Rocket Design Steps

Hello!

I am trying to design a rocket for a competition in which rockets need to rise 1500 meters. However, I do not know where to start. I only know the altitude.

I think that I need to determine the dimesions first, then select the proper engine which is able to meet the needed power for lifting a determined weight. But I do not how I can determine dimensions. Because I do not have any information except the altitude.

What can I do to begin the process? I am a little bit confused now.

Thanks for your help!

You are more than a little bit confused. And you are going to get lots and lots of answers. There is no one rocket/motor combination that goes 1500 meters. I am guessing you are not in the USA. Do you have rocket building materials and motors available to you? Have you ever built or launched a rocket before? Do you know anything about safety and recovery?

Thank you very much for your answer Bat-mite.

Actually, I will not build the rocket alone. We are a group of engineering students, and yes, I am not in the USA. We do not have any rocket materials, but we will get some after we decide what kind of rocket we are going to build. We have a workplace in our university in which we will carry out the process.

The problem is, there are many things ambiguous to us. For example, how do we determine the nose cone length? Or base diameter?Or body lenght? Do we choose those parameters randomly in Open Rocket? Then find a motor which can lift the rocket up to the desired altitude?

When we start Open Rocket and click the Nose cone, the program gives some default parameters. So, we think that how we can change them.

I can guess there is no one combination which will meet the expectations. This is also a part of the problem. I do not have any border or restriction. I can select the body length 30 cm, 100 cm or 150 cm. I can build a long, medium or short rocket. I just can not decide what kind of rocket would be a better choice.

I would indeed try throwing together a design in OpenRocket and experiment. Use parts from the build-in parts database so that you'll be using realistic values for things. It's a good way to get a feel for what you need to do to get to 1500m, which is pretty high if you're not experienced in flying rockets.

Any sort of design can be thrown up to 1500m on a big enough motor. You're probably restricted on motor size, though, so you'll want your design to be simple and light. A fairly "standard" rocket proportion would be something like 10:1 (length:diameter).

Perhaps you can get some sim files for existing rocket kits, and play around with the number a bit. You can try swapping in different nose cones, fin shapes, etc.

I agree with Neil. Start building things in OpenRocket. It's pretty fun, and will be a good way to get some ideas of what works. The other information that you will need is what kind of motor you are allowed to use, and how much motor can you afford. You will have to find out what is allowed in your area. Here is an introduction to commercial rocket motors:

https://www.apogeerockets.com/Rocket-Motor-Basics-Quick-Start-Guide

If you want to maximize altitude, you will want the rocket to be "minimum diameter"--meaning that you will want the rocket to be just wide enough to contain the motor. If you end up launching a relatively small rocket to 1500 m, you will probably also want to look into some method of tracking it (probably GPS).

I suggest to first find out what, if any, are the restrictions on motor, rocket, and/or materials.
Then find out what materials are available to you. And settle on the material that fits best with your available motors, weight-wise. If you have access to standard size body tubes and rocket parts, things will be easier.
For that altitude, a small rocket will be difficult to see. But a larger rocket requires a bigger motor to reach that altitude. 3" about 30" long with 3 fins is a good place to start.
It all starts with what you have available for parts and motors.

An important basic dimension is the motor diameter.
Commercial high power motors have Outside Diameters of 29mm, 38mm, 54mm, 75mm, and 98mm.
Some of those motors are single use, others are propellant reloads that go in metal motor cases. Either way, the final outer diameter will be one of those figures.

In which country is your university? We can possibly find contacts for you that are closer to your region

one good source of information is 'The Handbook of Model Rocketry' by G Harry Stine. chapter 10 deals with aerodynamics...one example given has the body/airframe at 10 - 12 to 1, and a nose of about 3 to 1(length to diameter). open rocket has an optimize function wherein you can let it vary various aspects of your design. agreed using standard size materials is an immense help.
Rex

The problem with simply playing around in OpenRocket without any actual materials on hand is that you don't have accurate weights for anything. I find that the default material mass included in OR is rarely accurate, and everything gets overridden.

However, I would suggest going with a 5:1 ogive nose cone, a 4" airframe, single-stage, simple three fins. Depending on materials, and I or J motor will probably get you the 1500 meters. You'll need to think about materials: cardboard? PVC? Fiberglass? XX phenolic? Canvas phenolic? Different weights of materials will yield dramatically different altitudes based on weight.

There was another Turkish student asking similar questions on the forum just a little while ago. Are the competition rules published someplace? (in english, if available).

Göktuğ YILMAZ said:

Hello!

I am trying to design a rocket for a competition in which rockets need to rise 1500 meters. However, I do not know where to start. I only know the altitude.

I think that I need to determine the dimesions first, then select the proper engine which is able to meet the needed power for lifting a determined weight. But I do not how I can determine dimensions. Because I do not have any information except the altitude.

What can I do to begin the process? I am a little bit confused now.

Thanks for your help!

Click to expand...

I would like to suggest that you not begin by simulation, but rather by building some kits to become acquainted with common construction techniques. Then build a simulation of those kits and begin applying what you learn along the way.

Steve Shannon said:

I would like to suggest that you not begin by simulation, but rather by building some kits to become acquainted with common construction techniques. Then build a simulation of those kits and begin applying what you learn along the way.

Click to expand...

I'll second what Steve said. I know I encouraged you to play with OpenRocket earlier in this thread. That can help you design a rocket for a specific purpose, but there is no substitute for the experience you will get by building low-power and mid-power rockets first. It is very easy to have something go wrong, so it's better to learn with cheaper and less powerful motors first.

Thank you very much for your explanations. I am from Karadeniz Technical University in Trabzon/Turkey. Actually, we are thinking of buying a cheap model rocket kit or building one. We appreciate the experience we will gain by doing instead of only researching. However, when it comes to design something as an engineer, we think that we must know what we are exactly doing. For example, how many fins should we use? Three or four? Some people say that four is the best, others say that three is good and simple, and some says that it depends. We want to be able to explain our reasons for each choice.
It looks that we will find out many things by trial and error. So, as a first step, we are going to build a cheap model rocket.

Competition rules are published, but only Turkish version is available. Motors must be smaller than M class. They will publish a catalog and we will select one of them for our rocket.

Thank you very much for your answers again.

Göktuğ YILMAZ said:

Thank you very much for your explanations. I am from Karadeniz Technical University in Trabzon/Turkey.

Competition rules are published, but only Turkish version is available. Motors must be smaller than M class. They will publish a catalog and we will select one of them for our rocket.

Click to expand...

Göktuğ YILMAZ said:

The problem is, there are many things ambiguous to us. For example, how do we determine the nose cone length? Or base diameter?Or body lenght? Do we choose those parameters randomly in Open Rocket? Then find a motor which can lift the rocket up to the desired altitude?

Click to expand...

Göktuğ YILMAZ said:

I do not have any border or restriction. I can select the body length 30 cm, 100 cm or 150 cm. I can build a long, medium or short rocket. I just can not decide what kind of rocket would be a better choice.

Click to expand...

Do the rules say anything about the dimensions of your rocket?

Are there no limits or requirements for length? For diameter? For total mass?


Are there requirements for the materials you must use to construct the rocket?

Do you have to fabricate all of the parts yourself, or will you purchase parts?

Are there requirements for how the rocket will be recovered?

What payload must the rocket carry? Will all of the teams use the same instruments to measure altitude?

Is the point of the contest to reach exactly 1500 meters? Or to go at least 1500 meters? Or to go higher than 1500 meters?

When do you plan to launch?

Thank you very much for your answer.

There are no limits for length, diameter or total mass. We do not have any restriction for the materials.

No, we do not have to manufacture all parts. We will purchase some materials such as motor and computer.

Yes, recovery system must include two parachute, one is called drag and other is called main parachute.

The payload must be 4 kg. If your payload is 4kg, the instrument is not important( of course, we can not use an animal as a payload.).

We need to use altimeter 2 or 3 to measure the altitude.

The purpose of the competition is to reach exactly 1500 meters.

The competition will happen on September.

Göktuğ YILMAZ said:

Thank you very much for your answer.

... recovery system must include two parachute, one is called drag and other is called main parachute.

The payload must be 4 kg. If your payload is 4kg, the instrument is not important( of course, we can not use an animal as a payload.).

We need to use altimeter 2 or 3 to measure the altitude.

The purpose of the competition is to reach exactly 1500 meters.

The competition will happen on September.

Click to expand...

Okay, this is better. With these constraints, you can start to ask real questions.

A good place to start might be with the parts you need to get the rocket back safely. Figure out the volume you will need inside the airframe for the parachutes and the mechanisms that will deploy them. This will help you choose the diameter of the rocket you must build.