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Incorrect trajectory of the BR21 rockets?


xvii-Dietrich
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I have been experimenting with the 21cm Bordraketen (BR21 rockets) on the FW 190 D-9 (DCS v2.5.2.18521) and I believe that the trajectory may be incorrect.

 

 

Evidence

 

br21_testfire_1.jpg -- In this first test, I use lorries placed at fixed distances and use this to calibrate the image. By analysing the frames of some video footage, I could determine that the fuse from firing to exploding is exactly 3.0 seconds. The travel distance is approximately 762 metres, which gives a velocity of approx. 254 metres per second. This is slow compared to the reported values of 320 metres per second. The range is low, but if the speed of the aircraft (say, 500 km/h) is included, then the values are roughly correct.

 

What is not consistent, however, is the trajectory. There appears to be no "drop". Although the BR21 was spin-stabilised (using angled rocket motor apertures), there should still be some drop (and this is mentioned in the sources I have found). This also accounts for the reason for the upward angle of the launch tubes.

 

br21_testfire_2.jpg -- This second test compares the angle of the fired rocket from a stationary FW 190 on the ground. The pitch and AoA of the aircraft is such that the measured angle of the rocket compared to the aircraft is approx. 5.4 degrees.

 

br21_fw190a8.jpg -- The angle of the rocket in DCS (5.4) is extremely close to the measured angle of the rocket on the FW 190 A-8 (approx. 5 degrees). Yes, I am aware that the use of the BR21 is anachronistic when used on the D-9, but the implementation should be the same as the A-8.

 

br21_schematic.jpg -- Here is a plan confirming the 5.2 degree angle. The schematic is actually for a Bf 110, but the result is essentially the same as what I can discern from photographs of units mounted on FW 190 aircraft.

 

br21_mount_angle.jpg -- Confirmation that to first order, the mount angle is correct (the FW 190 in the test was carefully trimmed and flown with vertical velocity = 0.0). Note the angle, but also the variation between the pitch and the AoA (which accounts for the 1 degree discrepancy).

 

 

The effect

 

br21_explosion_alt.jpg -- However, as indicated by the first two images, there is no "drop" during the trajectory. The rocket flies in a straight line at the upward included angle. This results in the effect shown in this image... even when flying carefully trimmed and flown with vertical velocity = 0.0, the rocket will explode high above the flight-line of the aircraft.

 

 

Summary

 

The BR21 rocket tubes are correct on the aircraft. However there is no "drop" of the rocket itself during its trajectory. As a result, the rocket explodes far above the aiming point. This is inconsistent with the historical records for this weapon. The range of the rocket seems low but, unlike the incorrect trajectory, I do not have enough evidence to state whether it is correct or not (but I mention it, in case it is somehow part of the trajectory issue).

 

 

 

References

 

http://www.lexikon-der-wehrmacht.de/Waffen/raketenwerfer.htm

http://www.nevingtonwarmuseum.com/werfer-granate-21.html

https://en.wikipedia.org/wiki/Werfer-Granate_21

br21_testfire_1.jpg.7933c0ec813e932b318bb9a5d701d9e8.jpg

br21_testfire_2.jpg.e91bc85a7f9e96d6d2cbfce3fc17c6b2.jpg

br21_mount_angle.jpg.6d3f75055e8a27d470966271e6d28cf6.jpg

br21_fw190a8.jpg.0c8075ca8951ed3a2073f790a2e4f786.jpg

br21_schematic.thumb.jpg.244355b1c471948ed8f158f28cada015.jpg

br21_explosion_alt.jpg.283acc84e94748be1da44bdda2338f81.jpg

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  • 3 weeks later...
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In assistance to any developer investigation of this problem, I have found some historical documentation describing the system. This may also be of use for implementation of the Wgr.21 on future aircraft (such as the FW 190 A-8, Bf 109 G-6 or Me 410 A-2).

 

The main source is the following link:

 

http://www.deutscheluftwaffe.com/archiv/Dokumente/ABC/b/Bordwaffen/21%20cm%20Wurfgranate/21%20%20Wurfgranate%20BR%20Gereat.html

 

It has a host of very useful documents on the entire BR21 topic.

 

 

From this, I would draw attention to the following specific diagram.

 

Angriff%20mit%2021%20cm%20Granaten.jpg

 

Diagram ref: http://www.deutscheluftwaffe.com/archiv/Dokumente/ABC/b/Bordwaffen/21%20cm%20Wurfgranate/Text/Angriff%20mit%2021%20cm%20Granaten.jpg

 

 

 

Also, the following manual has some information regarding the installation and systems: http://www.deutscheluftwaffe.com/archiv/Dokumente/ABC/f/FockeWulf/Fw%20190/Handbuch%20Fw%20190%20D-9%20Sonderwaffenanlage.pdf

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  • 2 years later...
On 8/3/2018 at 8:42 AM, NineLine said:

Reported

 

@NineLine@BIGNEWY@Wags @Kate Perederko... is there any chance of these bugs moving from the "Reported" status to the "Fixed" status? We have numerous problems that affect WW2 external ordnance, from bombs to rockets. We have very carefully followed your rules and posted detailed explanations, track files and historical references and data. It can take months to get an issue acknowledged and reported into your system, but then it may languish for years.

 

Please, in these cases, we are not asking for new features or aircraft. Merely that the existing implementations are corrected. These problems sometimes span multiple modules. For example, this particular bug affects both the Dora and the Anton - the later of which was released after this bug was reported. It is difficult to express sufficiently, how much DCS WW2 is suffering as a result of the accumulating problems. It is nice, but at the same time frustrating, to see resources poured into DCS Jets and DCS Helicopters, and yet there is a deficit for DCS WW2. We entreat you to consider addressing some of the long-standing problems. and help us, as your community, sustain this aspect of DCS world. Thank you.

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Well said @xvii-Dietrich. Yes, there are a lot of great elements to this sim. In my opinion the large number of long standing bugs, including all of the axis munition bugs, lack of MP trains, Dora engine failures, etc. are overshadowing all the great work that has been put out in DCS. 
 

As a customer, it is frustrating to pay what we do for these modules and be left with something that is incomplete and bugged. Then when we go to report these bugs on the forum, within the guidelines asked for, it can takes months before it is recognized, after that months and months if not years for the bug to be fixed and merged into the game. 
 

I understand the WWII team is small and they have a lot on their plate, but I feel dedicating a chunk of time in the near future to resolve all of these bugs would make a world of difference to all of us. 


Edited by Ketchup
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On 6/27/2021 at 3:08 PM, Vatikus said:

Bump.... all planes are out of EA now for quite some time, yet majority of weapons still do not work correctly at all...
Come on ED, you can do this...

fufxPi0.jpg

I would be very grateful if this excerpt is translated to English to understand better the point but as for the AVERAGE rocket speed I can see here I can say that the rocket in DCS has the exact AVERAGE speed your document stated - 250 m/s.
Regarding 'it has no drop" - if you fire a shell at initial elevation of roughly 5 degrees at 380 m/s you have about 33 m/s of pure vertical speed. It's very easy to say how much time you will await for it dropping...
The only thing I can see a bit different is that in DCS the lifetime is set to 3 seconds. I guess it was done to have better aiming.

That's why it were two years...

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Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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  • NineLine changed the title to Incorrect trajectory of the BR21 rockets?
2 hours ago, NineLine said:

This is reported guys, it will be fixed. Thanks!

What will be fixed? Exact rocket average  speed? 😉

 

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Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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22 hours ago, Yo-Yo said:

I would be very grateful if this excerpt is translated to English to understand better the point but as for the AVERAGE rocket speed I can see here I can say that the rocket in DCS has the exact AVERAGE speed your document stated - 250 m/s.
Regarding 'it has no drop" - if you fire a shell at initial elevation of roughly 5 degrees at 380 m/s you have about 33 m/s of pure vertical speed. It's very easy to say how much time you will await for it dropping...
The only thing I can see a bit different is that in DCS the lifetime is set to 3 seconds. I guess it was done to have better aiming.

That's why it were two years...

 

Translation:

Quote

To get into the required attack position, the last machine of the formation will be chosen as auxiliary target. If the missiles are launched at a distance of 1200 m, they will overtake the targeted plane after 4.4 s and detonate after an additional flight time of 1.1 s, approx. 295 m in front of the targeted plane in the midst of the formation. The missiles will have traveled a distance of 2107 m.

 

Calculation:

Fighter 480 km/h = 133 m/s

Bomber 400 km/h = 111 m/s

 

Mean speed of the missiles = 250 m/s

Mean flight time of the missiles = 5.5 s

 

 

Speed of the missiles = 250 m/s

Speed of the fighter = 133 m/s

Sum: 383 m/s

 

Distance traveled by the projectile in 5.5 s: 2107 m

Distance traveled by the enemy plane I 5.5 s: -613 m

 

KE (Kampfentferung?, Combat distance) for center of the formation: 1494 m

KE for the last, targeted plane: 1200m

Point of detonation: 294 m

 

If the lifetime of the missiles is set to 3 s instead of 5.5 s in DCS the tactic described in the document is obliviously not possible and the bomber formation has to be attacked from a closer distance, possibly within the effective range of bomber gunners. 

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1 hour ago, Cunctator said:

 

Translation:

 

If the lifetime of the missiles is set to 3 s instead of 5.5 s in DCS the tactic described in the document is obliviously not possible and the bomber formation has to be attacked from a closer distance, possibly within the effective range of bomber gunners. 

Right. 5.5 s seems to be balanced to the initial elevation and the whole trajectory and the detonation will be just at the cross of the sight. But all complaints to "no gravity drop" or " wrong velocity" are off.

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Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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7 hours ago, Yo-Yo said:

5.5 s seems to be balanced to the initial elevation and the whole trajectory and the detonation will be just at the cross of the sight.

 

This a test that ED could try internally.

 

Set the detonation time to 5.5 seconds and then fly at a constant, low-altitude ( e.g. right at sea-level). If the trajectory is set correctly then, indeed, "the detonation will be just at the cross of the sight."

 

In the tests that we have done, with the current timing, the detonation point is high above the sight-line. See, in particular, the last screenshot in the original bug report. If the trajectory is correct, we should fly through the smoke cloud, not way below it, which is what we currently have.

 

 

( As an hypothesis, at sea-level I would expect to fly slightly over the smoke cloud. This is because then increased atmospheric density would correspond to drag and thus would result in the rocket falling further in a given time. )

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The problem I see is that there seems to be a dual pulse instead of single.
I was experimenting and if I reduce the impulse to lower number as a walkaround of that dual thrust boost, I am able to increase fuse timer and can achieve trajectory which will explode shell in the more realistic location....
 

wgr21impulse.png

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5 hours ago, Vatikus said:

The problem I see is that there seems to be a dual pulse instead of single.
I was experimenting and if I reduce the impulse to lower number as a walkaround of that dual thrust boost, I am able to increase fuse timer and can achieve trajectory which will explode shell in the more realistic location....
 

wgr21impulse.png

There is no reason to play with the impulse as the rocket has average speed exactly as it's specified in the document. Just the time of flight must be set to 5.5. s
This tooth your graph shows is not detected in the game and, probably, is a result of improper data export. 
The rocket is single pulse in DCS and, by the way, dual pulse (booster) motor would give very different speed curve.

 

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Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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