Naye ;

One can whittle , thin , repitch and coustomise Timber Propellors . Off Olde , Ye Masters
would endevour to produce pitch varyation in flight , under load . To increase performance .
The idea being they fine off under load to haul the coal up the mountain .
You generally look for one with symetrical grain . And if you must mess with them , Trimming down & thinning
a oversize one , means theres something left when youve finished .
