Anyone tried oversized propellers | DJI Mavic, Air & Mini Drone ...

I'm not an engineer, or propeller designer, just an airplane pilot and owner. It's been said that propeller design is part science and part black art, but here's a few rules and thoughts:

Think of prop pitch like transmission gears. A flatter pitch is like low gear, faster to accelerate and quicker to respond, but with lower top speed and less efficient in cruise. Conversely, a coarser pitch will be less responsive to power input changes and will have a higher top speed. My airplane gets around this problem by having a variable pitch prop, analogous to the transmission in a car. For take off, a flatter pitch is used for faster acceleration, and for cruise,, a coarser pitch for higher top speed and efficiency. Another rule of thumb is that a longer, slower turning prop is more efficient than a shorter, faster turning prop. Higher prop tips speeds generate more noise. As prop tips approach the speed of sound, noise increases dramatically and efficiency drops.

Your drone has limited room and clearance for a longer prop, the tips need to clear the drones structure. The props are designed with flexible blades, to a degree this allows the prop to behave like my airplane's variable pitch prop, but it also means they prop needs more clearance to avoid striking the structure.

Prop pitch and length will also needs to match available motor power. Too much prop (pitch and length) will bog down a lower power motor, yet an undersized prop, or one with too flat a pitch, won't be able to harness and use more power from the motor.

Prop tip vortices detract from efficiency, the swept, thinner tips are designed to help improve efficiency, reduce tip vortices and reduce noise.

For the larger DJI drones, like my M2P, "Master Air Screw (MAS) makes slightly larger props that eek out a small increase in efficiency - they don't yet make them for the Mini.

Im a new drone pilot. Ive had my MM for a couple weeks now, and am having a blast. I have noticed that the MM struggles in any kind of wind, and has caused a few fly away situations that ive read about.

My experience with the Mini is that whilst it doesn't cope particularly well with strong winds, it does a good job in moderate winds as long as you're sensible about what you do with it. For example, avoid flying a long way downwind from the home point (ideally, position yourself so you fly upwind for most of your flight), generally fly as low as you can to achieve what you want and set the RTH height so that it's the minimum required to safely clear local obstacles. Most flyaways aren't really flyaways, they're blowaways - the Mini doesn't actually fly away, it just can't fly back against a strong wind. The Mini has a maximum flight speed of 29 mph in level flight so you can work out how fast (or not) the drone will be able to return to you if it's coming from a downwind position - if the wind is 30 mph, if you maintain height it will only ever get further away no matter how much you try to bring it back!

The only thing that helps is more attitude or weight.

Attitude (for a drone), yes. Weight - why?

Just think about it, the forward driving force can be written (a little bit simplified, not include wind drag increases with attitude):
F=m*sin(attitude)

Wouldn't that just apply to an aircraft in the glide? If you have 2 identical aircraft with the same power units and you increase the mass of one of them, there's no reason why it would penetrate the air any better in level flight - you'd just need more power to maintain the height at a fixed airspeed. There is no "wind drag" as such - aerodynamically, the aircraft doesn't know if it's windy or not. As far as it's concerned, it's just moving at a particular airspeed through an airmass. The fact that the airmass is moving (what we refer to as wind) doesn't change the amount of air moving past the aircraft at a particular airspeed, it just changes the groundspeed. Increasing the mass would just make it more stable in turbulence because it would have more inertia.

Attitude (for a drone), yes. Weight - why?



Wouldn't that just apply to an aircraft in the glide? If you have 2 identical aircraft with the same power units and you increase the mass of one of them, there's no reason why it would penetrate the air any better in level flight - you'd just need more power to maintain the height at a fixed airspeed. There is no "wind drag" as such - aerodynamically, the aircraft doesn't know if it's windy or not. As far as it's concerned, it's just moving at a particular airspeed through an airmass. The fact that the airmass is moving (what we refer to as wind) doesn't change the amount of air moving past the aircraft at a particular airspeed, it just changes the groundspeed. Increasing the mass would just make it more stable in turbulence because it would have more inertia.

The reason is that all mavics are attitude limted to about 30 degrees. It refuses to go more than that unless you hack some parameters. It also is ground speed limited (not so much in sport mode), which ever come first.

So for an aircraft that weight 500g you get a forward force like
F=0.5*sin 30 => 0.25N
For a 1kg you get
F=1*sin 30 => 0.5N

So you will have a stronger force to driving it forward.
Why you not see any speed increase in no wind is that the speed limit in firmware kicks in and lower the the attitude.

You get drag from the TAS, otherwise it would accelerate to infinity speed, which don't happen.
If you don't believe me, try it for yourself. You need an app that can show the attitude though, or use atti-mode

I think you mix up things since the mavic are booth attitude limited and speed limited which ever come first. Took me a while before I realized this myself. So you can't just calculate:
ground_speed = wind_speed - max_speed

its more like:
ground_speed > wind_speed - max_speed
since the firmware adds attitude to 30 degrees when going against the wind.

Edited:
Think of a weightless drone, will it get any forward speed when you tilt it
I always compares 0 and infinty to understand things.

I will try to do an video about it where I show the difference. I flew my MM last week near my house in moderate winds that some may consider questionable. I received wind warnings suggesting it wouldn't be able to RTH, even though I was flying away from home into the wind, not going full forward stick, and still able to go at least 3mph. I was flying 90 to 120ft, enough to clear all trees.

Mass won't help thrust, but it will dampen it appearing to struggle as it compensates for constant wind changes.
The MM may sound horrible hovering in moderate and shifting winds, but it handles well for me. Just take it easy and gradually learn what it can and cannot handle.

The only no win situation I can think of is when you lose signal and RTH altitude and wind can't get it home. If you still have signal and you're drifting, lower altitude or just land. Point gimbal down while you land so you can see by landmarks where you're landing.

The unassuming propellers on your drone are marvels of engineering, silently generating the thrust that keeps your machine aloft. Choosing the right drone propellers goes beyond aesthetics; it significantly impacts performance, flight time, and even motor health. Let's delve into the technical details to pick the perfect prop for your drone.

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Before you read this article, I would recommend you to read our previous blog post regarding How to build your own drone with drone build kit options.

Propeller Sizing: Diameter and Disc Loading

• Diameter: Measured in inches, propeller diameter is directly related to the amount of air it can push. Larger diameters create more thrust but are also heavier and require more powerful motors. A common rule of thumb is that larger, heavier drones need larger propellers (think 6-inch props for a racing drone vs 2-inch props for a tiny whoop drone).
• Disc Loading: This refers to the ratio of the propeller's mass to the area of air it pushes (diameter squared). A higher disc loading indicates more mass per unit area, requiring more power from the motor for adequate thrust. Lighter weight props with a lower disc loading will be more responsive but may not provide enough thrust for heavier drones.

Propeller Pitch: Understanding the Angle of Attack

• Pitch: Imagine the propeller as a screw moving through air. Pitch is the distance a prop would theoretically travel forward in one revolution if it were moving through a solid medium. A higher pitch propeller "bites" more air with each rotation, generating more thrust but demanding more power from the motor. Lower pitch props offer faster acceleration and better maneuverability due to their lower drag, but with slightly less thrust. Pitch is usually denoted by a two-number system (e.g., 5x4), where the first number represents the pitch in inches and the second is the diameter in inches.

Balancing Performance: Thrust, Efficiency, and Flight Time

The ideal propeller will create enough thrust for your desired application while maximizing efficiency and flight time. Here's how these factors interplay:

• Thrust: Primarily determined by propeller diameter and pitch. Higher thrust allows for heavier payloads and more aggressive maneuvers, but comes at the cost of higher power consumption.
• Efficiency: The ratio of useful work (generating thrust) to electrical energy input. Lower pitch props tend to be more efficient, especially at lower throttle settings. However, a prop that's too low pitch might not provide enough thrust at higher throttle, forcing the motor to work harder and reducing efficiency overall.
• Flight Time: Directly linked to efficiency. Props that maximize efficiency will allow your drone to stay airborne for longer durations.

Additional Considerations for Fine-Tuning

• Material: Plastic propellers are the most common due to their affordability and decent performance. Carbon fiber propellers offer significant weight savings and improved durability for high-performance applications, but come at a higher price point.
• Number of Blades: More blades generally provide more stability and thrust due to increased air interaction. However, they also create more drag, reducing efficiency and top speed. Two-blade and three-blade propellers are the most common choices, with some racing drones opting for four or even five blades for maximum stability.
• Noise: Consider noise output, especially if you'll be flying in noise-restricted areas. Lower pitch props tend to be quieter due to their lower rotational speeds.

Choosing Drone Propellers according to payload:

In the context of drones, the payload refers to anything the drone is carrying besides its own weight. This can include a variety of items, depending on the purpose of the flight. Here's a breakdown of what falls under the umbrella of drone payload:

Common Payload Categories:

• Cargo: This is the most general term for anything the drone is transporting. It could be packages for delivery, supplies for remote locations, or even emergency medical equipment.
• Imaging Equipment: This includes cameras for aerial photography and videography, multispectral sensors for agricultural applications, or thermal imaging cameras for search and rescue operations.
• Scientific Instruments: Drones can be used to carry scientific instruments for tasks like air quality monitoring, weather data collection, or even wildlife observation.
• LiDAR (Light Detection and Ranging) Systems: These high-tech sensors create detailed 3D maps of the environment, used for surveying, construction planning, or archaeological research.
• Passenger Drones (Future): As drone technology continues to evolve, passenger payloads might become a reality, carrying people for short-distance transportation or scenic flights.

Additional Considerations:

• Weight: The weight of the payload is a crucial factor in choosing the right propellers and ensuring sufficient thrust for stable flight. Drone manufacturers specify maximum payload capacities for their models.
• Size and Shape: The size and shape of the payload can also affect the drone's flight characteristics. For example, a bulky object might create more drag compared to a streamlined package.
• Center of Gravity: The payload's position affects the drone's center of gravity, impacting its stability and maneuverability. It's important to ensure the payload is well-balanced and positioned according to the manufacturer's recommendations.

By understanding what constitutes a drone payload and its various considerations, you can make informed decisions about the type of drone and propellers needed for your specific application.

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The Perfect Partnership: Propeller Selection and Its Impact on Motor Performance

The propeller and motor choices for your drone are intricately linked, forming the heart of your machine's ability to generate lift and fly. Selecting the wrong propeller for your motor can have significant consequences. Imagine a high-powered motor struggling to spin a large, high-pitch propeller – it would drain battery life quickly and potentially overheat the motor. Conversely, a small, low-pitch propeller on a powerful motor wouldn't provide enough thrust, hindering performance and flight time. For optimal performance, the propeller needs to be matched to the motor's KV rating (kilovolts per revolution). A higher KV motor spins faster and is suited for lower pitch propellers that require less torque to turn. Lower KV motors, with their slower rotational speeds, benefit from higher pitch propellers that demand more torque. In our next blog post, we'll delve deeper into motor selection based on drone size and payload capacity, helping you choose the perfect motor to power your ideal propeller selection for a truly optimized drone!

The Perfect Match: Balancing Efficiency and Thrust

Now, let's see how motor KV and propeller pitch work together:

• Lower KV Motors (KV-KV): These motors excel at efficiency with their slower, high-torque rotations. The ideal propeller partners for such motors would have a lower pitch (e.g., 4x4 or 5x4). This combination allows the motor to operate efficiently without straining, resulting in longer flight times – perfect for lightweight drones and agile maneuvers.
• Mid-Range KV Motors (KV-KV): These motors offer a good balance between efficiency and power output. They can handle propellers with a moderate pitch (e.g., 5x4.5 or 6x4.5), providing sufficient thrust for mid-range payloads (1kg to 2kg) without sacrificing too much flight time.
• High KV Motors (KV and Above): Designed for raw power, these motors are ideal for heavy payloads exceeding 2kg. They can handle high-pitch propellers (e.g., 7x5 or 8x5), generating the necessary thrust to lift heavier weights. However, be aware that high KV motors and high-pitch propellers can be less efficient, potentially reducing flight time.

Case Studies: Motor & Propeller Pairings for Payload Lifts (1kg - 3kg)

Choosing the ideal motor and propeller combination for your drone hinges on the weight it needs to carry (payload capacity). Here are 5 case studies showcasing effective motor-propeller pairings for different payload ranges (1kg - 3kg):

Case 1: Lightweight Payload & Agile Flight (Up to 1kg)

• Motor: Brushless Motor (around KV)
• Propeller: 5-inch diameter, 4x4 pitch (plastic or carbon fiber)
• Number of Blades: 2 or 3
• Reasoning: A motor with a moderate KV rating (around KV) offers a good balance between efficiency and power for lighter drones. A 5-inch propeller with a 4x4 pitch provides enough thrust for basic photography or light FPV racing with a payload under 1kg. Two or three blades can be chosen depending on the desired balance between agility (fewer blades) and stability (more blades).

Case 2: Mid-Range Payload & Extended Flight Time (1kg - 1.5kg)

• Motor: Brushless Motor (around KV)
• Propeller: 5.5-inch diameter, 5x4.5 pitch (plastic or carbon fiber)
• Number of Blades: 3
• Reasoning: A slightly larger motor with a higher KV rating (around KV) tackles the increased weight of a 1kg to 1.5kg payload. The 5.5-inch propeller with a 5x4.5 pitch offers a good compromise between thrust and efficiency for extended flight times. Three blades provide a good balance between stability and maneuverability for this payload range.

Case 3: Moderate Payload & Stable Filming (2kg)

• Motor: Brushless Motor (around KV)
• Propeller: 6-inch diameter, 6x5 pitch (carbon fiber)
• Number of Blades: 3 or 4
• Reasoning: For a heavier 2kg payload, a motor with a lower KV rating (around KV) provides the torque needed to spin a larger propeller efficiently. A 6-inch diameter propeller with a 6x5 pitch generates sufficient thrust for stable flight. Carbon fiber props are recommended for their lighter weight and improved efficiency compared to plastic at this size. Three or four blades can be considered depending on the desired stability for filming applications.

Case 4: Heavy Payload & Professional Applications (2.5kg)

• Motor: Brushless Motor (around KV)
• Propeller: 6.5-inch diameter, 7x5 pitch (carbon fiber)
• Number of Blades: 3 or 4
• Reasoning: Professional drones carrying heavy payloads (2.5kg) often require powerful motors. A motor with a lower KV rating (around KV) offers the torque needed to handle a larger 6.5-inch propeller with a high pitch (7x5) for adequate thrust. Carbon fiber props are essential for both weight savings and efficiency. Three or four blades can be considered depending on the specific application, prioritizing stability with four blades for heavy payloads.

Case 5: Extended Range & Light Payload (Up to 1kg)

• Motor: Brushless Motor (around KV)
• Propeller: 6-inch diameter, 5x4 pitch (carbon fiber)
• Number of Blades: 2
• Reasoning: For prioritizing extended flight time with a light payload (under 1kg), a lower KV motor (around KV) can be paired with a larger, more efficient propeller. A 6-inch diameter propeller with a lower pitch (5x4) creates less drag while offering enough thrust for a lightweight drone. Two blades further minimize drag, maximizing flight time at the expense of some agility.

Resources and Experimentation

• Manufacturer Recommendations: A great starting point, manufacturers often suggest compatible propellers for their specific drone models.
• Online Communities: Drone forums dedicated to your model can be a valuable resource for prop selection advice based on real-world experience.
• Consult an Expert: Drone shops or experienced flyers can provide valuable insights tailored to your specific needs.

Remember, experimentation is key! Start with small adjustments and test fly in a safe, open area. By understanding the technical aspects of propellers and experimenting within safe parameters, you'll be well on your way to selecting the perfect propellers to propel your drone to new heights!

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