The future of aviation is in electric motors, or is it? An Australian drone concept does something new, even though it’s far from new, using a gas engine to drive the propellers of their drone. That’s right, a quadcopter that runs on fuel instead of electricity.
The news is simple enough, the tech a little less so, join me on a thought experiment to answer the question, are gas engines good for drone flight?
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SOAPdrones is an Australian company that set out to delivery snake anti-venom to remote locations around the country. Electric motor driven propellers provided more than enough lift to carry their life saving payloads, but, as any drone pilot already knows, battery life was a huge problem.
Instead of messing with heavier batteries, SOAPdrones (that’s Snakes on a Plane drones, love it!) opted for a different technique, gas powered RC engines. A single two-cylinder two-stroke engine makes for a drone that can lift 22 lbs, which is good, but can then keep it aloft for about three hours, which is just a little bit better than good.
In addition to gas power, they deploy a variable pitch 6-bladed propeller system, again different from what you’d find on an electric powered drone. Long term, the company hopes to scale up their design, eager to carry over 400 lbs from Canberra to Sydney at speeds up to 60 mph. They have my support.
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Gas vs electric drones
Exploring the tech, your typical electric drone utilizes a dedicated motor for each propeller. The flight controller sends the signal to each motor to control the speed, providing the proper lift to keep aloft and balanced. Electric motors are extremely responsive – you may not realize it, but each motor may receive hundreds, even thousands of speed changes each second just to maintain a steady hover.
The SOAPdrone approach uses just one fuel powered engine. A drive system sends power from the engine out to all four propellers. Immediately you must be wondering how the drone then stays balanced, if just one powerplant drives all the propellers. Let me set the stage for learning: that engine doesn’t even change speeds, spinning all the propellers at the same pace.
The magic is in the propellers. Variable pitch propellers have the ability to change their angle, creating more air movement simply by exposing more surface area as it spins. It is far more technical than that, learn more about propellers to see what we mean.
As the propellers spin in a flat orientation, they provide no lift, then they twist, the angle increases and lift is generated. As the name implies, the flight controller adjusts the pitch of each propeller independently, creating different amounts of lift from each propeller.
You may be wondering why they did not put a gas engine on each corner of their quadcopter. The simple truth, as fast as small RC engines can be, they are much slower at adjusting speeds than electric motors. Slow enough that stable flight is essentially not possible when a gas engine is just put in place of an electric motor. Funnily enough, I understand the propeller pitch on the SOAPdrone is controlled by small electric motors.
In the end, an electric drone is far simpler to build, maintain and operate than a gas powered flier. However, the fuel powerplant, combined with this variable pitch propeller system, is extremely fuel efficient. Until there is a breakthrough in battery technology, our electric cars, electric planes, drones and more will remain limited to operation measured in minutes instead of hours.