Vertical wind tunnels like this one simulate the experience of skydiving with air speeds up to 270 km/h (168 mph). Here expert freefallers perform a routine similar to synchronized skydiving. By changing the angle and shape of their body with respect to the air flow, they are able to control their lift and drag to produce complex motion in three dimensions.
Search results for: “lift”
Wind Tunnel Testing
A scale model of the Space Shuttle attached to its modified 747 carrier hangs in a NASA wind tunnel. Wind tunnel tests can be used for flow visualization, lift and drag measurements, control system checks and so forth, but mounting models correctly and safely in the tunnel is crucial. Many models use sting mounts that project forward, as this one does, in order to expose the model to freestream flow unimpeded by the mounting mechanism. Any mounts and models must also be sturdy enough that all or part of them does not break off mid-test and fly into the wind tunnel’s fans. #
Stall-Sensing Hairs
Bats use tiny hairs on their wings to sense the direction and speed of air flow. Researchers found that removing these hairs caused bats to fly faster and make wider turns, likely because the bat believed it was on the verge of stalling and losing lift. Engineers are considering whether artificial versions made of flexible polymers that respond to strain could provide improved stall sensing on fixed-wing aircraft. # (Photo credit: justynk)
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.
Water-Walking Basilisks
Some animals, like the common basilisk (a.k.a. the Jesus Christ lizard) are capable of running across water for short distances. The basilisk accomplishes this feat by slapping the water with sufficient force and speed to keep its body above the surface. This slap also creates a pocket of air around its foot. The lizard propels itself forward by kicking its leg back, then lifting its foot out of the water before the air bubble collapses. Water birds like the Western Grebe and tail-walking dolphins rely on similar physics to stay above the water line. # (submitted by Simon H)
Airplane Vortex Wake
The wingtip vortices in the wake of a commercial airliner distort the clouds as the plane descends. Wingtip vortices form as a result of high pressure air from the underside of the wing accelerating around the wingtips to reach the low pressure on top of the wing. They can be hazardous to other (lighter) aircraft. They also contribute to downwash that decreases the effective lift of a wing. Geese use the same mechanism to their advantage when flying in a V-formation, and some snakes use it to glide.
Rocket Exhaust
This image of the Apollo 11 launch shows the Saturn V’s underexpanded nozzle (identifiable by the excessive width of the exhaust jet) shortly after liftoff. The faint diamond shape of the exhaust is a series of shock waves and expansion fans that equalize the exhaust pressure to the ambient. In general, a rocket nozzle is most efficient when it expands the exhaust to ambient pressure, but, since ambient pressure changes with altitude, designers have to choose a particular altitude for peak efficiency or design a nozzle capable of changing its shape with altitude.
The Ekranoplan
The ekranoplan, the monster of the Caspian Sea, was a Soviet-era aircraft nearly 74 meters in length and weighing 380,000 kgs fully loaded. (In contrast, the C-17 is 53 m long and weighs 265,350 kg fully loaded.) This enormous craft relied on ground effect to stay aloft, where it was capable of 297 knots. Flying close to the ground or water increases the possible lift on wings through a “cushioning effect” that increases pressure on the lower wing surface and by disrupting the formation of wingtip vortices which typically reduce lift through downwash.
Wind Tunnel Testing
This photo shows a prototype of the X-48C blended wing body aircraft being tested in NASA Langley’s 12-Foot Low-Speed Tunnel. Blended wing bodies have many advantages over conventional tube-and-wing designs: the entire surface of the craft can generate lift; the usable cargo/passenger area of the craft is increased; and, structurally, the craft is easier to manufacture. Flight tests of a remote-controlled version of the craft have also taken place.
Discovery Wingtip Vortices
Wingtip vortices mark the path of Discovery as she makes her final landing. Though not always visible, these vortices are generated by any lifting body planform and can be a major source of induced drag on the craft. Here the vortices are visible because the low pressure in the core of the vortex caused a local temperature drop below the dew point, thus causing condensation. Such vortices persist for significant lengths of time in the wake of aircraft; they are a major source of wake turbulence, which limits how frequently aircraft can take-off or land on a single runway. (Photo by Jen Scheer)
