The flight of the butterfly

Transcription

1 The flight of the butterfly Yani Dearness Castle Cove Public School INVESTIGATION AIM To find out the best angle for a butterfly to hold its wings at, to get the strongest glide. HYPOTHESIS I think an angle of approximately 30 degrees will generate the most lift during a glide. BACKGROUND RESEARCH Butterflies Butterflies are flying insects with small, light bodies and large colourful wings. There are thousands of different species of butterfly. Not only are butterflies amazing and beautiful animals, but they have a big part to play in pollinating plants. Like bees, they contribute to the life cycle of

2 plants. So as well as making our world more beautiful, butterflies help provide us with food like fruit, nuts and vegetables. Butterflies start off hatching from eggs as caterpillars. After feeding and growing they turn into a chrysalis (cocoon) hanging from a plant. Their body changes and eventually a butterfly emerges. This is called metamorphosis. Butterflies fly about to find food, mate and lay eggs. Butterflies are cold-blooded, their body temperature depends on the temperature of their surroundings. Some species of butterflies escape from cold winters by migrating to warmer places. One of the most amazing animal migrations is by the American Monarch butterfly. In autumn a Monarch butterfly will fly thousands of kilometers from Canada down to warm Mexico. For such a delicate creature to make such an incredibly long journey it must be an expert flyer. The National Geographic documentary Great Migrations shows that a lot of the time the Monarch butterflies aren t actually flying by beating their wings up and down, but are holding them out and gliding. Gliding saves them a lot of energy. At the Tropical House in Sydney Zoo I watched several species of butterfly in flight. They usually flapped their wings to fly by they also used gliding, sometimes only for an instant, but occasionally on long swooping gradually falls.

3 Even for butterflies that don t migrate, being an efficient flyer means more food and a better chance of living long enough to lay eggs and keep the species going. Butterfly wings A butterfly has four flat wings; a pair of wings on each side of its body. Each front wing is hooked to the wing behind it so as to make one big flat surface. Each pair of wings beats as one. The wing structure is made of the veins. The membrane that stretches over the structure is as thin as a thousandth of a millimetre and covered with tiny overlapping scales. Power for flapping the wings comes from powerful muscles in the thorax. Other muscles adjust the angle of the wings. How the butterfly flies through air There are forces that act upon a butterfly when it flies: Weight - the force that is pulling down toward the ground (gravity). Lift - the force that allows the butterfly to move upward. Thrust - the force that pushes the butterfly forward. Drag - the force that pulls the butterfly backwards.

4 Diagram 1. This diagram shows weight, lift, thrust and drag acting on a butterfly. To fly through the air a butterfly usually flaps its wings. This creates lift and thrust. By flapping its wings a butterfly creates enough lift to overcome drag and gravity, and is able to push itself forwards and up. Gliding Sometimes butterflies don t flap their wings but glide. Gliding uses less energy than flapping wings. This makes for efficient flying. If it s already high, a butterfly can spread out its wings and ride the air down in a controlled fall. If there s a thermal, the butterfly can glide up on it. A thermal is a rising current of air. Thermals occur where the wind is forced upwards by cliffs or hillsides, or where the air has been heated by warm ground (because hot air rises). The thermal pushes up under a butterfly s large outspread wings. EXPERIMENT It is very difficult to study real butterflies. At Harvard University, scientists have used artificial butterfly wings to investigate butterfly flight. The Harvard scientists tested the effect of the angle of a butterfly's wing on the lift force.

5 In this diagram the letter α represents the angle between the wing when viewed from the side and the direction of the wind. The diagram shows angles of 0, 45, and 90. I decided to follow the Harvard study and to use paper wings to find out the best angle for a butterfly to hold its wings at, to get the strongest glide. I would find out how much air lift there was when the wings were at different angles. I made paper butterfly wings (much larger than real) and put them on in an outstretched (gliding) position on a craft-stick stand. I put the wings on their stand in front of a fan. When I turned on the fan I could see the blowing air lifting the paper wings. I put the wings and stand on a set of scales and set the dial to zero. When I turned on the fan the dial went down to a minus amount. The airflow from the fan was creating lift. I could put the paper wings at different angles and using the scale, test the strength of the lift at each angle. I could find the best angle for the strongest lift.

6 STEPS: 1. Make paper butterfly wings (using pattern Science Buddies) 2. Build 10 craft stick "supports" to test in 10 degree increments from Clip paper butterfly wings onto each support structure in turn (using two binder clips). 4. Place scale and fan on the floor exactly 80 cm away from each other. 5. Place the first support structure, with a butterfly clipped on at 0 (horizontal), on top of the scale with the butterfly facing toward the fan. Set the scale s dial to zero. 6. Turn on the fan and after 30 seconds record the measurement that is on the scale. 7. Repeat experiment for 20 angle, and in increments of 10 degrees, up to 90 (at right angle to the fan s breeze). Record results. 8. Repeat tests over again 5 times. Record results on table.

7 CONTROL OF VARIABLES: I set up my experiment as far away from any walls or other obstructions (like furniture) as possible. I closed all the windows. I made sure the fan was always on the same speed and direction each time. I made sure the butterfly wings on the scale was always the same distance from the fan. RESULTS Lift (grams) Angle Test 1 Test 2 Test 3 Test 4 Test 5 Average 0 0g -1g/0g 0g -1g/0g -1g - 0g 0.3g 10 0g -1g/0g 0g -1g/ 0g 0g 0.2g 20-1g -1g -1g -2 /-1g -1g 1.1g 30 0g 0g -1g 0g 0g 0.2g 40-1g/0g -1g 0g -1g 0g 0.5g 50-1g/0g 0g -1g -1g 0g 0.5g 60 0g 0g 0g 0g 0g 0g 70 0g 0g 0g 0g 0g 0g 80 0g 0g 0g 0g 0g 0g 90 0g 0g 0g 0g 0g 0g Note: When the dial on the scale varied from showing 0 and -1 degrees I have recorded this as -1g/0g.

8 ANALYSIS My tests showed that the butterfly wings get some air lift when they are at an angle between 0 degrees (horizontal) and 50 degrees. My hypothesis was that the strongest lift would be at 30 degrees. But my experiment showed that it was 20 degrees. Over five tests, the strongest lift of the paper butterfly wings was when they were angled up at 20 degrees. When the butterfly wings were 60, 70, 80 or 90 there was no lift. I had expected this because the angle was too steep and the air from the fan pushed the wing back more than lifting. Problems I noticed that four of the five tests at 30 degrees resulted in no lift at all. There was more often lift when the angle was less (at 0, 10 and 20 ), or when the angle was a bit more (at 40 and 50 ). I hadn t expected this and I can t explain it. Perhaps one of the variables changed. Perhaps even though I didn t notice it there was a draft. My set of scales was able to measure differences of one gram. Maybe scales that could measure less than one gram would have been better. CONCLUSION My experiment shows that butterflies get the best glide when they angle their wings 20 off the angle of the air flow. My hypotheses was 30 (I wasn t far off). When butterflies can hold their wings at 20 they can glide best. This would help them fly further on less energy and find more food and survive longer. Maybe other gliding animals (such as birds and bats) might also hold their wings at 20 for their strongest & longest glide. IMPLICATIONS If you wanted to build something that would have a strong gliding action, based on my experiment results, set the wings at 20. If you wanted to make a

9 paper plane, or a set of hang-gliding wings. A drone could save energy by sometimes gliding if the wings were at 20. From my experiment results, base jumpers and sky divers could try holding their bodies at 20 to get the best lift and most efficient glide. FINALLY Not only are butterflies amazing and beautiful animals, but they have a big part to play in pollinating plants so that plants don t die out. The way people are rapidly changing the natural environment has a big impact on butterflies. Clearing land of flowering plants means butterflies have to fly further to find food. In Australia, some butterflies, such as the Purple Copper, are in danger, and it's going to need all the help we can give it. Learning what helps butterflies survive is the first step towards helping them. ACKNOWLEDGEMENTS My mum took me to Sydney zoo, took some of the pictures and helped me get some of the materials for the experiment. Nanami helped me observe butterflies at the zoo. Mrs Rao helped me find a topic, set a timeline for my work and leant me a small fan for my experiment.

10 Great Migrations DVD - National Geographic, Exploring Life Science Encyclopedia. Vol 2 : B & C - Marshall Cavendish, New York, What is flight? - Peter Mellett and John Rostron, Armadillo, London, REFERENCES "Butterfly Wings: Using Nature to Learn About Flight" Science Buddies