wip Top speed of the R-27ER

[tavarish palkovnik]

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Edited December 27, 2024 by tavarish palkovnik

[tavarish palkovnik]

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Edited December 27, 2024 by tavarish palkovnik

[FoxAlfa]

If I am not mistaking burn times seam to correspond to the ones, we are having in DCS currently, not sure about the impulse and weight. 

@Маэстрo or @Chizh,maybe can give input. 

Edited July 27, 2023 by FoxAlfa

[tavarish palkovnik]

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Edited December 27, 2024 by tavarish palkovnik

[tavarish palkovnik]

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Edited December 27, 2024 by tavarish palkovnik

[BlackPixxel]

Great stuff, I hope ED really considers this!

In DCS it would also greatly benefit from the higher boost to sustain ratio, right now the thrust is very similar and causes the missile to take longer to achieve the same end speed.

 

On 7/27/2023 at 4:03 PM, FoxAlfa said:

If I am not mistaking burn times seam to correspond to the ones, we are having in DCS currently, not sure about the impulse and weight. 

@Маэстрo or @Chizh,maybe can give input. 

 

 

In DCS it used to be 10 s with 7500 boost thrust and 2500 sustain thrust, but then it was somehow reduced to just 8 s with a very weak boost. That causes the missile to now take much longer to cover the same distance in the early phase of the launch.

Edited July 31, 2023 by BlackPixxel

[tavarish palkovnik]

It would be my pleasure and honor if these stuffs would be taken in consideration and if I could give some contribution to get this motor in more realistic form, for all you guys that like this rocket as I do.

Team that makes model of this motor for ED is always welcome to contact me and I will very gladly share what I have behind all these steps in finding answers how it actually works 

[tavarish palkovnik]

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Edited December 27, 2024 by tavarish palkovnik

[okopanja]

1 hour ago, tavarish palkovnik said:

Few days ago new source of information appeared, nice view of launching R-27ER seen thru ILS (HUD). Helpful for additional determination of actual and real behavior of this rocket.

Sorry but how did you conclude this is R-27ER?

[tavarish palkovnik]

Take a look on indicator down right, obviously «27ЭР»

[okopanja]

14 hours ago, tavarish palkovnik said:

Take a look on indicator down right, obviously «27ЭР»

I missed that, interesting fired at such a short distance...

[DSplayer]

Maybe porting over the R-27 series to the same schema/API as the AIM-7 might improve results and fix any anomalies introduced by using the older schema/API. 

[tavarish palkovnik]

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Edited December 27, 2024 by tavarish palkovnik

[BlackPixxel]

The RSN is selected to that at the expected point of seeker activation (and distance to target), the seeker points at the target. But why is your point of seeker activation directly at the same altitude as the launch altitude? It would be somewhere below, as it takes into consideration the extrapolated movement of the target.

So the RSN angle would be much less, and the missile would not fly into the opposite direction first, which is a pure waste of energy.

 

After all, there is a negative sign in the angle calculation:

So in your scenario, the RSN angle would be less than the line of sight angle, causing the missile to lead more in the beginning towards the direction of the target, and not to fly into the opposite direction.

Maneuvering directly after launch will also be very smooth due to the range dependand guidance coefficient, so the missile will not drastically start to lead instantly.

Similar to how normal PN with fixed guidance coefficient also becomes more smooth the further the missile is away from the target.

Edited October 14, 2023 by BlackPixxel

[tavarish palkovnik]

Great, comrade for communication is here 

For start, let’s forget where I pointed point for SARH start, is it on line of launch altitude or not, above or below, doesn’t matter for now. Like said it is unscaled imaginary case. It is more important where it is relatively to target because I see it always or almost always with IN, above. Principle is to hold missile to have in very end of terminal approach maximally released position, with no kinematic overload.

By the way,  negative sign on angle is always in clockwise side, it is mechanical principle and rule.

We will continue for sure, I hope so, momentarily I’m out battery 

 

Edited October 14, 2023 by tavarish palkovnik

[BlackPixxel]

But in this case the negative sign means opposite direction of Omega_0.

So the offset angle is towards the opposite direction of angular rate of target line of sight, resulting in less angle for RSN.

[tavarish palkovnik]

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Edited December 27, 2024 by tavarish palkovnik

[tavarish palkovnik]

Can you make some sketches, for example on these 3 cases, it will be easier to follow and to understand. How you would position missile’s inertial navigation trajectories chasing these targets 

[BlackPixxel]

I have removed my previous post, it had an error.

It is propably best to simply post the formulas + descriptions of the modified PN guidance with 2 terms of the R-27

Here is the commanded overload in SARH mode:

 

And here is the flight in inertial navigation:

 

Left side of the formula is in both cases the same:

(navigation constant * projection of target velocity onto seeker plane) / remaining time

This is essentially the proportional navigation, just that instead of seeker angular rate they take projection of target velocity onto seeker plane and divide it by remaining time of flight. But both are proportional to each other for small angles (small angle approximiation), which is also described in the text.

Then there is the second term (which turns it into modified PN), that is depending on the component of angular rate that is created only due to target maneuvering plus some filtering. But, as the text says, it also has its equivalent in the formula for inertial flight, where it is the position of the target projected onto the seeker plane divided by the squared remaining time.

 

According to this, there should not be that much of a difference in trajectory between both types of flight. Although during SARH stage it propably uses angular rate instead of calculating the velocity projection of the target onto the seeker plane first.

 

 

Your third image is how I would say the missile would fly and how RSN would be pointed. Target is flying to the right, so angular rate of seeker line of sight is rotating to the right. Additional RSN offset according to the formula has inverse sign of angular rate, therefore the offset goes a bit to the left of the pure line of sight. That makes the missile lead a bit more and also creates the most reasonable looking flight path.

But to me it seems as if you don't use angular rate, but the derivative of angular rate for RSN offset, which doesn't seem correct. Therefore your sign depends not on the direction of travel of the target, but on its derivative. That creates weird trajectories that don't make sense.

Edited October 15, 2023 by BlackPixxel

[tavarish palkovnik]

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Edited December 27, 2024 by tavarish palkovnik

[tavarish palkovnik]

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Edited December 27, 2024 by tavarish palkovnik

[BlackPixxel]

1 hour ago, tavarish palkovnik said:

Just from curiosity, what if, no matter of fact that orbital speed of target is positive so RSN rotation should be negative (clockwise), what and how it would looks if RSN line goes in other side 

 

What exactly do you mean with orbital speed? The angular rate of the line of sight to the target? That is what the Omega in the little formula refers to I think. And in your case, it is negative, as the line of sight from the fighter to the target rotates clockwise. So RSN offset becomes positive, and it causes a flight similar to your last image. But as the formulas show both error components (projection of both position and velocity onto the seeker plane) get divided by values that depend on the remaining time to target. So the commanded overload will be very small in the beginning, which makes the missile turn gently and smoothly after launch, and not instantly try to pull as hard as possible in order to put RSN onto the target.

As a result, the RSN offset means the missile will travel less distance and fly a more straight path to the target than if RSN was simply equal to the line of sight direction from the moment of launch.

Edited October 15, 2023 by BlackPixxel

[tavarish palkovnik]

38 minutes ago, BlackPixxel said:

What exactly do you mean with orbital speed? The angular rate of the line of sight to the target? That is what the Omega in the little formula refers to I think.

Yes that is Omega, and yes orbital speed how I call it, is angular rate of the line of sight.

However, it is speed and speed can be constant, with acceleration or with retardation. Only here it is not m/s but deg/s.

In circular (but really circular) motion target with constant velocity around point is with constant orbital speed. If angle like in case of this last declined 45deg trajectory is with every new second bigger and bigger, then it is orbital speed which is with acceleration, positive sign.

It is not about clockwise or against clockwise when speed is matter, only about kind of speed, acceleration or retardation 

Edited October 15, 2023 by tavarish palkovnik

[BlackPixxel]

But for the determination of the direction of RSN offset, the rate of change in angular rate doesn't matter. The direction of the angular rate itself is what matters.

Target line of sight rotates to the right -> RSN is set a bit left of current line of sight line

Target line of sight rotates to the left -> RSN is set a bit right of current line of sight line

[tavarish palkovnik]

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Edited December 27, 2024 by tavarish palkovnik