Optimizing Fin Shapes in Rocksim

[Alan15578]

I'm currently delving into optimizing fin planform shapes and their geometric dimensions for a water rocket project highschool project. to obtain maximum stability (which I would determine by the static margin) and I've been using Rocksim for this purpose, and I've come across a methodology question that I'm hoping someone here might be able to shed some light on.

In my approach, I've been contemplating the idea of altering one variable at a time to find its optimal value before moving on to the next. For instance, I'd first optimize the root chord length while keeping other parameters constant, and then, once that's optimized, I would proceed to optimize the next variable, like semi span, and so on.

However, I'm uncertain about how effective this method is in Rocksim, especially considering the complex interactions between various fin parameters. My main questions are:

1. How is Rocksim programmed to handle the optimization of fin shapes? Can it effectively account for the nuanced interactions between different fin dimensions when only one variable is altered at a time?
2. Is the method of optimizing one variable at a time, then moving onto the next, a viable approach in Rocksim? Specifically, I'm interested in understanding how this approach might impact the overall performance and stability of the rocket, given the interdependencies of fin dimensions. Might a certain fin span only apply to be optimal when adjoint to a certain sweep angle? And the many instances of contradictions inside the rocketry literature (elliptical is optimal due to its induced drag working, but for low reynolds number rectangular/parallelograms are better).

I have been reading many different articles for my research purposes (such as articles posted on the apogee website, Stine's Handbook of model rocketry, Gregorek's TR11 report, countless rocketry forum threads and many other articles and presentations such as this. I am obviously interested in the subsonic regime, but there are still so many factors to take into account. It's almost like the more information I read, the less clear my head gets about an approach to my optimization problem (I guess that is why they say ignorance is a bliss).

P.S I found an article with a similar methodology to what I am aiming to accomplish (I will not be doing CFD, but their OpenRocket methodology aligns somewhat), yet I still don't understand how the interdependency of factors was adressed, nor how they reached some of their conclusions such as the optimal number of fins being three without testing, I am just taking a guess and assuming the rocket models they made ALWAYS had 3 fins, and therefore it was a controlled variable).

On another note, does anyone dispose of a copy/method of contact with Mr. Cipolla, who created FinSim. I was looking into using it for a possible section on flutter analysis in my research, but all copies have been taken down from the website and I have not found any way to contact the man himself.

It occurs to me that I could be more helpful. I can't help you with any optimization built into Rocsim or Open Rocket, and I have already cautioned you on optimization of an approximate simulation model. However, you could try the Simplex method for optimization over several variables, It requires no gradients, Hessians, etc., but it does work. You could probably find a downloadable routine to use, or you can find it in "Numerical Recipes in Fortran" (because I am old) or "Numerical Recipes in C" ( If you like that sort of thing.) There are also design options that are not continuous variables. For a while is seemed like every professional missile design started out with a rocket vs ramjet trade study, You could do the same thing with three vs four fins, and even tube fins. You just do multiple designs and develop each with the same level of care, until the inferior design can be determined and eliminated.

 

[Brandon.L]

I'm currently delving into optimizing fin planform shapes and their geometric dimensions for a water rocket project highschool project. to obtain maximum stability (which I would determine by the static margin) and I've been using Rocksim for this purpose, and I've come across a methodology question that I'm hoping someone here might be able to shed some light on.

In my approach, I've been contemplating the idea of altering one variable at a time to find its optimal value before moving on to the next. For instance, I'd first optimize the root chord length while keeping other parameters constant, and then, once that's optimized, I would proceed to optimize the next variable, like semi span, and so on.

However, I'm uncertain about how effective this method is in Rocksim, especially considering the complex interactions between various fin parameters. My main questions are:

1. How is Rocksim programmed to handle the optimization of fin shapes? Can it effectively account for the nuanced interactions between different fin dimensions when only one variable is altered at a time?
2. Is the method of optimizing one variable at a time, then moving onto the next, a viable approach in Rocksim? Specifically, I'm interested in understanding how this approach might impact the overall performance and stability of the rocket, given the interdependencies of fin dimensions. Might a certain fin span only apply to be optimal when adjoint to a certain sweep angle? And the many instances of contradictions inside the rocketry literature (elliptical is optimal due to its induced drag working, but for low reynolds number rectangular/parallelograms are better).

I have been reading many different articles for my research purposes (such as articles posted on the apogee website, Stine's Handbook of model rocketry, Gregorek's TR11 report, countless rocketry forum threads and many other articles and presentations such as this. I am obviously interested in the subsonic regime, but there are still so many factors to take into account. It's almost like the more information I read, the less clear my head gets about an approach to my optimization problem (I guess that is why they say ignorance is a bliss).

P.S I found an article with a similar methodology to what I am aiming to accomplish (I will not be doing CFD, but their OpenRocket methodology aligns somewhat), yet I still don't understand how the interdependency of factors was adressed, nor how they reached some of their conclusions such as the optimal number of fins being three without testing, I am just taking a guess and assuming the rocket models they made ALWAYS had 3 fins, and therefore it was a controlled variable).

On another note, does anyone dispose of a copy/method of contact with Mr. Cipolla, who created FinSim. I was looking into using it for a possible section on flutter analysis in my research, but all copies have been taken down from the website and I have not found any way to contact the man himself.

As far as I know, programming Rocksim for wing shape optimization and considering nuanced interactions between different wing dimensions can be challenging to determine without direct access to the program's internal logic. While they do take nuances into account, the accuracy of this may be limited.

Regarding the method of optimizing one variable at a time, I also sometimes employ this approach. However, it can be effective in some cases but may not account for all possible interactions between different parameters. In the case of rocket wing optimization, changing one variable may affect other parameters such as stability and aerodynamic characteristics, so it's important to carefully analyze the results and make corrections during the optimization process.

I want to extend my gratitude and encourage everyone to keep exploring and sharing their knowledge and questions with the community.

thank you