# Yakovlev Yak-9K

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What is [WiP] ?

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What is [WiP] ?

Work in Progress.

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Work in Progress.

Oh ok, thank you.

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Will it stall or crash after fire of NS-45 in slow speed (apr. 350km/h)?

• 7

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Will it stall or crash after fire of NS-45 in slow speed (apr. 350km/h)?

Sure. As soon as the 262's engines combust when throttling too fast. Seriously, too much realism, is not fun at all.....

• 6

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Sure. As Soon™™ as the 262's engines combust when throttling too fast. Seriously, too much realism, is not fun at all.....

Pretty much this.

It's just not fun if aircraft have things like random failures, all it would do is cause frustration.

• 1

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How is that throttle thing on the Me 262 a random failure? It's a failure caused by the pilot himself, and if you ask me we can never have enough of that.

• 11

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Basically we've come to the conclusion (pending evidence otherwise) that the 9K stalling when firing its gun is a myth.

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Yes. Essentially, to recap:

What is in effect is conservation of momentum.

Now let's take a Yak-9K with a, eg. mass of 2700kg with normal combat load, moving at 80m/s [288 km/h], yielding a total momentum of 216.000 kg m/s.

Now it fires a 47mm shell, which weights 1kg and flies at 780m/s, in addition to about 0.5kg of gas which we will evaluate also as flying at 780m/s [actually, multiplying this by a factor somewhat bigger then one is normal, but let's say the muzzle brake is negating it], for a total of 1170 kg m/s.

Now we subtract the total momentum of three shells fired from the total momentum of the plane,  divide it by the new weight of the plane and we get 78.85 m/s.

The net effect on speed appears to be quite small after all. If we add a correction factor to ejected gas velocity, and if the propellant weighted more the 0.5kg, it may be a bit higher, at around 78m/s.

Note:  We are assuming that:

(1) The gun and all other parts are completely fixed to the plane and cannot actually move.

(2) That the cannon is mounted inline with center of mass and recoils towards it, producing no rotation.

Yes, if these assumptions are not correct, then the situation can be somewhat worse - eg. if the gun does not recoil inline with center of mass, some pitching up or pitching down moment (rotation) is possible. However that would require design data on the Yak-9 weight distribution which I simply don't have.

However the massive speed loss from firing the gun seems to be a myth, and I see no actual controlled test data on it.

That it was uncomfortable for the pilot is actually possible (what you perceive is not only speed loss, but also deceleration and also jerk [rate of change of acceleration]). However, the pilot reference I read for being tossed about in the aircraft if fired at low speed was for an alleged Yak-9 with a 57mm gun, which was apparently a prototype of some sort. This pilot perception of recoil might be the source of that story.

[Note, even if the NS-45 had a muzzle velocity of 850m/s which is what I see somewhere, the speed loss for a three round burst is still 3m/s in the worst case assuming all the above holds.]

Edited by Cpt_Branko
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If the shot is fired at 1100 kg m/s the plance is slowed down by 0.36 m/s or 1.3 km/h.

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• 4 weeks later...

Just watch the recoil of the 6pdr (57mm). That's a one ton gun in a 6-8 ton twin engine fighter. It recoils the gun half a meter and still throws the plane around on the ground.

The NS-45 is mounted in a fixed mount in the 2.5-3.2 ton Yak-9 and it fires about 4.5 rounds per second (not one every several seconds).

The whole recoil has to be absorbed by the plane itself.

I don't think "stories" of Yaks falling out of the sky are realistic but automatic fire would shake the plane in flight which might make control of the plane very hard (especially at slow speed) and in in turn might actually push the plane below stall speed for a second.

And here is the NS-45 firing:

• 5

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I don't think "stories" of Yaks falling out of the sky are realistic but automatic fire would shake the plane in flight which might make control of the plane very hard (especially at slow speed) and in in turn might actually push the plane below stall speed for a second.

That is possible, yes.

I can think of three things which could potentially be a problem:

(1) CG of a WW2 fighter plane is typically below centerline and the recoil would produce some pitching up moment

(2) Strong jerk could potentially make the pilot move the stick

(3) Sudden deceleration could disturb airflow over the wing.

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• 1 month later...

It seems concerning the Yak-9K's climbing and turning stats it's simply copied from the Yak-9T.

Even with it's seemingly slight difference in weight there is a noticeable difference in speed.

As such:

The climb speed according to this source would be 6.5 min

and

The Turning speed would be 24 seconds

Source used: http://www.wio.ru/tacftr/yak.htm

It's seems rather weird that a plane that is slower would have the same climb speed. Also I don't find it completely unlikely there would be a difference in turning time. Just curious about what ElBarca's source is for the Yak-9k's stats above and what the same source says for the 9T?

Also I was under the impression early 9k's carried 680-litres of fuel and were later retrofitted to carry 480-litres tanks which were still larger than the 9T's fuel capabilities even though the 9K had shorter range. According to this the 9T and 9K had identical fuel weights even though the 9K seems to have required more fuel and would carry more if full.

Edited by Baldeagle91

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It's seems rather weird that a plane that is slower would have the same climb speed. Also I don't find it completely unlikely there would be a difference in turning time.

It just means that the drag difference, which results in the lower top speed, is simply not apparent at speeds that the aircraft would achieve it's best turn/climbing ability.

The sources giving 6.5 min to altitude and a 24s turn time are most certainly using the larger fuel load. Essentially, most 9K data is for the prototype and those with large fuel tanks. In practice, the 9K was nearly identical as they entered production without such tanks. I'm not sure where you get this 480L tank from (wiki?). Clearly, the datasheet shows the characteristics of a standard Yak-9k, instead of one produced with extra large fuel tanks.

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It just means that the drag difference, which results in the lower top speed, is simply not apparent at speeds that the aircraft would achieve it's best turn/climbing ability.

The sources giving 6.5 min to altitude and a 24s turn time are most certainly using the larger fuel load. Essentially, most 9K data is for the prototype and those with large fuel tanks. In practice, the 9K was nearly identical as they entered production without such tanks. I'm not sure where you get this 480L tank from (wiki?). Clearly, the datasheet shows the characteristics of a standard Yak-9k, instead of one produced with extra large fuel tanks.

So Russia now is modelled with normal production or prototype tests? Because then we should see lower values in top speed and such for the other fighters, since until late in the war the quality wasn't the same as the prototype for production. ^^

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It just means that the drag difference, which results in the lower top speed, is simply not apparent at speeds that the aircraft would achieve it's best turn/climbing ability.

The sources giving 6.5 min to altitude and a 24s turn time are most certainly using the larger fuel load. Essentially, most 9K data is for the prototype and those with large fuel tanks. In practice, the 9K was nearly identical as they entered production without such tanks. I'm not sure where you get this 480L tank from (wiki?). Clearly, the datasheet shows the characteristics of a standard Yak-9k, instead of one produced with extra large fuel tanks.

However source after source states a lower top speed. In game that lower top speed is "still" represented despite what your saying about it being "virtually" identical. Also there is a direct quote from Major A. Nikashin from the 812th IAP, a participant of the service trials (seeing the 9K was dropped after them) who agreed with it's lack of vertical maneuverability and climb ability.

The source for the fuel tanks (while yes from wiki under the NS-45) is in a russian book called "SV Ivanov. Yak-1/3/7/9 in World War II. Part 3. War in the Air" which sadly is only in russian. Even then I doubt the link I posted above is based on the prototype with the larger fuel tanks seeing how much lower it's range is when compared to the 9T.

Site after site, some using direct extracts from other peoples books states the rate of climb and maneuverability was lower.  ARX-005 Yakovlev Yak-9: Soldiers of the Sky by Dmitry Leipnik is another source recently used that states the climb-rate and top speed suffered.

I'm more curious about the OP's sources for the data more than anything else. I don't speak Russian sadly but it seems weird if they have used the prototypes top speed and then used the non prototypes climb and maneuverability? Either way it would need to be fixed.

What would you use to explain the 20-40Km/H difference? Even if it was due to drag difference it would still affect turning and climbing ability. Either use the prototype stats or non prototype stats... seems a mix of both here if what you say is correct.

Edited by Baldeagle91
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It doesn't make sense though, difference in top speed but no difference in climb.

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It doesn't make sense though, difference in top speed but no difference in climb.

Exactly, it's like saying there's difference in acceleration and not in climb...I think the Yak9K might be wrong in something and should be worse than the T...

• 6

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• 3 months later...

Yes. Essentially, to recap:

What is in effect is conservation of momentum.

Now let's take a Yak-9K with a, eg. mass of 2700kg with normal combat load, moving at 80m/s [288 km/h], yielding a total momentum of 216.000 kg m/s.

Now it fires a 47mm shell, which weights 1kg and flies at 780m/s, in addition to about 0.5kg of gas which we will evaluate also as flying at 780m/s [actually, multiplying this by a factor somewhat bigger then one is normal, but let's say the muzzle brake is negating it], for a total of 1170 kg m/s.

Now we subtract the total momentum of three shells fired from the total momentum of the plane,  divide it by the new weight of the plane and we get 78.85 m/s.

The net effect on speed appears to be quite small after all. If we add a correction factor to ejected gas velocity, and if the propellant weighted more the 0.5kg, it may be a bit higher, at around 78m/s.

Note:  We are assuming that:

(1) The gun and all other parts are completely fixed to the plane and cannot actually move.

(2) That the cannon is mounted inline with center of mass and recoils towards it, producing no rotation.

Yes, if these assumptions are not correct, then the situation can be somewhat worse - eg. if the gun does not recoil inline with center of mass, some pitching up or pitching down moment (rotation) is possible. However that would require design data on the Yak-9 weight distribution which I simply don't have.

However the massive speed loss from firing the gun seems to be a myth, and I see no actual controlled test data on it.

That it was uncomfortable for the pilot is actually possible (what you perceive is not only speed loss, but also deceleration and also jerk [rate of change of acceleration]). However, the pilot reference I read for being tossed about in the aircraft if fired at low speed was for an alleged Yak-9 with a 57mm gun, which was apparently a prototype of some sort. This pilot perception of recoil might be the source of that story.

[Note, even if the NS-45 had a muzzle velocity of 850m/s which is what I see somewhere, the speed loss for a three round burst is still 3m/s in the worst case assuming all the above holds.]

GIB GIB GIB GIB!!!

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• 1 month later...

How is that throttle thing on the Me 262 a random failure? It's a failure caused by the pilot himself, and if you ask me we can never have enough of that.

It was a failure by using the wrong materials for the engine ...

Yes. Essentially, to recap:

What is in effect is conservation of momentum.

Now let's take a Yak-9K with a, eg. mass of 2700kg with normal combat load, moving at 80m/s [288 km/h], yielding a total momentum of 216.000 kg m/s.

Now it fires a 47mm shell, which weights 1kg and flies at 780m/s, in addition to about 0.5kg of gas which we will evaluate also as flying at 780m/s [actually, multiplying this by a factor somewhat bigger then one is normal, but let's say the muzzle brake is negating it], for a total of 1170 kg m/s.

Now we subtract the total momentum of three shells fired from the total momentum of the plane,  divide it by the new weight of the plane and we get 78.85 m/s.

The net effect on speed appears to be quite small after all. If we add a correction factor to ejected gas velocity, and if the propellant weighted more the 0.5kg, it may be a bit higher, at around 78m/s.

Note:  We are assuming that:

(1) The gun and all other parts are completely fixed to the plane and cannot actually move.

(2) That the cannon is mounted inline with center of mass and recoils towards it, producing no rotation.

Yes, if these assumptions are not correct, then the situation can be somewhat worse - eg. if the gun does not recoil inline with center of mass, some pitching up or pitching down moment (rotation) is possible. However that would require design data on the Yak-9 weight distribution which I simply don't have.

However the massive speed loss from firing the gun seems to be a myth, and I see no actual controlled test data on it.

That it was uncomfortable for the pilot is actually possible (what you perceive is not only speed loss, but also deceleration and also jerk [rate of change of acceleration]). However, the pilot reference I read for being tossed about in the aircraft if fired at low speed was for an alleged Yak-9 with a 57mm gun, which was apparently a prototype of some sort. This pilot perception of recoil might be the source of that story.

[Note, even if the NS-45 had a muzzle velocity of 850m/s which is what I see somewhere, the speed loss for a three round burst is still 3m/s in the worst case assuming all the above holds.]

You have notice the big muzzle brake on the 9K's NS-45 gun? And you know what a muzzle brake does?

It seems concerning the Yak-9K's climbing and turning stats it's simply copied from the Yak-9T.

May the reason is, that a 9K was simplay a 9T who get fited with the NS-45 gun instead of the NS-37 gun? And just by the way, the NS-45 had a motor mount weight from 152kg while the NS-37 had a motor mount weight from 170kg ;)

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• 3 months later...

May the reason is, that a 9K was simplay a 9T who get fited with the NS-45 gun instead of the NS-37 gun? And just by the way, the NS-45 had a motor mount weight from 152kg while the NS-37 had a motor mount weight from 170kg ;)

The russians certainly felt the 9K was inferior in many respects to the 9T. Just looking at their own data it's apparent that it had inferior flight characteristics.

Just going by this thread most people are at a loss to precisely why, personally I think it's something to do with either the fuel load or gun. Possibly ammunition weight?  :dntknw:

The actual weight difference of the plane was rather minimal which is why I think it 'may' have been the fuel load, but even then it had a much lower range so not too sure.

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The russians certainly felt the 9K was inferior in many respects to the 9T. Just looking at their own data it's apparent that it had inferior flight characteristics.

Just going by this thread most people are at a loss to precisely why, personally I think it's something to do with either the fuel load or gun. Possibly ammunition weight?  :dntknw:

The actual weight difference of the plane was rather minimal which is why I think it 'may' have been the fuel load, but even then it had a much lower range so not too sure.

Not realy ... they stoped the 9K production becuase they comes to the reason that the biger gun gives not enough advanges at the point fire power to compensate the problem with the high structural strain truth the higher recoil powers ... so they chose the 9T who becomes even the fourth-most produced variant of the Yak-9

And about the weights, even with ammunition the NS-45 gives a advange from ~ 9kg to the NS-37 ;)

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Not realy ... they stoped the 9K production becuase they comes to the reason that the biger gun gives not enough advanges at the point fire power to compensate the problem with the high structural strain truth the higher recoil powers ... so they chose the 9T who becomes even the fourth-most produced variant of the Yak-9

And about the weights, even with ammunition the NS-45 gives a advange from ~ 9kg to the NS-37 ;)

Well the vehicle had a fair few things wrong with it, IIRC they never managed to fix the recoil issues. But as you stated they did improve the planes ability to fire the gun, less leaks etc.

I've never been too sure how the plane did have worse flight characteristics, all the data sheets and info I've seen regarding the 9K all state it was slower, longer turn times, albeit a couple said it climbed at the same speed or even faster.

It's a bit of an oddity stat wise.

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• 1 year later...

Datasheet updated