Adjustments in RocSim for Aerotech's 38mm spacer kit

[RandyT0001]

I meant to do this earlier but forgot until now. I was able to purchase an Aerotech 38 mm 360 hardware Special which includes the 360 casing, 38mm aft closure, two grain spacers, a floating forward closure and a forward sealing ring. The usual 38mm forward closure is replaced by the two piece floating forward closure and the forward sealing ring. Since I design rockets in RocSim I needed to get the mass of my motor and each spacer so that I can adjust the mass for simulations. The motor without any spacers has a mass of 141.5 grams, slightly less than what Aerotech lists for the standard 38/360 motor at 147.4g. The spacers had slightly different masses, one was 21.0g and the other was 20.8g so I will average them out to 20.9g for adjustments to RocSim simulations. So now if I want to fly H123W which normally flies in a 38/240 motor that has a mass of 125.5g in my 38 Special I look up the propellent mass for the same type of propellent, White Lightning in this example, that normally uses the full 360 motor casomg, the I161W. The I161W has a mass of 187.5g and the H123W has a mass of 125g and fits in the next size motor smaller (the 38/240) so I will have to use one spacer. So 187.5 - 125 + 141.5 - 125.5 + 20.9 = 99.4g so I would add 99.4g to the mass of the rocket design centered about (an estimated(1)) one quarter down from the front of the 38/240 motor I load in the RocSim simulation. That 3.5 ounce difference in weight behind the normal CG of the rocket that uses a H123W in a 38/240 motor could cause stability problems if not accounted for in the simulation.

I will use a similar method when I use the spacers and floating closure in my 38/720 motor. Hopefully Aerotech will soon make a plugged floating closure for those people that like to fly dual deployment. :confused2:
:pop:


(1) Until I can obtain the two reloads in the example and a 38/240 motor for measurement I will use this estimate.

[cjl]

You can fly dual deployment without a plugged closure. All you need to do is leave out the BP.