Motor weight in OpenRocket

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Sirbrad
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Motor weight in OpenRocket

Postby Sirbrad » Fri Nov 02, 2018 9:08 pm

I have been using OpenRocket for some time and noticed an anomaly with regard to the weight of the chosen motor.

I am using a CTI J400 which weighs 726g according to the sim. I am assuming the the weight of the casing is included.

Looking at the motor data on Cesaroni website I note that the loaded weight for this motor is 702g (which I assume does not include the casing).

I weighed the motor at 640g and the casing at 202g making a total of 842g. This does not match the published data from Cesaroni.

I also checked my digital kitchen scales by weighing a known weight. So I can trust the scales.

Can anyone explain what is going on. I’m confused. Should I add a mass component to achieve the actual weight of the motor?





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SpaceManMat
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Re: Motor weight in OpenRocket

Postby SpaceManMat » Fri Nov 02, 2018 11:11 pm

The motor files for open rocket originate from the Thrust Curve web site. However when I look for a J400 the total weight is 702 same as the CTI web site, which should be the weight of the reload and case. So I’m not sure what’s going on in Open Rocket, perhaps you’ll need to send some screen shots. The 640g weight does seem quite high, it looks like even the 6xl reloads will be less than that. Are you sure of the designation and that it’s a 38mm CTI reload?
QRS: 124
AMRS: 32 L2 RSO
Highest Altitude: 13,647 feet
Fastest Flight: Mach 1.55
Largest Motor: CTI 1115J530 IM
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Sirbrad
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Re: Motor weight in OpenRocket

Postby Sirbrad » Sat Nov 03, 2018 6:53 am

I am certain of the motor being a 38mm 6 grain J400SS, it was supplied to me last weekend to participate in the drag race. I had an igniter failure and the rocket did not launch.

Now that I have the motor in my possession I was able to weigh it.


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Sirbrad
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Re: Motor weight in OpenRocket

Postby Sirbrad » Sat Nov 03, 2018 6:57 am

Ignoring Open Rocket for a moment, why does the motor weigh less than the published data. Ie 640g actual versus 702g published?




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SpaceManMat
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Re: Motor weight in OpenRocket

Postby SpaceManMat » Sat Nov 03, 2018 12:20 pm

Sirbrad wrote:Ignoring Open Rocket for a moment, why does the motor weigh less than the published data. Ie 640g actual versus 702g published?
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702g is the total or loaded weight this includes the case. I weighed my 6G case and can confirm your weight 202g is within a few grams of mine. The propellant weighs 489g according to CTI which leaves about 11g for the closures and liner. So the CTI website to me is at least consistent.
QRS: 124
AMRS: 32 L2 RSO
Highest Altitude: 13,647 feet
Fastest Flight: Mach 1.55
Largest Motor: CTI 1115J530 IM
Current Project: X Wing


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