[REPORTED] Incorrect trajectory of the BR21 rockets? - ED Forums
 


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Old 06-20-2018, 01:32 AM   #1
xvii-Dietrich
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Default [REPORTED] Incorrect trajectory of the BR21 rockets?

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/...etenwerfer.htm
http://www.nevingtonwarmuseum.com/we...ranate-21.html
https://en.wikipedia.org/wiki/Werfer-Granate_21
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Old 07-05-2018, 10:50 AM   #2
ACG_IronJockel
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Interesting find.
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Old 08-03-2018, 06:42 AM   #3
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Old 09-20-2018, 02:36 PM   #4
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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/arc...%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.



Diagram ref: http://www.deutscheluftwaffe.com/arc...20Granaten.jpg



Also, the following manual has some information regarding the installation and systems: http://www.deutscheluftwaffe.com/arc...ffenanlage.pdf
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