For more than a century, the internal combustion engine has dominated road transport. Its operation is founded on linear pistons moving up and down in a straight direction, their movement translated into a turning force that drives the wheels. It is a strong system, but it is also essentially inefficient; its energy is lost mainly as heat and vibration. To rethink this cornerstone technology, engineers are now turning away from the machine shop and into the natural world, or rather, to one of its most dexterous and dynamic animals: the hummingbird. The objective is not to create a small motor, but to rethink fundamentally the conversion of energy by emulating the bird's extraordinary biology, leading perhaps to a new model of efficiency, power, and adaptability in how we drive our cars.
The hummingbird's mystique is that of its flight characteristics, which are essentially different from those of any other bird. While other birds create the majority of their lift during the downstroke, a hummingbird's wing can produce lift on both the upstroke and the downstroke. They do this by being able to rotate their wings nearly 180 degrees in their shoulder joint. This forms a figure-eight shape in the air, a fluid, smooth movement that enables them to suspend themselves in mid-air with pinpoint stability, fly backward, and whip from side to side with dazzling rapidity. This is referred to as a reciprocating motion, but it is much more intricate and efficient than the back-and-forth of a piston. For engineers, this is a fantasy of steady, all-around power production, the antithesis of the stop-and-start, one-way shove of a conventional piston.
Turning this biological wonder into mechanical engineering suggests a very different idea than a typical engine: the spherical engine. Envision a sphere, or a dome, within which a succession of chambers is disposed. Rather than pistons going up and down in straight cylinders, the "pistons" in this system are vanes or rotors that travel in a curved, complex path inside the sphere, much as a hummingbird's wing travels through space. Intake of fuel and air, compression, ignition, and exhaust would all occur as this rotor passes through various zones within the sphere. This configuration obviates the crankshafts, camshafts, and all the connecting rods—the heavy, intricate components that convert linear movement into rotation and contribute to much of an engine's friction and bulk. The output of power would be a straight, smooth turn, similar to the direct lift created by a hummingbird's wingbeat.
The gains in efficiency from such an arrangement could be revolutionary. A conventional engine is a work of compromise. Its pistons are extremely massive, and they're repeatedly stopping, starting, and reversing at unbelievable velocities. This generates enormous inertia and vibration, losing a tremendous amount of energy released in each fuel explosion simply to maintain the weighty parts in motion. The hummingbird-like, spherical engine would not have any such issue. Its motion would be smooth and continuous, with no jarring direction changes. The moving components would be lighter and in equilibrium, cutting internal friction and inertial losses by a huge factor. That leaves more of the energy in the combustion of the fuel being turned directly into useful rotational force to drive the wheels, instead of being wasted on shaking the engine itself. It would be quieter, smoother, and essentially more efficient.
In addition, the hummingbird's anatomy has lessons on fuel economy and high-speed flight. A hummingbird has the highest metabolism of any animal in proportion to its size. Its heart beats more than 1,200 times a minute, and it needs to eat more than its own weight in nectar every day just to exist. In order to accomplish this, it is a very efficient processor of energy. It has no single, high-powered "power stroke" followed by a glide; all of its wingbeats are power strokes. An engine based on this would seek the same principle: a high-frequency, uninterrupted series of small, very efficient combustions. Rather than four big explosions per cycle in four big cylinders, a spherical engine might have dozens of small, quick, and full combustions occurring in quick succession in its chambers. This could mean more efficient burning of fuel, lowering emissions, and getting more energy out of each and every drop.
The possible uses for this technology go well beyond the mere replacement of the engine in a family sedan. The high power, compact, and vibration-free characteristics of a spherical, biomimetic engine make it well-suited for new modes of transportation. In electric cars, such a tiny, high-efficiency engine might serve as a "range extender," a generator to charge the batteries that consumes a fraction of the fuel and space that a conventional engine does. Its smoothness would be ideal for the quiet, high-class ride that comes with an EV. For aviation, particularly drones and personal flying vehicles, the power-to-weight ratio is paramount. A light, strong, and directionally maneuverable engine modeled on the master of hover itself would revolutionize, allowing vertical take-off and landing that is now hard and inefficient with traditional engines or even electric motors.
It goes without saying that the journey from biological inspiration to a functional engine on a showroom floor is filled with gigantic engineering hurdles. Spherical engine sealing is a nightmare. In an old-fashioned cylinder, a few piston rings make a good seal against a straight, simple wall. In a complicated, curved chamber, making a seal that will keep up with the high heat and pressure of combustion without leaking or generating too much friction is an engineering challenge that has frustrated people for decades. Materials science would have to improve to develop parts that are both extremely light yet strong enough to withstand the stresses of prolonged, high-speed use. The level of manufacturing precision needed to produce the perfectly smooth, intricate internal structure of a spherical engine would be many orders of magnitude higher than that needed to fabricate a simple cylinder block, perhaps making it economically impossible, at least in the short term.
Even so, the quest is worth it. The internal combustion engine has been honed over more than a century, and we're now extracting the final percentage points from its potential. In order to make a genuine step forward, we can't just tweak the current design; we have to be prepared to look at a fundamentally different one. The hummingbird, through evolution over millions of years, has optimized a type of high-frequency, omnidirectional, and extremely efficient propulsion. It is a living proof of concept. Through observation of its wings, its muscles, and its energy metabolism, we are not merely duplicating nature but discovering its deepest laws of efficiency and power. Designing a car engine based on the hummingbird is more than designing a more efficient machine. It is about learning from a master and applying billions of years of natural research to overcome the limitations of our own century-old inventions, paving the way for a future of cleaner, smarter, and more agile propulsion.