to this the BIS has some kN more thrust than the other 21 types...

 

From a 5minute google search basis I find the 7.1G "ok".

 

The graph seems to be in english. Can it be from the "Have Doughnout" project? That one was a MIG-21 F-13. IIRC

[Hummingbird]

one short search reveals that EM chart:

 

According to that, the highest sustainable g-loading should be slighlty lower than 7G.

Gut there is no exact MIG-21 model given, so you never know if this is the correct engine.

 

According to this the BIS has some kN more thrust than the other 21 types...

 

From a 5minute google search basis I find the 7.1G "ok".

 

That is the F-13 G chart, which as I said features a wing loading that is a whopping 50% lower than the Bis version we have ingame.

 

Hence I have my reservations regarding wether a 7.1 G STR at SL is "ok".

[Hummingbird]

The graph seems to be in english. Can it be from the "Have Doughnout" project? That one was a MIG-21 F-13. IIRC

 

Yes it's from said project.

[Esac_mirmidon]

From the Mig-21Bis russian manual.

 

 

Mig-21 Bis - 7.500 Kg - 2 x R-3S.

 

6.6 G Sustained Turn Rate at 1.000 meters

 

Full Afterburner.

[Frischi234]

Thats the only picture i found in german manual.

MiG-21bis in comparison to the MiG-21M

Emergency Afterburner - 500m

 

Thats a bit to much i think :huh:

 

[Esac_mirmidon]

According to the russian manual, maximum G for the Mig-21 Bis is 8 at Mach less than 0.8 and with less than 1.200 liters fuel.

[Hummingbird]

From the Mig-21Bis russian manual.

 

 

Mig-21 Bis - 7.500 Kg - 2 x R-3S.

 

6.6 G Sustained Turn Rate at 1.000 meters

 

Full Afterburner.

 

Do you have one with the lift line on it too?

[Frischi234]

According to the russian manual, maximum G for the Mig-21 Bis is 8 at Mach less than 0.8 and with less than 1.200 liters fuel.

 

I think max G is 8.5 with less than 900 liters.

[Esac_mirmidon]

https://www.dropbox.com/sh/eyh14uxc89acs4j/AACqoNSB1CZhKvqT0QHv20aba/Russian/%D0%9C%D0%B8%D0%93-21%D0%91%D0%98%D0%A1%20%2875%D0%90%29%20%D0%A2%D0%B5%D1%85%D0%BD%D0%B8%D1%87%D0%B5%D1%81%D0%BA%D0%BE%D0%B5%20%D0%BE%D0%BF%D0%B8%D1%81%D0%B0%D0%BD%D0%B8%D0%B5.%20%D0%9A%D0%BD%D0%B8%D0%B3%D0%B0%201.%20%D0%9B%D0%A2%D0%A5.pdf?dl=0
Edited February 15, 2016 by Esac_mirmidon

[Hummingbird]

Alright found the translated manual:

 

From this chart it can be accurately estimated that at a weight of 7500 kg and in emergency afterburner 7.1 to 7.2 G's sustained at SL is possible.

 

I was under the impression that the weight of the Bis was ~8,700 kg, i.e. ~1,200 kg heavier. At such a weight 7 G's would not be possible and it would be closer to 6 G's.

[Esac_mirmidon]

The second reheat of the Mig-21Bis engine has a lot of thrust. A lot extra thrust.

[Frischi234]

Another Pic. Left side without and right side with second reheat.

7500kg - 2x R-3S

 

[Hummingbird]

Another Pic. Left side without and right side with second reheat.

7500kg - 2x R-3S

 

 

At 7500 kg that makes perfect sense.

 

At 8,700 kg the STR would decrease markedly however, to around 6 G's, which is what had me wondering.

Edited February 15, 2016 by Hummingbird

[Hummingbird]

Alright according to the manual the combat loaded weight of the MiG-21Bis clean with no external stores is 8,620 kg, or 1,120 kg heavier than weight figure we have performance figures for = 7,500 kg.

 

At a weight of 8,620 kg the aircraft wil not be capable of sustaining 7.1 G's at SL, instead it will be closer to 6 G's.

 

Edited February 15, 2016 by Hummingbird

[HugePanic]

since i don't have anything better to do:

 

 

F13:

m 7500 kg

a_max 7,1 g

Lift 522382,5 N

Thrust 60600 N

wing_area 23 m³

v 300,6 m/s

 

This leads to:

cl_sust 0,4103710712

cd_sust 0,0476058959

 

 

 

First approach:

the F13 and the BIS have the same cd and cl at max-sustained g-load turn

--> speed is higher at the BIS

 

I use these parameters to calculate a manoever speed for the BIS, and then drag.

 

BIS:

Assumption Cl = const Cd = const

 

m 8200 kg

a_max 7,1

Lift 571138,2 N

thrust 69600 N

wing_area 23 m²

 

cl_sust 0,4103710712

cd_sust 0,0476058959

 

 

Maneuever speed:

v 314 m/s

 

Drag 66256 N

 

This leads to the conclusion, that the available thrust (69kN) is higher than the actual drag (66kN).

---> BIS can do 7.1g sustained turns

 

 

Second approach:

Speed = const

cl/cd = const

 

m 8200 kg

a_max 7,1

Lift 571138,2 N

thrust 69600 N

wing_area 23 m²

 

v 300,6

 

 

cd 0,0546760785

cl/cd 8,6201732673

Ca 0,4713172699

 

 

Lift 599964 N

 

 

Again, the available lift (60kN) is higher than the needed lift (57kN).

---> BIS can do 7.1g sustained turns

 

 

I know that cl/cd is not a constant. But the operation points will not differ that much, so this assumption does not seem to be that bad.

 

 

What do you think? Are my calculations wrong? Are my assumptions wrong? Are my input data wrong?

 

Attached you will find my calculation file...

mig_21_calculation.zip

[DNice]

Low radar visibility, instantaneous turn rate, acceleration and the helmet mounted sight combined with high-off-boresight R-73 air-to-air missiles were among the factors that made the upgraded MiG-21 a deadly adversary for the U.S. F-15s.

- From a report about the Cope India 04 exercise.

 

To be noted, they are speaking about the Mig-21 Bison, is there any info if anything aerodynamically was improved? Because videos I have seen of the MiG-21Bis do show quite a slow turning rate, but then again, I'm quite sure the ones I've watched, no one was pushing for any high G maneuvers in them.

[Hummingbird]

since i don't have anything better to do:

 

 

F13:

m 7500 kg

a_max 7,1 g

Lift 522382,5 N

Thrust 60600 N

wing_area 23 m³

v 300,6 m/s

 

This leads to:

cl_sust 0,4103710712

cd_sust 0,0476058959

 

 

 

First approach:

the F13 and the BIS have the same cd and cl at max-sustained g-load turn

--> speed is higher at the BIS

 

I use these parameters to calculate a manoever speed for the BIS, and then drag.

 

BIS:

Assumption Cl = const Cd = const

 

m 8200 kg

a_max 7,1

Lift 571138,2 N

thrust 69600 N

wing_area 23 m²

 

cl_sust 0,4103710712

cd_sust 0,0476058959

 

 

Maneuever speed:

v 314 m/s

 

Drag 66256 N

 

This leads to the conclusion, that the available thrust (69kN) is higher than the actual drag (66kN).

---> BIS can do 7.1g sustained turns

 

 

Second approach:

Speed = const

cl/cd = const

 

m 8200 kg

a_max 7,1

Lift 571138,2 N

thrust 69600 N

wing_area 23 m²

 

v 300,6

 

 

cd 0,0546760785

cl/cd 8,6201732673

Ca 0,4713172699

 

 

Lift 599964 N

 

 

Again, the available lift (60kN) is higher than the needed lift (57kN).

---> BIS can do 7.1g sustained turns

 

 

I know that cl/cd is not a constant. But the operation points will not differ that much, so this assumption does not seem to be that bad.

 

 

What do you think? Are my calculations wrong? Are my assumptions wrong? Are my input data wrong?

 

Attached you will find my calculation file...

 

As pr the US HaveDoughnut performance charts the F-13 could manage ~6.7 G's at 5 kft at a weight of just 5,620 kg (12,400 lbs) for a wing loading of 50 psf. So that should be your input data.

 

However we already have an even better base figure as we know that the MiG-21Bis can sustain 7.1-7.2 G's @ SL using emergency AB at a light weight of 7,500 kg as stated in manuals. However the loaded weight of the Bis is 8,620 kg (clean), or 1,120 kg heavier than the weight figure on the performance chart.

Edited February 16, 2016 by Hummingbird

[Hummingbird]

- From a report about the Cope India 04 exercise.

 

To be noted, they are speaking about the Mig-21 Bison, is there any info if anything aerodynamically was improved? Because videos I have seen of the MiG-21Bis do show quite a slow turning rate, but then again, I'm quite sure the ones I've watched, no one was pushing for any high G maneuvers in them.

 

Often a high instantanous turn rate is mentioned however it is actually just the initial pitch rate or nose pointing ability that is high, and that thanks to the pure delta planform wing.

 

The F-13 did boast a good ITR during the US tests though thanks to its very low wing loading in those tests.

[Hummingbird]

Is it possible someone can translate this ITR chart? (esp. the description of the lines at the bottom of the page):

 

[Hadwell]

These charts.... Just don't go over 30 degrees aoa, and you won't stall...

Speed and altitude aren't things you can depend on getting to decide, so either you will, or won't survive a turn fight with someone...

as long as you never go past 30ish aoa you turn, you stand a chance, stalling out constantly, you will lose... Anything else is too unpredictable to expect and its difficult to increase or decrease your speed and altitude on the fly when you're trying to shake someone and they're on you good, and if you're on them, then its their choice for speed and altitude

 

Pretty well anything you will fight multiplayer in dcs makes the mig21 look like it has the turn radius of a b29

 

So all you really need to remember is 30 aoa, and avoid turn fights.

[Hummingbird]

You've misunderstood the point of the thread Hadwell, this is about how the ingame MiG-21 performs in comparison to its real life counterpart in terms of raw performance, i.e. sustained & instantaneous rate/load factor.

[Hadwell]

Sure its kinda interesting as any kind of historical documentation is, but it doesn't help with flying the mig21 in dcs...

 

I was just being practical.

[Harle]

Пy - load factor

Cy - lift coefficient