Aerodynamically impossible for bees to fly?
Until about 15 years ago, scientists found it difficult to explain why bees can fly, considering their wings can support a cargo of pollen as well as their own weight.
Recent research has revealed some of the complex mechanisms that enable bees to fly:
1. Wing movements
The theory of the flight of aeroplanes is fairly simple compared to that of bees. Aeroplanes have fixed wings that are pushed through the air by engines. Bees do not need engines because they flap their wings. But this is not a simple action. They must move their wings up and down in a very complex manner to be able to fly.
Bees are able to hover, move forwards and turn. They use their wings to control these movements:
The bee is also able to rotate its wings:
On the downward stroke, as the end of the wing goes from point 1 to point 2, the front or leading edge of the wing faces forwards.
(The asterisk shows the leading edge.)
On the upward stroke, as the wing goes from point 2
to point 3, the wing faces backwards (again the
asterisk shows the leading edge). This gives lift on
the upward stroke.
So we can see that the wing flips through approximately 120° at the end of each stroke.
The bee performs these precise wing movements a staggering 200 times a second.
Slight variations in the actual angles of the wings determine whether the bee hovers, moves forwards or turns.
But there is more to honey bee flight than this! Researchers have found that bees use no less than three other principles to gain extra lift to be able to stay airborne. These effects are too complex to explain in detail.
One mechanism is called 'delayed stall'. This occurs as the insect sweeps its wings forward at a high 'angle of attack', cutting through the air at a steeper angle than that of a typical aeroplane wing. A 'leading edge vortex' is formed which gives additional lift.
Additional lift is also produced when the wing rotates at the end of each beat. This effect is known as 'rotational circulation'.
The third mechanism to produce extra lift is called 'wake capture'. As the wing moves through the air, it leaves whirlpools or vortices of air behind it. The wing is rotated before the start of the return stroke and intersects with its own wake, capturing extra uplift to keep the bee in the air.
2. Wing structure
Bee’s wings are thin membranes of cuticle stiffened and supported by veins, as the picture shows. Throughout the life of the bee, a chemical is moved through the hollow veins to ensure the wings remain stiff but flexible. The bee has two wings on each side of its body. The picture shows the wings coupled together for flight.
In the resting position the wings are uncoupled over the back of the bee. As the forewing rotates over the hindwing to the flying position a row of hooks on the front edge of the hindwing engage in a fold on the back edge of the forewing. This means that both wings open together and form a single wing surface.
The diagram below shows the location of the hooks and fold:
The next diagram shows the intricate detail of the coupling mechanism.
Researchers are uncertain what the hairs do. They think that they may have some kind of sensing function.
Once the wings are coupled together securely, the bee uses its muscles to flap its wings in the complex manner that we saw earlier. It has no less than eight different sets of muscles.
- raise and lower the wings
- pull the wings forward and backward
- move the wings to the correct angle
The bee must coordinate all of these functions correctly to be able to fly.
3. Control in flight
Once the bee is in the air, it must be able to control its movement.
The diagram below shows just how complex this is:
The upper picture shows that the bee can move: vertically (v) up and down, longitudinally (l) forwards and backwards and horizontally (h) side to side. All of these movements are achieved by slight variations in the angle of the wings.
The lower picture shows how the bee can rotate in the air, these are known as: roll (r), pitch (p) and yaw (y).
Bees must take off, fly in a controlled and directed manner and land at an appropriate place. It is obvious that a great deal of control of their eight sets of flight muscles is essential.
Take-off sequence of honey bee:
Fixed-wing passenger aircraft are designed to have a high degree of stability in flight, but they are not very manoeuvrable. Bees are more like combat aircraft, which fly on the edge of instability and require complex control systems to keep the aircraft stable. Engineers spend years designing the complex systems required to control these aircraft. These systems constantly monitor the aircraft and rapidly make the necessary minor adjustments to keep the aircraft in the air. The correction must be quick and accurate to avoid disaster.
Bees flying on the edge of instability must also monitor their situation continuously and take immediate corrective action.
Bees monitor body position and motion through sense special organs and through their eyes.
Landing sequence of heavily laden worker honey bee:
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