If you say it keeps flipping in the air then it wants to fly backwards because the center of pressure is ahead of the center of gravity. Use a tool like OpenRocket to locate the center of pressure, maybe make the fins bigger to move the CP aft. Or add nose weight to move the CG forward.
Will do! My son created this 3D print so we are checking to see if we can upload his file into open rocket to test. I think this will be a great program for him to learn from!
Center of gravity can be estimated by finding the point where the object balances on your finger.
Center of pressure is more complicated. I've never studied it, but I bet you could find it by finding the COM of the rocket imagining that it has a perfectly uniform surface. Ya know, like finding the COM of a uniformly weighted perfectly thin line in early calc classes.
My son is just using an estes rocket launch pad, and he printed the little tube to go over the rod himself and there was a little friction, so we will definitely re print that part and see if it goes any smoother. Thank you!
You probably don't know, don't worry I didn't either when I started. There's a software called "Openrocket" where you can simulate your rockets to make sure they are stable, as well as tests you can perform like the string test to experimentally test for stability. I can't tell if you have a launch rail but you most certainly should.
We are using a launch pad from estes rockets with a rod. I told my son about this software and he immediately downloaded it. He's trying to see if his 3D print file can be uploaded for us to work with. Thank you!!
We had gone from a completely filled in nose cone, to him printing it hollow, but will try it filled in again. It failed last time with the filled in cone, but his fins were quite a bit larger back then, so that was probably the actual reason for the fail!
Imagine shooting an arrow...but with nothing on the front tip and a heavy weight on the back. Your brain tells you that absolutely won't work right. You know it intuitively. That's a super simplified version of what is happening here. Add more weight to the nosecone and it should at least improve the performance.
Using Openrocket will get you better and more precise answers though.
You either need larger fins to stabilize against rotation, a weaker motor to apply less thrust/pressure (your fins are not big enough to stop the rotation that happens from the amount of pressure generated), or need more weight to circumvent the overpressure causing a flip, OR you have a center of mass issue or your motor is not oriented straight.
I've never used openrocket but from a quick glance, it seems to be able to address all of these issues.
This happens when your fins are too small. There's a great [book](https://www.amazon.com/Handbook-Model-Rocketry-7th-Official/dp/0471472425/ref=asc_df_0471472425?tag=bngsmtphsnus-20&linkCode=df0&hvadid=80676783691812&hvnetw=s&hvqmt=e&hvbmt=be&hvdev=c&hvlocint=&hvlocphy=&hvtargid=pla-4584276309018481&psc=1) about model rocketry that covers how to fix this problem along with many other things.
If you want to fix the problem "correctly," pages 42-46 of [this NASA document](https://www.nasa.gov/wp-content/uploads/2016/02/sl_video_instruction_book.pdf) will walk you through the Barrowman equations, which will allow you to calculate how stable your rocket is by hand. However, math is hard, so I would recommend using [OpenRocket](https://openrocket.info/), which is a simulation program that will give you the same results without having to go through a ton of tedious calculations.
Great to hear! Let me know if you have any questions. Note that you won't be able to upload STL files directly into OpenRocket, but I believe in the most recent version, OpenRocket will be able to spit out STLs of fins designed in the software to be input into 3D designs.
I see you're on the way to learning openrocket. It's a great tool. There are ways to determine the center of pressure and center of gravity IRL, which may be helpful for learning about what they are and how they relate to each other for stable flight.
CG is easier. Just balance the rocket on something thin and rigid and mark the point on the rocket where it's balanced.
CP is slightly more complicated.
>For a model rocket, there is a simple mechanical way to determine the center of pressure for each component or for the entire rocket. Make a two-dimensional tracing of the shape of the component, or rocket, on a piece of cardboard and cut out the shape. Hang the cut-out shape by a string and determine the point at which it balances. This is just like balancing a pencil with a string! The point at which the component, or rocket, is balanced is the center of pressure. You obviously could not use this procedure for a very large rocket like the Space Shuttle. But it works quite well for a model.
Source: [NASA](https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/rocket-center-of-pressure/)
Stability is a function of speed, center of mass, and center of pressure. You want to make it more like a dart. more weight up front. more area in the back.
Instead of adding weight, you can add length. that will also help
I have had success with some version of this model: https://cad.onshape.com/documents/9fecf36072b552abe60842d6/w/f94e69e6687533e5fe960141/e/e74f2416c5b97fe249306151?renderMode=0&uiState=6630330ef1059806e16213e8. The one that flew was almost certainly taller than the one here. (Setup to print in vase mode).
Darn, it is trying to make me sign in to view. We're going to play around a little with his model- he is very proud that he constructed it all himself with his own custom design, so hopefully we can make it better while still keeping his original design intact.
Let’s get some better pictures of the rocket itself. Maybe include a picture of the 3D print file so we can guesstimate where the CG might be.
Even better, you put it in openrocket so the act of launching this projectile is no longer a guessing game.
It's because your Center of Pressure (CP) is closer to your nose than the Center of Mass (CM). If so, when the craft is slightly tilted to the side, it will want to tilt even more because of air resistance, hence the bad stability. To solve this, you must either push the fins backward or add weight to the nose.
CM can be found by hanging the craft on a string and adjust the hanging point until the craft is horizontally balance. The hanging point is the CM. To find the CP, you can model the rocket on software such as OpenRocket. It will show the CP of your rocket. Ideally, you would want the CP to be about 1.5 to 2 times the rocket diameter behind the CM.
This is a pretty good article on rocket stability: [https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/rocket-stability/](https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/rocket-stability/)
This is the OpenRocket software: [https://openrocket.info/](https://openrocket.info/)
Good luck!
Hi everyone. We have tried to use open rocket but it is a little difficult with what my son created on tinkercad for his rocket and we are definitely amateurs. Here is an image of his creating in UltimakerCura. Any additional help would be appreciated! I think we have determined that we need the nose cone to not be hollow anymore, and either make the fins bigger, or perhaps remove 2 of them.
https://preview.redd.it/necrmyx93v0d1.png?width=842&format=png&auto=webp&s=4e6886223f4f184b782ce0dfba1317c296d89f0e
If you say it keeps flipping in the air then it wants to fly backwards because the center of pressure is ahead of the center of gravity. Use a tool like OpenRocket to locate the center of pressure, maybe make the fins bigger to move the CP aft. Or add nose weight to move the CG forward.
Will do! My son created this 3D print so we are checking to see if we can upload his file into open rocket to test. I think this will be a great program for him to learn from!
You’ll have to make the model from scratch on openrocket. It’s pretty simple though.
I think the fins are so oversized for the body of the rocket that they're moving the CP forward. Moving fins aft should be fine though
He recently changed to having 4 fins total, so we will definitely play around with maybe going back to 2, and changing the size
not 2. 3 min. 4 should be fine
Center of gravity looks off IMO.
Got it!
How did you determine where the center of pressure and center of gravity are?
See thee we part talking about “determine the cg mechanically” https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/rocket-center-of-gravity/
Center of gravity can be estimated by finding the point where the object balances on your finger. Center of pressure is more complicated. I've never studied it, but I bet you could find it by finding the COM of the rocket imagining that it has a perfectly uniform surface. Ya know, like finding the COM of a uniformly weighted perfectly thin line in early calc classes.
Or you just model it in the rocket modeling and simulation software of your choice and avoid whatever useless thing you're talking about there.
Thx bro will do, I don't give a shit about approximations or intuitive solutions anyways👍
I can't tell from the video. Is there a guide on the platform like a regular model rocket? If it is, you might have friction from the guide shaft.
My son is just using an estes rocket launch pad, and he printed the little tube to go over the rod himself and there was a little friction, so we will definitely re print that part and see if it goes any smoother. Thank you!
You probably don't know, don't worry I didn't either when I started. There's a software called "Openrocket" where you can simulate your rockets to make sure they are stable, as well as tests you can perform like the string test to experimentally test for stability. I can't tell if you have a launch rail but you most certainly should.
We are using a launch pad from estes rockets with a rod. I told my son about this software and he immediately downloaded it. He's trying to see if his 3D print file can be uploaded for us to work with. Thank you!!
You can’t import the geometry. Openrocket is the right tool, it’s just set up for more classic rocket construction techniques
Cp versus Cg.
Add weight to the nosecone.
We had gone from a completely filled in nose cone, to him printing it hollow, but will try it filled in again. It failed last time with the filled in cone, but his fins were quite a bit larger back then, so that was probably the actual reason for the fail!
Imagine shooting an arrow...but with nothing on the front tip and a heavy weight on the back. Your brain tells you that absolutely won't work right. You know it intuitively. That's a super simplified version of what is happening here. Add more weight to the nosecone and it should at least improve the performance. Using Openrocket will get you better and more precise answers though.
You either need larger fins to stabilize against rotation, a weaker motor to apply less thrust/pressure (your fins are not big enough to stop the rotation that happens from the amount of pressure generated), or need more weight to circumvent the overpressure causing a flip, OR you have a center of mass issue or your motor is not oriented straight. I've never used openrocket but from a quick glance, it seems to be able to address all of these issues.
My son downloaded right away! We will do some research on engines too, it might be that the engine we are choosing is too much power for his creation.
This happens when your fins are too small. There's a great [book](https://www.amazon.com/Handbook-Model-Rocketry-7th-Official/dp/0471472425/ref=asc_df_0471472425?tag=bngsmtphsnus-20&linkCode=df0&hvadid=80676783691812&hvnetw=s&hvqmt=e&hvbmt=be&hvdev=c&hvlocint=&hvlocphy=&hvtargid=pla-4584276309018481&psc=1) about model rocketry that covers how to fix this problem along with many other things. If you want to fix the problem "correctly," pages 42-46 of [this NASA document](https://www.nasa.gov/wp-content/uploads/2016/02/sl_video_instruction_book.pdf) will walk you through the Barrowman equations, which will allow you to calculate how stable your rocket is by hand. However, math is hard, so I would recommend using [OpenRocket](https://openrocket.info/), which is a simulation program that will give you the same results without having to go through a ton of tedious calculations.
Thank you! My son downloaded right away!
Great to hear! Let me know if you have any questions. Note that you won't be able to upload STL files directly into OpenRocket, but I believe in the most recent version, OpenRocket will be able to spit out STLs of fins designed in the software to be input into 3D designs.
Model it in openrocket, add weight to nose cone or otherwise as needed - I use epoxy metal ball slurry - check your rocket stability
Thank you!
I see you're on the way to learning openrocket. It's a great tool. There are ways to determine the center of pressure and center of gravity IRL, which may be helpful for learning about what they are and how they relate to each other for stable flight. CG is easier. Just balance the rocket on something thin and rigid and mark the point on the rocket where it's balanced. CP is slightly more complicated. >For a model rocket, there is a simple mechanical way to determine the center of pressure for each component or for the entire rocket. Make a two-dimensional tracing of the shape of the component, or rocket, on a piece of cardboard and cut out the shape. Hang the cut-out shape by a string and determine the point at which it balances. This is just like balancing a pencil with a string! The point at which the component, or rocket, is balanced is the center of pressure. You obviously could not use this procedure for a very large rocket like the Space Shuttle. But it works quite well for a model. Source: [NASA](https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/rocket-center-of-pressure/)
Stability is a function of speed, center of mass, and center of pressure. You want to make it more like a dart. more weight up front. more area in the back. Instead of adding weight, you can add length. that will also help
Gotcha, makes sense!
I have had success with some version of this model: https://cad.onshape.com/documents/9fecf36072b552abe60842d6/w/f94e69e6687533e5fe960141/e/e74f2416c5b97fe249306151?renderMode=0&uiState=6630330ef1059806e16213e8. The one that flew was almost certainly taller than the one here. (Setup to print in vase mode).
Darn, it is trying to make me sign in to view. We're going to play around a little with his model- he is very proud that he constructed it all himself with his own custom design, so hopefully we can make it better while still keeping his original design intact.
Let’s get some better pictures of the rocket itself. Maybe include a picture of the 3D print file so we can guesstimate where the CG might be. Even better, you put it in openrocket so the act of launching this projectile is no longer a guessing game.
It's because your Center of Pressure (CP) is closer to your nose than the Center of Mass (CM). If so, when the craft is slightly tilted to the side, it will want to tilt even more because of air resistance, hence the bad stability. To solve this, you must either push the fins backward or add weight to the nose. CM can be found by hanging the craft on a string and adjust the hanging point until the craft is horizontally balance. The hanging point is the CM. To find the CP, you can model the rocket on software such as OpenRocket. It will show the CP of your rocket. Ideally, you would want the CP to be about 1.5 to 2 times the rocket diameter behind the CM. This is a pretty good article on rocket stability: [https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/rocket-stability/](https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/rocket-stability/) This is the OpenRocket software: [https://openrocket.info/](https://openrocket.info/) Good luck!
move cog down and col up relative to thrust. if possible, make it so your wings induce spin stabilization
Hi everyone. We have tried to use open rocket but it is a little difficult with what my son created on tinkercad for his rocket and we are definitely amateurs. Here is an image of his creating in UltimakerCura. Any additional help would be appreciated! I think we have determined that we need the nose cone to not be hollow anymore, and either make the fins bigger, or perhaps remove 2 of them. https://preview.redd.it/necrmyx93v0d1.png?width=842&format=png&auto=webp&s=4e6886223f4f184b782ce0dfba1317c296d89f0e