Here you go GMan, an honest to goodness experimental data containing article that looks at power needed to generate rotation and VACUUM in a commercial flail mower. You might have fun working out the calculations to double check theirs.
GMan, found an article for you with real live experimental data to determine power needed to generate both rotation and vacuum with a flail mower. Get out your calculator to check their math.
Note that while this article (PDF link below) is in reference to a commercial flail, the drawings indicate they are using the typical Y style blades not the scoop blades. And, all kidding aside, virtually ANY blade and mount will generate rotation of air when spinning at 60-90 mph.
a model for determining the power in kW at the PTO:
(SORRY TBN cut and paste didn't include the elegant equation but you can see it in the article here:
http://www.scielo.cl/pdf/ciagr/v36n1/art05.pdf)
where, n is the total number of cutting blades, p the air density (p = 1,225 kgキm-3), Fa the surface facing the air during the cutting blades' move-ment (m2), Cx the non-dimensional coefficient of air resistance that includes the effects of the cutting blade shape (Cx = 0,1.. .1), R the radius of the extreme cutting blades (m), r the ratio of the cutting apparatus of the shredder (m), ωthe angular speed of the cutting apparatus (rad-s-1), Y the mass of remnants in humid base (kgキm-2), B the width of machine work (m), V the shredder's work speed (mキs-1), M? the moment of the friction force in the supports (Nm), ns the number of cutting blades cutting the stemキssimultaneously, ε the work consumed for cutting per area unit (Jキm-2), bc the projection in the horizontal plane of the cut width of a cutting blade (m), k the relationship between the actual cutting area and the working area, Rh the distance from the rotor's cutting zone (m), and η PTO PTO the efficiency of the transmission from the tractor's PTO to the cutting mechanism of the shredder.
The equation that determines the power needed to overcome the opposing forces during the vacuum work (air resistance and friction in the supports of the cut mechanism) and the power needed to make the technological process (cutting and spreading of the shredded material) can be stated as:
(SEE PDF for equation)
where a, c, b and d are coefficients related to the power losses by air resistance, spread of shredded material, and the moment of the friction force in the supports and cut, respectively.
Have fun!:thumbsup: