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Magin

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Hi folks. I have some problem with the desing.My rocket will be a supersonic rocket that's why there are some diffrences with desinging. ı did a lots of simulation, althought my stabilitiy ghraphic is fine there is a warning about body calculations. ı dont know what to do. Could you help me about that?
upload_2020-2-11_3-16-56.png
 

scsager

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The warning about body calculations is because the program is less accurate at supersonic speeds


Vücut hesaplamaları ile ilgili uyarı, programın süpersonik hızlarda daha az doğru olmasıdır.
 

Magin

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The warning about body calculations is because the program is less accurate at supersonic speeds


Vücut hesaplamaları ile ilgili uyarı, programın süpersonik hızlarda daha az doğru olmasıdır.
so you are not suggesting to desing on openrocket for supersonic. Will it be work on rocksim?
 

djs

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so you are not suggesting to desing on openrocket for supersonic. Will it be work on rocksim?
In this case you can probably ignore the error.

However- in looking at your design- your fins are kinda small compared to the size of the rocket. If there's a moderate amount of wind, your rocket will not behave as expected.
 

BABAR

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"Body calculations may not be entirely accurate at supersonic speeds."

Okay, what's with the "entirely" qualifier? Once you are talking about a rocket that is predicted to go supersonic, does it make a difference if the calculations are not ENTIRELY accurate, vs MOSTLY accurate, vs PARTIALLY accurate, vs MINIMALLY accurate?
 

mikec

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I've used Openrocket for flights up to mach 2.6 and never had any severe mismatches. RasAero may be more accurate in some cases.
 

cbrarick

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if only i spoke metric...

Being American, not so much.

Long live the Imperial System....

:>
 

NateB

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I'm not sure if anyone here will know this reference or not, but here goes:

"You're drunk with your tradition
That has no validity
Well, I'm intoxicated in support of metrics
Come drink a decaliter with me"
 

manixFan

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Hmm, I don't see any mass objects to compensate for the weight of the parachute and other recovery/electronics gear. Unless you have added manual over rides for weight and CG (without motor) it is a poor reflection of the actual flight.

What is your design goal? If it is to go supersonic:
  • a Von Karman shaped nosecone (4:1 or 5:1) will be better than the one displayed
  • typically a minimum diameter design is used, although that makes fin attachment more difficult
  • body length should also be as short as possible to reduce overall drag
  • use nose weight or slightly larger fins to balance your Cg/Cp
  • your fin shape is good to avoid flutter
  • you should plot stability over time during the flight to make sure it is maintained
Good luck,


Tony
 

kbRocket

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I find that RASaero typically sims within 10% on my supersonic flights and both open rocket and Rocksim significantly under predict altitude.
 

Igotnothing

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N2540-0. I think the fins are going to say, "bye", the motor mount is going to go through the front, and/or the whole thing is going to lawn-dart if the up portion magically holds together. It needs some parts and parachutes.
 
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