Hey all,For my internship I have to carry out a batch of experiments on an electric motor - propeller combination for a drone in order to determine the most efficient motor - propeller choice. At my disposal I have a 6 DoF load-cell to which I mount the motor and which can then give me readings on thrust and torque. I will be using only the readings for thrust in the vertical axis and the torque about the vertical axis. I also have at my disposal a stroboscope to measure propeller RPM. I do not have a wind tunnel and thus all my experiments will have to be static-thrust (hence, advance velocity of propeller =0).I have read a few papers on the subject (see here and here ) and all of them use the advance/free-stream velocity as their independent variable because they all have a wind tunnel and so can plot graphs of (something) vs. advance ratio (=distance the propeller moves forward through the fluid during one revolution/diameter of the propeller). What's worse, they define the propeller efficiency proportional to advance ratio; since in a static test the advance ratio =0, then the formula for efficiency would give me propeller efficiency=0 which is obviously not true!My question : how do I calculate propeller efficiency for a static test? Is there a way of changing free-stream velocity in order to "emulate" a wind-tunnel (some kind of idea like moving air around the wing rather than the wing through the air?)?If you have done such experiments or know of experiments that have been done by others, please suggest to me what to measure and to compare keeping in mind that I am searching to find the optimalmotor - propeller combo. So far, my idea is (excluding efficiency calculation which I hope you will be able to help me out with) to record:The experiment will go like this: for each motor type, test 5 prop types where for each prop type I apply different signal types to the motor (=> different duty cycles) in order to determine the best signal type for that motor-propeller combo. In total with 5 motor and prop types and, say, 5 different duty cycles it will make for a [5 X 5 X 5] thrust reading matrix of in total 125 elements. Therefore I will have to do 125 experiments.I appreciate your help for the efficiency calculation and also for suggesting, if you can, what other data I should collect!Best to you!
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Propellers are the essential component of any FPV drone as they determine the power, smoothness and responsiveness of the aircraft. These specialized airfoils attach to the motor hub and come in a variety of shapes, sizes, and blade counts. Understanding the basics of propellers is crucial for optimizing the performance of your quadcopter.
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Propellers are designed for different purposes, the pitch, shape and material all play a part in performance and flight characteristics. Here I will share what I think are the best propellers that you should get.
I’ve tried all major propeller brands and found HQ props to be one of the smoothest and easiest to tune. They seem to be more balanced and cause less vibration than others. I’ve also had better luck with triblades than twinblades when it comes to achieving smoothness.
The “smoothness” of the prop plays a big part in how well the drone flies, and how much we can push PID and filters in tuning. Propellers that produce less vibration will inherently have an advantage in that regard. The weight distribution of the blade and overall weight of the whole prop also matters, the easier it is to spin up and slow down, the faster it is to change RPM, which translates into faster response of the drone and better “propwash” handling.
I love the HQ 5×4.3×3 for its linear throttle response, which gives me very precise control through the whole throttle range. The responsiveness and grip are just awesome, the quad feels snappy and connected to the sticks.
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For a good racing prop, responsiveness and thrust output play a big part. To be responsive, the prop should be relatively light weight, and the weight distribution of the blade has to be optimized in order for RPM to change quickly.
The Gemfan Hurricane is a great performer in the high end of your throttle, lots of punch and very smooth, but perhaps slightly less precise in the lower end. They have reinforced hub and meant to take a beating around the race course. Bent props? Just bend it back and keep flying!
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If you prioritise smoothness and efficiency over raw power, these props are for you. The HQ 5.1×2.5×3 is an extremely efficient props based on my static thrust tests, and the prop wash handling is second to none.
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Not necessarily the best propellers in terms of performance, but they are cheap, durable and offers decent performance, it’s good enough for daily practice and bashing around.
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Great option for 5″ class that is under 250g (e.g. paired with 2004 motors).
Product Page:
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Hands down the best 7″ props I’ve flown, responsive, low vibration, decent thrust output.
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A decent alternative to the HQ DP, a great choice for cinelifters.
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Great props for long range builds. Works well on smaller 2506 motors.
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Recommendations for 6-inch propellers:
Recommendations for 3.5″ propellers:
Best 3.5″ Cinewhoop props:
Recommendations for 3″ propellers:
Best 3″ Cinewhoop Props:
What’s A Propeller?
Propellers, also known as 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 enables it to move in different directions. However, many drone pilots often overlook the importance of choosing the right propellers, leading to issues such as increased noise, reduced flight time, or even motor failure.
In this tutorial, we provide a comprehensive guide to the different factors that affect the performance of FPV drone propellers, including pitch, shape, and the number of blades. Whether you’re a beginner or an experienced pilot, this guide will help you understand how to choose the right propellers for your quadcopter, enhancing your flying experience. Learn everything you need to know about propellers and take your FPV drone flying to new heights.
Propeller Directions
Propellers are designed to spin in either a clockwise (CW) or counter-clockwise (CCW) direction. In a quadcopter, two motors spin CW and the other two spin CCW, so it’s important to match the propellers to the motors based on their intended direction of rotation.
On an FPV drone, the off-center placement of the propellers produces both thrust and rotation around the center of the drone. To counteract this rotation, it’s necessary to use two CW and two CCW props.
When purchasing propellers, they usually come in pairs of CW and CCW.
To generate downward thrust for the drone to take off, the propellers should spin in a way that allows the leading edge to cut through the air first, with the air then escaping through the trailing edge. You can easily determine the direction of a prop by identifying its leading edge, which is often labelled as either CW or CCW on the blade.”
How to Mount Propellers?
By default, Betaflight expects the motors to spin as shown in the diagram below. This means that you should install the CW prop on the motors at the top left and bottom right.
Pro tip: To make it easier to remember, just note that all front props spin into the FPV camera, while the rear props spin into the rear of the quadcopter.
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There are three types of propeller mounting in FPV drone motors: M5 threaded shaft, T-mount, and press fit.
M5 threaded shaft (5mm) is the most common in 5″ FPV drones (and larger rigs). The propeller is attached to a shaft with an M5 thread at the end and screwed tight with a self-locking nut (also known as a “nylon nut”). There are often spikes on the motor bell, which dig into the propeller and hold it in place.
In the T-Mount, the propeller is attached to a 1mm or 1.5mm thick motor shaft, secured by two M2 screws onto the top of the motor bell. This mounting is popular in less powerful 2″, 3″, and 4″ FPV drones.
Press-fit (or friction fit) is popular in small FPV drones such as tiny whoops and toothpicks because this mounting is extremely light weight. These drones are relatively low-powered, so the props are unlikely to fly off even in crashes.
Propeller Size
Propeller size is given in imperial inches (1″ = 2.54 cm).
When describing propellers, there are two types of formats:
L – length, P – pitch, B – number of blades:
For example, 6×4.5×2 (also known as 6045×2) propellers are 6 inches long 2-blade propeller and have a pitch of 4.5 inches. Another example is 5x4x3 (also known as 5040×3), a 3-blade 5″ propeller with a pitch of 4 inches.
You might sometimes see “BN” at the end of the numbers, which means “Bullnose.”
You might also see “R” or “C” after the size numbers, such as 5x3R. “R” indicates the rotation of the propeller, which stands for “reversed.” It should be mounted on a motor that spins clockwise. “C” is the opposite and should be used with motors that spin counter-clockwise, but usually, the letter “C” is ignored.
A propeller is said to be “heavier” when you increase the diameter, pitch, the number of blades, or all. It takes more torque to spin a heavier prop than a lighter prop.
Propeller Length
The length of a propeller refers to the size of the disc that it creates when it spins (or the distance from one tip of a two-blade prop to the other).
Propellers generate thrust by spinning and moving air. The faster the propeller spins, the more air it can move, which generates more thrust.
Did you know? FPV drones can’t fly in space because there is no air for propellers to move.
When the propeller pitch (explained below) and blade count are the same, a longer propeller can generate more thrust because it increases the surface area. This means you can accelerate faster, but it also requires more power from the same motor. However, longer propellers don’t necessarily mean faster flight – pitch is a more important factor (as explained below). Shorter propellers can spin up and slow down faster due to lower drag and momentum, which makes the drone more agile and responsive.
Propeller Pitch
Propeller Pitch refers to the distance a propeller travels during one revolution, and it’s measured in inches. Essentially, it’s how far the propeller would move forward if it were moving through a solid medium instead of air.
A propeller with a higher pitch moves more air with each revolution, which can create more thrust when the aircraft is traveling at high speeds. However, it also means that the propeller generates less thrust when the aircraft is not moving.
A higher pitch propeller can also create turbulence and prop wash, which can affect the performance of the aircraft. It also spins slower, which can make the aircraft less responsive. On the other hand, a lower pitch propeller is more responsive and can spin up and down faster, making it better for manoeuvrability.
Blade Count
Adding blades increases the surface area and hence creates more thrust. This is similar to making the propeller longer, except you can fit it in a smaller disk area. By increasing blade count improves grip in the air, but it also makes it less efficient and puts more strain on the motor.
For FPV drone pilots, both two and three-blade propellers are popular for racing and freestyle flying. Most pilots prefer three-blade propellers as they are a great balance between efficiency and power, they provide more grip in the air due to the extra surface area compared to two-blade. On the other hand, two-blade is more efficient as they creates less drag and draw less current, hence great for long range flying.
There are propellers with even more blades, such as quad-blade and hex-blade propellers. Quad-blade propellers are said to be great for indoor tracks and cornering, but they are less efficient than tri-blade and spin at a lower RPM at the same specs. Hex-blade propellers are not recommended for normal flight due to its extreme inefficiency, but they can be used to put on a show due to their unique appearance. These props with more than 3 baldes are more common on micro quads, where space is limited and you can’t simply make the blade longer to increase surface area.
Weight
When it comes to 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 spin them. This can lead to higher torque loading, making the motor work harder and possibly decreasing overall performance.
Lighter propellers have less moment of inertia and can change RPM faster, making your drone feel more responsive. They also work better with a wider range of motors because they require less torque to spin up.
The weight distribution of the blades also makes a difference. Propellers with the blade’s center of mass closer to the hub are better. However, this means the tip of the prop gets thinner and easier to break. If the center of mass is further away from the hub, there is more drag and the propeller is harder to speed up and slow down.
What Propellers To Use on an FPV Drone
Here is a table that shows which size propeller to use with different motors and voltages..
It’s important to choose your propeller size first because it determines the size of the frame you can use.
The propeller size you choose also depends on the type of flying you want to do. The 5-inch propeller is the most popular because it’s versatile and can be used for racing, freestyle, and even carrying a full-size GoPro camera. The 7-inch propeller is better for long-range flights because it can carry a much larger battery. You can learn about all the different drone sizes in this post, I won’t repeat it here.
Here are my recommendations for 5-inch propellers..
Thrust
Thrust is measured in grams. For your drone to hover, the propeller needs to produce at least 1 gram of thrust for every gram that your drone weighs. To perform stunts, or even just to take off or fly forward, your drone needs 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 perform well when the drone is stationary, but not so well during a cruise, while others perform well at high speeds but poorly when hovering. You want a prop that balances these factors and can create a good amount of thrust at different speeds.
To find the best prop for your drone, look up motor thrust tests to see what prop size work best with your motor. Keep in mind that props perform wildly differently when strapped to a thrust stand in a static setting compared to when they’re actually flying through moving air. Props can produce 20-30% less thrust in the air than on the ground.
To accurately assess prop performance, it needs to be tested at the speed your drone normally flies at. However, few people have access to wind tunnels for this type of testing. So, take performance tests with a grain of salt as they may not be an accurate representation of real-world use.
Smoothness
In the hobby, people often use the term “smoothness” to describe the quality of a motor or propeller. It’s not something that can be measured quantitatively, but more of a feeling that pilots have. In my experience, lower pitch props tend to be smoother because the motor can change RPM more easily and quickly. This allows the drone to respond faster to correct errors and reduces something called “prop wash”.
Speed
A propeller that creates lots of thrust with high pitch doesn’t necessarily make a drone faster than a lower pitch propeller that generates less thrust. As the propeller’s speed increases (which is measured in rotation per minute – RPM), so does the drag, requiring more torque from the motor to turn.
The theoretical maximum speed of an aircraft can be calculated using the equation:
Max Speed (in inch per second) = Max RPM * Propeller's Pitch / 60
In real life, factors such as air resistance, head wind, and angle of attack etc can all affect a drone’s speed.
Thrust affects acceleration and angle of attack, while RPM affects top speed. To achieve the best speed for your FPV drone, you need a balance between thrust and RPM.
Are Larger Props Better?
1. Responsiveness: A larger prop means a higher moment of inertia, leading to reduced responsiveness. This is particularly noticeable when using motors that typically drive 5-inch props like the 2207 size. On these motors, a 7-inch or even 6-inch prop will be less agile in responding to quick, sharp control inputs compared to a 5-inch prop. You will need a bigger motors to compensate but it will add weights and requires more powerful battery and electronics.
2. Thrust and Efficiency: Larger props generate more thrust, making them more efficient – they can carry more weight, even with the same motor. The increased efficiency means you get more thrust for the same power or the same thrust at a lower power requirement.
3. Vibration: As you increase prop size, expect more vibration. This is amplified by larger, less stiff frames.
4. Top Speed and Prop Wash Handling: Larger props tend to have a lower top speed but better prop wash handling. However, they are often more efficient, capable of maintaining higher speeds over longer periods.
Weather and Temperature
Cold weather poses significant challenges for drones. As explained in our guide “How to fly FPV in the winter“, not only does it negatively impact battery performance, but it can also affect propellers. Depending on their material, propellers may stiffen and become brittle in cold temperatures, increasing the likelihood of breaking upon collision.
Impact of Altitude
Altitude can drastically affect air density and, consequently, the performance of your FPV drone. In areas of lower air density, such as high altitudes, you’ll experience less thrust from the same motor RPM. This results in the drone feeling more sluggish and less powerful, similar to the effect of using lower-pitch propellers. Therefore, when flying at high altitudes, it’s advisable to use higher-pitch propellers to compensate for the reduced air density.
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