In my youth I worked on the AST412 project at Brough. We started out with the the P164 - side by side (well if you ask JP QFIs what they would replace a JP with) high wing, and very short. Unusually a tunnel model was made and tested and the drag was pretty awful - even after they eventually corrected for the tares. About the only useful thing I learnt from it was the drag hole effect on the tailplane and the fin - it's fuselage drag was that bad.
Finally someone saw sense and some more elegant mini Hawks were drawn but never tested. From the outset we were trying to keep the speed up to avoid the transition to Hawk speeds being too much, hence the initial designs were jets. The economy of turboprops came to the fore and we then drew aircraft not unlike the PC-9.
The PC-9 and Tucano flew in for evaluation, the Tucano clearly displayed it's Piper origins and we realized it would need an awful lot of rework structurally and a bigger engine to get a useful level speed whereas the PC-9 sold itself by taking off in about the length of the piano keys and went straight into a vertical 8.
We even had help. Looking at the fatigue requirements we wondered what sort of loadings occurred in tail chases. A quick call to a nearby base and our PC-9 met up with a JP and flew a full sortie tail chasing, performed half an hour of aerobatics over the airfield whilst the JP landed and refueled and then a second sortie with the gloves off.
When the winner was announced we were all stunned.
A couple of years later we hosted 20 Saudi PC-9s for training and delivery (they let us stick the transfers on them) that went and beat up a Tucano-less Scampton on the day they were handed over.
I know t' Baron and his minions come in for a lot of stick but some of us really wanted our Armed Forces to have the best kit bought in or even designed by ourselves.
Silly us.