Remember this ?
The navy had the vintage Russian rocket RGB-60 with a maximum range of 5.3km to fire from the RBU-6000 ASW rocket launcher. They wanted more range so the ARDE-HEMRL jointly built the ER-ASR(shown below) with a range of 8.5 km. The ER-ASR used the same airframe as that of the RGB-60 as it was also meant to be fired from the RBU-6000. The only changes were engine, fuel and thus thrust output.
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It seems the increase in range often brings its own problems. The rocket when test fired was consistently missing the target. Remember its a non-guided rocket. So if it is flying off target, the reason isn't guidance failure, but design of the rocket. But the airframe of the rocket is the same as that of the RGB-60 which has worked well all these years. How would there be any problems with the airframe ?The inaccuracy as it turns out was due to increase in range. Well as ARDE put it :
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Fascinating isn't it ? In the end all they had to do is slightly change the tail fins, the change was so small that it isn't even visible. That solved the problem.
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Aerodynamics is a lovely subject, assuming you know what to do. Its not that lovely otherwise though.
More pics of the ARDE made ER version of the Anti-Submarine rocket. The rocket is now making it into Navy's service.
This is the plot of the drift seen in the flight path of the rocket with time due to the newer propulsion. With a lot of testing the drift problems were solved.