Nature includes many animals that are so-called fliers: flying squirrels, flying snakes, and draco lizards, to name a few. These animals aren’t true fliers like birds, bats, or insects, though. Instead, they are expert gliders, able to produce enough lift to control their descent and land safely at a distance far greater than a normal leap could carry them. Like the flying squirrel, the draco lizard extends a thin membrane that acts as its wings. The additional area provides enough lift that the lizards can glide as far as 60 m (200 ft) while only losing 10 m (33 ft) in altitude. That’s an impressive glide ratio – about 3 times better than the Northern flying squirrel and twice as good as a wingsuit. (Video credit: BBC/Planet Earth II)
Tag: glider
Wing-Warping
This replica of the Wright brothers’ 1902 glider demonstrates one of the important innovations the brothers contributed toward powered heavier-than-air flight. To control an aircraft in roll, the Wright brothers developed the idea of wing-warping. The pilot would lie in the cradle (center of image) and shift his body to one side. A system of wires and pulleys would then twist the wings from their rear edge, pulling one side down and the other up. This deflection is akin to changing the wing’s angle of attack. Deflecting the right wingtip downward increased the lift on the right side of the glider, while simultaneously the upward deflection on the left decreased the lift on that side. This causes the glider to bank, or roll, with the right wing up, thereby generating a leftward turn. The lift differential also caused a drag differential, though, with increased drag on the lifted (right, in this case) wing. That extra drag tended to pull the aircraft’s nose rightward, a condition known as adverse yaw. To counter it, the Wright brothers installed a steerable rudder and linked it to the wing-warping mechanism, allowing them to turn with much less effort than other conventional craft. Although wing-warping has been replaced with ailerons, the control principles remain the same. For more, watch this demo of the wing warping mechanism on a 1903 Wright Flyer replica. (Image credit: C. Devers)
Sochi 2014: Ski Jump
Great ski jumpers are masters of aerodynamics. There are four main parts to a jump: the in-run, take-off, flight, and landing. An athlete’s aerodynamics are most vital in the in-run and, naturally, the flight. During the in-run, the athlete is trying to gain as much speed as possible, so she tucks down and pulls her arms behind her back to streamline her body and keep her frontal area as small as possible. This limits her drag so that she can maximize her speed at take-off. Once in the air, though, the jumpers act like gliders. In flight, there are three forces acting on the the jumper: gravity, lift, and drag. Gravity pulls the jumper down, and drag tends to push her backwards up the hill, but lift, by counteracting gravity, helps keep jumpers aloft for a greater distance. To maximize lift, a jumper angles her skis outward in a V and holds her arms out from her sides. This configuration turns the jumper’s body and skis into a wing. The best jumpers will tweak their positions with training jumps and wind tunnel time to maximize their lift while minimizing their drag in flight and on the in-run. Technique is critical in ski jumping, but conditions play a significant role as well. Tomorrow’s post will discuss why and how judges account for changing conditions. (Photo credits: L. Baron/Bongarts/Getty Images; D. Lovetsky/AP; E. Bolte/USA Today)
FYFD is celebrating the Games with a look at fluid dynamics in the Winter Olympics. Check out our previous posts on the aerodynamics of speed skating, why ice is slippery and how lugers slide so fast.
Ground Effect Vehicles
Ground effect vehicles (a.k.a. wing-in-ground-effect vehicles) rely on their proximity to a flat surface to inhibit the wingtip vortices that create lift-induced drag. This effectively increases the lifting capabilities of the vehicle in comparison to regular flight, but only so long as the vehicle remains close enough to the ground. This video features many model gliders that rely on ground effect.
Feathering on SpaceShipTwo
Virgin Galactic and Scaled Composites recently performed their first feathered flight with SpaceShipTwo, which is on track to be the first commercial spaceship. Feathering is a re-entry technique devised by Scaled Composites founder Burt Rutan:
Once out of the atmosphere the entire tail structure of the spaceship can be rotated upwards to about 65º. The feathered configuration allows an automatic control of attitude with the fuselage parallel to the horizon. This creates very high drag as the spacecraft descends through the upper regions of the atmosphere. The feather configuration is also highly stable, effectively giving the pilot a hands-free re-entry capability, something that has not been possible on spacecraft before, without resorting to computer controlled fly-by-wire systems. The combination of high drag and low weight (due to the very light materials used to construct the vehicle) mean that the skin temperature during re-entry stays very low compared to previous manned spacecraft and thermal protection systems such as heat shields or tiles are not needed. During a full sub-orbital spaceflight, at around 70,000ft following re-entry, the feather lowers to its original configuration and the spaceship becomes a glider for the flight back to the spaceport runway. #
Though it works well for decelerating from sub-orbital speeds, feathering is sadly not useful for orbiting spacecraft due to the much higher kinetic energies that have to be dissipated.
Wright Brothers’ Wind Tunnel
A large part of the Wright Brothers’ ultimate success in creating the first powered heavier-than-air craft came as a result of work done in their homemade wind tunnel, shown above. In the aftermath of the failure of their 1901 Glider, the brothers decided that the lift and drag data they had used from Otto Lilienthal must be inaccurate. They built this wind tunnel and its force balances to measure lift and drag on two hundred different airfoils themselves and were rewarded with far more successful flights with their 1902 Glider, which led directly to the Wright Flyer in the following year. #
Perching Gliders
Researchers at MIT are studying stall to understand how birds land and come up with new ways for gliders to perch instead of requiring a runway. This photo shows a smoke visualization of the glider stalling. #
