For example, doing wind tunnel tests on scale model planes. Assuming that there are no significant differences between the scale model of a plane and the actual fully built plane, will the aerodynamics be the same, but just scaled up?
In: Engineering
Kinda. There’s scaling factors.
Most notably, the viscosity of air is a set value at standard conditions. So if your model is 1/10th scale, the viscosity of air isn’t 1/10th (or whatever) which means that there could be some differences in performance (this is called the Reynolds number)
Other notable differences include the effects of the tunnel walls on vortex formations, a lack of engines and internal airflow being modeled (usually), and aero elastic effects not scaling identically (so as the wing flexes under air loads, the aerodynamics of it change, and then the air loads change, and this coupled behavior is very hard to predict with either wind tunnels or with computational models, since a scale model won’t have the same stiffness and resonant frequencies as full scale).
So it’s not an exact science but it can get you decently far along.
There are various conflicting factors when scaling size, velocity, media, etc. This applies for boat models, whether ordinary surface ships, or submarines. Also for aircraft, especially at speeds near Mach 1. You will encounter the terms Froude Number, Reynolds Number, Mach Number, and a few others.
Reynolds Number relates the viscous and inertial forces of the medium (air, water).
Froude Number is about the wake/wave making aspect of surface ships.
Mach Number is about the relation of a a model’s speed to the speed of sound in the medium.
Generally, the problem is that It is not possible to have the same “Numbers” both at full-size and at scale-size..
I highly recommend the book “On Size And Life” by McMahon and Bonner, from the Scientific American Library collection. It is very accessible to the layperson.
Latest Answers