RC Airplane Flight Time Calculator
Estimate flight time from measured current in takeoff, cruise, and motor-off phases instead of one assumed throttle setting. The same profile can also estimate the nominal battery capacity needed for a target flight time while preserving your selected reserve.
Estimated flight time (min)7.33
- Weighted average current (A)
- 14.4
- Usable battery capacity (mAh)
- 1,760
- Capacity required for target time (mAh)
- 2,400
- Capacity margin at target time (mAh)
- -200
Phase shares are normalized by their total, so they describe the relative time spent in each phase.
Use measured current that includes the receiver, servos, BEC, and other loads supplied by the flight battery.
The selected battery is short of the nominal capacity estimated for the target flight time.
How to use this calculator
- Enter the nominal mAh capacity printed on the flight battery and the portion you plan to use before landing.
- Enter measured current for takeoff power, normal cruise, and motor-off or glide periods.
- Estimate how much of a typical flight belongs to each phase; the calculator normalizes shares that do not total 100%.
- Enter the flight duration you want, then compare the required capacity and margin with the installed pack.
How RC airplane flight time is calculated
Battery capacity is charge, not minutes. An electric airplane may draw a high current while taking off or climbing, a lower current in level cruise, and a small but nonzero current with the motor off because the receiver, servos, and BEC are still powered. Treating every minute as one throttle percentage can hide the effect of those phases.
This calculator first combines the phase currents into a time-weighted average:
Iavg = (It × pt + Ic × pc + Ig × pg) ÷ (pt + pc + pg)
- It, Ic, and Ig are the takeoff, cruise, and glide currents in amps.
- pt, pc, and pg are their time shares. If they do not total 100%, their relative proportions are normalized by their sum.
The capacity available for the estimate is Cuse = C × U, where C is the labeled capacity in mAh and U is the usable-capacity percentage as a decimal. Flight time is test = 60 × (Cuse ÷ 1000) ÷ Iavg. To size a pack for a target time T, the relationship is solved backward: Creq = 1000 × Iavg × (T ÷ 60) ÷ U.
What affects the estimate most
The current during climbs and the fraction of the flight spent climbing usually have the largest effect, because current rises quickly with propeller load and throttle. A few long climbs can consume as much energy as many minutes of light cruise. Use a wattmeter with the installed propeller and battery, or a flight logger, rather than a motor specification alone. The Limestone County R/C Club design guide likewise treats required amp-hours as average current multiplied by flight time.
Choose usable capacity as a landing reserve, not as a promise that the labeled capacity is fully available. A 100% setting deliberately models no reserve. If the phases total less or more than 100%, the calculator can still use the mix, but revisiting the estimates makes the result easier to interpret.
What this calculator leaves out
This is an energy-budget estimate, not a flight timer or a battery safety determination. It does not model battery age, temperature, voltage sag, propeller changes, wind, repeated climbs, aerobatics, pack internal resistance, or changing aircraft mass and trim. A larger battery can add useful capacity but also adds weight, which can change the current draw and the way the airplane handles.
Include receiver and servo consumption in the motor-off current whenever they are powered from the flight battery. Verify the whole installed power system against the motor, ESC, battery, BEC, connector, and propeller limits, and use transmitter timers and telemetry as independent cues to land.
Worked example
Suppose a 2,200 mAh pack is used to 80% of its label capacity. A representative flight spends 20% at 35 A during takeoff and climbs, 60% at 12 A in cruise, and 20% at 1 A while gliding. The weighted average is (35 × 20 + 12 × 60 + 1 × 20) ÷ 100 = 14.4 A.
Usable capacity is 2,200 × 0.80 = 1,760 mAh, or 1.76 Ah. Estimated flight time is 60 × 1.76 ÷ 14.4 = 7.33 minutes. For an 8-minute target, the required nominal capacity is 1000 × 14.4 × (8 ÷ 60) ÷ 0.80 = 2,400 mAh. The selected 2,200 mAh pack therefore has a 200 mAh shortfall at that target.
Common questions
How do I measure cruise current in an RC airplane?
Use telemetry or a flight logger in the battery lead during representative level flight, or use a wattmeter on the ground to compare throttle settings with the installed propeller. Ground measurements are useful, but an in-flight log better captures airspeed, cooling, and the actual throttle changes you make. Include any load supplied by the flight pack.
What usable-capacity percentage should I enter for a LiPo?
Enter the part of the label capacity you intend to use before your normal landing reserve. The appropriate reserve depends on the pack, load, temperature, cutoff settings, and the manufacturer guidance. Start conservatively and adjust only after comparing the estimate with telemetry and the charge returned after a safe flight.
Why is actual flight time shorter than the estimate?
Actual current may be higher than the representative profile, especially during repeated climbs, wind correction, or aerobatics. Cold packs, aging, voltage sag, a different propeller, and extra servo load can also reduce the useful energy. Treat the result as a planning number and retain a reserve.
How should I estimate takeoff, cruise, and glide percentages?
Use a representative flight log if you have one, then group its current trace into high-power, level-flight, and motor-off periods. Without a log, sketch a typical flight and estimate each phase in minutes before converting them to percentages. The three shares do not need to be exact because this calculator normalizes their relative proportions.
Does a larger battery always produce a longer flight?
It usually adds charge, but it also adds weight. More weight can raise required thrust and current, affect balance, and change handling, so the runtime gain may be smaller than the capacity increase suggests. Check that the larger pack fits, maintains a safe center of gravity, and stays within component limits.
Should receiver and servo current be included?
Yes, when they are powered from the flight battery through an ESC BEC or a separate BEC connected to that pack. Their contribution is especially important for the motor-off figure, because zero motor current does not mean zero battery current. Do not include them here if they use an independent receiver battery.