4

I have heard that tip losses in propellers can occur when a propeller is highly loaded (when there is a much higher pressure under the prop blade than above it). This can happen with drones that fly quickly and create a very highly loaded prop. Are there any prop designs that can remove or lessen the drag caused by tip losses on drones?

1

There are a few ways to reduce the tip losses of drone propeller blades. The best way to improve efficiency is to simply increase the propeller size, as this will be much more effective than adding winglets to the propellers. An explanation for why larger propellers are more efficient can be found here: Why are larger propellers generally more efficient than smaller ones?

But when space is limited, and you are stuck with small props, winglets are supposed to be able to help, but don't always help that much. It is a trade off between the winglets "ability to reduce induced drag traded off against their added wetted area increasing the profile drag." Profile drag is the drag caused by the shape of the wing section. You can read more about winglets here.

Another thing that can work well is to have very slight winglets, or small curves on the end of the propeller blades like this: Blended winglet

This creates some of the efficiency benefits of winglets without really increasing the profile drag.

So, really the best option is to use larger propellers if you want maximum efficiency. Winglets, however, can also increase the overall efficiency of a propeller, but with some tradeoffs and they don't always improve efficiency much. And I'm sure there are also some other propeller designs built to reduce tip losses.

| improve this answer | |
  • 1
    The problem with winglets is that they have to be designed for a narrow range of Angle of Attack. Outside of that range they just make things worse. That's OK for an airliner that spends a lot of time at cruise speed, but no use for us. – Robin Bennett May 19 at 10:30
  • Yeah, Like I said, It's a tradeoff. – Jacob B May 19 at 19:39
  • 2
    This answer addresses the question obliquely. It mentions increased prop diameter as the best solution for prop loading which would reduce the amount of tip losses. Yet the tip losses are affected by various factors. Prop size should not be considered a primary answer. If it were, all drones would be single rotor helicopters. We should presume that the multirotor is designed to meet a set of flight characteristics and design criteria including frame size, number or rotors (propellers), type and size of motors, propeller size, pitch, and prop cord design, and battery weight and capacity. – HansenJC001 May 26 at 5:17
  • @HansenJC001 While I see your point (there are a lot of factors), I don't agree with all of it. Prop size is a big factor, which is why drones often use the largest propellers that will fit on the drone. Drones wouldn't all be helicopters because having four or more motors increases the potential performance and maneuverability of a drone. And because drones use propellers, any aerodynamic principles relevant to propellers (like winglets) are relevant to drones. – Jacob B May 26 at 19:22
  • Feel free to make an answer to the question. I am always open to more answers. – Jacob B May 26 at 19:33
1

Propeller tip losses are a function of, or perhaps we could say it is a side effect of the propeller design itself. The designer of a propeller can influence the tip losses, but a user is unlikely to find a practical way to accomplish it for a propeller they already own. So this question is theoretical.

The overall size and geometry of a propeller can influence the tip losses, but for any particular multirotor, the size or length of the propeller is most likely to be at its maximum size already. Or, if it is not at the maximum size, the length of the propeller is at the optimum size for the multirotor it is installed on. Making the propellers any longer than the airframe can accommodate makes the question morph to one of: "What changes to a multirotor influence the tip losses of the propeller." Ok, now the answer can include making the prop longer.

In the real world, the answer is: "Buy a better propeller".

In the theoretical world, redesign the propeller. And one could also add a well designed shroud with a very precise gap (very narrow) between the tip of the propeller and the shroud. And to accomplish this, the tip of the propeller would then need to have a shape that is different than one designed for free air. It would fit precisely with the shroud just a fraction of a millimeter away. This prevents the tip vortexes from rolling off the end of the propeller. But if this theory were practical for multirotors, one or more drone maker would have employed it already. And so far, it is not being done. I have not yet seen it. They are also claimed to be quieter and more efficent, but that too is not proven with any experimental evidence on an entire drone. It is all laboratory results. So there must be trade-offs that make that solution unattractive.

And to actually add a shroud, we are back to changing the entire multirotor to reduce the tip losses. I am not sure that is what the question was.

Most prop manufacturers make claims that their props are better, but provide little proof or clues regarding how they did it. We can see unique shapes used on the tips, but there is little published data that helps us replicate it for ourselves.
Was this question one of theory or a practice?

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.