Update 11/4/2016 – The speed calculations for all of the props were off due to some mis-readings of the time code data from our video.  This has been fixed. Thanks to YouTube user Kevin for pointing this out.

Many of you may have noticed a plethora of videos and miniquad builds featuring the radical new prop design from RaceKraft emerging on the internet over the last month. This prop is the RaceKraft 5051 tri-blade, and it’s like nothing that’s been released in the multirotor world before. In this article, we’re taking a close look at these beasts to try to get a grip on how they really perform.

Overview

The designers of this prop have stated that the design goal was maximum aerodynamic efficiency at 60MPH – about the speed of your average racing quad. If you managed to slug through our Propeller buyer’s guide, you’ll remember that strapping a prop to a static test bench really doesn’t tell the whole story. Props designed to excel in this sort of testing will inevitably perform poorly when actually flying. When the manufacturer suggests that this prop operates most efficiently at racing speeds that means you can expect more thrust and better control at those speeds – resulting in a faster top speed, better maneuverability and better battery consumption for a given flight speed.

Despite the name “5051” – this prop actually has a static pitch of 4.6″. The designer of the prop talks about why it is named the way it is in a post on RCGroups. TLDR – pitch is not always a good measurement of how a prop will perform in flight. We’ll take an in depth look at that in this article.

Form Factor

Probably the most noticeable aspect of these props is their appearance is their design:

racekraft-5051-tripale-02

The blade tips rise nearly an inch above the prop hub. This is due to the massive “bite” of the first inch of the prop – necessary because airfoil spins proportionally slower the closer to the hub you get. Radical designs like this mean you are getting more thrust across the entire prop instead of most of your thrust from just the tips. The RaceKraft 5051 also features an upturned wingtip device that attempts to increase the efficiency of the prop by reducing prop vortices. Such a device might also have the added benefit of reducing propwash oscillations – but it is hard to verify either of these claims without access to a wind tunnel.

Because they are such a departure from traditional prop design, you may have installation difficulties with these props. For instance, the tips of the RaceKraft 5051 were hitting the antenna mounts on my Bolt 210 during flight:

blade_clearance

Since the blade tips of the RaceKraft 5051 are so high, I ran into some chafing problems we haven’t seen with other props – like with my Bolt’s antenna mount as seen here.

This isn’t an issue with most other props because the tips are more than half an inch lower. The Lisam 210 we recently built had some similar problems.

How Fast Are They?

We used a nice smattering of props to compare against the RaceKraft 5051s.

We used a nice smattering of props to compare against the RaceKraft 5051s.

As one of the primary advantages of the RaceKraft 5051 props is better performance at speed, it seemed natural to put together some sort of speed test in this article. To keep the test simple, I selected a short straight-line course about 2 football fields long. I would use a long “run-up” stretch before entering the course from each direction to let the quadcopter get up to full speed before entering the course. Full throttle would be used until passing the end waypoint on each leg. This method would allow us to calculate the speed regardless of wind. All of the testing was done at the same time, to counteract any performance changes that may come from temperature or pressure changes in the area.

I wanted to compare the RaceKraft props to several other prop types that are commonly used by drone racers. To that end, I included the following props in my test:

Prop Specs Blades Description
RaceKraft 5051 5×4.6 3 The point of the article of course!
DAL TJ5045 5×4.5 3 One of our favorite props on the market.
Gemfan BN5045 5×4.5 2 A popular 2-bladed prop for comparison
HQProp 5040 5×4 4 Does more blades make better speed? Let's find out..
KingKong 5040 5×4 3 This is the "industry standard" 5040 triblade design.

For the test, I flew my Bolt 210 with the following power system:

gps

GPS enabled BetaFlight quad – that doesn’t work..

I originally wanted to measure speed using a spare MTK3339 GPS chip I had laying around from some other projects. I threw the chip onto our Lisam 210 quad and hooked it up to the Blackbox recorder as pictured to the right. Unfortunately, I found that some sort of RF noise was causing the GPS chip to lose it’s satellite lock when at full throttle. Not super surprising when you consider these little motors are being switched at 50+ Amps and 10k+ RPM, but a little disappointing.

The alternative speed measurement approach I came up with is a classic one – I picked two landmarks along the course I flew and measured the time it took to traverse the distance in between them. The timing was done by analyzing video I recorded using my Fatshark goggle’s DVR feature. There are a few issues with this testing method that I considered:

  • Hard to control altitude at the two capture points.
  • Accuracy is limited by the framerate of the recording.
  • Tilt variations in the quadcopter can make it hard to determine when a checkpoint is “passed”.

For this reason, I did 4 runs on the course for each prop. I would have done more but did not have enough batteries to do so. I cross referenced the data with some of the valid readings I had obtained from the GPS chip and the readings are within 10% of each other (for different quads) so I think that this test has a fair degree of accuracy despite the problems discussed above.

I recorded the passes and posted an edited video on our YouTube channel:

 

Here are the results:

Prop Avg Speed (MPH) Avg Speed (KM/H) Avg Current (Amps)
RaceKraft 5051 83 133.6 58
DAL TJ5045 71.9 115.8 47
Gemfan BN5045 74.6 120.1 48
HQProp 5040 73.1 117.7 47
KingKong 5040 66.9 107.7 39

I was expecting these props to do well – but not this well. 83MPH average is well above any margin for error that this test had, especially considering the fact that this prop never scored less than 20% faster on it’s slowest pass than any other prop’s fastest! I bet that with some less worn-out batteries and a less draggy airframe, these props will could push past 100MPH – an incredible figure for our tiny quadcopters. These things are the real deal.

Battery Consumption

I won’t beat around the bush – these props are power hogs. It’s not a fair fight though, and here’s why:

The performance envelope of the quadcopter is increased dramatically with the RaceKraft props. You saw above that they increased the average top speed by over 20% over the next fastest prop – this simply means that when you are flitting around a race course or through trees at speed, the RaceKraft props are giving you more thrust. More thrust requires more power and if you don’t change your flying style you’re going to burn more batteries.

I didn’t do any formal testing on this – but when I put my flight camera back to the 30 degree tilt I am comfortable with and did a few acro sessions with these props, I saw the same flight times I get with all my other props.

Durability

During my testing time so far, I haven’t had any major incidents with the RaceKraft 5051 props. I’ve done a few tumbles through the dirt and had one rough landing where the quad flipped end over end a few times – but I haven’t slammed into any trees or concrete yet. Through the minor scuffles the 5051 props have performed fine. These were crashes that definitely would have destroyed the fragile HQProp 5040 triblades, so the 5051s are at least more durable than the least durable prop on the market.

I’ve seen a few videos of people running into trees and flying off as if nothing happened with the 5051 props. Many reviews are claiming they are similar to the DAL TJ props – they bend but do not break. If so, that’s great news for my wallet because I want to fly these things all the time now.

Flight Performance

overheadThis one is a tough one to make a call on. Both sets of RaceKraft 5051 props we bought for the review were very well balanced from the factory and sounded very smooth from the moment they were installed. I feel they have the same “pop” that any other tri-blade prop has – perhaps more, but I felt they were comparable to the good old DAL TJ5045 tri-blades. This makes sense as both props have similar static pitch. Acro was smooth and crisp like all tri-blades but again I didn’t feel a noticeable improvement.

Some people have reported that these props experience less propwash oscillations but since upgrading to Betaflight 3.0 these types of oscillations have become pretty rare on all my quadcopters – regardless of the prop I fly. Other reviews claim these props perform way better than the competition in acro. I consider myself a pretty good acro pilot but I’m definitely no pro. Maybe I’m not pushing the limits enough but I can only report that these felt just as good as my current favorite props in flight.

One thing to note is related to the speed figures above – with a full camera tilt (about 35 degrees on my Bolt) – I have a lot more power for recovery and rapid stops. Other props struggle to keep up with the quad at these tilt angles but the RaceKraft 5051 props just laugh at it. So if you like high speed acro, these are frankly the only way to go.

Conclusion

I like to think of these props as unlocking a new avenue of potential performance for our racing quadcopters. If you study the amp draw seen in the above video, you’ll notice that every other prop other than the RaceKraft 5051 “maxed out” at well under 50 amps. This is because at max forward speed, these props simply were not able to demand much torque from our 2300kV motors anymore. If you want more performance at these speeds, you have a few options:

  • Upgrade to 2600kV motors
  • Move to 5S batteries
  • Improve prop design to cater towards higher speeds

Without going off topic – each of these options has their problems, including the last one. Thing is, the third option simply wasn’t available to us until now and the other two can cost a lot of money and time. With the RaceKraft props, its just $4 and a quick prop swap to pump up your speeds by 20% or more – and that goes for our $150 Lisam 210 just as much as my Bolt. That’s a pretty sweet deal if you just want something you can swap in on race day when you really want that extra boost. Liken it to drag radials at a race track – you don’t drive in on them but they’re hands down the cheapest way to shave a few seconds off of your lap time.

In conclusion, these props are a fantastic step forward for the hobby. I wouldn’t say everyone should go out and replace all their props with RaceKraft 5051, but I do think every serious racing pilot should have a set in their gearbag.

RaceKraft props are available from pretty much every major vendor in the USA and Europe. If you would like to support our website, please consider buying your set from Amazon here.

Can I Has 2-Blade?

I know the industry standard for drone racing these days is the tri-blade. Heck, we might be one of the loudest proponents of using them. Thing is – the biggest reason for using tri-blades is that all the available 2-bladed prop designs don’t pull enough performance out of the small 5″ props that we all use on our racing miniquads. I think that with a blade design like the RaceKraft 5051 it might finally be time to explore 2-bladed props again. I bet it would retain a lot of the high speed performance while drastically reducing the current draw that is the main disadvantage of these props. RaceKraft – if you read this – pretty please??

 

 

 

 

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