Teros or weather vane?

The Rocketry Forum

Help Support The Rocketry Forum:

tktmsa

Member
Joined
Apr 2, 2010
Messages
6
Reaction score
0
Thought I had a good eyeball for scale on the fins - maybe not.
How do you guys upscale a rockets fins?
20170627_163715 (1).jpg
 

Rex R

LV2
Joined
Apr 21, 2010
Messages
6,101
Reaction score
147
I've had some issues with upsizing LPR rockets where the fins turn out HUGE. is this the case here? usually lpr birds have oversize fins t start with simply to ensure stability. for a scale model I would check to see what the actual fin size is and scale that down to match the model's scale. for a non-scale rocket such as the Estes Goblin, I would scale the rocket up to whatever tube size I wanted (a 3" dia. tube is 234% upscale) then scale the fins down to 75 - 90% of the upscale version(so they are not as large).
Rex
 

neil_w

Ennui poster child
TRF Supporter
Joined
Jul 14, 2015
Messages
11,835
Reaction score
4,648
Location
Northern NJ
I suspect most (?) do it in OR or Rocksim. They'll do the scaling for you. Certainly, if it would make sense to subsequently scale the fins down (as Rex suggest), you can do that in there as well.
 

tktmsa

Member
Joined
Apr 2, 2010
Messages
6
Reaction score
0
Just starting to use OR, I'll dig deeper into it. Where is the feature where I post the nose cone and it builds a rocket around it? Ha!
 

Nytrunner

Pop lugs, not drugs
TRF Supporter
Joined
Oct 15, 2016
Messages
7,943
Reaction score
3,625
Location
Huntsville AL
For upscale/downscale brainstorms, I usually make a list of the relevant dimensions in excel and multiply the column by the scale factor.

I have heard of OpenRocket's scale feature, but I've never remembered to use it.

If you generate your nosecone, any body tube/couplers will be scaled to its diameter. Same for tubes after a transition. When you choose your motor mount size, centering rings will automatically conform to the space between airframe and motor tube. That just leaves the fins.
 

Micromeister

Micro Craftman/ClusterNut
TRF Lifetime Supporter
TRF Supporter
Joined
Jan 19, 2009
Messages
15,074
Reaction score
47
Location
Washington DC
Scale Factor is needed to determine material and part size differences. It's no more then a simple math problem.

If you have a model based on say BT-20 (.736"OD) and you want to Up-scale it to BT-60 (1.637" OD) divide the Up-scale diameter by the base model diameter to get the Scale Factor in this case 1.637 - .736 = 2.224 scale factor. You can now Up-Scale all the remaining dimensions of the model (except Angles which remain the same) to build you larger creation. example: Base model Fin Root edge @ 1.5" x 2.224 = Upscale fin Root @ 3.336"

To Down-Scale the same BT-20 (.736") model to say T3 (.375") body, you'll use the same process to find the scale factor .736 - .375 = 1.963 Scale factor. but you'll reverse the process to find the multiplier .375 div by .736 = .5095108. Base model fin root 1.5" x .5095108 = .7643" Down-Scale Fin Root.

Computers are great but we should also know how to work the problems manually. Helps to keep the grey matter a little sharper:)
 
Last edited:

tktmsa

Member
Joined
Apr 2, 2010
Messages
6
Reaction score
0
Yeah the nose and tubes are easy math, getting an original pattern/ measurement on the fins is where it went awry.
 
Top