The best hoaxes mimic unlikely, yet plausible scenarios, and play on our fears or aspirations. Two videos that went viral this year were skillfully created by art students and released on an unsuspecting public. The first was a toddler-snatching golden eagle that had us gaping in horror, while the second (below), featured a human bird wings project that sent many office-bound viewers soaring out of their cubicles. Both videos affirmed, at some level, the human obsession with flight. The second video went further, touching on what we feel at our core to be true — humans can fly under their own power.

Though probably not the first to flesh the Icarus myth, Da Vinci wrought the culture of human flight. To really fly — as a bird does — we must abandon the naive and distracting approaches that seemingly work so well for rotary-powered aircraft and embrace the principles that make sound engineering sense given a human’s power and scale.

No doubt eagles are strong creatures — Harpy eagles snatch monkeys from Amazonian trees, Martial eagles grab adolescent gazelles from the African savanna, and Golden eagles topple large goats from mountains. How much can they actually lift? As we will see, the obvious questions do not have obvious answers. An exceptionally large eagle might weigh 25 pounds and have a 9-foot wingspan. It would be conservative to say it could take off easily with an extra 10 pounds and maintain flight with at least double that. This year’s toddler hoax may be a stretch, but certainly not a huge one.

So how about the human birdwings hoax? The designers actually built a realistic-looking but hopelessly underpowered machine. A better design was explored some time ago by Douglas George. In his Project Falcon concept, he calculated that a 40-foot wing could produce around 200 pounds of lift at an airspeed of 15 miles per hour. While that would certainly require a very lightly-constructed airframe to accommodate most pilots, with modern materials a 30-pound machine may not be totally out of reach. What really captures the attention though, is the thought of loosely coupling the power of the legs with tendon-like elements to smoothly transition a short take-off jaunt into flight.

Several human-powered contraptions have recently received a fair amount of media attention. Pedal-powered helicopters and flapping aircraft have made brief hops and captured incentivizing prizes. The fixed-wing Gossamer Condor, pedaled across the English channel, appeared almost commuter-ready from the vantage point of one’s armchair.

Unfortunately, as viable routes to human-powered flight for the masses, each of these designs ultimately fail at both ends of the power conversion cycle. The methods they use to capture power input from the human source, and the way power output is applied to the air are both hugely inefficient. Combustive machinery, with piston or turbine power prepackaged in rotary form, cannot be the benchmark for human-powered machines. Propellers are the logical mating partner when your mechanical power comes in turning fast and your airspeed is high, but propellers are inefficient — they make highly effective power converters, but only when you have it to spare.

As airspeed and propeller speed decreases towards the human-powered regime, propeller size must grow exorbitantly if it is to deliver comparable thrust. At the lower speeds, you need to accelerate the largest air mass possible. At some point, the ideal propeller would begin to approach the size of the wings themselves. If you already have wings though, why would anyone want to add a propeller full of mass, drag, and the associated destabilizing torque it produces on the aircraft body as it turns against the air?

The fixed wings of Gossamer Albatross are certainly too lightly constructed to be flapped — they are also far too light to be safe. If flapping wings move too slowly there will be little gain. At sufficient speeds though, things begin to happen. The difference between a dive and a bellyflop becomes more relevant. If you are turning a propeller, pedals might initially seem appealing — if you want to flap a wing, they are an engineering nightmare.

Next page: Learning from the masters…