RC Plane Calculator: Wing Loading, Stall Speed, CG & Tail Volume

For a symmetric trapezoidal wing with full projected span $b$, root chord $c_r$, tip chord $c_t$ and taper $\lambda=c_t/c_r$:

NASA's Wing Geometry defines projected area and aspect ratio. CODE Lab's Wing Planform Sizing, sections “Taper Ratio” and “Summary”, gives

The leading edge of the MAC is $x_{LEMAC}=y_{MAC}\tan\Lambda_{LE}$. All longitudinal positions are positive aft from the root leading edge, including the centreline balance mark. These geometric quantities do not predict the lift distribution.

Using standard gravity $g_0=9.80665\,\mathrm{m/s^2}$, weight is $W=mg_0$. Mass loading is $m/S$; force loading is $W/S$. The RC output uses mass per area, in g/dm² or oz/ft², so ounces here are mass ounces. Rearranging NASA's Lift Equation at $L=W$ and the entered complete-wing maximum lift coefficient gives

This is ideal true airspeed at the entered density. For a steady coordinated level turn, vertical force balance gives $n=1/\cos\phi$ and $V_{s,turn}=V_s\sqrt n$. The sensitivity plot divides mass and stall speed by their current wings-level values; its second curve assumes 20% less CLmax.

Conventional CG: $x_{CG}=x_{LEMAC}+h\bar c$, with the selected $h$ in the brief's 25–33% exploration band. This is a geometric guideline, not a computed neutral point or stability clearance. Green shading marks that band at the MAC station. The orange centreline mark is the selected balance position.

Flying-wing CG: use the entered neutral point $h_{NP}$ and static margin $SM$: $h=h_{NP}-SM$, then use the same datum conversion. RC Aero's Flying Wing CG Calculator explains the forward-of-neutral-point margin. The separate blue mark shows the entered neutral point; no conventional band is drawn.

Tail sizing: CODE Lab's Tail Sizing defines quarter-MAC (aerodynamic-centre) to quarter-MAC arms:

Rearranging gives $S_{H,target}=V_{H,target}S\bar c/l_H$ and $S_{V,target}=V_{V,target}Sb/l_V$. Areas include control surfaces. The default targets are editable comparison goals, not stability limits. Tail coefficients and target areas are zero in flying-wing mode.

Electric power: the selected empirical input-power band comes from E-flite Power 46 Instructions, p. 1. Convert its W/lb values explicitly to W/kg, then multiply by flying mass. Page 2 supplies the independent 600 W example. The band midpoint is a comparison value, not a required continuous motor rating.

Low-speed screening: compare the higher of the wings-level and banked stall speeds with an author-selected limit of 80 m/s (about 179 mph). NASA's Mach Number page states that air density is approximately constant at low speeds, typically below 250 mph, and explains how compressibility changes aerodynamic forces. The lower 80 m/s threshold provides a conservative screening margin; it is not a NASA-prescribed limit or a universal Mach-number boundary.

• One symmetric, straight-edged, projected trapezoidal wing; no inverse taper. The centre section through the fuselage is included.
• The entered CLmax represents the whole wing at the relevant Reynolds number and configuration. The illustrative default of 1.2 is not an airfoil specification.
• Steady flight, incompressible flow, constant density and negligible vertical thrust. Tail download, trim drag, gusts and transient stall dynamics are omitted.
• Conventional layout means a main wing and separate aft horizontal and vertical tails. Tail moment arms are longitudinal AC-to-AC separations; data based on CG-to-tail arms must be converted before comparison.
• The flying-wing neutral point is supplied by the user; this tool does not solve for it. Positive static margin alone does not establish a trimmable or dynamically stable design.
• Power means full-throttle electrical input to the ESC. It excludes predictions of propeller thrust, shaft efficiency and flight duration.

A warning appears if either predicted stall-speed result exceeds 80 m/s (262.5 ft/s). Check mass, wing dimensions, density, CLmax and bank angle; use a suitable compressible aerodynamic model when those speeds are intentional. The screen concerns these two predicted speeds only, not maximum cruise or dive speed. Sound speed depends on temperature, so evaluate actual Mach number separately under unusual atmospheric conditions.

Use for preliminary RC aircraft and small fixed-wing UAV sizing. Geometry is exact within the stated trapezoidal model; aerodynamic accuracy is dominated by the entered CLmax and neutral point. At low model Reynolds numbers, section data and whole-wing stall behavior can differ substantially. High sweep or unusual aspect ratio needs more detailed aerodynamic analysis.

The conventional 25–33% MAC interval is not a safe CG envelope for every aircraft. Follow established manufacturer/designer limits, check pitch trim and control authority, and validate the finished configuration. Flying wings require appropriate reflex, twist or elevon trim and independently verified neutral-point data.

Tail volume is a comparison metric, not a proof of longitudinal or directional stability. Canards, tandem wings, V-tails, biplanes, multi-panel or elliptical planforms, fuselage interference, propwash and structural design are outside the model. The bank-angle calculation does not establish permissible manoeuvres or a structural limit.

Power bands are empirical starting points. Their upper endpoint is not a maximum permissible power; demanding 3D models may need more. Verify the installed motor/propeller/ESC/battery combination using manufacturer data and a wattmeter. No takeoff, landing-speed, endurance or airworthiness approval is implied.