How does one "scale up" a rocket. Let's say there's a 6" one that you really like and you want to scale it up to 12". Does everything get doubled like fin dimensions, nosecone length, etc? Or is there a trade secret about this that I don't know about?
Basically, yes. All dimensions (lengths, diameters, spans) scale up equally. Angles, however, do not change. So if your leading edge is
45 degrees, don't alter this, whether you scale up or down. It may seem like plain old common sense, but I've seen it happen....
Note that as the dimensions double, area is squared, and volume goes up with the CUBE. Weight usually tracks along with the volume, too, although this varies depending on what you employ in your construction. The practical upshot of this is that you may only upscale by 2X, but wind up needing to upscale the total impulse by a factor of 8, for performance approximating the original.
Yes. Absolutely. Interestingly enough, you could get as little as only the square of the scale factor using lightweight techniques, but I find myself going the other way and coming in at cubed or more :(
Another thing to keep in mind is that the relative CG can move, and move aft. Having built numerous upscales of the Estes Midget, I've seen how the aft end can accumulate mass much faster than the forward end resulting in the need for noseweight. So, while the CP should remain in the same relative position, keep an eye on the CG.
Everything the others have said is true. However, sometimes it isn't convient or possible to scale up or down certain things like fin thickness.
When I upscale an old Estes Goblin with 1/8" fins, I have to decide what flight profile I need. If it is to be a school demo/small field model, I can scale it up to ~2X with BT-80 tubing and the fin thickness will be
1/4". I use balsa fins to keep it kinda light, but the draggy fins give me a nice slow and super stable flying rocket where the kids get to see a lot of fire from the business end.
With a ~3X upscale, 4" dia. rocket, I'm looking at HPR motors. I don't really want fins that are almost a half inch thick on a three and a half foot tall rocket that flies on H-J motors, so I use some 1/8" or 3/16" aircraft ply in this case.
Dimensions scale just like you assume. In order to keep the rocket stable, you need to determine where the CG is on the original and keep it in the same scaled location on the upscale. If it is 5" from the nose on the original and your scale factor is 2x, the upscale rocket should have the CG 10" from the nose or forward of that to keep the same stability. You need to check stability with the engine installed in both cases.
You can use any dimension you want such as a fin length, etc, but I find upscaling is easiest by working off of the body tube sizes.
So if you had an Estes BT-60 rocket that you wanted to scale up to a 6" rocket, you would divide the 6" by 1.637" (BT-60). That works out to 3.66, or 366% upscale. Then just multiply bodytube length, fin dimensions, stripe sizes, or whatever else by 3.66 to get the sizes you need on the upscale version. Like others have already mentioned, it's not really practical to scale the fin thickness.
Not sure if it has been mentioned yet, but one *gotcha* with scaling (unless you make your own body tubes) is that doing a 2 to 1 up scale or a half scale can be very difficult as you typically won't find any body tubes that are twice or half the diameter of any *other* body tube. To pick your scale, you are better off deciding what body tube DIAMETER you want to go to. Then divide your body tube diameter by the diameter of the original rocket and use *that* number as your scale.
For example, if I had a BT-50 based rocket (.976" OD) and wanted to build it up-scale with a BT-60 (1.637" OD), I would to the math
1.637/.976 = 1.67772 or 167.72% up scale. Then use this number to multiply by all the other dimensions of the rocket to get your new design
That would be 266% upscale, or a 366% copy, i.e. a scaling factor of 3.66.
i.e. if you upscaled from BT-50 to BT-60 (0.976" to 1.637"), you'd be upscaling by 68%, or making a 168% copy.
If you're talking in terms of any increase equal or greater than 2X the original, it's clearer to forget the "%" completely and just talk in terms of scaling factor, i.e. a "2.5X copy".
-B. "dreaming about a BT-80 based Scissor-Wing Transport" -B.
There was a nice table of body diameter ratios in a mid 80s edition of the Leading Edge. This same table was rediscovered and included in "The Art of Scale Modelling" by Peter Alway, now out of print.
Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!
Dimensions are from the list of tubes on Sven's web site; Estes, Centuri, and Quest tubes. Any one have a more complete list with LOC, PML, AT, et al tube sizes, so I can make a more complete chart?
Scale modellers: Calculate the tube diameter ratio for the rocket you want to build. For example my Conestoga-1 (NARAM-25, the model that got me to make the table in the first place) had IIRC 38" and 44" diameters. That's a ratio of .864 or 1.159 depending on how you look at it. BT70/BT80 is 1.173 which was close enough for me.
Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!
On Mon, 22 Sep 2003 23:26:03 GMT, Jim Flis is alleged to have written:
Excellent advice, but I have one minor nit to pick: a scale factor of
1.67 indicates a 67% upscale, not a 167% upscale.
The copy's dimensions are 167% of the original size, which means that the copy has linear dimensions that are scaled up by 67% from the original (100%) size.
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