Roda Abokor Physics coursework: Helicopter

[Roda Abokor Physics coursework: Helicopter]January 1, 2014

ResearchHow the turning rotor makes a helicopter move upward?A helicopter is a type of rotorcraft in which lift and thrust are provided by rotors. Helicopters have a rotor that turn and make the helicopter move in different direction. The upward movement is produced by the main rotor. As the rotors spin they cut into the air and produce lift. Each blade creates an equal amount of the lifting force. The rotor spins against the air which causes a lift, allowing the helicopter to rise upward or hover. Helicopter will take off when lift produced by main rotor is greater than the weight of helicopter. If you tilt the spinning rotor, it will cause flight in the direction of the tilt. The shape of the helicopter is very important; it is designed to enable the air passing over the upper surface to move faster, this causes a difference in pressure between the upper and lower surfaces, producing an upward force known as lift.(1) 2) How the rotor is made to turn in a helicopter or in an autogyro?The engines provide power for the blade to rotate in a helicopter. However, in an autogyro it is made to turn by aerodynamic forces, through autorotation. The rotor of Autogyro is not powered therefore it needs a separate source for propulsion, like an airplane. The Autogyro is driven forward by a pusher propeller and the rotor spins due to the air flow alone. In others the autogyro gets its power by the wind passing through. Since the blades are in an air foil shape, they turn into the airstream fairly easily. To generate lift, the rotor blades must be turning really fast. This creates a lot of resistance to upward airflow, and this resistance provides lift.(4)3) How autorotation is used to help land a helicopter safely if the engine fails?Autorotation is a state of flight where the engine of the helicopter is no longer supplying power to the main rotor; the engine is disconnected from the main rotor system and the rotor blades are driven just by the upward flow of air through the rotor- this is called windmilling. Autorotation in helicopter occurs only when the main rotor is rotating faster than the engine. Lift is produced by the rotor rotating the freely airfoils and the aerodynamic force are caused by the upward flow of air. In helicopter, autorotation only occurs when the aircraft is descending with the blades at a low pitch. (2)

.

Figure 1: helicopter to show autorotation

4) Why a helicopter, falling during autorotation, could reach a terminal speed without the pilot changing any controls?The two forces acting on the helicopter are weight and air resistance. The helicopter has a force pulling down (weight) and a force pushing up (air resistance).Initially as the helicopter falls, air resistance is low. As the velocity increase, the air resistance increases but the weight stays the same, so the resultant force is not as great as before but the object is still accelerating. Eventually the air resistance force is the same as the weight of the helicopter; this makes the resultant force zero. Therefore the object falls at a steady speed - it is no longer accelerating. The helicopter has reached terminal velocity. (6&7)5) The effect of the weight of the helicopter on the terminal speed The force of (gravity) weight causes a constant acceleration, regardless of mass; with no air resistance (in a vacuum), free falling objects will accelerate at the same rate because the drag factor due to air has been eliminated.(3) However this only applies to falling object in a vacuum with no air resistance; the existence of air resistance in the atmosphere makes it impossible for every falling object to have the same terminal velocity/speed and to accelerate at the same rate. With the existence of air resistance in the atmosphere, the greater the mass of the helicopter the greater the force (weight) on the helicopter therefore a greater force is required to counter-act the force due to the additional mass added. Because air resistance increases as the velocity increases, helicopter with a greater mass will have a higher terminal velocity and will reach the ground quicker. (5)

Figure 2: Graph to show mass against terminal velocity

Bibliography The following websites and books were used in order to provide secondary research for my experiment.Websites:1)http://science.howstuffworks.com/transport/flight/modern/helicopter5.htm7

2)http://geophil.hubpages.com/hub/Helicopter-auto-rotation#

3) http://www.grc.nasa.gov/WWW/k-12/airplane/ffall.html

4) http://www.jefflewis.net/autogyros.html

5)http://www.ihmc.us/groups/voluntology/wiki/5b93d/Helicopters_Science_Background.html

Books:6) Collins OCR Gateway additional science (p3) by Colin Bell7) Collins OCR revision guide (p3) by Collin Bell

Planning and Collecting Primary DataAim: I will be investigating the time taken for the helicopter to reach the ground and how different masses effect the landing time.Hypothesis: My hypothesis is that as the mass of helicopter increases the time taken for the parachute to reach the ground will decrease and the average speed will increase with increasing mass. Reasons: At first, the weight of the helicopter is greater than the air resistance, there is resultant force acting downward and the helicopter accelerates. As the helicopter accelerates, the helicopter displace more air molecules every second so air resistance increase. The helicopter with a greater mass requires a greater speed to accumulate sufficient upward air resistance force to balance the downward force of weight. The weight does not change but the air resistance increases until it is equal to the weight. Terminal velocity is when the weight equals with air resistance and at this point the speed is constant as there is no resultant force. The greater the mass of the helicopter the greater the force (weight) on the helicopter therefore a greater air resistance is required to counter-act the force of weight. This means that a helicopter with a greater mass will have to accelerate for longer period of time before there is sufficient upward air resistance to balance the large downward force of gravity. A greater mass will mean it will reach a higher terminal velocity and continue to fall with constant high velocity hence why the helicopter with a greater mass will reach the ground quicker.Controlled Variables: Type of paper (size and mass) Type paper clips (size and mass) Surface area of the paper Height Uncontrollable variables: Wind/breezeDependent Variables (Y axis): Time taken for helicopter to fall (graph A) & speed( graph B)The time taken for the helicopter to fall is the dependent variable and this will be plotted on the y-axis, the dependent variable is called the effect. This means it is the effect of the independent variable. Therefore the time taken for the helicopter to fall is dependent on the mass of the helicopter.Independent variable (X axis): Mass of helicopter The mass of the helicopter is the independent variable because I will be adding paperclips which will change the mass. The aim of my experiment is to investigate how the mass of the helicopter affects the landing time therefore I will have to change the mass of the helicopter in order for me to come to a conclusion. The independent variable is the cause of the dependent variable therefore I will plot the mass of the helicopter on x-axis.The factors below will affect my experiments therefore I need to carefully monitor these factors and make sure that they are kept constant in order to make my experiment fair and accurate. To carry out a fair experiment I will:1. Use the same helicopter with the same size, mass and surface area. The surface area of the helicopter will have an effect on the air resistance, which would in turn affect the acceleration of the helicopter. If the helicopter had a larger surface area, it will displace more air molecules every second which will increase the air resistance reducing the acceleration of the helicopter. To prevent this happening and causing an unfair test, I am going to use the same helicopter for each experiment I perform.

2. Drop the paper helicopter at same height. The height from which I drop the paper helicopter is important. We will use the same height for timing in each experiment - this will make it a fair test. The height we have decided to drop the helicopter is approximately 4.71m (3.s.f).

3. Do the experiment in the same place because both the wind and weather will be the same. The wind and the weather are uncontrollable variable however the wind will not change massively therefore it should not affect my result. Modification: (Preliminary Work) I was going to add 1 paperclip each time (increasing the mass by 0.44g) but after my pre-experiment I realised that the mass difference was too small to make a difference. Therefore I have increased the number of paperclip to five at a time, increasing the mass by 2.20g each time. Before the experiment, we were going to drop the helicopter at height of 2m but we realised 2m was not enough and the helicopter merely reached its terminal velocity therefore we decided to drop it at a height of approximately 4/5m. This will allow us to have more accurate reading as it minimises the error. Initially, we were going to use 5 helicopters but we realised this was not a fair test so we used one helicopter throughout the experiment.Minimising Error Replication: I will repeat my experiment three times in order to get reliable result and to minimise errors. By repeating the experiment, I am sure that I will obtain consistent results. We will also use the three trails to work out an average time.Minimising human error: We will use the same person for the timer and the dropper of the paper helicopter because people have different reaction time and also they might drop the helicopter at different height which will affect our result. It is going to be very hard to be accurate with the timing of landing of the paper helicopter. Our results may be affected by the fact that the timer and dropper will be doing lots of experiments after another and their reaction time will decrease as the time goes on. To prevent this we allow the timer and dropper to have short breaks between the experiments. Apparatus: Paperclips (to put on paper helicopter and use it as a mass) Balance (to measure mass of paperclips) Paper (to make paper helicopter) Stopwatch (to measure the time taken for the helicopter to reach the ground) Scissors (to cut the paper) Tape measure ( to measure the height of the banister)Method:1. Get an A4 paper and fold it in half2. Cut along the folded line to get a paper of 29.7cm x 10.53. Fold one of the two strips of paper in half lengthways and then in half widthways 4. Take one side and cut just before the middle point where both folds meet5. Cut evenly along the fold widthways just before the middle point 6. Fold both sides inwards 7. Fold the top two flaps in the opposite direction to create the helicopter blades8. Time how long it takes for the helicopter to reach the ground using a stopwatch9. Repeat the experiment for another two times for reliable and accurate results10. Repeat steps 1-9, adding a different number of paperclips to increase the mass

Figure 3: diagram to show the method step by step

Risk Assessment:The risks of this experiment are extremely low and highly unlikely but I have identified all the possible risks below, before doing the experiment. I have completed the risk assessment to ensure we had solutions and strategies in place to our possible risks. We needed to make sure that all possible safety precautions were taken in order to carry our experiment safely.

HazardHow risky?How could it harm youWhat to do if risk occursHow can the risk be prevented

Falling over banistershighYou could fall down and hurt yourselfContact a teacher/school nurse to see if everything is okay and also consult your doctor.Dont lean over the banisters and make sure to keep your distance

Tripping over the stairLow/mediumYou could hurt yourself , your feet might be swollen or worseTell a teacher, if it is swollen put some ice on it and if it gets worse make sure you see a doctor.Dont run down /up the stair and be careful not to trip over obstacles

Falling tape measure with heavy crank Very lowIt could be a hazard to the people below ( the heavy crank could land on their head)It is very low hazard but if it occurs they could consult a teacher and get it checked out.Look carefully at the people going pass and wait for them to pass-Dont continue with the experiment.

Balance Low/mediumThe heavy balance could land on your feetTell a teacher and get checked out if your feet is okayDont leave the balance at the edge of the table

Data Processing: Table of result Table to show how increasing the mass of the paperclips affects the time taken for the paper helicopter to reach the groundTime taken(s) for the helicopter to fall a distance of approximately 4.70m

Number of paperclips Mass of paperclips(g)1st(seconds)2nd(seconds)3rd(seconds)Average(seconds)Speed of fall=Distance/time(m/s)

Range

00.003.503.543.553.531.340.05

52.102.973.034.21*&

3.001.571.24

104.202.442.452.592.491.900.15

156.302.072.162.222.152.200.15

208.401.691.681.631.672.830.05

2510.501.311.281.351.313.600.07

*The value in the ellipse is an anomalous number, and Ive excluded it when calculating the mean average Time & average speed.Calculations: To get the mean/average, you have to add the three trials together then divide it by three. For example: 3.54+3.55+3.50=10.59 10.59/3=3.53 To calculate the speed, you have to divide distance of 4.71(3.S.F.) by the mean of the three trials. For example: 4.71/3.53=1.34 To work out the range take away the maximum trail by the minimum trailFor example: 3.55-3.50=0.05I have calculated the product moment correlation coefficient for both graphs to measure the degree of correlation and determine the strength of the linear relationship between the variables. Product moment correlation coefficient for graph A: R=0.96594217 Product moment correlation coefficient for graph B: R=-0957837385

Part 3 Analysing and evaluation:Q1)Process the data you have collected and plot a graph(s) of the result of your investigation. (See the graph)Q2) describe any patterns or trends in your result. Comment on any unexpected result.Graph A: My graph displays how increasing the mass of the paperclips affects the time taken for the paper helicopter to reach the ground. The x-axis show the mass of the paperclips added to the helicopter and the y-axis show the average time taken for the helicopter to reach the ground. The graph shows that as the mass of helicopter increases the time taken for the parachute to reach the ground decreases. There is clear negative correlation between the mass of the helicopter and the time taken for the helicopter to reach the ground. The value of the product moment correlation coefficient (-0.957837) shows that it is a strong negative correlation and most of the values are near the regression line (line of best fit).The third trial of when the helicopter had a mass of 2.10g added was anomaly and I have decide to exclude this when I was calculating the average time. This result refutes the trend as the average time taken increases when it should have decreased. When the helicopter had no mass added, the average time taken for the helicopter to touch the ground was 3.53 seconds. However when the helicopter had a mass of 10.50g, the average time taken for the helicopter to reach the ground was only 1.31 seconds. Overall, the average time taken for the helicopter to reach the ground has decrease by 2.22 seconds when the mass of the helicopter has increased by 10.50g. Graph B: The second graph shows how increasing the mass of the paperclips affects the average speed of the paper helicopter. The x-axis show the mass of the paperclips added to the helicopter and y-axis show the average speed of the falling helicopter. The graph show that as more mass is added to the helicopter, the average speed of the falling helicopter increases. Most values are close to the regression line (line of best fit) and the value of the product moment correlation coefficient (0.965942) show there is a strong positive correlation between the mass of the helicopter and the average speed of the helicopter. At first when the helicopter had no mass added, the average speed of the falling helicopter was 1.34m/s. The average speed of the falling helicopter increased from 1.34m/s to 1.57m/s when the mass added was 2.10g. The third trial of when the helicopter had 2.10g added might be an anomaly as it does not fit with the trend. This third trial would have affected the average speed of the helicopter therefore I have excluded from my calculation. I will discuss the possible cause of this anomaly on my evaluation. Scientific explanation: The two graphs are related as both average speed and time taken for the helicopter to land are dependent on the mass added to the helicopter. As the mass added to helicopter increases, the force (weight) on the helicopter increases therefore a greater air resistance is required to counter-act the force of weight. This means that a helicopter with a greater mass will have to accelerate for longer period of time before there is sufficient upward air resistance to balance the large downward force of gravity. A greater mass will mean, it will reach a higher terminal velocity and continue to fall with constant high velocity hence why the helicopter with a greater mass will reach the ground quicker. Q3) Compare results of your own investigation (part 2) with the data from other groups and any information you collected in your research (part1). Suggest and explain reasons for any similarities and differenceWe compared our result to another group, there are lots of similarities but there are differences too. We compared our result to Shadias group as they were the only group who used the same amount of paperclips however the distance we dropped the helicopter is different to theirs. They used a distance of 4m and we used a distance of approximately 4.7m. Therefore we need to be aware that the result we get will be completely different as the distance is variable which will affect the speed of the helicopter however the overall trend will be similar.Differences Graph A: (mass of paperclips against average time taken to reach the ground) They used a distance of 4m and we dropped from a distance of 4.7; theres a difference of 70cm. Therefore, the result we collected are quite different as the distance is a major factor that has an effect on speed and time. For instance, When there was no mass added to the helicopter, the average time taken for their helicopter to reach the ground was 3.21s where as our helicopter took 3.53s to reach the floor. After 2.10g was added to their helicopter is took only 2.26s. Our helicopter took 2.62 to reach the ground when 2.10 g was added to our helicopter. These results are different and our helicopter always takes longer to reach the ground because the distance our helicopters have to travel to reach the ground is longer. There is also an unexpected result in their graph as the last two results remain constant. This would mean the helicopter with 8.40g and 10.50g both reached their terminal velocity at same time.Similarities:Graph A: Despite the fact that we used different distance, both our graph have lots of similarities in common. The two graphs both show a negative correlation between the mass of paperclips and the average time taken to reach the ground. In other words, as the mass of paperclip increase, the average time taken for helicopter to reach the ground decreases. A greater mass will mean, it will reach a higher terminal velocity and continue to fall with constant high velocity therefore the helicopter with a greater mass reaches the ground quicker.Graph B: The two graphs which show the mass of paperclip against the speed have a positive correlation. This means that as the mass of the paperclip increased, the speed also increased. This can be explain as the helicopter with greater mass reaches its terminal velocity slower therefore the helicopter with greater mass has higher terminal velocity which it continues to fall at such high speed.In my research, I have found out that the mass does affect the terminal velocity. From my research I have found out that a helicopter with greater mass has higher terminal velocity and therefore a higher average speed. The graph that is included in my research supports my findings; the graph shows a positive correlation between the mass and the terminal velocity. This is because a helicopter with a large weight needs a greater air resistance is to balance the two forces and the helicopter has to travel further to reach their terminal velocity thus a helicopter with a greater mass reaches a higher terminal velocity.

Q4) Evaluate your results, the method you used and how well you managed the risks.My results were fairly good as I dont have many extreme anomalies and my investigation is fairly precise and accurate. I have repeated my result 3 times and got similar result so my results are repeatable. I have found the average (mean) of the 3 experiment we did, this made my data more precise. The ranges between my results are small as shown in the table and graph, this shows that my result are precise and reliable.During my experiment, I ensured that the same person dropped the helicopter from the first floor to enable accurate results as the helicopter would have been dropped at exactly the same height each time. We also decided to use the same person as the timer because people have different reaction time and this will affect our result.We used the same helicopter to ensure we carried out a fair test. Using different size helicopter would mean we will also be changing the surface area of the helicopter. The surface area of the helicopter will have an effect on the air resistance, which would in turn affect the acceleration of the helicopter. If the helicopter had a larger surface area, it will displace more air molecules every second which will increase the air resistance reducing the acceleration of the helicopter. Therefore, we used the same helicopter throughout the experiment. However, we realised the helicopters blade became damaged due to numerous times we did the experiment. This might had an effect on our result especially for the third trial results.There is a clear anomaly in my result and this value is the result from when the mass of the paperclip was 2.10g. The average taken by the three trials would have being affected by the third trial which was an extreme outlier therefore I have excluded the third trial from my average calculation. From the table the first trail reading was 2.97s, the second was 3.03s (these two result have small differences) but the third trail took 4.21s for the helicopter to reach the ground. Clearly the third trial is anomaly as there is massive range of 2.24s (4.21-2.97=1.24s). The cause of the anomaly might be due to reaction time; the reaction time of my partner has reduced due to the fact that she was doing lots of experiment. In addition, my partner might not have dropped the helicopter from the same point each time therefore the distance could also be inaccurate at different point of the experiment which affected my result.From my observation, I have found out that the some of the paper helicopter such as the helicopter with 10.50g did not reach their terminal velocity as the helicopter went straight down without the rotor spinning. This shows that the4.7m was not long enough and I will consider increasing the distance next time to minimise errors.If we did this experiment again, we will minimise errors and make sure we had no anomaly. If we get any unexpected result, we will repeat the anomaly to minimise errors. There are many ways to extend this investigation; I could also see if changing the size of the blades will have an impact on the terminal velocity or if changing the surface of the helicopter would have any effect.

Q5) Do your results from part 2, support the hypothesis you suggested?My hypothesis states that:as the mass of helicopter increases the time taken for the parachute to reach the ground will decrease and average speed for the falling helicopter will increase with increasing mass. My result support my hypothesis; my result show that as the mass of the helicopter increase the time taken for helicopter to reach the ground decrease and as the mass of the helicopter increase the average speed of the falling helicopter increase. This is because a greater air resistance will be required to balance a helicopter with a large weight and therefore the helicopter reaches terminal velocity later on .The greater the mass of the helicopter the greater the force (weight) on the helicopter therefore a greater air resistance is required to counter-act the force of weight. This means that a helicopter with a greater mass will have to accelerate for longer period of time before there is sufficient upward air resistance to balance the large downward force of gravity. A greater mass will mean it will reach a higher terminal velocity and continue to fall with constant high velocity hence why the helicopter with a greater mass will reach the ground quicker.However, there is one result which does not support my hypothesis. When the helicopter had no mass added, the average time taken for the helicopter to touch the ground was 3.53 seconds. However, when 2.10g was added to the paper helicopter, the third trial for the time taken to reach the floor was 4.21s. This result contradicts my trend as the average time taken increases when it should have decreased. I believe this is an anomaly and this should not refute my hypothesis.Q6) The speed of a helicopter, falling under autorotation, will change during its fall Using information from your research (part 1) and your knowledge of forces, describe how the speed changes and explain why the changes happen. The terminal speed of your paper helicopter is also affected by its weight. Explain this using your results from Part 2.From my research, I found out that the speed of a helicopter, falling under autorotation, will change during its fall. Initially the weight is greater than the air resistant so the helicopter accelerates as there is a resultant force acting downward. As the helicopter accelerates, it displaces more air molecule each second and therefore air resistance increases. The rotor will spin automatically under the effect of pressure displacing more air molecule each time and causing the helicopter to decelerate as air resistance increases. During autorotation, there is an increase in airflow beneath the helicopter; this greater amount of airflow causes the helicopter to decelerate. Eventually, the air resistant and weight become equal and at this rate the helicopter has constant speed. There is no resultant force as the helicopter has reached terminal velocity (terminal speed).The terminal speed of my paper helicopter was affected by the weight; I have found out that as weight increases the terminal velocity of the helicopter increases. This is because a helicopter with a large weight needs a greater air resistance is to balance the two forces. Therefore a helicopter with a greater weight will have to accelerate longer until there is sufficient upward air resistance to counteract the downward force of weight. From my observation, I have found out that some of the helicopter reached terminal velocity however the helicopter which had 25 and 20 paperclips attached did not reach their terminal velocity due to the short distance. These two helicopters went straight down with high acceleration due to their weight been greater than the air resistance .However the other helicopters accelerated first and then their rotor rotated, after this they speed was constant as they have reached terminal velocity.

12 | Page