# What is the rule of thumb when upscaling a model rocket?

### Help Support The Rocketry Forum:

Hello,

I am going to upscale a Custom Serin to a BT60 sized model rocket. I can't find the exact upscaled sized BT60 nose cone. Sould I make sure the total length is upscaled exactly to the BT60 size or should I upscale the body tube lengths and have the total length be off slightly?

Brian

#### jflis

##### Well-Known Member
IF at all possible, see about getting the correct nose cone. Use the "body tube lengthening" as a last resort (personal opinion )

As for your topic question: "What is the rule of thumb when upscalig a model rocket?", the answer is "go for it!"

#### hokkyokusei

##### Well-Known Member
I agree with Jim!

#### Fore Check

##### Well-Known Member
The rule of thumb?

Bigger = Better

Clusters = Cool

#### lalligood

##### Well-Known Member
Right off my head there are a couple of resources where you can get help finding the right size nose cone...(in no particular order)

* Our very own Sandman. PM/email him specs of what you need.
* Balsa Machining Service (https://www.balsamachining.com/)

I'm sure other folks will chime in with more places to look! Good luck

HTH,

#### Fore Check

##### Well-Known Member
Ok, I'd say this will work.

The Custom Serin has an ogive cone that is 2.625" long above the shoulder. Upscaled to a BT60, you'd need a cone that is 4.40" long above the shoulder.

The Estes Stormcaster is Bt60 based and uses an ogive cone that is 4.75" long. Personally, I'd call our friend at Estes and tell her you need a replacement Sormcaster nose cone. She'll hook you up!

(I'm looking at my Stormcaster cone next to my Custom Raven cone - which is the same cone as the Serin - and they look like a *great* match.)

Then I'd just upscale the tube. The way I figure it, you've got a net 11.75" of airframe tube on the Serin. This works up to 19.70" of airframe on a BT60. Just to make it easy to measure, I'd go with 19.5" on the airframe.

Having built a number of upscales, I truly believe that no one would ever notice the minor differences there unless you told them. I wouldn't make that recommendation if your were upscaling a "scale" rocket, however.

Good luck!

#### sandman

##### Well-Known Member
I love upscaling...AND downscaling even better.

Here is what I do:

https://www.ninfinger.org/~sven/rockets/body_tubes.html

Print it out and keep it handy (I have a copy on my workbench and a few "extra" copies at my computer).

Also go to Totally Tubular's site.

Download and print out those pages too. Totally tubular has some handy odd sizes that are useful...especially for scale projects.

Now take the size of the body tube you want to use...BT-60 is 1.637" and divide it by the original size (I think the Serin is a BT-50 or .976.")

The results (in this case it's 1.67725...) is your multiplier.

Multiply all the existing dimension by this number and you're all set.

If you want to "blow-up" the plans or fin patterns just go to a copy machine and enlarge it by the 1.677 factor or 168%.

Easy.

sandman

Thanks for all the input.

Fore Check,
I have an extra StormCaster nose cone and that was the one that I was thinking about using. You must have read my mind.

Brian

#### Fore Check

##### Well-Known Member
Originally posted by bswan72
Thanks for all the input.

Fore Check,
I have an extra StormCaster nose cone and that was the one that I was thinking about using. You must have read my mind.

Brian

This brings up a different angle to your "rule of thumb" question, IMO.

When you're upscaling one of your favorite rockets, just go for it and get reasonably close on your dimensions.

When your scale factor is in the 1.6x or larger, no one will notice the odd 0.5" on a body tube here and there. Likewise, if the design calls for multiple diameter tubes, you can get away with fudging the odd 0.2" or so on the OD if need be. Really, no one will notice. It will be so cool anyway.

#### Bill

##### Well-Known Member
Originally posted by Fore Check
The Custom Serin has an ogive cone that is 2.625" long above the shoulder. Upscaled to a BT60, you'd need a cone that is 4.40" long above the shoulder.

Congratulations, you have all just stumbled upon that magical 1.67 factor for upscaling. I accidentally did so by noticing the likeness between the Squirrel Works JX-1 and the Screamin' Mimi. A little calculation showed me that if I upscaled the BT-50 of the JX-1 to the BT-60 of the Mimi, the BT-5 upscales to a T-.908" (Centuri ST-8 equivalent) available from Totally Tubular or BMS.

Since then, I have done calculations for other common Estes tubes and created this amazing little table:

Code:
original tube	upscale tube

BT-5		T-.908" (ST-8)
BT-20		T-52H (29mm motor mount tube)
BT-50		BT-60
BT-55		BT-70
For this reason, I bought quite a few of the T-.908" tubes from Bill of BMS at NARAM when nobody else appeared to be interested in this "odd" size.

There are no common tubes to use as the upscaled equivalents of BT-60 (2.73"), BT-70 (3.71" BT-100???) or BT-80 (4.34"), but fortunately, there are many designs to upscale with the tubes which are available.

Bill -so much to build, so little time

#### powderburner

##### Well-Known Member
Here on TRF, I think the rule is:

POST PICTURES!