Combines Effect of going to a larger cross flow cylinder and cage

You're missing the point. Greater tip speed does increase separation force. However, a smaller rotor also creates greater centrifugal force. If a 30" rotor and 40" rotor each had the same tip speed, the 30" rotor will have greater separation force, using less power to achieve. The 40" rotor at the same tip speed runs the risk of causing more grain and straw damage because the grain is flowing at greater velocity (feet per second) caused by the rotor speed and its dimensions. It is also taking more horsepower for that 40" rotor to equal the same tip speed as the 30" rotor. The differences in power used between these two rotors to achieve the same tip speed is huge related to the other horsepower requirments on the combine. Therefore, two smaller rotors will be far more effective in providing early and more effective separation. Two 17.5" rotors will take far less power to operate than one large 40", as well as there will be muxh more separation area with the twin rotors too.

Please calculate tip speed for the 30" and 40" rotor.

I'm with you guys here. Torque on gearbox output shaft, gear, coupling, and related parts will all go up with larger rotor if consuming same HP. Now let's think about what consumes power other than what it takes to spin rotor empty. Wouldn't that be the resistance of straw to flow along the stationary surfaces. Design of stationary surfaces and design of rotor elements dictate how well the crop flows. The faster you flow the crop around a circle the more centrifical force. Yes you will have more centrifical force in a 15" cage as a 27" cage with the straw moving the same feet per minute but who knows what would be to large or small. Straw doesn't flow near the speed of the rotor so a guy would need to figure the speed of straw in whatever size rotor to somehow figure the centrifical force on seeds. I can see a couple things on a larger rotor that would reduce power requirements. One is larger circle which will allow straw to flow easier. Another is less pitch on helicals to move crop same distance toward discharge. Myself I think Gleaner could easily go to larger rotor with minimum changes but tweaking the feeders like we do is first. With the cylinder options available lately I don't think the cage diameter or length is used up anyway so we'll see.

Some good discussions on threshing, centrifugal force Fc, and torque. Eventually, rotating the cage in the same direction as the rotor will result in crop mat speed plus cage speed creating exponentially more Fc while reducing grain damage from bounce back between rasp bars and cage bars. Varying the speed of the cage rpm also creates the effect of dynamic vane angles and the effect of variable concave hole openings. With a slight increase in cage speed in the same direction of the rotor speed, the effect is longer exposure to the hole as grain moves by while also increasing centrifugal force. The theories of the Bi-Rotor might then be proven successful. Seems like the R series Gleaner would also be a good candidate for a rotating concave with its existing 360 degree open cage.