Fin replacement question

[johnnyrockets]

Hi all,

The question I'm about to ask seems either a super simple "yes" or an emphatic "no way", with little room in between. Admittedly this is a newbie question, as I am a newbie for sure.

But here goes...

I just purchased the Custom Rockets Elite "Egg Launcher" type rocket kit. I don't like the looks of the fins. Can I put larger more traditional ones on it without destabilizing it?


Thank you!


JR

 

[Nytrunner]

Larger fins probably won't destabilize it. I highly recommend doing some design calculations or making a simulation of the model in Openrocket

Considerations:
-there should probably be some fin area out in the free air past the diameter of the wide payload
-fins that are too big will shift the CG backwards

 

[kuririn]

To make things easier, there's a Rocksim file of the Custom Elite you can download here:
https://www.rocketreviews.com/unknown-custom-elite-10025.html
You need to download, install and run Open Rocket.
OR reads both Rocksim (rkt) and OR (ork) files.
You can change the shape and size of the fins and see how that affects degree of stability (calibers) and changes in the centers of pressure and gravity.
BTW the elliptical shape of the Elite is the most efficient fin shape, it allows for maximum apogee. Which is what you want in egg lofting competition (higher apogee = maximum duration). However if you are flying for sport/recreation, then do what pleases you most aesthetically.
Have fun!

 

[johnnyrockets]

Okay, thanks guys! One more question (for the moment!). Where can I get Open Rocket? And I will DEFINITELY check out "rocketreviews", sounds great!

Thanks for the tip on the Apogee, I will keep the fins as is.

JR

 

[ewomack]

Open Rocket link: https://openrocket.info/

 

[Nytrunner]

Go to the sticky in the electronics and software forum. Neil's compiler executables are the best

 

[stevemco]

Increasing the semi-span (width) usually makes things more stable but I would recommend using Rocksim or OpenRocket to be sure

 

[dpower]

A qualified "Yes". Any modification that does NOT decrease span (what Steve said), and does NOT move the fins farther forward should be fine (in other words, any change that doesn't move the CP forward or the CG aft). There are other ways to determine stability than OpenRocket or Rocksim, search around here for swing-test and cardboard-cutout methods (or read about them in the "Handbook of Model Rocketry". With experience, just looking at a design can tell you a lot about it's stability. While I use Rocksim for most of my high power flights, I often just eyeball my low power designs.