It’s hard to determine flight time on a quadcopter without actually test it, because it depends on many factors: average flying speed, battery, motor/propeller efficiency, payload, wind speed etc. However there are ways you can do to maximize your flight time in the air.
There are differences between “flight time” and “hover time”. Hover time is pretty much a constant value, but flight time varies depends on throttle level and wind condition. Therefore you can’t really compare the “flight time” between 2 different multicopters, it’s not fair as it’s influenced by so many factors.
Generally speaking, low KV motors with large propellers have higher efficiency and can carry larger battery, and thus longer flight time.
But you don’t have to build a gigantic quadcopter to stay longer in the air. In this post we will discuss what impacts battery life, and some of the things you can do to maximize your hover time as well as flight time.
Throttle and Power Efficiency
Brushless motors and propellers tend to have the worst efficiency at maximum throttle, and higher efficiency at lower throttle.
Therefore flying around fast, doing acrobatics etc, will use more power thus shorter flight time. If you are doing aerial filming, and want some more time in the air, the best thing to do is to fly gently and avoid unnecessary turns.
Weight – Payload
As you can probably guess, the simplest and most effective way of increasing your drone’s flight time, would be to get rid of unnecessary weight. Every gram you shave contributes in extra flight time.
Here are a few suggestions for keeping your quad as light as possible:
- make motor/ESC/power wires as short as possible
- avoid gold bullet connectors and just direct solder
- remove HD camera (GoPro/Mobius) when you are not recording
- use light weight components and hardware
Battery capacity directly affects flight time. Bigger battery doesn’t necessary give you longer flight time, because battery weight increases with capacity. There is a trade off (balance) between capacity and flight time.
Check out this post about how I choose the optimal battery capacity.
You can experiment with different sizes batteries, time it and find out which one gives the best result.
LiPo Battery C rating not only affects the max continuous current draw, but also flight time in my opinion.
How? Let’s assume, you use up 80% of the battery capacity when the voltage drops to 3.5V per cell. If you have a low C rating LiPo battery, and your multicopter demands more current than the battery can handle, you will notice your battery voltage will start dropping very quickly. In the end, you might only have used 70% of the total capacity when the voltage sags to 3.5V per cell (and recovers to 3.8V after landing). This is a symptom of insufficient C rating, and you will have shorter flight time.
Battery Condition and Maintenance
This could well be a whole new topic, and there is simply too much to cover. But basically, your batteries will get old and the capacity they hold will start diminishing. It’s important that you keep them in good condition, avoid over-discharging them, and do not leave them fully charged for too long. Here is a guide on how to use and look after LiPo batteries.
Motor and Propellers
If flight time is more important than power for you, then by choosing an efficient motor and prop combination will help immensely. You can find out motor efficiency information from the data sheet, or thrust tests done by other hobbyists.
Motor, propeller efficiency is calculated by dividing thrust by power, which is gram per watt (g/W). The higher g/W, the more thrust is generated at a given amount of energy. For example when I am using the Cobra 2204 1960KV motors, 6045 propepller gives me a lot of power, but I will get longest flight time by using 5030 props because of the higher efficiency.
Also balancing your propellers could increase your flight time too. Unbalanced propellers introduce vibration to your aircraft, not only the aircraft woulfd use more energy trying to stabilize it, energy is also wasted on friction between propeller and air.
Although not a very big deal, but flight mode does affect flight time too! Here I mainly refer to Rate mode (AKA manual mode or acro mode) and Self-Level mode (AKA Angle/Horizon mode). To find out the difference, check out this post.
Self-level mode is fantastic, because it helps your control by attempting to keep the quadcopter level. However as it’s constantly trying to fight with changes of craft attitude, the motors speed are changing more rapidly too and use more energy.
Rate mode doesn’t correct the change of attitude as hard as self-level mode, so in theory it’s more power efficient.
Just like what we have mentioned above, aircraft with vibration could cause overheat motors and use more energy. A well tuned, smooth, and stable multicopter is more efficient and gives you longer flight time.
Wind causes instability to the quadcopter, and the motors have to work harder to correct the errors to stay level. This means that flying in windy weather drains battery faster than flying in a calm day.
Additional parts such as LED, FPV gear, camera gimbals etc can reduce your flight time. Firstly they draws current although not a lot. Secondly they are extra weight to your quadcopter.
Each LED used on multicopters generally only draw 20mA to 30mA of current, so at 5V, the power consumption is only about 0.1W each LED. Say if you have 10 LEDs that’s 1W in total.
Your FPV gear could draw up to 0.5A at 12V for example, which is about 6W.
Now assume you have a mini quad, at hover 1 single motor draws 15A at 16V – 4S (pretty normal for a mini quad at forward flight), which is 240W, and 960W in total for 4 motors.
LED and FPV gear combined is less than 1% of the total power usage. Put that in flight time terms, if your flight time is about 5 mins (300 seconds), that’s only 3 seconds that you lost.
But the weight of the hardware would have a much bigger impact on flight time.