Designing Asymetric Fins in OpenRocket

[Screaminhelo]

I have been doing some design studies in OR just to see how different elements affect rocket flight and I have hit a bit of a stumbling block for certain asymmetric designs. I am trying to sim an asymmetric design similar to the Aerospace One with a wing mounted on a tangent to the BT and I have been unable to figure out way to get the wing where I want it to be. I have tried searching the forums for information but I have not had much success ( could be my fault). I have also had poor results on the web.

One thought that I had was to just have the "wings" mount at a more conventional location to approximate their area. This would account for the fin area relative to length but there could be factors that this arrangement does not account for that may have a significant effect on stability. I just don't have enough experience to be sure.

How do y'all sim unconventional designs in OR?

 

[Sampo]

Hi,

OR supports only radial fins. If I were designing a rocket with a "wing" tangent with the body tube, I'd simulate it as regular fins, but with the height reduced by 3/4 - 1 times the body radius, because the body "shadows" part of the wing. This should give a conservative estimate for the CP.

Cheers,
Sampo N.

 

[Vaportrail]

Hello,
This is a place I've spent some time trying to "fool" OR. I have done my best to run simulations of Bomarc with relative success. I just make the wings as if they were fins with the actual area minus the body tube. The CP generated this way on OR has always been further AFT than a cardboard cut-out has shone it. So, I balance more towards the cardboard and they fly well. The rockets turn out real heavy but fly exactly as OR says once true CG and weight overall has been measured and imputed. I think the ramjet pods on that design hinder CP calculations more than wings.

 

[Tiger]

I ran into this problem earlier today myself. Also it doesn't seem to support tubes as fins. But overall, it's still an impressive piece of software!

 

[Screaminhelo]

I ran into this problem earlier today myself. Also it doesn't seem to support tubes as fins. But overall, it's still an impressive piece of software!

Tiger, if you look in the wiki pages you will find info on how to sim tube fins. Here is the link: Tube Fins in OR The wiki is not complete but I have found some useful ideas there, it is a worth while reference.

I'd simulate it as regular fins, but with the height reduced by 3/4 - 1 times the body radius, because the body "shadows" part of the wing. This should give a conservative estimate for the CP.

Thanks Sampo, I hadn't considered reducing the fin area when representing the wings with standard placement.

 

[Screaminhelo]

Here is the concept that I started with


And here is the OR file showing how I set everything up. I am not sure if I was successful in representing the intakes, it looks kind of wonky with all of those fins now. Any thoughts on this? Am I heading in the right direction?
View attachment My_Shrox_Intakes.ork

 

[Tiger]

Thanks for that link! Some helpful info indeed, although I have another issues that prevent this build I'm tinkering on from simming properly.

Those intakes look cool, although at 0 and 20 deg they look lopsided to me. I think they looked better at -10 and 10 deg.

 

[Screaminhelo]

Right now, I am just working on getting everything represented in the simulation. It appears that designing this in OR will require quite a few compromises so I am also mocking it with wrapping paper tube and cereal boxes for a real life comparison.