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Whether it's the old-school puppet version or the more recent animated reboot, most of us will have enjoyed the classic 'Thunderbirds' TV show at some time in our lives. As I child (and a bigger man-child) I remember being thrilled when, after the suspenseful countdown, the huge ships would take off and slowly but surely power into the sky. I know I don't look it but I'm old enough to remember being even more excited watching some of the later Apollo spacecraft launches. I'm also lucky enough to have seen one of those Saturn V moon rockets for myself. How could such an immense beast 'slip the surly bonds of Earth', as the poet John Gillespie McGee Jr. so memorably put it? (If you don't know that poem, search for “High Flight”. Don't say these blogs aren't educational and far-reaching.)
This week I felt that same exhilaration as I watched another 'immense beast' take off, but this one was much less metallic. It was an all-natural male Mute Swan, weighing in at around 12 kg and yet, with a Herculean effort, he was able to raise himself from the water and up into the air. Imagine what it must take to put the equivalent of a dozen bags of sugar into flight. A creature that size needs a huge amount of power to generate its initial launch. The aforementioned fictional Thunderbirds, the very real Apollo space craft and any other man-made flight machine needs jet or propeller engines to achieve this take-off. Birds of course don't have these mechanical contraptions in their front or rear ends. They have wings.
Our avian friends move these wings in a similar manner to how we humans our arms when swimming. We push backwards against the water to propel ourselves forwards; they push against the air with long, downward strokes to provide the power and more relaxed upwards strokes to reset. Like our best swimmers, much of this power comes from the large muscles around the chest. When people eat any birds the best meat is usually in the breast, right? That's where most birds largest muscles are, and bigger muscles are needed to provide the most power. Bigger birds also need larger wings to get airborne, but once they're in the sky these same big wings have a greater surface area to enable soaring and gliding. Smaller birds have much less need for this flight strategy but a much greater need for manoeuvrability as they search for safety from predators in their home environments. That's why their wings are smaller and more agile. As we've seen so many times in these blogs, natural selection meets each creature's needs in turn.
Just like an aeroplane's wing, a bird's wing is thicker at the front (where the bones and muscles are) and thinner at the trailing edge. They're also flat underneath and curved on top. Human designers have copied these traits for our own flight machines. In both natural and human creation these wing thicknesses and curves make the air on the top of the wing move faster than the air underneath which generates lift – one of the four fundamental principles of flight.
This is where this week's piece gets difficult. Hang on everyone, we've got to the sciency bit. In researching this blog I've tried hard, I really have, but I just can't get my head around how these principles combine to keep even a Wren aloft, let alone a Boeing 737 Max 10. I apologise for the bits that I've missed or got wrong but the best I can manage is as follows. As I understand it there are two pairs of opposite forces involved. These are lift versus weight, and thrust versus drag. As long as the first of both these pairs is greater than the second, then we have flight. If you don't have enough lift to overcome your weight, then you won't take off. Simple. Similarly, if you aren't streamlined and have too much drag, then you'll need a massive amount of thrust to keep you from stalling and crashing.
Once you're in the air you need to be able to steer in this 3D environment. Move a rudder at the back and reshape the trailing edge of the wings and you can control side-to-side or up-and-down movements respectively. Pilots can do this with a directional joystick. Birds do it instinctively with slight muscle movements such as lowering one wing slightly to turn in that corresponding direction, or tilting both wings backwards to slow down.
Although everything has to move in perfect unison, from my perspective the tail is perhaps the most impressive part of a bird in flight. Watch a Kestrel or a Red Kite for proof. These birds' heads will remain completely still yet to achieve this the tail will be moving all the time, constantly making the tiniest of adjustments so that the head – and more importantly, the bird's eye – can remain totally focussed. Or look at a Gannet coming in to land on a cliff face. It needs to brake almost instantly to drop onto the tiniest of ledges yet do so in a perfectly controlled manner. See how it opens its tail out and curves it underneath its body to make an air brake. It's incredible to watch.
Wings, chest muscles, tails – not to mention the hollow bones to reduce weight – every tiny part of the bird is somehow involved in allowing it to fly. It's what makes birds so impressively... birdy. So next time you see a bird in flight, be it a regal Swan or a humble Blue Tit, take a moment to watch how simple it makes the entire process seem.
Prepare to be amazed.
See my weekly RSPB Old Moor blog at "View From the Shed". I usually wear a big hat.