Quantcast

What does "semiscale" mean?

The Rocketry Forum

Help Support The Rocketry Forum:

lcorinth

Well-Known Member
Joined
Aug 5, 2014
Messages
1,008
Reaction score
32
Just kinda looks a little like the real thing?
My understanding of semiscale is that the dimensions are pretty close, but not exact. I think usually this is because of stability. The fins (if they exist) on the real thing may not be sufficient for stability on the flying model, so the fins on the semiscale model are slightly larger than scale, or the rocket may be slightly longer. So, it mostly looks like the real thing, unless you scrutinize it closely.
 

rstaff3

Oddroc-eteer
Joined
Jan 18, 2009
Messages
11,765
Reaction score
13
My understanding of semiscale is that the dimensions are pretty close, but not exact. I think usually this is because of stability. The fins (if they exist) on the real thing may not be sufficient for stability on the flying model, so the fins on the semiscale model are slightly larger than scale, or the rocket may be slightly longer. So, it mostly looks like the real thing, unless you scrutinize it closely.
That's my understanding too. Other examples may be: When the rocket used multiple tube diameters, the overall dimensions may be set by one, but the other(s) may be off so that standard tube diameters can be used; the nose cone is off because you wanted to use a plastic one vs turning your own; or, you are lazy like me.
 

K'Tesh

OpenRocket Chuck Norris
TRF Supporter
Joined
Mar 27, 2013
Messages
14,395
Reaction score
1,004
In addition to the other reasons cited above, there is also the chance that the shape of the nosecone isn't 100% accurate. Making molds (injection or blow molded) isn't exactly cheap when it comes to mass production. A stock nosecone may be close to the shape but scaled up would be several inches taller, shorter, or maybe with a different curvature.

Also, the manufacturer may not be able to get accurate specs on the rocket being modeled. I'm thinking primarily of the Scud B missile here.
 

watermelonman

Well-Known Member
Joined
Sep 22, 2014
Messages
2,597
Reaction score
7
How many IQSY Tomahawk kits include the sheeting for the fin can, and not a sticker or even nothing? How many Nike Smoke kits have properly bevelled fins or the nose spigot?

To me, all of that is what makes up semi scale or sport scale. Tube sizes or nose shapes being off a little are great places to compromise too.
 

fyrwrxz

latest photo
Joined
Jun 6, 2011
Messages
6,575
Reaction score
45
Sing it with me: 'Some of these parts are not like the others, some of these parts do not belong..." LOL!
( I would have loved to see launch lugs on the Saturn V! )
 

Incongruent

Well-Known Member
Joined
Oct 25, 2016
Messages
1,735
Reaction score
5
My understanding is that it's (as stated above) a model based off an actual item but slightly different due to material limitations, stability, weight, motor availability, etc.

In my experience, it can also be an actual scale model you got lazy/ messed up on.

I also seem to recall that scale models are actually measured (to 1/2 mm) but sport scale models are judged from looks (maybe a photo.) Both are judged on craftsmanship and flight.

Maybe that's Sport Scale though. Are they the same thing?
 

kjohnson

mox nix
Joined
Jan 19, 2009
Messages
1,300
Reaction score
4
Sport scale models from a competition standpoint have to have a high similarity of outline to the real thing, but aren't measured for accuracy.
 

dr wogz

Fly caster
Joined
Feb 5, 2009
Messages
5,681
Reaction score
917
Location
Land of Poutine!
You'll see this more with R/C airplanes; Sport Scale / Semi scale. Mainly due to the the fact that a plane is designed for that size, weight, wing load, airfoil, power, etc etc... Making a true "Scale" P-51 (or P-38 or TA-152 or ..) will be a bear to fly due to many aspects mentioned being too small, or too large, or the wrong proportions, etc..

Best to say the design is "based off" the original, hence 'semi scale / sport scale..
 

OverTheTop

Well-Known Member
TRF Supporter
Joined
Jul 10, 2007
Messages
4,350
Reaction score
1,575
Location
Melbourne Australia
Just scaling aircraft changes the Reynolds number (dependent on lengths) and can really mess with the aerodynamics and handling qualities. These are often improved by subtle variation of the design.
 

Micromeister

Micro Craftman/ClusterNut
TRF Lifetime Supporter
TRF Supporter
Joined
Jan 19, 2009
Messages
15,074
Reaction score
41
Location
Washington DC
Sport scale models from a competition standpoint have to have a high similarity of outline to the real thing, but aren't measured for accuracy.
Ditto Kevins Post:
Sport Scale (Semi-Scale Models) are judged for Similarity of outline from a minimum of 3feet away. Where as Scale models are actually measured compared to a minimum of 5 scaled dimensions compared to the prototypes actual dimensions.

Most Manufacturers do NOT product true scale models. They can sometimes be a good starting point, but like the Estes Bull-pup are Way far away from actual Scale in both outline and configuration. Did you know that boattail on all Bull-pup varients except the practice rounds are two piece clamshell surrounding 2 exhaust nozzles not a cone at all?

Both Estes, Centuri & Apogee's Saturn-V's are a lot closer to Scale but again there are Lots of varients that are not addressed so the "KIT" is Semi-Scale" to start.

Most Plastic models are closer to being scale out of the Box, but with all the varients of the prototype cannot be accurate to all varient so they too are "semi-scale" to start.

To produce True Scale Models, one must Choose a "Specific Round" prototype with at least 2 very good view photos of the actual vehicle, modeling to that vehicle only using dimensions from that vehicle or if mass produced from "typical" dimension values listed by the vehicle manufacturer.

MM 276a1-sm_AGM-12b Bullpup A 26.9149_02-10-04.jpg


Tiamat-01_Fullview-Vehicle-(right)-08-95.jpg


MM 422_Tiamat-JB-3 & Booster(Clustered-2-Stage)_09-02-16.jpg


MM-422a03_Tiamat & Booster- 23.5765 Scale(RearView)_09-02-2016.jpg
 
Last edited:
Top