If you can get a hold of "Engineering Fluid Mechanics" Prof I Clayton (Hodder and Stoughton 93) from a Library there is a small chapter on Renolds number which explains it in simple terms. Although it is only really used by Mechanical, Marine and Aerodynamic Engineers as a fudge factor it is extreamly useful in design.
This is because models do not function in scale with there proportions. ie a one fifth scale model in a wind tunnel should be exposed to an fluid flow less than one fifth of the original vehicle. speed of a/c = 100m/s in the wind tunnel the model ought to be subjected to less than 20m/s. (factor Rennolds number in here ie 20 times renolds number = correct m/s. This is from memory when working at Rolls and Bae during my summer holidays at Uni.
I don't really think it ought to be on a syllabus for Pilots..
Renolds is used because molecoles are relativly bigger to a model than the real thing and therefore they are 'sticker' ie less boundary layer for flow separation to occur. Molecules are effectivly bigger and do not flow as easily around a body.
hope this helps
Incidentaly is there any thermodynamics in the new JAR syllabus?
[This message has been edited by G-OOFY (edited 10 September 2000).]