Nozzle diameter and CG of Aerotech G80?

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RocketRoll

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Looking to simulate in RAS Aero before I build the rocket and buy the motor. Therefore, I don't have the engine with me to physically measure these things. I've searched online and can't find this info. Anyone know the nozzle diameter and CG of an Aerotech G80-7t (or -4t, -10t)?
 

rcktnut

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How is the nozzle dia. and CG of the motor going to help in the design of your rocket? Your question doesn't make much sense to me, unless you are putting fins and a nose cone on the motor.
 

RocketRoll

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BLKKROW

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I'm using RAS Aero, which even when I load the .eng file, leaves the nozzle exit diameter and CG input blank. It turns out I misread the CG input; it's the CG of the rocket, not the engine, but I do still need the nozzle exit diameter.
Nozzle Exit Diameter is not crucial or needed. You can still sim in RASaero without it.
 

markkoelsch

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I'm using RAS Aero, which even when I load the .eng file, leaves the nozzle exit diameter and CG input blank. It turns out I misread the CG input; it's the CG of the rocket, not the engine, but I do still need the nozzle exit diameter.
You do not need it. It will not make an appreciable difference.
 

Chuck Rogers

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The nozzle exit diameter is used to calculate the nozzle exit area, which is used in the power-on drag coefficient (CD) calculations, and to vary thrust with altitude. With the nozzle exit diameter entered you will see two CD curves, power-off (coast) and power-on (thrusting). If you have a large nozzle exit diameter, filling the base area of the rocket, there will be a significant reduction in the power-on CD. If your rocket gains a significant amount of altitude during the motor burn, or is an upper stage ignited at high altitude, there will be a noticeable increase in thrust at altitude compared to the rasp motor data.

That said, these effects are very small for a small nozzle exit diameter on a low altitude model or very low end high power rocket, and can be ignored. As noted, you can leave the entry line blank, and RASAero II will assume a nozzle exit diameter of zero. CD power-on will equal CD power-off, and there will be no variation of thrust with altitude.


Chuck Rogers
Rogers Aeroscience
 
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