Scale Factor ?

[Rocketclar]

Are there any 'rules of thumb' for scale factors on BG? I built a "Flying Jenny" years ago from plans out of a 1964 Model Rocket News article. Over the years it flew 52 times (with minor repairs on A and B motors before finally blowing itself apart. It was well trimmed and always flew nice lazy circles. My ? is if I want to scale this up to "D" power, any advice on a scale factor or is it just trial and error? I assume I'd want the same sort of CP to CG ratio. Other thoughts? THX!

 

[BABAR]

Squirrel Works makes an 18 mm and a 24 mm version of the Red Baron, which is pretty darn close to the Jenny

dimensions are on the site
Hope this helps

18 mm A and B

https://www.squirrel-works.com/catalog/baron/RedBaron.html

24 mm D and E

https://www.squirrel-works.com/catalog/megabaron/megabaron.html

 

[kuririn]

If you want to do an exact upscale, then find the ratio of a bt50 tube to a bt20:
bt50 = .976" OD
bt20 = .736" OD
.976/.736 = 1.33x
This is your scale factor.
Plans are here: https://www.spacemodeling.org/jimz/eirp_21.htm
Enlarge the templates by 133% on a scanner. Don't forget to lengthen the motor tube as well.
Here's a nose cone for a bt50 that is close in shape to the bnc-20A: https://www.erockets.biz/dr-zooch-balsa-nose-cone-falcon-heavy-for-bt50-drz-bnc-50fh/
Since it's the same design, only upscaled, the RELATIVE CP should remain the same. CG will depend on build technique and materials. Adjust trim and CG with clay or lead weight.
Build, trim, and launch.
Let us know how it turns out.
Cheers.

PS I should add if you're feeling REALLY adventurous try a 2X upscale. The Squirrel Works Mega Baron that Babar references is more than twice the size of it's smaller counterpart. Of course, simming with a program is a good idea before any building.
A 2X Mega Jenny would have a wingspan of approx. 17", close to the Mega Baron. Yowzers.

 

[Rocketclar]

Thanks much!

 

[JohnCoker]

You might find this helpful:
Upscale Calculator

 

[Ez2cDave]

Here is the "Flying Jenny" . . . https://www.rocketreviews.com/plans---estes-industries-flying-jenny-mike-salter.html

PDF's below.

Dave F.