Calculate hinge moment coefficient, hinge moment, dynamic pressure, control surface area, or mean aerodynamic chord from four inputs.
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Hinge Moment Coefficient Formula
The hinge moment coefficient is calculated from hinge moment, dynamic pressure, control surface area, and mean aerodynamic chord.
C_h = H / (q*S*c)
The calculator can also rearrange the same equation to solve for any one missing value:
H = C_h*q*S*c
q = H / (C_h*S*c)
S = H / (C_h*q*c)
c = H / (C_h*q*S)
- Ch = hinge moment coefficient, unitless
- H = hinge moment
- q = dynamic pressure
- S = control surface area
- c = mean aerodynamic chord
The calculator works by taking any 4 known values and solving for the missing fifth value. It converts the entered units to its base units before applying the formula: hinge moment in lb-ft, dynamic pressure in lb/ft², control surface area in ft², and mean aerodynamic chord in inches. The hinge moment coefficient is unitless.
Supported Units and Base Conversions
The table below shows the unit options used by the calculator and how they relate to the base units used internally.
| Quantity | Supported units | Base unit used |
|---|---|---|
| Hinge moment coefficient | Unitless | Unitless |
| Hinge moment | lb-ft, N-m | lb-ft |
| Dynamic pressure | lb/ft², psi, kPa, Pa | lb/ft² |
| Control surface area | sq ft, sq m, sq in, sq yd | ft² |
| Mean aerodynamic chord | in, ft, cm, m | in |
Common Dynamic Pressure Conversions
| Input unit | Equivalent in lb/ft² |
|---|---|
| 1 psi | 144 lb/ft² |
| 1 kPa | 0.0208854 lb/ft² |
| 1 Pa | 0.000208854 lb/ft² |
| 1 lb/ft² | 1 lb/ft² |
Example Problems
Example 1: Calculate hinge moment coefficient
Given:
- Hinge moment = 120 lb-ft
- Dynamic pressure = 25 lb/ft²
- Control surface area = 8 ft²
- Mean aerodynamic chord = 12 in
C_h = 120 / (25*8*12)
C_h = 0.0500
The hinge moment coefficient is 0.0500.
Example 2: Calculate hinge moment
Given:
- Hinge moment coefficient = 0.040
- Dynamic pressure = 30 lb/ft²
- Control surface area = 10 ft²
- Mean aerodynamic chord = 15 in
H = 0.040*30*10*15
H = 18.0000
The hinge moment is 18.0000 lb-ft.
FAQ
What is a hinge moment coefficient?
The hinge moment coefficient is a unitless value that relates the aerodynamic hinge moment on a control surface to dynamic pressure, control surface area, and chord length. It is commonly used when analyzing control surfaces such as elevators, rudders, ailerons, tabs, and flaps.
Why is the hinge moment coefficient unitless?
It is treated as a coefficient because it normalizes hinge moment against the aerodynamic loading terms in the denominator. This lets you compare hinge moment behavior without using the raw moment alone. In practical calculations, you still need to keep the input units consistent with the formula or use the unit selectors in the calculator.
Why do I need to enter exactly 4 values?
The equation has 5 variables. To solve for one unknown, the other 4 values must be known. If more than one value is missing, there is not enough information to find a single result. If all 5 values are entered, there is no missing variable to calculate.