wip Top speed of the R-27ER

[LetMePickThat]

Hi all,

 

A few months ago, ED released a very interesting paper about the aerodynamics of the R-27 family. This has prompted me to do some testing on the R-27ER, and I found that the missile could reach a top speed of almost Mach 6, depending on the launch condition. See below an FL500 shot during which the missile reached Mach 5.9. Is such a speed consistent whith what's known of the missile?

Thanks !

 

 

 

R-27R-Mach58.trk

[GGTharos]

I would wait for the new FM.  The missile itself may or may not be capable of it, but only a CFD can tell with better accuracy than the existing FM.   This basically depends on two things other than the motor, IMHO:

 

1) The drag coefficient at those speeds, which in the old FM always tends down as a line function (it does IRL too, but perhaps not as linearly)

2) The drag induced by the control surfaces (trim drag) which is not accounted for in the old FM.

[LetMePickThat]

33 minutes ago, GGTharos said:

I would wait for the new FM.  The missile itself may or may not be capable of it, but only a CFD can tell with better accuracy than the existing FM.   This basically depends on two things other than the motor, IMHO:

 

1) The drag coefficient at those speeds, which in the old FM always tends down as a line function (it does IRL too, but perhaps not as linearly)

2) The drag induced by the control surfaces (trim drag) which is not accounted for in the old FM.

 

Judging by the boost/sustain times, this is in line with the new model described in the document I mentionned above (the new model boosts for 2s, the old model did so for 4s. 

I tried to find the relevant .lua file to plot the current zero-lift drag and lift-induced drag curves, but it was nowhere to be found.

[GGTharos]

Yes, all the relevant files were hidden as of 2.7 IIRC.

 

The current rocket motor has been defined such that is there is almost no boost/sustain difference (based on new data) AFAIK, but I maybe talking out of ignorance here.

[okopanja]

17 hours ago, LetMePickThat said:

depending on the launch condition.

And those are?

[Raven (Elysian Angel)]

5 minutes ago, okopanja said:

And those are?

High altitude and high Mach speed of the launching aircraft, would be my guess.

[LetMePickThat]

6 minutes ago, okopanja said:

And those are?

 

M2.1+, FL450+.

The shot I used to illustrate the thread was from an FL500, M2.2 engagement.

[okopanja]

4 minutes ago, LetMePickThat said:

FL500

Sorry, this is where I stumbled on? FL500 means? (try to replay trk, but got rewarded by steam update, so now I have to wait...)

[LetMePickThat]

Just now, okopanja said:

Sorry, this is where I stumbled on? FL500 means? (try to replay trk, but got rewarded by steam update, so now I have to wait...)

 

Flight Level 500, 50 000 feet.

 

https://en.wikipedia.org/wiki/Flight_level

[okopanja]

Btw: do you have the link to that ED paper?

[LetMePickThat]

2 minutes ago, okopanja said:

Btw: do you have the link to that ED paper?

 

Sure do !

 

https://www.digitalcombatsimulator.com/upload/medialibrary/bda/xnncgbqcdftgat1awbmcegln17yf2c8m/R-27_Missile_Family.pdf

[okopanja]

5 minutes ago, LetMePickThat said:

Sure do !

 

https://www.digitalcombatsimulator.com/upload/medialibrary/bda/xnncgbqcdftgat1awbmcegln17yf2c8m/R-27_Missile_Family.pdf

Shape on page 4 looks different from your diagram, but is on 1 km, where the drag is much more pronounced than up there at 15km.

 

How did you collect the data?

Perhaps it make sense to baseline first at 1km and compare with ED paper?

[okopanja]

Page 8, at 10km it becomes more linear, which is logical since the air is less dense and the engine has finished burning => the drag force coefficient is lower.

[LetMePickThat]

6 minutes ago, okopanja said:

Shape on page 4 looks different from your diagram, but is on 1 km, where the drag is much more pronounced than up there at 15km.

 

How did you collect the data?

Perhaps it make sense to baseline first at 1km and compare with ED paper?

 

Yes, true. However my original test was done with ED's R-27ER, so I doubt there will be any difference. Note that I'm not claiming that the R-27ER is too fast, I'm just surprised at the *very* high speed. It might be right, but I was wondering if there were some documents that could shed some light on the performances of the missile in real life. 

For comparison, the Super 530D is quoted at Mach 5, as are the AIM-54C and R-33. Apart from the R-37, I don't think I've heard of an air-to-air missile that fast.

[GGTharos]

The AIM-54 is capable of Mach 5 for a scant few seconds anyway IRL.

 

In any case, again please keep in mind that the old missile FM didn't take a lot of parameters into consideration and the high speed part (>mach 4) of flight is an edge condition for every missile in-game.

[okopanja]

Also I am not sure if you should use the Mach number since it depends on altitude.

In addition Chizh used m/s, which does not depend on altitude (so it is difficult to compare to yours).

Mind experiment: you fly at equivalent of 2.2 Mach + 4,5 Mach in Vacuum with no gravity => 6,7 Mach.

Add some atmosphere and you will get the drag forces in opposite direction, then you reach less, the question is how much?

On top of it add the gravity and additional drag to compensate it which will slow it down further. (assumption: trying the level flight).

 

Perhaps you could try to calculate this yourself and compare it to the "measured"?

Edited September 17, 2021 by okopanja

[okopanja]

The funny thing is that RE is at peak much faster. 1400 m/s vs 800 ms/

Back to mach: RE is at peak on 10km : 4.673 Mach

https://www.grc.nasa.gov/www/k-12/rocket/machu.html

At 1 km:

RE: 3.269 Mach
R: 2.377 Mach

 

He omitted 10km altitude for R variant, which is much more near your measurements.

I guess you would have to calculate to verify if the 15km performance is actually true.

Edited September 17, 2021 by okopanja

[LetMePickThat]

1 hour ago, GGTharos said:

The AIM-54 is capable of Mach 5 for a scant few seconds anyway IRL.

 

Like the other missiles I mentionned. 

1 hour ago, GGTharos said:

In any case, again please keep in mind that the old missile FM didn't take a lot of parameters into consideration and the high speed part (>mach 4) of flight is an edge condition for every missile in-game.

 

True, but  for missiles that spend a significant part of their flight time above Mach 4, that's a bit annoying.

Are you sure that the R-27ER still uses the old API though?

[GGTharos]

Yes.  It uses a polynomial curve generated from 3-4 parameters for the drag coefficient graph, a fairly simple lift coefficient graph and none of the other parameters that you see in the new format.  Chizh mentioned transferring it to the new format some time in the future when they complete more accurate CFD on it.

[Cmptohocah]

6 hours ago, LetMePickThat said:

 

Sure do !

 

https://www.digitalcombatsimulator.com/upload/medialibrary/bda/xnncgbqcdftgat1awbmcegln17yf2c8m/R-27_Missile_Family.pdf

Oh wow, I am very surprised how close my simulations are to the ED's at M2.5 and above. For lower values of Mach's number I got much different results.

[nighthawk2174]

9 hours ago, Cmptohocah said:

Oh wow, I am very surprised how close my simulations are to the ED's at M2.5 and above. For lower values of Mach's number I got much different results.

Same here Subsonic and M3.4+ are very close to each other, my transonic drag however (M1-1.8) is much higher (peak transonic drag at 1.2 Cd0 of .081).  Imagine a blending of the two between M1.0 and 3.0 and that's what I got as my results. 

Edited September 18, 2021 by nighthawk2174

[Cmptohocah]

53 minutes ago, nighthawk2174 said:

Same here Subsonic and M3.4+ are very close to each other, my transonic drag however (M1-1.8) is much higher (peak transonic drag at 1.2 Cd0 of .081).  Imagine a blending of the two between M1.0 and 3.0 and that's what I got as my results. 

 

My highest was 0.093 for M1.0, but that's probably 'cause I am missing the calculation at M1.2.
What did you use for CFD? Just out of curiosity.

[tavarish palkovnik]

@LetMePickThat

 

Mach 6 should not surprise you. Even with simplified mathematic that is what you can get

 

ln (m0/m1) * Isp + v0 = ln (350/220) * 2600 + 600 = 1800 m/s

1800 / 295 = 6,1 M

 

@Cmptohocah

 

With all those coefficients, it is always preferable to specify reference area as well since without it everything is unclear. I saw once that you gave your Cx pick as 0,0093 and with 7,423m2 referent area

 

@nighthawk2174

 

In your diagram reference area also are missing, I will guess it is 0,9m2 as DCS used because you are comparing those figures.

But this pick area you have is really huge for missile with ogives. Just as comparison, no intention to judge.
Let’s compare your result at 1,5 M converted to reference area as cross section

0,076/0,9*0,053=1,29

 

1,29*0,053=0,068 * q   (Cx*S*q)

 

with one old Soviet project where we have everything 

 

 

 

 

And for this archaic rocket let’s see Cx f(M) of second stage

 

 

So it has confirmed Cx 0,2 at 1,5M with reference area 0,3m2

 

0,2*0,3/0,0615=0,975

0,975*0,0615=0,06 * q

 

So and only if you used 0,9m2, you gave to R-27ER which is shorter, smaller caliber, with smoother nose, better formed wings some 13% more drag resistance then this prehistoric rocket had.

 

 

[nighthawk2174]

15 minutes ago, tavarish palkovnik said:

@LetMePickThat

 

Mach 6 should not surprise you. Even with simplified mathematic that is what you can get

 

ln (m0/m1) * Isp + v0 = ln (350/220) * 2600 + 600 = 1800 m/s

1800 / 295 = 6,1 M

 

@Cmptohocah

 

With all those coefficients, it is always preferable to specify reference area as well since without it everything is unclear. I saw once that you gave your Cx pick as 0,0093 and with 7,423m2 referent area

 

@nighthawk2174

 

In your diagram reference area also are missing, I will guess it is 0,9m2 as DCS used because you are comparing those figures.

But this pick area you have is really huge for missile with ogives. Just as comparison, no intention to judge.
Let’s compare your result at 1,5 M converted to reference area as cross section

0,076/0,9*0,053=1,29

 

1,29*0,053=0,068 * q   (Cx*S*q)

 

with one old Soviet project where we have everything 

 

 

 

 

And for this archaic rocket let’s see Cx f(M) of second stage

 

 

So it has confirmed Cx 0,2 at 1,5M with reference area 0,3m2

 

0,2*0,3/0,0615=0,975

0,975*0,0615=0,06 * q

 

So and only if you used 0,9m2, you gave to R-27ER which is shorter, smaller caliber, with smoother nose, better formed wings some 13% more drag resistance then this prehistoric rocket had.

 

 

I used the frontal area of the R27 so a little over .0415m^2.

 

additionally its highly missile dependent on the exact shape of the drag curve.  Nose shape in particular seems to have a major impact on this.  The above example i'd expect a relatively flat curve as it's a rather high finesse ratio nose cone.   Now this was one of if not the very first missile I did CFD on so maybe I should go back and redo it considering I've gotten a lot better at making more accurate geometry, meshes, and dealing with the small quirks of the cfd program I used.

This is an example of a validation run I did as part of my R24 cfd. 

[tavarish palkovnik]

I wouldn't like to discourage you, but seams to me that you have some cardinal mistake in your calculations. If this lighted function is for R-24 and with ref.area 0,0415 and with such figures then I'm must say it can't be true.

Maybe it would help, if you like this, to try some step by step calculations in old fashion style and after several samples you will able to recognize immediately results given from software and programs.    

 

Do not guarantee hundred percent but shouldn't be far from this, R-24R and R-24T for altitudes 0, 5, 10, 15 and 20 km