Open Rocket

[Lt72884]

Ok, i am not really understanding how to use this software. i can do youtube for this, but i feel i would miss some major principles that are not discussed.

one of my questions is how do you actually figure out what size of fuselage tube to use for your rocket? IE, do i use a 3 foot by 3 inch diameter tube, a 4 foot by 6 inch tube, or a 10 foot tube?

thanks

 

[PayLoad]

I found a great way to start is to open an existing design, then just play with changes to fins, length, motors, etc. After that you an start from scratch, as long as you know what you are trying to accomplish (which you should lay down first)

 

[Charles_McG]

Those aspects of a design usually come from other sources - they go _into_ the sim, rather than being a product of it.
So what are you trying to accomplish? What's the design goal? Max altitude for a specific motor size? A specific scale of a historic rocket? What are the material availability limits - if any? Can you buy or make any size parts? Catalog parts only?

 

[tsmith1315]

That's for you to decide based on your constraints. Then simulate, evaluate, and iterate.

Class project? Do you know what your motor choices are? How about payload dimensions? If so, then that's where you need to start.

 

[neil_w]

That's for you to decide based on your constraints. Then simulate, evaluate, and iterate.

Yes. To a certain extent, the original question is like asking what color are you supposed to use in Photoshop.

Openrocket is a tool to model and simulate your rocket design. To a certain extent it can provide assistance in creating the design, but ultimately it all starts with your input. If you're designing a new rocket, then you'll need to decide how big you want it to be based on a whole assortment of criteria. Then you can choose from the available parts in the library included with OR and start constructing your model.

A good place to start here would be to describe what you're trying to do.

 

[Lt72884]

Yes. To a certain extent, the original question is like asking what color are you supposed to use in Photoshop.

Openrocket is a tool to model and simulate your rocket design. To a certain extent it can provide assistance in creating the design, but ultimately it all starts with your input. If you're designing a new rocket, then you'll need to decide how big you want it to be based on a whole assortment of criteria. Then you can choose from the available parts in the library included with OR and start constructing your model.

A good place to start here would be to describe what you're trying to do.

Capstone project for university class. Need to build a rocket that can hit 10,000 feet with a 9lb payload. No spaceport america cup.
to me, i have no idea if a 3 foot 6 inch tube could go 10,000 feet. im guessing the first constraint is moto size?

 

[PayLoad]

.....to me, i have no idea if a 3 foot 6 inch tube could go 10,000 feet. im guessing the first constraint is moto size?

You're gonna need a bigger boat.

Get an .ork file of a larger rocket, 54mm motor at least, and PLAY with different motors in it

 

[neil_w]

Yeah, 10k ft with 9 lb payload is a big rocket. I second @PayLoad ‘s advice. Go find some existing files and see what combination of motor and rocket size gives you the performance you need, then you can refine and use the info to create your own design.

 

[thzero]

Especially if it's for a university class.

 

[Antares JS]

to me, i have no idea if a 3 foot 6 inch tube could go 10,000 feet. im guessing the first constraint is moto size?

You're asking the wrong questions. The length of your tube matters a lot less to altitude achieved than drag, the weight of the rocket and the motor you use.

Is this nine pound payload to be in addition to the weight of your rocket?
What is your nine pound payload and how big of a space do you need for it?
How big of a motor are you allowed to use for the project?

 

[thzero]

You're asking the wrong questions. The length of your tube matters a lot less to altitude achieved than drag, the weight of the rocket and the motor you use.

Is this nine pound payload to be in addition to the weight of your rocket?
What is your nine pound payload and how big of a space do you need for it?
How big of a motor are you allowed to use for the project?

It's all explained in the Spaceport America Cup challenge pdf available from NASA ...

 

[Antares JS]

It's all explained in the Spaceport America Cup challenge pdf available from NASA ...

Post #6.

Capstone project for university class. Need to build a rocket that can hit 10,000 feet with a 9lb payload. No spaceport america cup.

 

[tsmith1315]

im guessing the first constraint is moto size?

Physical dimensions and impulse. Also payload size.

You're probably going to want the airframe as small in diameter as practical to keep drag down.

I doubt you're going to have so much "motor" available that this is a design project. Start at the beginning- It's an engineering project, what are your goals and what do you have available to achieve those goals? Details matter.

Until you have specifics, do like others have suggested and pick a kit to sim. Not for your project, but to get familiar with the software and experiment with motor choices, mass and fin sizes and how they affect flight.

Look into CG/CP relationship and how it affects stability.

 

[PayLoad]

Over-stating the obvious - getting a 9lb payload to 10,000 feet, with a successful recovery, is not an easy (or cheap) endeavor

 

[waltr]

As someone said: Start with the examples.
Also, many of the builds in the forum have OR or RockSim files posted (Note: OR can also open RockSim (*.rkt) files).
Search and Read. When you find larger (L3 rockets) rocket sim file download and open in OR to see what was done.
There may even be a few Spaceport America Cup sim files posted.

In addition, manufacturers do have RockSim or OR files on their webs sites for the kits they sell. Another source of sim files.

Engineering is part Coping what others have done and part being Creative to solve specific problems.
You will need to do a lot of both.

 

[JoePfeiffer]

Is this intended as a paper design, or is the plan to actually build and fly the rocket and payload? I sincerely hope the former, though that would be decidedly unusual for a capstone project.

You're asking a novice question (and there's nothing wrong with that. We were all novices once, and asking novice questions is how you advance). If you have a mentor, that is who you should be asking. This project is definitely in the "big leagues" as the hobby rocketry community goes. If your instructor is expecting you to design, build, and fly a rocket like this with no experience and no help, they're being completely irresponsible.

 

[prfesser]

You're gonna need a bigger boat.

Get an .ork file of a larger rocket, 54mm motor at least, and PLAY with different motors in it

It doesn't have to be a larger rocket. But you do have to sit and play with it.

Load a simple .ork file (or .Rocksim .rkt file, OR handles both). Stick in a suitable motor, look at the altitude.

Now click Edit/Scale. Select 200%. Check the altitude. Obviously going to be less...but how much less?

Change to a motor with twice the total impulse. What happens to altitude? Did it double? (no, it didn't).

Double the total impulse again. Altitude?

Add a Mass Component to the body tube or nose cone. Make it large enough to double the weight. Altitude? What happens when you double the length of the body tube, or cut it in half? Four fins instead of three? Fins that are longer and stubbier? Nose cone rounded instead of sharp? Etc.

Keep playing to learn what parameters affect altitude/speed, and to what degree. Here's one conclusion you'll draw: for most big rockets, reducing rocket diameter increases altitude to a much greater extent than decreasing mass does.

 

[user 30299]

Is this intended as a paper design, or is the plan to actually build and fly the rocket and payload? I sincerely hope the former, though that would be decidedly unusual for a capstone project.

You're asking a novice question (and there's nothing wrong with that. We were all novices once, and asking novice questions is how you advance). If you have a mentor, that is who you should be asking. This project is decidedly in the "big leagues" as the hobby rocketry community goes. If your instructor is expecting you to design, build, and fly a rocket like this with no experience and no help, they're being completely irresponsible.

Amen brother!

This student, Lt72884, has another thread going on this capstone project. So between the two threads it's clear the student
needs a proper mentor/advisor to pursue this project in a timely, safe and successful manner.

 

[thzero]

I got simulated 10k on a L (oops, typo).

 

[user 30299]

I got simulated 10k on a L (oops, typo).

Post your sim file.

Which L motor?

 

[thzero]

Post your sim file.

Which L motor?

Nah...

Mid-sized L, 75mnm. Hit about 13k, but based on the sim I need bigger parachutes so that'll add a bit more weight so it'd probably 12k. Then we all know the sims aren't perfect so maybe between 10-11k IRL? Sim'd it does flirt with Mach 1 velocity.

So its doable. I used one of my L2 projects as reference. I probably would want to swap around where the 9lb mass is in order to not have as high of stability margin.

 

[user 30299]

Nah...

Mid-sized L, 75mnm. Hit about 13k, but based on the sim I need bigger parachutes so that'll add a bit more weight so it'd probably 12k. Then we all know the sims aren't perfect so maybe between 10-11k IRL? Sim'd it does flirt with Mach 1 velocity.

So its doable. I used one of my L2 projects as reference. I probably would want to swap around where the 9lb mass is in order to not have as high of stability margin.

I've never seen a mid-sized L at the Spaceport Cup competition - which Lt72884's rocket is supposed to be designed for. Just sayin' . . .

 

[Off Grid Gecko]

I assume this is in reference to your other post that I spotted last night.

I'm going to be brief as this forum is not playing nice with my computer rn.

You were looking at some Wildman kits from what I understand. You should be able to get whatever specs you need from the kits. Some stuff is more or less standard and other stuff not so much. I don't know if they list all of their exact specs on the website but they may have a file you can download as a starting point. My guess is deep the tube diameter to 4inches max for what you are doing, also look at tracking supplies and what kind of altimeter-deployment devices you guys want to use.
If you have not reached out to the Utah club guys yet make that a priority, and go to the first launch of theirs that you can make. They can help you IRL better than people online just seeing bits and pieces about your project.
Also, did you get confirmation on the payload size requirements? Obv a 5" diameter payload won't fit in a 4" tube.
CTI lists specs for all of their motors so you can get and idea about Delta-V for your rocket equation, but at 10,000 feet it's more a question of the tube and thrust vs the atmosphere.
With a 9lb payload you are going to have a long coast on the ascent, so getting as much speed behind it as you can is good, but this brings up other problems, like fin flutter.

Rockets are designed as a complete system, not in parts. My first steps if it was me, get the payload size, select a tube big enough to hold it, assume a 5:1 length to diameter ratio ogive for the nose cone, slap some fins on it (in the simulator) and try some different motors. That will at least give you an idea of what you are working with. For tube specs check out some different tube dimensions on the apogee website, that will give you some numbers to play with. There will be extra weight for glue fillets and stuff like that so take a wide margin of error into account. That 9lb payload if attached is going to give you a lot of stability if it's up near the nose too. And of course you need a long enough launch system to get to a stable velocity after liftoff. The L3 assigned to the flight can help you volumes so find them and start that dialogue as soon as you can.

 

[user 30299]

As a follow-up to the Gecko's note on the payload size - For the Spaceport Cup, if a team just does the 8.8 lbs. as a
boiler plate load (just dead weight), then the rocket must be designed with a 4"x4"x12" area to contain the 8.8 lbs.

The 4" dimension basically forces you into a 6" dia. (OD) body tube.

It's details like these, and many others, that Lt72884 and the team should look into if they are going to lead the
way for future teams.

 

[Off Grid Gecko]

As a follow-up to the Gecko's note on the payload size - For the Spaceport Cup, if a team just does the 8.8 lbs. as a
boiler plate load (just dead weight), then the rocket must be designed with a 4"x4"x12" area to contain the 8.8 lbs.

The 4" dimension basically forces you into a 6" dia. (OD) body tube.

It's details like these, and many others, that Lt72884 and the team should look into if they are going to lead the
way for future teams.

That def makes it a little trickier doesn't it. I thought this could be an L2 all the way but might need a motor that's a little more stout so I guess my L3 mentor suggestion wasn't far off the mark. I've seen some 5.5" stuff either from MadCow or Wildman I don't remember, I don't build kits for the most part. I wonder if that's a 4x4 square or 4" diameter. He had mentioned something about cube-sats. If it's square then def a 6" tube.
Thanks for the insight about the comp, I was wondering about that last night.

 

[user 30299]

That def makes it a little trickier doesn't it. I thought this could be an L2 all the way but might need a motor that's a little more stout so I guess my L3 mentor suggestion wasn't far off the mark. I've seen some 5.5" stuff either from MadCow or Wildman I don't remember, I don't build kits for the most part. I wonder if that's a 4x4 square or 4" diameter. He had mentioned something about cube-sats. If it's square then def a 6" tube.
Thanks for the insight about the comp, I was wondering about that last night.

That's a 4"x4" square. The CubeSat is 4"x4"x4" - so it's a cube (lol). The 12" length is (3) CubeSats stacked on top of each other.

In the Spaceport Cup you can only sidestep the 4"x4"x12" requirement if the payload is a functional payload - and not boiler plate.
A team is not penalized points for not meeting the 4x4x12 condition. But a team can get bonus points if they make their functional
payload fit in the 4x4x12 area.

Just one of the many challenges in the Spaceport Cup.

 

[JoePfeiffer]

Every year we get an entry or two that tries to do it on an L. I don't think there's been one yet that's come anywhere near the 10K altitude.

 

[Lt72884]

ok, so im still trying to figure out some design stuff.

Length of tube, diameter of tube has to play a role in the rockets flight height, does it not? A fatter tube means more drag since it is a bluff body, youll get more separation of flow. a 6inch rocket vs a 6 foot rocket is going to have a huge flight difference.

These are all things i have to also present and the maths of things since this is a capstone haha.
we will be finding a lvl 3 mentor this week.

 

[Off Grid Gecko]

ok, so im still trying to figure out some design stuff.

Length of tube, diameter of tube has to play a role in the rockets flight height, does it not? A fatter tube means more drag since it is a bluff body, youll get more separation of flow. a 6inch rocket vs a 6 foot rocket is going to have a huge flight difference.

These are all things i have to also present and the maths of things since this is a capstone haha.
we will be finding a lvl 3 mentor this week.

Changing tube lengths is easy in OpenRocket, luckily. I usually start with a diameter and profile, then add my internal components and the biggest motor I plan on flying. Then check the CG/CP ratio and add weights or extend the length as needed. Make sure to leave plenty of room for separation charges and chutes.

 

[PayLoad]

Here - Load this into Open Rocket and PLAY. There are no skipping steps in learning this stuff, no real shortcuts, and you really have to know what changes on part "A" are going to effect part "B". You have to understand why CG and CP are important. You need to know why fin size & placement are important. Change things around & see what it does to the simulation flight.

You sound like it may be a FANTASTIC idea for you to buy a kit to build just to learn from first, instead of going for a moon landing on your first try. I mean no insult at all - we've all been there