Can't imaging what size prop the 72 will actually turn...
Practical max on the 72 is 14". Practical max on the 91 is 15". The 40A is from another planet and it seems to make its own rules concerning props.
14" max on the 72 is a helluva lot of prop if you consider that a supercharged YS 175 can turn a max of 17x12. Again, I run my big block with APC 12x6-devastating.
Tony Naccaratto of Burbank,CA launched one of my ships for with the above combo, and after the flight commented that the ship accelerated like a rocket! That said, Windy Urtnowski made the Walker Cup flyoff at the Nats flying his 4 stroke powered Typhoon with a monster prop-16". I have video of his flights-looked good to me!!
Windy's own comments on his Saito 91 powered Hawker Typhoon: "Sorry, I don't have any photos,Saito 91,first 4 stroke ever in top 5 flyoff,first with ZTRON to taxi and have engine control in flight,CARBON FUSE,TANK,16 by 4.5 prop,BRODAK DOPE FINISH,CARBON COWL,this list could go on forever. Removable cockpit was another cool feature!!!!!!!!! Full take apart,Windy"