Mi26 Downwash Velocity
Could some kind soul please check my math? I need to calculate an approximate figure for downwash velocity for the Mi26 (!!)
So:
Following the law that Force = (Mass) x (Acceleration), rotor velocity can be expressed:
Downwash Velocity (ft/sec) = √Weight (lbs) ÷ 2 x (air density) x RotorDiskArea (sq. ft.)
In other words, the square root of: the weight of the helicopter divided by two, times Air Density (assume sea level), times Rotor Disk Area in square feet.
In this case, the parameters are:
Weight = 62,170 lbs (empty weight)
Air Density = .002378 slugs/feet cubed (assuming sea level)
Rotor Disk Area = 8,656.8 sq. ft.
Rotor Diameter = 105 ft.
So:
Downwash velocity = √31,085*.002378*8,656.8 = 799.944 feet/sec.
799.944 fps = 545.41 mph.
However, this is at the rotor. Since the air reaches it's greatest velocity 1.5 - 2 rotor diameters below the disk, thus the effective velocity at 210 feet below the rotor disc, the approximate downwash velocity is 1,090 mph.
Do I have this right??
Thank you so much in advance!!
Luca