If air density increases while airspeed remains constant, what will be the effect on both lift and drag?

If air density increases while airspeed remains constant, what will be the effect on both lift and drag?

• A. Both lift and drag increase.
• B. Lift decreases, drag increases
• C. Both decrease
• D. Lift increases, drag decreases

Answer: (A)

Lift and drag both scale with dynamic pressure, which increases when air density goes up while airspeed stays the same. Dynamic pressure is q = 0.5 * rho * V^2. The lift and drag equations are L = q * S * Cl and D = q * S * Cd. If you keep the speed and wing characteristics constant, increasing rho raises q, so both lift and drag rise in proportion to the density increase. The lift coefficient and drag coefficient stay the same if the angle of attack and wing shape don’t change, so the only effect is higher L and higher D.

Lift and drag both scale with dynamic pressure, which increases when air density goes up while airspeed stays the same. Dynamic pressure is q = 0.5 * rho * V^2. The lift and drag equations are L = q * S * Cl and D = q * S * Cd. If you keep the speed and wing characteristics constant, increasing rho raises q, so both lift and drag rise in proportion to the density increase. The lift coefficient and drag coefficient stay the same if the angle of attack and wing shape don’t change, so the only effect is higher L and higher D.