The Beecraft Model 18 or 'Twin Beech' was in continuous production from 1937 to 1969 in a huge variety of configurations for both civialian and military (transport) use. A specialised advanced military trainer, the AT-11 Kansan (or Kansas) was also produced. This model is representative of the military transport (C-45) series from WW2 but many of the civilian versions differed only in detail.
The spherical depression under the model is for mounting it on a 6mm BB.