All about Multirotor Drone FPV Propellers

FPV Drone Propellers are the key component that keeps your multirotor in the air,
they have the most direct impact on how your machine flies, and over the lifetime
of your multirotor they are likely to add up to be the biggest investment that you make to
keep flying. They are also going to be the component that is damaged and replaced the most often.
Taking time to choose the right propeller for your multirotor, and how you
want to fly, will allow you to get the best out of your machine.

There are 5 main variables that need to be considered when choosing a multirotor propeller:

1. Size
2. Pitch
3. Blade Configuration
4. Material (Durability)
5. Design (Efficiency)

The first thing to understand about multirotor propellers is that all the above
variables are interlinked, and everything is a compromise. A common multirotor
system has a maximum amount of power that it can provide which is mainly limited by
the discharge capacity of the Lithium Polymer batteries and the motors. Propellers,
depending on the variables chosen, change how this power is delivered when flying.

A common analogy is to think of propellers on a multirotor
like the wheels and gearbox in a car.

Propellers are commonly described using a series of numbers separated by an
X that relate to size, pitch, and blade configuration. For instance, you may see a
propeller being described as a 5×4.3×3, the first number corresponds to the Size,
5 inches in this case. The second to the pitch, 4.3 inches in this case.
And the third to the number of blades, which in this case would be a 3 bladed propeller.

Size (in inches) X pitch (in inches) X number of blades

FPV Drone Propellers Size

The first thing to consider when looking for a propeller for your multirotor is the size.
This will most often be physically dictated by the type of frame you are flying.
Though in some cases, there can be benefits to running smaller or larger propellers
than recommended, if you are looking for a particular flying characteristic.

Propeller size is directly linked to thrust, responsiveness and the
amount of ‘grip’ the multirotor will have in the air.

A larger propeller sweeps through more air and therefore takes more energy
to get spinning and will respond slower to inputs from the motors and consume more power.
The benefits of a larger propeller are increased thrust, and because it is working
over a larger area, it will have a better ‘hold/grip’ in the air and more authority when making
direction changes.


Like having larger wings on a plane, having larger propellers will also change
how the multirotor falls through the air. Because of this people will often say that
multirotors with larger propellers feel more ‘floaty’, as they take longer to fall
and sometimes even feel like they glide when the throttle is closed.

Smaller propellers will respond faster to inputs because they are sweeping
though less air and require less power to change speed. If used on the same frame,
smaller propellers will in general provide less thrust and have less control
authority due to the fact they cannot move as much air but will also consume less
power. A multirotor with smaller propellers will feel less floaty and fall faster,
sometimes this can be a desirable attribute for instance if needing to regularly
change altitude quickly to get under gates/branches etc.

Just like wheels on a car, the size of the propeller needs to be matched to the
rest of the power system. For example, putting 3” props on a motor designed for
5” propellers will result in extremely high RPM and power draw and will create
very little thrust. Likewise, putting large props on a small motor will likely be
too much for the motor to spin, this will create very little thrust,
lots of heat and excessive current draw.
Extreme mismatches can damage motors and ESC’s.

The most common prop size used in FPV multirotors is 5”, these are in
general most suited to motors in the 2204 – 2307 size range.
For more information on motors please refer to the motors article.

FPV Drone Propellers Pitch

Pitch refers to the angle of each of the blades on the propeller.

Most simply put, the pitch of a propeller is how far forward that propeller would
move in one revolution in a perfect world. (no drag or losses etc).

Propeller pitch can be thought of like gearing in a car or bike:

High pitch will usually result in more overall thrust and top end speed, but less
low-end torque. Like trying to drive a car only in 5th gear. A high pitch propeller
will respond to inputs slowly, use more power and will only be efficient when
the multirotor is moving quickly

Low pitch will result in less overall thrust and top end speed, but more low-end torque.
Just like driving a car in first or second gear. A low pitch propeller will respond
quickly to inputs and use less power but will only be efficient at low speeds,
fast direction changes are much easier and more responsive with a lower pitch
propeller due to the increased low end torque.

Choosing the correct FPV drone propellers for your application comes down to
picking something that will work with the rest of your multirotor system and the
type of flying that you would like to do. If you have chosen large powerful motors
and plan to fly fast in large open areas then a high pitch propeller will be suitable,
if you have smaller motors or are planning to use the multirotor in more confined
spaces and make lots of direction changes then a lower pitch propeller will be
suitable as it will be more responsive and the low end torque will help it change
direction quickly.

Based on the most common 5” size propellers, a pitch between 4 and 4.5 inches will suit most
applications and be a good blend of responsiveness/torque and top end speed/thrust.

FPV Drone Propellers Blade Configuration

Blade configuration refers to the number of individual blades on a propeller.
The most Efficient propeller is actually single bladed, but due to it’s imbalance it is
not practical for use in most flying aircraft.

Increasing the number of blades on a propeller is a suitable substitute to
increasing the size where space is constrained, and has very similar characteristics.
This is why small fighter planes in WW2 used to have 3 and 4 bladed propellers,
they needed more thrust and power but could not fit larger propellers because they
would hit the ground, so they added more blades.

Originally multirotors largely used 2 bladed propellers like planes, they are more efficient for their size because they only have two blades creating drag in the air. But as motors became more powerful, higher performance was required and frames became smaller, there was not enough space to increase the size of the propellers to get the required thrust and power needed.

Due to complicated physics and fluid dynamics, increasing the number of blades is not as efficient as increasing size. So a prop with double the number of blades will not perform as well as one twice the size but it does provide more thrust at the cost of slightly more power.

Similar as discussed in the size section, increasing the number of blades will increase the amount of thrust and grip in the air, at the cost of responsiveness and increased power consumption. If you are planning to fly somewhere where you will be making lots of fast flowing turns and need lots of grip in the corners, more blades will be suitable. Just like increased prop size, more blades will have a more floaty feel, and feel like it will glide off throttle.

Less blades are preferable where faster motor response is needed and thrust is not as critical. Serious racers with new ultralight racing frames will quite often use bi-blade propellers because the frame is so light that the amount of thrust required is much less, and therefore the faster response of the lighter and less ‘draggy’ props can be realised.

In the most common 5 inch category, it is generally agreed that tri-blade (3 blades) FPV drone propellers provide the best balance of efficiency, thrust and grip.

One aspect of prop configuration that is often overlooked is durability. If you are just beginning to get into FPV you will be crashing A LOT! It is also highly likely that you will not be using the full power of your multirotor. So while all the pilots that inspire you run tri-blades, it can be a very good move to learn on bi-blade props. Just like old school road spikes, there is no way for a tri-blade propeller to hit the ground without contacting two blades before the hub/motor hits the ground. This means that you are likely to bend or break a blade in most crashes. Bi-blades simply by design can rotate out of the way in a crash, and because of this are much less likely to bend or break. Depending on how long it takes for you to become proficient with flying, this can add up to a significant saving over the course of the learning period.

FPV Drone Propellers Material

The material a propeller is made from has a significant effect on its attributes including efficiency and sound. Generally, the most critical effect for multirotor pilots is durability.

Originally propellers were predominantly manufactured in fibreglass reinforced plastics which are very stiff for their weight and this allows the propeller to keep the correct and most efficient shape regardless of how fast it spins, but when it hits something like the ground or a branch, that stiffness means it will shatter and the quad can no longer fly. Recently propellers are being made using polycarbonate a type of plastic that has good stiffness but will bend rather than break if it hits something hard. This means that if you crash a blade may bend but it can quite often be bent back into shape rather than having to replace the prop.

There are other materials used in propellers but polycarbonate or PC as it is often referred to is generally considered to be the best.

Another factor to consider is the climate in which you fly, the plastics used to make propellers for multirotors are mainly thermoplastics, meaning their properties change depending on temperature.
If you are flying in winter or in a very cold climate you might want to use a ABS prop, as PC can become brittle and break more often. If you are flying somewhere very hot you may need to use a glass fibre reinforced propeller as both ABS and PC can become very soft and less efficient/durable. For most pilots in most locations, PC propellers will be suitable and the most durable.

FPV Drone Propellers Design

Propeller design can vary wildly, as all manufacturers want to create something that is eye-catching and looks cool on your multirotor. When shopping for propellers, consider how the design will affect all aspects of the use and performance of your machine. Efficiency is a big focus for propeller design, everyone wants the holy grail of more thrust and longer flight times. This leads to creative ways to reduce drag, like little wingtips on the FPV drone propellers blades. Often these efficiency increasing features are very fragile and once damaged will affect the balance of the propeller significantly, causing vibrations that will show up on HD footage.

Sometimes it is tempting to go for a very durable solidly built propeller because you will have to replace them less after crashes. It is important to note that as the forces from crashing are dispersed through the multirotor, usually the prop acts like a fuse and bends or breaks, absorbing a lot of the crash energy. If you choose a very tough/strong propeller, that energy may be transferred further into the frame and may damage the motors or the carbon components.

Conclusion

Overall, FPV drone propellers are probably the most critical component on a multirotor, but quite often the level of attention paid to finding the best suiting propeller is much less than what is spent looking for the best motors/ESC’s etc. Hopefully this article has provided a little more insight into what features to look for to find the prop that will best suit your flying needs. At the end of the day, specs only go so far to describe how a propeller will perform, so experiment until you find something that feels good for you.