Drones

Passive-tilting rotors shown to boost drone speed and efficiency

Passive-tilting rotors shown to boost drone speed and efficiency
Conventional quadcopters (pictured) have to tilt their whole body in forward flight, decreasing their aerodynamics
Conventional quadcopters (pictured) have to tilt their whole body in forward flight, decreasing their aerodynamics
View 2 Images
Conventional quadcopters (pictured) have to tilt their whole body in forward flight, decreasing their aerodynamics
1/2
Conventional quadcopters (pictured) have to tilt their whole body in forward flight, decreasing their aerodynamics
The QUaRTM drone, in its default and tilted configurations
2/2
The QUaRTM drone, in its default and tilted configurations

Ordinarily, quadcopter drones have to tilt their front end downward when flying forward, increasing their frontal area and thus increasing drag. An experimental new drone gets around this problem, by only tilting its rotors.

Developed by a team at the University of California - Berkeley, the aircraft is known as QUaRTM, which stands for "QUadcopter with an unactuated Rotor Tilting Mechanism." It features a rectangular body with four arms, each arm incorporating a rotor/motor module at the end. Instead of being rigidly joined to the main body, the arms are all connected to it via spring-loaded hinges.

In this setup, when modest amounts of thrust are produced, the springs hold the rotors horizontally in line with the body. Once a high enough level of thrust is produced, however, the rotor arms overcome the force of the springs, temporarily tilting into the forward flight direction by up to 20 degrees relative to the rest of the drone.

This allows the copter to move forward while keeping its body horizontally level, reducing aerodynamic drag. And importantly, unlike some other tilt-rotor drones, its tilting mechanism requires no powered actuators – the thrust that's already being produced by the rotors does all the work.

The QUaRTM drone, in its default and tilted configurations
The QUaRTM drone, in its default and tilted configurations

In outdoor test flights, the QUaRTM drone autonomously flew both with and without its tilting mechanism enabled. It was found that when the mechanism was enabled, the aircraft was able to reach a 12.5% higher top speed, plus it showed better high-speed agility (its maximum "crash-free cruise speed" was 7.5% higher). Additionally, its power consumption was over 20% lower in the speed range of 15 to 20 meters (49 to 66 ft) per second.

A paper on the research – which was led by Jerry Tang, Karan P. Jain and Mark W. Mueller – was recently published in the journal Frontiers. The drone can be seen in action, in the video below.

A Quadcopter with Unactuated Rotor Tilting Mechanism for Faster, More Agile and Efficient Flight

Source: UC Berkeley HiPeRLab via IEEE Spectrum

6 comments
6 comments
Freddy Bell
One has to question the longevity of the springs. Also is there a weight benefit compared to actuators? What happens if someone wants to ascend vertically at a high speed? Will the drone automatically tilt forward?
P51d007
NO! That means they will release "new" ones with this feature, and I'll have to buy 2 new ones to replace the ones I have now. LOL
I also would like to know how long the spring would last.
Martin Hone
I would think that these figures would be even more impressive if the body and arms were more of an aerodynamic shape...
Laszlo KRUPPA
Good proposal to improve present day quadcopter flight parameters such as top cruising speed and fuel efficiency, at a low cost. Improvements ("12.5% higher top speed" and specific "power consumption over 20% lower") have real marketing value. Questions remain about the feasibility of the solution in case of bigger quadcopters (VTOL-s carrying people), and about the effects on the maneuverability (steering) in real life situations.

It is good to remember that

(a) when cruising speed/efficiency are important you need (at least in the subsonic world) wings;

(b) the ultimate VTOL technology is built on a real tiltrotor solution. This will become ever more obvious when the new generation of rotors/propellers become available. Those which can perform equally well in vertical lift and in cruise flight.
TpPa
Spring life I doubt should even be considered an issue unless they are being worked past their designed limit. Springs last practically forever IF they are made of high quality material & not pushed beyond their limits.
Take a recoil spring in a "true" military full auto weapon, those springs are taking a hell of a beating and last thousands of rounds pending the caliber (50 bmg of course shorter life)
Back to the drone, after plenty more testing and tweaking, I'd bet DJI will bring it out on FPV drones 1st. Only thing is that you may not be able to fold up the drone anymore, so that will deter some.
Expanded Viewpoint
Spring life is not much of issue here, because the service life of drones is not very long. Car and motorcycle engines go for many years and the valve springs as well as suspension springs, are usually still pretty good.