At first glance, fixed-wing UAVs and multirotor UAVs have something in common: both use motors and propellers.
But put the same motor on both aircraft, and the result may be very different.
The reason is simple: they fly in different ways.
A multirotor uses its motors to stay in the air. A fixed-wing UAV uses its wings to stay in the air, while the motor mainly pushes the aircraft forward.
This difference changes almost everything about motor selection.
For a multirotor, the motor is doing a very demanding job.
It must continuously generate enough thrust to support the aircraft's weight. During takeoff, climbing, acceleration, and maneuvering, the motor may also need to provide additional thrust.
So when you select a multirotor motor, you normally pay close attention to:
Hovering thrust
Thrust-to-weight ratio
Torque
Fast response
Motor temperature
Maximum current
Suppose your multirotor weighs 4 kg.
The total aircraft weight is about 39 N. If your design target is a total maximum thrust of around twice the aircraft weight, the propulsion system needs roughly 78 N of total thrust.
With four motors, this means about 19.5 N of thrust per motor.
This gives you a starting point for motor and propeller selection.
But there is an important detail:
Do not stop at the thrust number.
You also need to check the current, motor temperature, propeller efficiency, battery capability, and actual operating time.
A motor can produce impressive thrust on a test stand and still be a poor choice for a real UAV.
Now look at a fixed-wing UAV.
The aircraft's wings generate lift when the aircraft moves forward. The motor does not need to continuously "hold" the entire aircraft in the air.
Its main job is to provide forward thrust.
This changes the selection priorities.
For a fixed-wing UAV, you should pay more attention to:
Cruise efficiency
Propeller matching
Power density
Motor efficiency
Continuous operating stability
Takeoff and climbing performance
Imagine a fixed-wing UAV cruising smoothly for one hour.
During that hour, you are not asking:
"How much maximum thrust can the motor produce?"
You are asking:
"How efficiently can the motor provide the thrust I need for the next hour?"
That is a very different question.
For a fixed-wing UAV, start with the aircraft's actual flight requirements.
Suppose your UAV weighs 6 kg.
You should not simply say:
"The aircraft weighs 6 kg, so I need 6 kg of thrust."
That logic makes sense for a multirotor in a simplified hovering calculation, but not for a fixed-wing aircraft in normal cruise.
For a fixed-wing UAV, the wings provide most of the lift. The motor mainly needs to overcome aerodynamic drag.
For example, if the estimated drag at your target cruise condition is 12 N, you need approximately 12 N of forward thrust to maintain that flight condition.
You can then add a reasonable margin for takeoff, climbing, and changing conditions.
Multirotor → start with lift and thrust.
Fixed-wing → start with drag, cruise speed, and required propulsion power.
This is one of the biggest differences between the two.
Once you know the required thrust and cruise speed, you can make a first estimate of propulsion power.
The relationship is:
Power ≈ Thrust × Flight Speed
For example:
Required cruise thrust: 12 N
Cruise speed: 20 m/s
The approximate mechanical propulsion power is therefore:
12 × 20 = 240 W
This is not the electrical power consumed by the battery. Motor and propeller losses must also be considered.
If the combined efficiency is assumed to be around 75%, the electrical input would be roughly 320 W.
Because two motors may both be capable of producing the required thrust, but one may consume more electrical power to do it.
For a UAV flying for only a few minutes, the difference may be less important.
For a UAV designed to cruise for one or two hours, it becomes much more important.
A few watts saved in the air can become a lot of energy saved over a long flight.
One common mistake is choosing the motor first and the propeller later.
For a UAV propulsion system, the motor and propeller should be considered together.
Motor KV, battery voltage, propeller diameter, propeller pitch, and operating speed all affect each other.
For example, a 500 KV motor connected to a 24 V battery has a theoretical no-load speed of approximately:
500 × 24 = 12,000 RPM
The actual loaded speed will be lower.
If you then select an unsuitable propeller, the motor may draw too much current or operate outside its efficient range.
Think of it like a bicycle:
The motor is your legs, the propeller is the gear, and the battery is your energy supply.
A stronger motor does not automatically make the whole system better. You need the right "gear" for the job.
It is tempting to think:
Bigger propeller = more thrust = better UAV.
But the relationship is not that simple.
A larger propeller can increase thrust, but it can also increase the load on the motor.
This may result in:
Higher current
More heat
Lower motor efficiency
Greater battery consumption
Increased risk of operating outside the motor's recommended range
A smaller propeller can have the opposite problem: the motor may run easily, but the system may not produce enough thrust efficiently.
The target is therefore not the largest propeller.
The target is the right propeller for the motor, battery, and aircraft.
Motor selection cannot be separated from the battery.
For example, if the propulsion system requires around 320 W of electrical power:
At 24 V, the current is approximately 13.3 A.
The same power at 48 V requires only about 6.7 A.
This does not mean that a higher-voltage system is automatically better. The motor winding, ESC, battery, insulation, connectors, and complete electrical system must all support the selected voltage.
But it shows an important engineering principle:
Motor selection is a system problem, not a single-component problem.
This is where fixed-wing UAVs become especially interesting.
A motor's maximum thrust is easy to notice.
Cruise efficiency is not.
But if your fixed-wing UAV spends most of its flight time cruising, the cruise operating point may have a much greater effect on total energy consumption.
Consider a simple example.
If your UAV consumes an average of 320 W during a one-hour cruise:
Energy ≈ 320 Wh
If another properly matched propulsion system can complete the same flight condition at 250 W:
Energy ≈ 250 Wh
The difference is 70 Wh per hour under these assumed conditions.
Over repeated flights, that difference becomes significant.
This is why you should evaluate the motor at the actual cruise operating point, not only look at the headline maximum power.
| Item | Multirotor UAV | Fixed-Wing UAV |
|---|---|---|
| Main job of motor | Generate lift | Provide forward propulsion |
| Key operating condition | Hover and maneuvering | Cruise |
| Main selection focus | Thrust and response | Efficiency and propulsion power |
| Thrust-to-weight ratio | Very important | Still useful, but not the only target |
| Propeller matching | Important | Critical for cruise efficiency |
| Motor response | Fast response is important | Stable continuous operation is important |
| Long-duration efficiency | Important | Often especially important |
| Motor selection approach | Start from required thrust | Start from cruise requirements and drag |
The difference can be summarized in one sentence:
A multirotor motor spends much of its life fighting gravity; a fixed-wing motor spends much of its life fighting aerodynamic drag.
That is why they need different propulsion strategies.
When you are developing a fixed-wing UAV, you can follow this sequence:
Record:
Total weight
Payload
Battery
Target cruise speed
Required flight time
Takeoff conditions
Determine the approximate aerodynamic drag at your target cruise speed.
This gives you the basic thrust requirement.
Use:
Propulsion power ≈ Thrust × Cruise speed
Then consider motor and propeller efficiency.
Check:
KV
Battery voltage
Propeller diameter
Propeller pitch
RPM
Current
Thrust
Efficiency
Do not evaluate any one parameter by itself.
Your cruise point is important, but your UAV still needs enough additional power for takeoff and climbing.
The final result should be verified with the actual motor, ESC, battery, and propeller combination.
The test data is more valuable than a single number on a motor specification sheet.
BG Motor provides customized brushless DC motor solutions and has a professional R&D team covering power, structural, and mechanical engineering. The company can customize motor dimensions, shafts, mounting holes, installation methods, and other parameters according to application requirements.
For fixed-wing UAV applications, models such as 4120, 4125, 5230, and 5330 can be considered according to the aircraft's actual requirements.
When you contact BG Motor, providing the following information will make motor matching more precise:
UAV weight
Payload
Battery voltage
Target cruise speed
Propeller specification
Required flight time
Takeoff and climbing requirements
From there, the motor, propeller, and battery can be considered as one propulsion system rather than three separate components.
Choosing a fixed-wing UAV motor is not a competition for the biggest number.
The right motor is the one that delivers the required thrust at the right speed, with the right propeller, while using energy efficiently for the mission.
For a multirotor, ask:
"Can this motor keep my UAV in the air?"
For a fixed-wing UAV, ask:
"Can this motor keep my UAV moving efficiently for the whole mission?"
That difference is the starting point for selecting the right motor.
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