How does sustained forward flight at high speed affect endurance compared with a hover?

Multirotor endurance in forward flight is genuinely airframe-dependent, and that is the honest answer rather than an evasion. Two effects work against each other. Translational lift means that as the aircraft moves forward the rotors work in undisturbed air rather than their own downwash, which reduces the power needed to stay up — so slow to moderate forward flight is often more efficient than a hover. But parasite drag rises with the square of airspeed, and at high speed the aircraft must also tilt substantially, committing more thrust to overcoming drag rather than supporting weight. Where those curves cross depends on the airframe's shape, weight, rotor loading and payload, so one aircraft may be most efficient at 15 knots and another quite different. Wind complicates it further, since endurance depends on airspeed while the useful work depends on groundspeed. The professional answer is to measure the specific airframe in the conditions it will fly, and plan from that data rather than from a rule of thumb.

Translational lift reduces power required at moderate speed while parasite drag rises sharply at high speed, and where those effects balance depends on the specific airframe, weight and payload — so it must be measured.

Multirotor power required varies with forward speed. Translational lift reduces power at moderate speeds; parasite drag increases with the square of airspeed at higher speeds. The optimum varies by airframe, weight and payload.

Measure Your Own Airframe. Translational lift helps, drag hurts, and where they cross is your aircraft's number.

Endurance depends on airspeed but useful coverage depends on groundspeed, so wind changes the optimum for a given mission.

• •Applying a fixed ratio between hover and cruise endurance
• •Assuming forward flight always costs more power than hovering
• •Ignoring wind when converting endurance into coverage