RC Airplane Wing Loading & Stall Speed Calculator
Enter the ready-to-fly weight, wing area, CLmax, and field conditions to estimate wing loading and stall speed. The target stall speed also reverse-solves the maximum weight that would meet that speed.
Estimated stall speed (mph)15.32
- Estimated stall speed (km/h)
- 24.65
- Initial approach speed (mph)
- 19.92
- Initial approach speed (km/h)
- 32.05
- Wing loading (oz/ft²)
- 11.52
- Wing loading (g/dm²)
- 35.15
- Wing cube loading (oz/ft³)
- 5.64
- Maximum weight at target stall speed (oz)
- 46.02
- Maximum weight at target stall speed (g)
- 1,304.56
- Weight margin (oz)
- -1.98
- Weight margin (g)
- -56.21
- Estimated air density (kg/m³)
- 1.23
CLmax drives the stall-speed result; verify it with airfoil data or flight testing when the number is critical.
For biplanes and multiplanes, enter summed projected wing area, but this calculator does not model wing interference.
Current weight is above the target-stall-speed limit, so the weight margin is the estimated reduction required.
How to use this calculator
- Enter the complete ready-to-fly weight with the battery, fuel, payload, and landing gear installed.
- Enter the total projected wing area in square inches, adding all lifting wings when appropriate.
- Use measured CLmax when you have it, or start with a conservative clean-wing estimate.
- Enter pressure altitude and temperature for the flying field so the air density can be adjusted.
- Set a target stall speed to see the maximum all-up weight and the remaining weight margin.
How the calculator works
The ordinary wing loading result divides ready-to-fly weight by wing area converted to square feet. With weight w in ounces and wing area A in square inches, the reference area in square feet is Af = A / 144, so WL = w / Af. The metric value converts ounces to grams and square inches to square decimeters.
Wing cube loading follows the Francis Reynolds comparison method: WCL = w / Af^(3/2). Because the wing area is raised to the three-halves power, wing cube loading is often more useful than ordinary wing loading when comparing models of different sizes. It is still a comparison number, not an aerodynamic proof.
For stall speed, the calculator uses the lift equation. Wing area is converted with S = A * 0.00064516, weight becomes force with W = w * 0.028349523125 * 9.80665, and temperature is converted to kelvins. Pressure at pressure altitude h below 11,000 m is estimated as p = 101325 * (1 - 0.0000225577h)^5.25588. Dry-air density is then rho = p / (287.05T).
The stall speed comes from rearranging L = 0.5 * rho * V^2 * S * CLmax for velocity: Vs = sqrt(2W / (rho * S * CLmax)). The initial approach-speed estimate is 1.3 * Vs. To solve maximum weight for a target stall speed, the equation is reversed: Wmax = 0.5 * rho * Vt^2 * S * CLmax, then the force is converted back to ounces and grams.
What moves the result most
Weight, wing area, and CLmax dominate the answer. Adding battery weight raises stall speed, while adding effective wing area or a higher verified CLmax lowers it. Hotter air and higher pressure altitude reduce density, so the same airplane must fly faster to make the same lift.
What this leaves out
The calculation assumes steady, level, unaccelerated flight. It does not include bank angle, gusts, maneuver load factor, propwash, Reynolds-number changes, surface roughness, control deflection, humidity, or wing interference. For biplanes and multiplanes, summed projected wing area is allowed, but the result does not correct for one wing reducing the effectiveness of another.
Worked example
For a 48 oz RC airplane with 600 in² of wing area, Af = 600 / 144 = 4.1667 ft². Wing loading is 48 / 4.1667 = 11.52 oz/ft², or about 35.15 g/dm². Wing cube loading is 48 / 4.1667^(3/2) = 5.64 oz/ft³.
At sea-level pressure altitude and 59 °F, dry-air density is about 1.225 kg/m³. With CLmax = 1.2, the lift equation gives an estimated stall speed of about 15.32 mph, or 24.65 km/h. The initial approach estimate is about 19.92 mph. If the target stall speed is 15 mph, the maximum weight is about 46.02 oz, so the current 48 oz airplane is about 1.98 oz over that target.
Common questions
What is a good wing loading for an RC airplane?
There is no single good number because size, airfoil, mission, and pilot skill matter. Small trainers often feel friendly at lower wing loading, while sport, scale, and faster models commonly carry more. Compare your result with proven models of similar span, wing area, and layout.
Why use wing cube loading instead of only wing loading?
Ordinary wing loading rises as airplanes get larger, even when the designs scale similarly. Wing cube loading adjusts the area term so different-size models can be compared more fairly. It is useful for broad handling comparisons, but it still does not replace flight testing.
How should I measure RC airplane wing area?
Use the projected planform area, not the curved surface area of the covering. For a rectangular wing, multiply span by chord. For tapered or multi-panel wings, add each panel area; for biplanes, enter the summed projected area of the lifting wings.
What CLmax should I enter?
Measured airfoil or flight-test data is best. If you do not have it, a clean sport or trainer wing is often estimated around 1.0 to 1.2, while effective flaps can raise the number. Because stall speed changes with the square root of CLmax, optimistic entries can make the result look safer than it is.
How do altitude and temperature affect stall speed?
Higher pressure altitude and hotter air both lower air density. Lower density means the wing needs more speed to produce the same lift, so stall and approach speeds increase. This is why a model that feels comfortable on a cool morning can need more runway on a hot high-altitude afternoon.
Why might actual stall speed differ from the estimate?
The equation assumes steady, level, unaccelerated flight and a known CLmax. Real models also see propwash, bank angle, gusts, surface roughness, Reynolds-number effects, control input, and measurement error. Treat the number as a planning estimate and confirm safe speeds progressively at altitude.