“How long can my drone fly with XYZ payload?” This is an important question to ask when evaluating drone platforms. Although it seems the answer regarding drone flight times should be straightforward, more than just payload weight will impact how long a drone can perform a mission. The following variables impact flight times to a greater or lesser degree:
- Low battery failsafe settings
- Payload weight and size
- Payload power draw
- Battery chemistry and lifespan
- Condition of props and rotors
- Density altitude
- Other factors (environment, flight plan, maneuvering aggression )
How Low Battery Failsafe Settings Impact Flight Times
On UAV spec sheets, the maximum flight time is usually measured in minutes. This is the total amount of time a drone can fly, without a payload, in ideal conditions. One of the major items that will impact the actual flight time is a setting for the Low Battery Failsafe.
Drone manufacturers provide this safety mechanism by default. The Low Battery Failsafe setting tells the aircraft to automatically Return to Launch (RTL) when the battery charge falls below a predetermined level. For Vision Aerial drones, the Low Battery Failsafe is set by default to trigger at 30% battery remaining. That means that 70% of the maximum flight time can be used for the mission. The remaining battery ensures that the drone lands safely.
In the Flight Time vs Payload Weight chart below, there are two lines. One line indicates the total flight time with the Low Battery Failsafe set to 0%. The second line indicates how many minutes of flight time you would expect with a 30% battery remaining failsafe setting.
IMPORTANT SAFETY NOTE: Vision Aerial does not recommend changing the battery failsafe settings. Doing so may result in a vehicle crash, causing damage to payloads, property, and possibly injury or death.
How Do Payloads Impact Flight Times?
The next greatest factor impacting flight times is the weight and size of the payload. The larger and heavier a payload is, the more power the drone needs to carry it. Additional power required to lift a payload will decrease overall flight times.
Larger payloads can also impact the aerodynamics of the system. More wind resistance will reduce the amount of time a drone can be in the air. Fortunately, many drone payloads are designed to be very small, compact, and lightweight.
Payload Power Draw
In addition to size and shape, a payload’s power draw can also affect flight times. It is common for payloads to draw power from the flight battery. This is because it is often more efficient to do this rather than carry the weight of a secondary payload battery.
Power used by the payload will slightly reduce the power available to keep the vehicle in flight. Some payloads, like high-resolution cameras, draw a tiny amount of power which will not have much of an impact on flight times. Other payloads, like LiDAR systems, may have higher power requirements that can deplete the flight batteries more quickly.
Battery Chemistry & Lifespan
Different kinds of batteries, known in the industry as “flight packs,” can provide longer or shorter flight times. Batteries with Lithium Polymer chemistry are some of the most common flight packs for drones and provide very good flight times. Solid State batteries have more advanced chemistry that packs more power. Therefore, Solid State batteries offer longer flight times.
As batteries become older, they also tend to lose their charge faster. This is known as battery degradation. In addition to the age of batteries, the more times they are charged and discharged (cycles) the quicker they will degrade. Therefore older batteries may experience shorter flight times than brand new ones.
Condition of Props & Motors
When a new drone comes fresh off the assembly line, all the components are pristine and function optimally. After hours of industrial use, rotors can chip and motors can become clogged with dirt and dust. When that happens the drone will lose some flight efficiency and flight times will go down. This is because the motors have to work harder to maintain lift.
How Does Density Altitude Affect Drone Flight Times?
Density altitude is the pressure altitude (feet above sea level) corrected for environmental temperature. More simply, Density altitude is the equivalent environmental condition to standard pressure and temperature distance above Mean Sea Level (MSL), typically expressed in units of feet. In denser air, it is easier for an aircraft to maintain lift. As temperature and altitude increase, air density decreases, and the aircraft requires more energy to stay in flight.
On a hot and humid day, a drone will need more power to attain lift than on a dry, cool day. Fewer air molecules in a given volume of air will result in reduced propeller efficiency. Therefore, a drone will experience shorter flight times on a hot, humid day.
Other Factors that Can Impact Drone Flight Times
In addition to the items mentioned above, there are additional factors that can impact flight times. Environment, the flight plan, or maneuvering aggression are some of the additional variables that can reduce flight times.
If it is a highly gusty day and the drone must fight to maintain its position, you will experience shorter flight times. Flight plans can also impact flight durations. Long, straightforward flights tend to be fairly energy efficient. A flight plan that includes a lot of hovering, stopping, and/or turning, may deplete the battery more quickly. Aggressive flying at high speeds with a lot of jerky motions can also see shorter flight times.
Conclusion
In sum, flight time vs. payload weight specifications should not be taken at face value. There are a variety of factors that should be taken into consideration when determining drone flight times with different payloads.