Oper Rocket fin help

bobby_hamill · Dec 1, 2016

I am trying to sim an upscale version of the Maxi Icarus to a 4 inch airframe

everything is going ok till I hit the fins . I import a fin shape into free form fin option

the original fin root of the Maxi Icarus is 5.6724" the upscale fin root is 13.8106"

I drew the fin in solidworks as an up scaled drawing and exported it as a jpeg file

when I first import the fin form and use the scale command it shows scale from 10.315 to 10.315

when I try to scale from 10.315 to 13.8106 the fin in the open rocket gets even bigger

you can see the before and after in the 2 attached files

Thanks for any help !

K'Tesh · Dec 1, 2016

look for my tutorial on using OpenRocket. I am not on my computer so I can't post the link.
On the left side of the scaling window, you have the current size, you want to change the right side to the desired size .

bobby_hamill · Dec 1, 2016

I have been using the helpful articles and have saved a bunch of them .
After 4 hours and some hair pulling ( not that I have much left ) I called it a night and will start fresh in the morning

dhbarr · Dec 1, 2016

I'm no expert, but moving the slider down from 100% down to 50% on the initial import seems like it may achieve what you want?

bobby_hamill · Dec 1, 2016

if I scale down to 50% that will result in fin root of 5.115 I need a fin root of 13.8106

K'Tesh · Dec 1, 2016

Bobby, your comment makes be believe that you didn't realize the "Scale Fin" box, is actually a button. Personally, I hate the slider, except for gross rescales, it lacks the sensitivity that I desire.

Please note that the Centuri Zebra II Payloader's fins are actually smaller than what you see here, these fins are place holders until I can find a measured image of the fins.

MikeyDSlagle · Dec 4, 2016

Looks to me like you are doing everything right. Just using a ratio of BT diameter to fin root chord, looks like it is spot on. They just look big.

Do you have a file for the original Maxi Icarus?

K'Tesh · Dec 4, 2016

MikeyDSlagle said:
Looks to me like you are doing everything right. Just using a ratio of BT diameter to fin root chord, looks like it is spot on. They just look big.

Do you have a file for the original Maxi Icarus?

I do... Yes. And seeing how Bobby posted something about the design in my .ork thread, I suspect he has too.

BTW, I never got a measured scan of the Maxi Icarus' decals (one w/a ruler in the scan), or a confirmed measurement of a part of them to be certain mine was scaled properly. So I didn't post the .ork file for the decaled version, and lost it w/the hard drive crash in September.

MikeyDSlagle · Dec 4, 2016

I was only asking because it is easier to scale the entire rocket than it is to build a scaled up version minus the fins in OR then use a separate program to draw fins, then import and scale those.
Just scale the entire rocket. Or drag the fins from the original onto the upscale version and then scale them, "from" will be 5.6724" and "to" would be 13.8106".
Maybe I am missing something but it really should be that easy. I'm not understanding the use of a separate program to draw the fins.
On a side not. Internet at my house is down, so I am on my phone. I have limited capabilities, OR not one of them.
Mikey D

K'Tesh · Dec 4, 2016

MikeyDSlagle said:
I was only asking because it is easier to scale the entire rocket than it is to build a scaled up version minus the fins in OR then use a separate program to draw fins, then import and scale those.
Just scale the entire rocket. Or drag the fins from the original onto the upscale version and then scale them, "from" will be 5.6724" and "to" would be 13.8106".
Maybe I am missing something but it really should be that easy. I'm not understanding the use of a separate program to draw the fins.
On a side not. Internet at my house is down, so I am on my phone. I have limited capabilities, OR not one of them.
Mikey D

I agree, scaling the entire rocket from a reliable file, then adjusting the details for the new scale (such as inner diameters, thicknesses of centering rings and fins, etc...) would be easier than starting fresh.

Oh, and I'm working on a decaled version of the .ork file again. I realized that the wrap should be the diameter of the rocket multiplied by Pi, and that should be close enough for my sim.

Oper Rocket fin help

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