Do Rocksim and OpenRocket produce the same results?

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majordude

majordude

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I have OpenRocket and was disappointed with the predicted delay I needed with a recent launch. It was off by a good 3-5 seconds. If i used the same file in Rocksim would I have had the same issue or are their algorithms/results pretty much the same? (Is one more accurate than the other?)

(Unless I used the CTI delay tool wrong! I used a motor that said 12. I wanted 9 so I set it to -3 to drill out the delay. The delay looks like it was 1/2" wide and the bit is only 1/4".)
 
Last edited:
majordude said:
I have OpenRocket and was disappointed with the predicted delay I needed with a recent launch. It was off by a good 3-5 seconds. If i used the same file in Rocksim would I have had the same issue or are their algorithms/results pretty much the same? (Is one more accurate than the other?)

(Unless I used the CTI delay tool wrong! I used a motor that said 12. I wanted 9 so I set it to -3 to drill out the delay. The delay looks like it was 1/2" wide and the bit is only 1/4".)
Click to expand...

More detail please.

Which direction was it off in?

What motor?

How much did it weathercock?

Did the motor behave as expected?

Did you make sure your rocket was the same weight as the simulations?

I have never had an issue with delay calculations. It is much easier to fairly accurately predict the apogee time than altitude, so I wouldn't expect a difference of more than half a second between programs unless you are going >10000 feet.
 
I've (mentally) timed apogees and found OR to be pretty close to the mark(provided your design file is accurate), delay times...that is another fettle of kish IIRC they can vary +/- 15% from the 'rated' time. the AT F40-7 always seems to give me a 'bonus' delay of about 3 sec.s in addition to the 7 sec delay.
rex
 
Rex R said:
the AT F40-7 always seems to give me a 'bonus' delay of about 3 sec.s in addition to the 7 sec delay.
rex
Click to expand...

Had to reply to this one: I've noticed the "bonus" MANY times with the F40-7 and a few other AT reloads in that impulse range (F52-8, F39-6). Setting the delay seems to come down to "feel", experience with the rocket, and a little SWAG (scientific wild a** guess)... :)
 
Hi,

Just to check, are you seeing an extra delay in OR simulations or in the actual motor delays? I checked the thrust curves and there's nothing strange in them that would explain extra delays. Of course if the actual motor delays vary by many seconds there's nothing we can do about it in the sim...

Cheers,
Sampo N.
 
JohnCoker said:
I suspect that the difference in quality of algorithms would be swamped by imprecision of input. (Most notably the CD fudge factor.)

Also don't forget that motors can vary quite a bit:
https://www.thrustcurve.org/certification.shtml
Click to expand...

My thoughts pretty much match John's.

The other factor would be whether you let OR estimate the weight of the final rocket, or if you put it on a scale, and used the actual weight?

-Kevin
 
The bit/ delay size is normal. It digs out enough that the center will burn through at the desired time.... usually. Both my CTI and Aerotech delay drillers work this way.
 

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