Info about Propeller
What is a propeller?
Propellers, also called props, are the unsung heroes of an FPV drone. They play a crucial role in generating thrust that lifts the quad off the ground and allows it to move in different directions. However, many drone pilots often overlook the importance of choosing the right propellers, leading to problems such as increased noise, reduced flight time, or even engine failure.
In this tutorial, we provide a comprehensive guide to the different factors that affect FPV drone propeller performance, including pitch, shape, and number of blades. Whether you're a beginner or an experienced pilot, this guide will help you choose the right propellers for your quadcopter to enhance your flying experience. Learn everything you need to know about propellers and take your FPV drone to new heights.
propeller instructions
Propeller direction: CW and CCW
Propellers are designed to rotate either clockwise (CW) or counterclockwise (CCW) . In a quadcopter, two motors rotate clockwise and the other two rotate counterclockwise. Therefore, it is important to match the propellers to the motors based on the intended rotation direction.
In an FPV drone, the off-center placement of the propellers creates both thrust and rotation around the center of the drone. To counteract this rotation, two CW and two CCW props must be used.
To create downward thrust for the drone to take off, the propellers should rotate so that the leading edge cuts through the air first and then the air escapes through the trailing edge. You can easily determine the direction of a propeller by identifying its leading edge, which is often marked as CW or CCW on the blade.
How do you mount propellers?
By default, Betaflight assumes that the motors are rotating as shown in the diagram below. This means that you should mount the CW support on the top left and bottom right motors.
Pro tip:
To make it easier to remember, just note that all the front props rotate towards the FPV camera, while the rear props rotate towards the back of the quadcopter.
There are three types of propeller mounting in FPV drone motors: M5 threaded shaft, T-mount and press fit.
M5 (5mm) threaded shaft is most common on 5" FPV drones (and larger rigs). The propeller attaches to a shaft with M5 threads on the end and is bolted on with a self-locking nut (also called a "nylon nut"). There are often serrations on the bell housing that dig into the propeller and hold it in place.
The T-mount mounts the propeller to a 1mm or 1.5mm thick motor shaft and secures it to the top of the motor bell housing with two M2 screws. This mount is popular for less powerful 2", 3" and 4" FPV drones.
Press-fit (or friction-fit) is popular on small FPV drones like Tiny Whoops and Toothpicks because this mount is extremely lightweight. Since these drones are relatively low-powered, the propellers themselves are unlikely to fly off in accidents.
propeller size
The propeller size is given in inches (1″ = 2.54 cm).
There are two types of formats for describing propellers:
L x P x W
LLPP x B
L – length, P – pitch, B – number of wings:
For example, 6x4.5x2 propellers (also known as 6045x2) are 6-inch long, 2-blade propellers and have a 4.5-inch pitch. Another example is 5x4x3 (also known as 5040x3), which is a 5-inch, three-blade propeller with a 4-inch pitch.
At the end of the numbers there is sometimes “BN”, which means “bullnose”.
You may also see "R" or "C" after the size specifications, such as 5x3R. "R" indicates the rotation of the propeller, which stands for "reverse." It should be mounted on a motor that rotates clockwise. "C" is the opposite and should be used on motors that rotate counterclockwise. However, the letter "C" is usually ignored.
A propeller is said to be "heavier" when the diameter, pitch, number of blades, or all of them are increased. More torque is required to turn a heavier propeller than a lighter propeller.
Propeller length:
The length of a propeller refers to the size of the disk it creates as it rotates (or the distance from one tip of a two-bladed propeller to the other).
Propellers generate thrust by spinning and moving air. The faster the propeller spins, the more air it can move, creating more thrust.
If the propeller pitch and number of blades are the same, a longer propeller can produce more thrust because it increases the surface area. This means you can accelerate faster, but it also requires more power from the same engine. However, longer propellers do not necessarily mean faster flight - pitch is a more important factor.
Shorter propellers can spin and slow down faster due to lower drag and momentum, making the drone more agile and responsive.
Propeller pitch:
Propeller pitch is the distance a propeller travels during one revolution and is measured in inches. Essentially, it is how far the propeller would move forward if it were moving through a solid medium instead of air.
A higher pitch propeller moves more air with each revolution, which can produce more thrust when the aircraft is traveling at high speeds. However, this also means that the propeller produces less thrust when the aircraft is stationary.
A higher pitch propeller can also create turbulence and propeller waves that can affect the aircraft's performance. It also rotates slower, which can make the aircraft less responsive. On the other hand, a lower pitch propeller is more responsive and can rotate up and down faster, improving maneuverability.
Adding blades increases the surface area and therefore generates more thrust. This is similar to making the propeller longer, except you can fit it into a smaller disc area. Increasing the number of blades improves grip in the air, but it also becomes less efficient and puts more strain on the motor.
Both two- and three-blade propellers are popular among FPV drone pilots for racing and freestyle flying. Most pilots prefer three-blade propellers as they offer a good balance between efficiency and performance and provide more grip in the air due to the larger surface area compared to two-blade propellers. On the other hand, two-blade aircraft are more efficient as they create less drag and use less airflow, making them great for long distance flying.
There are propellers with even more blades, such as quad blade and hex blade propellers. Four blade propellers are said to be great for indoor tracks and cornering, but they are less efficient than three blade propellers and spin at a lower RPM for the same specifications. Hex propellers are not recommended for normal flight due to their extreme inefficiency, but they can be used for staging a show due to their unique look. These props with more than 3 blades are more common on micro quads where space is limited and you can't easily extend the blade to increase surface area.
Weight:
With propellers, weight is an important factor to consider. In general, lighter propellers tend to perform better. Heavier propellers have more mass on each blade and require a more powerful motor to drive them. This can result in a higher torque load, making the motor work harder and potentially reducing overall performance.
Lighter propellers have a lower moment of inertia and can change speed more quickly, making your drone feel more responsive. They also work better with a wider range of motors because they require less torque to rev up.
The weight distribution of the blades also makes a difference. Propellers where the center of gravity of the blade is closer to the hub are better. However, this means that the tip of the prop becomes thinner and is more likely to break. If the center of gravity is further from the hub, there is greater drag and the propeller is harder to accelerate and slow down.
It is important to choose the size of your propeller first as this will determine the size of the frame you can use.
The propeller size you choose will also depend on the type of flight you want to do. The 5-inch propeller is the most popular because it is versatile and can be used for racing, freestyle, and even to carry a full-size GoPro camera. The 7-inch propeller is better for long-distance flights because it can accommodate a much larger battery.
Thrust:
Thrust is measured in grams. In order for your drone to hover, the propeller must produce at least 1 gram of thrust for every gram your drone weighs. To perform stunts or simply take off or fly forward, your drone will need more than 1 gram of thrust per gram of weight.
Propellers produce more thrust when they spin faster and less when they spin slower. The speed of the drone also affects the amount of thrust produced. Some props work well when the drone is stationary but not so well in cruise flight, while others work well at high speeds but poorly in hover. You want a propeller that balances these factors and can produce good thrust at a variety of speeds.
To find the best propeller for your drone, look at motor thrust tests to find out which propeller size will work best with your motor. Remember that propellers perform very differently when strapped to a thrust stand in a static environment than when they are actually flying through moving air. Propellers can produce 20-30% less thrust in the air than on the ground.
To accurately assess the propeller's performance, it must be tested at the speeds your drone normally flies at. However, few people have access to wind tunnels for this type of testing, so take performance tests with caution as they may not be an accurate representation of actual usage.
Smoothness:
In the hobby world, the term "smoothness" is often used to describe the quality of a motor or propeller. This cannot be measured quantitatively, but is more of a feeling that pilots have. In my experience, propellers with a lower pitch tend to be smoother because the motor can change speed more easily and quickly. This allows the drone to respond more quickly to correct errors and reduces what is known as "propeller wash".
Speed:
A propeller that produces a lot of thrust at a high pitch won't necessarily make a drone go faster than a lower pitch propeller that produces less thrust. As the speed of the propeller increases (measured in revolutions per minute - RPM), drag also increases, requiring more torque from the motor to spin.
The theoretical maximum speed of an aircraft can be calculated using the following equation:
Maximum speed (in inches per second) = Maximum RPM * Propeller pitch / 60
In real life, factors such as air resistance, headwind, angle of attack, etc. can affect the speed of a drone.
Thrust affects acceleration and angle of attack, while RPM affects top speed. To get the best speed for your FPV drone, you need a balance between thrust and RPM.
Are bigger props better?
1. Responsiveness:
A larger propeller means a higher moment of inertia, which results in reduced responsiveness. This is especially noticeable when using motors that typically drive 5-inch propellers, such as the 2207 size. With these motors, a 7-inch or even 6-inch propeller will be less agile in responding to quick, sharp control inputs compared to a 5-inch propeller. To compensate, you need a larger motor, but that adds weight and requires a more powerful battery and electronics.
2. Thrust and efficiency:
Larger propellers produce more thrust and are therefore more efficient - they can even carry more weight with the same engine. The increased efficiency means you get more thrust with the same power, or the same thrust with less power required.
3. Vibration:
As you increase the propeller size, you will have to expect more vibration. This is exacerbated by larger, less rigid frames.
4. Maximum speed and handling of propeller washing:
Larger propellers tend to have a lower top speed but better handling of propeller wash. However, they are often more efficient and can maintain higher speeds for longer periods.
Weather and temperature:
Cold weather presents major challenges for drones. As explained in our guide on How to Fly FPV in Winter, not only does this negatively affect battery performance, but it can also affect propellers. Depending on their material, propellers can become stiff and brittle in cold temperatures, increasing the likelihood of breakage in a collision.
Influence of altitude:
Altitude can drastically affect the air density and therefore the performance of your FPV drone. In areas with lower air density, such as high altitudes, you will experience less thrust at the same motor speed. This will make the drone feel sluggish and less powerful, similar to using lower pitch propellers. Therefore, when flying at high altitudes, it is advisable to use higher pitch propellers to compensate for the reduced air density.