CG and Openrocket help

I am very new into rocketry and need help with nose weight and CG. I have purchased and built the Alarm kit from The Launch Pad with a few modifications. Being so new to the sport, I’m just now realizing that a little modification here and there adds up to major effects in the performance in the air.

Go here for pictures of my rocket and a description of its performance on its first three flights.

https://www.rocketryforum.com/showt...d-Rocket-ALARM-(Modified)&p=591860#post591860



I’ve created an Openrocket file and have tried to accurately construct the completed rocket is it sits. Please keep in mind, this is the first time I have used Openrocket and still have allot to learn on its functions and proper use. I’m thinking about adding 4-5 oz of nose weight.

After reading almost every thread on this forum concerning CG and nose weight, am I correct that Openrocket is telling me to add that much weight. I’m extremely happy with this kit and how I’ve built it and would hate to mess it up due to lack of knowledge.

Attached is the openrocket file and I’ll list some specific on the rocket.

View attachment Alarm.ork

Weight with no motor or aero tech casing 356g
Casing used is the aero tech 24/40 20g
Motor used was the F24-w4
Next motor I have for it is a E11-3j 44g





Thanks in advance for any help you may provide,

There's a more accurate way to determine if you need nose weight. When the rocket is finished, weigh it including fully recovery (and allow for the chute and wadding to move aft,) but without a motor. Determine the CG. Do a manual over ride for the entire rocket. Then, when you set up flight simulations, the motor will be factored in automatically. If the stability is above about 1.0 you should be good. If not, you'll want to think about adding nose weight.

I use VCP Virtual Center of Pressure software to model my scratch built rockets with no weights at all. I build the rockets and then use the actual CG and weight after it is built to add a mass to the model that gives me the actual of the model. I can then add weights at the right locations for different motors to check the CG/CP relationship. I've found that I seldom need any nosecone weight.

VCP allows you to add mass to the components and it will calculate CG, but I find it too difficult to get the right mass for each of the components. I just use zero mass until it is built and then measure the weight and the CG and add an appropriate mass to the model. Once that's done, you can play with motor masses to determine the CG/CP relationship.

If you've sim'd all of your parts correctly, your model looks good! OR is giving you a 1.78 caliber of stability using you largest motor.

It is always important to check your stability when modifying a TLP kit. These are models of "guided" missiles! Not the most stable to begin with.

Personally I find using Rocksim and/or Open Rocket just about as much fun as building and launching the actual rocket!



Jerome

JeromeK99 said:

If you've sim'd all of your parts correctly, your model looks good! OR is giving you a 1.78 caliber of stability using you largest motor.

It is always important to check your stability when modifying a TLP kit. These are models of "guided" missiles! Not the most stable to begin with.

Personally I find using Rocksim and/or Open Rocket just about as much fun as building and launching the actual rocket!



Jerome

Click to expand...

Handeman said:

I use VCP Virtual Center of Pressure software to model my scratch built rockets with no weights at all. I build the rockets and then use the actual CG and weight after it is built to add a mass to the model that gives me the actual of the model. I can then add weights at the right locations for different motors to check the CG/CP relationship. I've found that I seldom need any nosecone weight.

VCP allows you to add mass to the components and it will calculate CG, but I find it too difficult to get the right mass for each of the components. I just use zero mass until it is built and then measure the weight and the CG and add an appropriate mass to the model. Once that's done, you can play with motor masses to determine the CG/CP relationship.

Click to expand...

Peter Olivola said:

There's a more accurate way to determine if you need nose weight. When the rocket is finished, weigh it including fully recovery (and allow for the chute and wadding to move aft,) but without a motor. Determine the CG. Do a manual over ride for the entire rocket. Then, when you set up flight simulations, the motor will be factored in automatically. If the stability is above about 1.0 you should be good. If not, you'll want to think about adding nose weight.

Click to expand...

Thanks Peter, Handeman, and Jerome for all the help. I’ve got a better grasp on how to figure out the CG now. I’ve decided on 90g of weight to the nose should do it.