Why is the smallest bird flapping its wings faster than the biggest bird to fly?
Well, physics is the reason -- it requires tremendous muscle power to flap a large wing, because it has to impact a much larger volume of air, and lift a lot more weight. This is why a hummingbird can have teeny wings, but a condor must have wings that are absurdly oversized for its body weight - wings don’t scale up evenly. You need a much bigger wing, proportionately, to lift a heavy weight than you do to lift a light one. The distance covered by the wing is also much greater, with a large wing — pull your arm up to your side, and flap only your hand - you can flap it really fast, right? Now try flapping your entire arm. It’s a lot slower, because you have to swing it a lot further, see? It’s the same for birds.The very largest birds flap only as much as absolutely necessary to get into the air, then they use thermals and air currents to glide. This saves them a tremendous amount of energy, because wing flapping is hard work and uses a lot of fuel. Birds like the albatross are basically gilders - their incredibly long wings are ill-designed for flapping, and they cannot lift straight off the ground. They must run vigorously and flap as best they can until they get up enough speed to launch. Once in the air, they barely flap - they are superb gliders. So good, the young ones won’t touch land again for years after they fledge and head out to sea. They spend their life on the wing, and land only to breed.Smaller birds can afford to use more energy - finding food is easier. The very smallest burn straight sugar from flower nectar, and have a metabolism so high, they must hibernate every night to survive until morning. More available energy means they can afford to have shorter wings, which are easier to flap, and to flap them more often. This makes them much more maneuverable. A hummingbird can instantly zip in any direction, and hover in place - quite a difference from the huge space taken up by a soaring large raptor, or the clumsy flapping of a great blue heron trying to get from one fishing ground to another.
Why are the tips of some airplane wings bent upward?
In an aircraft wing the lift is produced due to the difference in pressures on the upper and lower side of the wing. The upper side of the wing is subjected to lower pressure and higher velocity air (bernoulli's principle) and the lower side to high pressure. Difference in this pressure leads to a force being exerted on the wing in upward direction called lift force. The tips of the wings that are permenantly bent are called winglets. Due to the pressure difference high pressure air from lower side of the air tries going towards the upper side from the ends in an effort to equalise pressure. Such movement of air causes a vortex to form at the wing tip which results in loss of lift and an additional drag component called vortex drag. The presence of the winglet is an effort to reduce this unwanted migration of air from lower to upper side and thus reduce vortex drag.this type of vortex drag is found in axial compressors. but since there is no way in an axial compressor that a winglet can be fitted, losses are encountered.
Why do airplanes make a big circle around the city before landing?
Generally, this is called an approach or a holding pattern. At large busy airports, there are hundreds and flights landing and taking off each day. To keep things in order and avoid collisions, airplanes sometimes have to fly in a holding pattern to wait for their turn to land or to wait for another airplane taking off on the same runway to clear the area first.Additionally, for safety reasons airplanes generally don't fly right over the middle of downtown or close to talk buildings. The pilots fly set approaches (set paths) to land on particular runways at each airport. In conclusion, airplanes preparing for landing at major airports fly in holding patterns and fly set landing approaches to provide structure and order so that airplanes don't collide while trying trying to both land or land and take off at the same time.