Compute lift coefficient, drag coefficient, and L/D ratio.
What This Means For You
Get a personalized explanation of these results — what they actually mean for your situation, and how small changes would affect them.
How it works
Lift-to-drag ratio is the single number describing how efficiently a wing converts forward motion into lift. It also sets glide performance directly: an airframe at L/D of 10 covers ten metres of ground for every metre it descends with the power off.
L/D = Lift / Drag q = ½·ρ·V² C_L = L / (q·S) | C_D = D / (q·S) L/D = C_L / C_D
L, Dlift and drag forces, Nqdynamic pressure, Paρair density; 1.225 kg/m³ at sea level standardVtrue airspeed, m/sSreference wing area, m²
- q = 0.5 × 1.225 × 50² = 1,531.25 Pa
- q × S = 1,531.25 × 20 = 30,625 N
- C_L = 10,000 / 30,625 = 0.3265
- C_D = 1,000 / 30,625 = 0.0327
- L/D = 10,000 / 1,000 = 10, which matches C_L / C_D
- Coefficients are dimensionless, so the same C_L and C_D describe the wing at any speed or altitude provided Reynolds and Mach numbers stay in the range the data was taken at. That is what lets wind-tunnel results transfer to a full-size aircraft.
- Density falls with altitude, so holding lift equal to weight at 30,000 ft needs either a higher true airspeed or a higher C_L than the same aircraft requires at sea level.
- Peak L/D happens at one specific angle of attack, and that speed gives maximum glide distance rather than maximum time aloft. Minimum sink sits slower, near where C_L^1.5 / C_D peaks.
- Reference area S has to match the definition the coefficients were derived from. Gross wing area including the fuselage carry-through is the common convention, and swapping in exposed area shifts every coefficient by several percent.
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