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Aeronautical Engineering/Scale model similarity to actual aircraft

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Question
It has been said many times that model aircraft, if built to the same shape as a real aircraft they represent, display similar characteristics.

For example a model glider with high aspect ration wings will glide slowly without losing much height, just like real gliders.

Similarly a 1/20 or so scale model of a Mirage III will not glide very well, however will be capable of a high rate of roll, and possibly be able to operate at high angles of attack ( given the unrealistically high power developed by scale  model engines such as electric ducted fans)

My question is this - for small gliders of 1/30 scale or 1/20 scale and for larger 1/10 or 1/5 scale flying models of aircraft, to what extent can the builder get an impression of the characteristics of the actual aircraft by building and flying the model? Admittedly weight distribution, position of CG, power, these are all important. Suppose the builder paid careful attention to these?

Please see these aircraft:

http://www.modelairplanenews.com/blog/2010/12/21/2010-u-s-scale-masters-champion

For example :

- Rate of roll - response to ailerons
- Rate of pitch - response to elevators
- Acceleration - (scale power)
- Turn rates
- Hands-off stability
- Loop radius
- Minimum speed (with and without flaps, gear)
- Maximum altitude reached in a zoom climb from maximum (scale) level speed

It would seem that the ultimate in scale modelling would be achieved if, in addition to the faultless appearance and details, scale flight could be achieved as well.

Answer
We routinely use models in aerodynamics to test concepts prior to prototype development.  There are scaling laws that enable us to relate the model results to those of the full scale prototype.  Basically we work with non-dimensional parameters in our testing and data collection thus enabling the data to be used at other scales...

The scaling laws require that we maintain dynamic similarity which is a combination of geometric similarity (i.e. a perfectly scaled model) along with kinematic similarity (i.e. the flow streamlines must also match between the model and the prototype)

Look up Buckingham Pi Theory and/or dimensional similitude for more details..

Thanx,
mj

Aeronautical Engineering

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