#### uzt

Hi, I am currently working on a Hybrid Rocket which uses fuel grain as 3-D printed ABS and oxidizer as N2O, but i need to calculate some basic parts such as required thrust to reach specific altitude. I want to calculate the required thrust to reach 1.5km for 10kg rocket with 7cm radius. It will launched 85 degrees vectircally. I want you to guys who is interseting model rockets, tell me which procedure should I follow, such that the given information about this rocket is enough to calculate the required thrust or not, do i need to calculate any other quantities to obtain required thrust or any other ideas to approach to this problem ?
Thank You,

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#### phinds

Gold Member
You may well get some good answers here but I would expect that a model rocket forum is really where you should be looking. Ideal calculations are fine in the lab but you're talking about a practical situation where experience will tell you a lot in addition to a math model. For example, how much drag does your particular rocket shape have? Are there fins that add to the drag?

Also, you need to make some effort on your own. On this forum we don't spoon feed answers, we expect you to have shown some work of your own before we can jump in with help. Do you know any relevant equations to help towards your answer?

#### berkeman

Mentor
Hi, I am currently working on a Hybrid Rocket which uses fuel grain as 3-D printed ABS and oxidizer as N2O, but i need to calculate some basic parts such as required thrust to reach specific altitude. I want to calculate the required thrust to reach 1.5km for 10kg rocket with 7cm radius. It will launched 85 degrees vectircally. I want you to guys who is interseting model rockets, tell me which procedure should I follow, such that the given information about this rocket is enough to calculate the required thrust or not, do i need to calculate any other quantities to obtain required thrust or any other ideas to approach to this problem ?
Thank You,
Also, are you part of a rocketry club, or do you have an in-person Mentor to help you with this and make sure your work is safe?

#### uzt

You may well get some good answers here but I would expect that a model rocket forum is really where you should be looking. Ideal calculations are fine in the lab but you're talking about a practical situation where experience will tell you a lot in addition to a math model. For example, how much drag does your particular rocket shape have? Are there fins that add to the drag?

Also, you need to make some effort on your own. On this forum we don't spoon feed answers, we expect you to have shown some work of your own before we can jump in with help. Do you know any relevant equations to help towards your answer?
First of all, I tried to determine the regression rate of given propellent to obtain mass flow rate and then trying to obtain thrust from the formulation of;
T=m(dot)*Ve+(Pe-P0)*Ae, where m(dot) is mass flow rate, Ve= velocity at exit of the nozzle, Pe=Pressure at exit of the nozzle, P0=Free stream pressure, Ae=Area ratio of throat to exit.
But, then I realized that determination of the regression rate of the propellent is not easy. I faced several problems such that obtaining mass flow rate, and then I tried to calculate as projectile motion with the consederition of air resistance on particular body, but again I faced the problem which is coefficient of drag for this particular body. Then, I found a web site which contains several equations about maximum altitude and velocity of model rockets. Here is the site
-> http://www.rocketmime.com/rockets/rckt_eqn.html#Theory
but, I do not know the formulas are true or not because there is some untitled variables which is not understandable at all.
So, my question is what should I do. Am I doing right or not? How can i calculate the mass flow rate or is it possible to calculate with these given information? Also, if you know any relevant books or articles about rocket propulsion, I am glad to hear.

#### uzt

Also, are you part of a rocketry club, or do you have an in-person Mentor to help you with this and make sure your work is safe?
I am not a part of a rocketry club or something. Just trying to build by my own with help of the book Fundamentals of Aerodynamics by John D. Anderson.

#### anorlunda

Mentor
Gold Member
I am not a part of a rocketry club or something. Just trying to build by my own with help of the book Fundamentals of Aerodynamics by John D. Anderson.
@berkeman 's question was more of a hint. Doing it on your own may expose you to risk of injury. Model rocketry with the help of a local club is safer and is recommended whenever possible.

Edit: @phinds ' post was also a hint to bring your questions to a rocketry forum. Discussing dangerous topics on PF is not allowed.

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