Originally Posted by
Crash one
I have heard of the Reynolds number but no one has explained how to apply it.
So building a model just by scaling it down isn't going to work.
Anyway how can you scale the density of air? Depressurise the test flight building?
That is exactly what we used to do when I worked in high speed wind tunnel testing back in the early 90s. It was a very slow and expensive process.
The use of non-dimensional variables exists throughout engineering analysis, and there are all sorts of variables in various applications. The two most pilots are likely to familiar with are Cl and Cd; Reynolds Number is another, mainly used for matching wind tunnel results to full scale flight results - particularly the Cl.v.AoA and Cd.o.v.AoA curves are likely to be a function of Re, although don't change much (usually) within an order of magnitude change. Two orders, and it starts to become quite important.
The formulae for gust response are a function of lift curve slope and wing loading. Lift curve slope in turn is a function of Reynolds Number (and Mach Number, another nondimensional variable of-course).
G