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2 years ago in Mechanical By Aamir

We need to calculate wind loading torque on a rotating parabolic dish for a servo motor specification. What are the key aerodynamic coefficients (Cd, Cp) and the methodology for estimating the resulting torque?

I'm a mechanical engineer specifying the drive system for a 2-meter parabolic antenna that must operate in 30 mph winds. I need to estimate the maximum wind-induced torque on the elevation and azimuth axes to size the motors and gearboxes. I've found drag coefficient (Cd) values for flat plates, but a dish is concave/convex. Should I treat it as a shallow cup? Are there standard Cd values for parabolic dishes at various angles of attack? Also, how do I account for the torque arm, which is the distance from the center of pressure to the rotation axis?

All Answers (1 Answers In All)

By Meghna R Answered 1 year ago

For motor sizing, use a conservative approach. The TIA-222 standard is your authoritative source; it provides force coefficients for "parabolic antennas" (typically Cd ≈ 1.2 for the dish facing the wind). Don't treat it as a flat plate. The critical step is calculating the torque arm. For the elevation axis, the center of pressure for a dish is often taken at its geometric center. The torque is then: Torque = Wind Force * (Distance from rotation axis to dish center). Wind Force = 0.5 * ρ * V² * A * Cd, where A is the projected area. For worst-case, assume the dish presents its full frontal area. For azimuth rotation, you must consider the dish at various elevation angles, as the projected area and lever arm change. Always add a significant safety factor (e.g., 2x) for gust loading and stiction in your drive train.

 

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