(WK^2) Weight Moment of Inertia?
(WK^2) Weight Moment of Inertia?
(OP)
Trying to figure out the minimum HP required to accelerate a fan (blower) wheel. Nema publishes the Load Wk^2 values for motors at different RPM/HP. I have modelled the fan wheels in cad and have the inertial properties ie. mass moment of inertia in the axis of rotation (Iz). Is this the same? Thanks





RE: (WK^2) Weight Moment of Inertia?
As far as polar moments of inertia such as wr^2 and Iz, wr^2 does not include the g term so its units are pounds and inches. Iz should have the g term (it is based on mass instead of weight) so it will have sec^2 in the units. The only way to tell for sure is to look at the units. For acceleration calculations you need a moment of inertia that includes the g term.
Hope all this mumbo-jumbo makes sense.
RE: (WK^2) Weight Moment of Inertia?
RE: (WK^2) Weight Moment of Inertia?
Don't forget the aerodynamic drag if you connect the wheel to anything with wind resistance, it will become far more dominant than inertia as the speed increases.
RE: (WK^2) Weight Moment of Inertia?
RE: (WK^2) Weight Moment of Inertia?
kg m2
which would have the equivalent lbmass in2 in imperial units
For a cilinder
I = 1/2 M r2 or I = 1/8 M d2
where M = mass, r = radius and d = diameter
Oke things complicate when you have cavities like in impellers etc. These can be considered as composite entities with the cavities having negative mass. The total I is obtained summing all these positive and negative inertias.
It is obvious that when at the end you get a negative number, there is something wrong with your calculator
The Wk2 or Mk2 is used to compare an 8" fan with a mass M with an equivalent solid cylinder with mass M and equivalent radius k, which in this case will be much smaller then 8"