The use of large scale windtunnel models offers considerable advantages to an experimenter

• 1. the possibility of obtaining high Reynolds number, certainly significant and sometimes equal to that in flight, for moderate stagnation pressures

• 2. an accurate representation of geometric elements, i.e. good form similitude (it is necessary to emphasise the importance of being very thorough in this area)

• 3. large internal volumes which enable numerous transducers to be implanted, ambitious experimental devices and means of remote control of model motorisation

• 4. test conditions remain those corresponding to industrial manufacturing methods and so avoid problems related to extreme miniaturisation.

Additionally, there exist some test conditions for which scale reduction is limited or even impossible; for example, because of physical phenomena, limitation in industrial methods of miniaturisation, or quite simply because the subject is itself the flying object. These conditions are applicable to all tests whether industrial or research. They are especially true for industrial tests where these concern important decisions. They are also true for research tests whenever they need to be sufficiently close to flight reality. Wind-tunnels are always a means to reduce the costs and risks of aeronautical project developments. The risk taken in extrapolating from windtunnel tests to flight are lower when the test is more realistic and this gives a clear advantage to tests on large sized models.