It’s time to talk about miniquad propellers! Props are sets of specialized airfoils radiating from a strong central hub which bolts up to an engine or motor. For quadcopters, these things are the “wings” or the aircraft.  Like helicopters and airplanes, the wings make a huge difference in how your aircraft flies! So what do you look for when buying props? Lets get into it:

Measuring Performance

Your prop really only has two jobs on your quadcopter: to generate thrust and torque.

Thrust is the downward force created by the movement of air induced by the propeller. It is generally measured in pounds or grams. If, at any given moment, the net downward thrust from all four of your propellers is greater than the weight of your quadcopter, than your quad will climb. If it is equal to your quadcopters weight, than the quad will hover. The trick with quadscopters is thrust is both responsible for holding the copter in the air, and for propelling it forward. For this reason, most quadcopters can produce as many times more pounds/grams of thrust than they weigh.

Propellers fundamentally create more thrust by spinning faster, and less by spinning slower. They are also greatly affected by how fast they are moving through the air (e.g. how fast your quadcopter is flying). Some props produce tons of thrust while sitting still, but very little while actually flying. Others generate tons of thrust while flying at high speed while having pitiful thrust values in a hover. Ultimately you want a balance between the two – a prop that creates a good amount of thrust at a given RPM throughout the range of airspeeds your quadcopter is expected to fly. From this figure we can also derive efficiency – which is how much thrust a prop can produce with a given amount of power at a given airspeed. More efficient propellers will last longer on their battery power and will result in cooler motors – both very beneficial things!

Torque is generated when the propellers either speed up or slow down. It is a vital part of multicopter flight because it is responsible for giving the copter the ability to turn on the yaw (flat) axis. Torque is largely a result of a propellers resistance to increasing or decreasing in speed. Generally, a prop that requires more torque will mean your quadcopter has a crisper, more consistent yaw axis. You can increase the torque your props generate by making them longer, adding more blades or increasing the pitch of the blade – we’ll talk about all of that later.

Ultimately, props are difficult to measure. The reason is they perform wildly differently when strapped to a test stand compared to when they are actually flying around through moving air. Around the web, you will likely find many helpful people who do thrust tests on different types of props. These thrust tests are almost exclusively done on test set-ups in a static setting – the prop is strapped to the ground so that it doesn’t move while it rotates. This is a problem – props are designed to operate in moving air! It’s important to remember that the results of these tests are not the end-all be-all of performance of props. To get an accurate assessment of a propellers performance, it needs to have it’s thrust measured while it is traveling at the speed that your miniquad cruises at. Unfortunately, not many people in the hobby have wind tunnels to accomplish this with, so it’s unlikely we will ever get that kind of data.

For now, just take performance tests with a grain of salt. They do tell you some things, like how the props will perform in a punch out – but they don’t say much about how they handle themselves at speed.

The Numbers

When you are looking at props at your favorite store, they are generally organized by their “numbers”. These numbers look like “5045” or “5×4.5×3”. The first number (“5”) is the size of the prop in inches. The second number set (“45” or “4.5”) indicates the pitch of the prop in inches. In the former case, the number needs to be divided by 10. The last number (“x3”) will specify the number of blades on the prop. In many cases this is omitted and the prop is referred to as a “tri-blade” or “quad-blade”.

Tip: If you don't know the numbers of a prop, it is usually printed on the blades. 5x4R here denotes a clockwise rotating 5" sized prop with 4" of pitch. If the number was missing the 'R' it would rotate counter-clockwise.

Tip: If you don’t know the numbers of a prop, it is usually printed on the blades. 5X4R here denotes a clockwise rotating 5″ sized prop with 4″ of pitch. If the number was missing the ‘R’ it would rotate counter-clockwise.

Following explains how the prop size, pitch and blade count will affect your flying:

Size

This is simply the length from tip to tip of the prop in inches. When choosing a prop size, you are restricted to the sizes your frame supports. For instance, a frame that supports 6” props will support 6” props and down, but will not support 7” props. You should generally buy a frame that fits exactly the prop size you want to fly, for weight savings and agility. We recommend you buy a frame that supports 5” props and use those for your first miniquad.

Longer propellers generate more thrust when rotated at the same speed. This means you can accelerate faster but also means you pull more power from the same motor. Extra length does not necessarily mean you will fly faster – that is more determined by pitch (below). Shorter propellers are able to spin up and slow down faster, which translates to increased agility of the aircraft. Miniquads almost exclusively use 4”, 5” and 6” props, with a few 3” quadcopters appearing on the market as of mid-2016.

Blade Pitch

This is the “bite” of the propeller, specifying how much air it “screws” through in one full revolution. More pitch means you have more thrust when your aircraft is traveling at high speed, but also means you have decreased thrust when it is not moving.

pitch

Pitch represents the amount of air the prop wants to fly through for a single revolution. Source: pilotfriend.com

An aircraft can move no faster than the pitch of the prop allows it to. You can determine the speed at which your propeller will generate zero thrust with the following equation: MaxRPM * Pitch / 720. This will give you the maximum speed of your aircraft in feet per second. Your multirotor will be much slower than that calculated speed due to it’s high drag – probably something like 50% of that number. You only have a few options when picking pitch among most multirotor props. We recommend picking 4” or 4.5” pitch unless you specifically know what that you want less or more.

Number of Blades

The number of blades on the prop. Adding blades increases the amount of thrust a prop generates but generally makes it less efficient at creating that thrust. This is similar to going to a longer propellor – but in the case of using multiple blades, you don’t have to deal with the longer blades. This is why most WWII airplanes had multi-bladed props – their props were already so massive that they were within inches of the ground when the airplane was on the runway.

Miniquad pilots lately have migrated in droves to 5” tri-blade props. For whatever reason, the operating environment of our miniquads negates the inefficiencies of tri-blade propellors such that three blades are simply better than two blades. Tri blades also have a torque curve which makes the yaw axis of a quadcopter more responsive.

4, 5 and 6-bladed prop designs are also available. These additional blades have diminishing returns over the 3-bladed designs. Some pilots swear by 4-bladed props, though. These can be especially good if you are thinking of building a 4″ quad.

If you are a brand new pilot, you should start out with 2-bladed props. They are cheaper and easier to maintain and the flight characteristics you get out of tri-blades means nothing to a novice. Once you’ve become proficient in acro mode, we recommend you use up all your 2-bladed props and move to tri-blades. At least try them out. Everyone we’ve met who has tried tri-blades did not go back.

Price

Multirotor props are generally sold in 2 or 4 packs. Make sure when you buy them that you get an equal number of counter-clockwise and clockwise props. Most of the time each pack contains one prop of each type but sometimes that is not the case, so make sure you pay attention. Most plastic props will cost between $2 and $5 for a set of 4, with 3+ bladed props generally being slightly more expensive than the two-bladed varieties.

Other Propeller Attributes

There are a few other aspects to props that you should pay attention to when making your buying decision. As a beginner, these attributes probably won’t play much of a role because you won’t have much basis for comparison. As you get more stick time, though, you may choose to begin experimenting with bullnose props, durable props, or props with funky airfoils. When you do, it might be helpful to know what to expect and what sets these props apart from the rest.

Chord Size (or “Bullnose”)

The chord of the propeller is the relationship between the average width of the blade and its overall length. In airplane propeller design, the tip of the propeller blade is made smaller than the rest of the propeller to balance the thrust load across the blade (remember – the tips move faster than the rest of the prop). Quadcopter pilots care less about the load balance of the prop and more about the overall thrust it generates. As a result, drone pilots have found an easy way to create a prop that generates more thrust was to buy props that were 1 or 2 sizes too big, then cut off the thin tip of the prop – creating a big, fat prop in a smaller size. This style of prop is called “bullnose”. In the last year, manufacturers have begun selling this style of props direct from the factory so you no longer have to do the cutting yourself. Bullnose props have a very distinct look:

Regular chord vs Bullnose

Bullnose chord vs regular (Credit: innov8tivedesigns.com)

They can generally create the highest thrust levels for their pitch, size and blade-count. Similar to tri-blades, the extra weight on the tips of the blades increases the torque required to spin them and improves the responsiveness of the yaw axis on the quadcopter. Unfortunately these positive aspects come with a cost – they are considerably less efficient than standard props and will therefore stress your power system more and result in lower flight times.

Material Composition

Props are made out of all kinds of different plastic compounds (and sometimes composites like carbon fiber). These compounds affect the stiffness of the prop as well as its durability.

Stiffer props generally tend to fly better, but the props are liable to break in almost any crash. On the other hand, propellers made from more malleable plastics have the propensity to bend, rather than break, in a crash. These props do tend to have balancing problems as a result of their malleability.

It’s hard to make a call on which variant is better. And some props use plastics that settle in a good middle ground. You really need to try it out to see what you prefer.

Hub Size

The hole in the center of the prop can be an important consideration. Almost every miniquad motor uses a 5mm motor shaft, so you want props with a 5mm hole. If you get a prop with a bigger hole size, you’ll need to add on adapters, which often do not perfectly center, causing vibrations. If you get a smaller hole size, you’ll need to drill a bigger hole for each prop you want to use. Fortunately all of the props listed below will have 5mm holes so you can generally ignore this if you buy from known vendors.

Balancing

This is a nice prop balancer you can get from GetFPV here.

This is a nice prop balancer you can get from Amazon here.

The topic of balancing props pops up every once and awhile in the community. The idea is that most props you buy will not have each blade weigh exactly the same as its mates. By buying a balancing stand and adding or removing weights from the blades as needed, you can get your props perfectly balanced. A perfectly balanced prop will vibrate less, allowing you to tune your quadcopter more tightly so that it can fly at the bleeding edge of handling performance.

I have a homebuilt balancing stand and I’ve put many props from many manufacturers on it. The fact is that the pro-balancing crowd is right – most props are not perfectly balanced from the factory. Balancing these props will improve the tunability and thus performance of your miniquad.

However, do not fall into the trap of thinking this is a required task. None of us at propwashed balance our props, and most pro pilots we know do not either. The thing is, as miniquad pilots we go through so many props that the amount of time it would take to balance each one would kill the fun of the hobby (unless you are into that sort of thing).

The bottom line: your quad will fly great without balancing your props if you stick to the manufacturers below. Consider learning to balance once you become a more advanced pilot and want to push the boundaries.

Popular Prop Brands

There are currently only a few major prop brands on the market. Part of the fun of flying miniquads is experimenting, and all of these brands have their upsides and downsides. We recommend you try them all out as you learn to fly.

DAL

DAL 5045 Tri-blade V2

DAL 5045 Tri-blade V2

DAL has traditionally focused on extremely durable props. It is an accomplishment to break one of these things. Instead, they tend to bend. You can generally fix the bends by hand but after awhile they become so distorted that they cause un-flyable vibrations.

We did an overview of the different DAL offerings in this article.

2 Blades 3 Blades 4+ Blades
4” 4.5,4.5BN 4.5BN
5” 4.5,4.5BN 4,4.5,4.5BN,4.6 4x4b
6” 4,4.5,4.5BN 4.5

Legend: Numbers in the table are the prop pitches available in the given size and blade configuration. “BN” means a bullnose offering is available. Blade count in 4+ Blades column is given by “x4b” for 4 blades, “x6b” for 6 blades, and so on.

Purchase here: http://www.dalprops.com/

Gemfan

gemfan

Gemfan 5050 Triblade

A classic prop manufacturer that makes props for pretty much any type of model aircraft or UAV.

2 Blades 3 Blades 4+ Blades
4” 4.5,4.5BN 4.5,4.5BN
5” 3,4,4.5,4.5BN 3,4,4.5,5,5BN
6” 3,4,4BN,4.5 4

Legend: Numbers in the table are the prop pitches available in the given size and blade configuration. “BN” means a bullnose offering is available. Blade count in 4+ Blades column is given by “x4b” for 4 blades, “x6b” for 6 blades, and so on.

Purchase here: http://www.getfpv.com/propellers.html?manufacturer=256

HQProp

SKU276764-3

HQProp 5040 Triblade

Gemfan and HQProp are the “classic” prop manufacturers that have been making props for the multirotor market for years now. It seems HQProp has more of the world’s pros signed on to their hype-train than any other manufacturer. As a result, their 5x4x3 tri-blade prop probably appears in more YouTube videos than any other prop on the market – and it is a very good prop. Their props are relatively expensive and are very fragile. They do fly great, though. They also recently started releasing a “durable” line that should stand up well against the likes of DAL.

2 Blades 3 Blades 4+ Blades
4” 4.5,4.5BN 4,4BN
5” 3,4,4.5 4,4.5,4.5BN 4x4b,4x6b
6” 3,3.5,4.5,4.5BN 4.5

Legend: Numbers in the table are the prop pitches available in the given size and blade configuration. “BN” means a bullnose offering is available. Blade count in 4+ Blades column is given by “x4b” for 4 blades, “x6b” for 6 blades, and so on.

Purchase here: http://www.getfpv.com/propellers.html?manufacturer=292

 

King Kong

kingkong

KingKong 6045

Similar to DAL props, the Kingkong 2-bladed props started out with a reputation for being indestructible and extremely cheap. Their tri-blade offerings are reportedly not as durable, but they are still the best value on the market. It can be hard to find these shipping from American stores so make sure you buy a lot at once.

2 Blades 3 Blades 4+ Blades
4” 4.5 4,4.5
5” 4,4.5BN 4,4.5,5
6” 4.5

Legend: Numbers in the table are the prop pitches available in the given size and blade configuration. “BN” means a bullnose offering is available. Blade count in 4+ Blades column is given by “x4b” for 4 blades, “x6b” for 6 blades, and so on.

Purchase here: http://www.banggood.com/search/kingkong.html

Luminier

lum

Luminier 5×4 Quadblade

GetFPV recently came out with a line of props under their Luminier line. They are focused on racing and they have some great offerings in all of the popular sizes for that application.

2 Blades 3 Blades 4+ Blades
4” 4x4b
5” 3.5,4.5 4 4x4b
6”

Legend: Numbers in the table are the prop pitches available in the given size and blade configuration. “BN” means a bullnose offering is available. Blade count in 4+ Blades column is given by “x4b” for 4 blades, “x6b” for 6 blades, and so on.

Purchase here: http://www.getfpv.com/propellers.html?manufacturer=196

RaceKraft

RaceKraft 5040 Triblade

RaceKraft 5040 Triblade

RaceKraft is a relatively new manufacturer on the scene. Their standard-chord tri-blade props look very similar to the eponymous HQProp 5x4x3 while their “durable” bullnose variant looks like the DAL 5×4.5×3 racing edtion v2 – both very good props. Their major selling point is they offer clear plastic in addition to the normal colors, which can look very cool.

2 Blades 3 Blades 4+ Blades
4” 4 4x4b
5” 4,4.5BN 4x4b
6”

Legend: Numbers in the table are the prop pitches available in the given size and blade configuration. “BN” means a bullnose offering is available. Blade count in 4+ Blades column is given by “x4b” for 4 blades, “x6b” for 6 blades, and so on.

Purchase here: http://pirofliprc.com/Team-RaceKraft-5040×3-Race-Prop-2CW-2CCW-Blue_p_3314.html

Buying your props

We have some links above where you can buy the props we discussed. These are all links to great stores in the hobby, but you should shop around when you are making bulk buys of props. Many stores on the internet will offer incredible discounts when you buy large orders of props – and you should take advantage of that. Often, you can get your best deals by ordering directly from China – as long as you are willing to wait. You can also look for promo codes or discounts on forums, Facebook or Reddit. Happy shopping!

More Research

There are a ton of resources on propeller theory and design across the internet. Props are especially cool because nearly all aspects of full-size props that drive human-carrying airplanes apply to miniquad props as well. Here are a few great resources if you want to do more research:

More info on propellor design and theory – Link (PilotFriend)
Tri-blade static performance comparison video – Link (Youtube – EngineerX)
YouTube series on miniquad props – Link (Youtube – SF PV)