# Affect The Flight Time Of A Balsa Wood Glider Engineering Essay

The purpose of the study was to obtain the relation between the flight time and launch height of a balsa glider of different wing area. Also the effect on flight time was recorded by changing the position of wings of the gliders.

In the first part of the experiment the gliders were launched from four different height and the flight time was recorded. The experiment was conducted in a closed area in order to avoid the effect of wind. The gliders used were of different size and shape. The net acceleration acting on the gliders was also calculated by plotting a graph between square of flight time and launch height.

In the second part of the experiment the wing positions for three different gliders were changed and the flight time was recorded in each of the three gliders. The launch height of the gliders was kept same.

It was observed that as the launch height was increased the flight time also increased. The amount of lift could only be analysed by calculating the net acceleration in each of the gliders.

The variation in the flight time due to the change in the position of wings was interpreted in terms of the increase in the loops made by the gliders i. e. the instability of the gliders or the moments of wings.

## Introduction:

The question about aerodynamics has great importance in today’s times and the various factors that affect aerodynamics of an aircraft or a glider is necessary in order to improve the efficiency. By taking up this experiment I have tried to analyse the acting forces on the flight of a glider such as the lift, the drag, and the weight also the theory of projectile motion plays an important role in determining the flight time of a glider. Also keeping in mind the laws of physics that relate to flight and also checking whether they are in accordance with the following experiment.

## How the Wing area and position along with the launch height affect the flight time of a Balsa Wood Glider?

The aim of this experiment is to study how the wing area, wing position and the launch height have an impact on the flight time of a balsa glider.

In order to establish the above relations balsa gliders of different wing areas were hand launched from different heights and the flight time was recorded.

As for the relation with the wing position and flight time they were hand launched as well from a fixed height with different wing positions.

## Theory

The experiment is based on the theory of projectile motion, and fluid mechanics.

## Projectile Motion-

When a body is projected from a certain height with a certain velocity, the acceleration on the body acts only in the downward (along y-axis) direction and the acceleration along the horizontal (x-axis) direction is zero.

Since the air resistance also affects the horizontal motion of the body there might be some deceleration, however it is of a very small magnitude hence it can be neglected in the case of my experiment.

The same explanation can be taken for the wind; there might be some component of the force (due to wind) which might affect the horizontal motion as well. This is also taken care of in the experiment as it is conducted in closed area.

As the initial velocity is in the horizontal direction its vertical component is zero, by taking the vertical motion the flight time of the glider should depend on the height from which it has been launched and the net acceleration in the vertical direction.

By varying the height in the experiment the flight time should also vary proportionately. As the height is increased the flight time should also increase.

Due to the change in the forces acting on the glider the net acceleration can also change which in turn will affect the flight time.

## Forces

There are three types of forces acting on a glider which are:

## Weight

The weight of the body always acts in the downward direction.

The weight of a body dependent on the mass of the glider and gravitational acceleration which can be taken constant for a given space. By Newton’s 2nd law of motion, the weight is given by (F = mg)

It is the force due to the gravitational attraction of the earth on the glider. But this force weight, which is the gravitational force, is different from the aerodynamic forces, lift and drag. The lift and the drag are mechanical forces that will act on the glider only when it is in physical contact with air which generates these forces. The gravitational force or weight is a field force; and is a non-contact force.

The gravitational force (weight) between two objects depends on the masses of the two objects and the inverse of the square of the distance between these objects. The more the masses of the objects the stronger is the attraction, and closer the object are the stronger the attraction.

## Lift

Lift is the force that acts on a glider upward and helps the glider to stay in the air. The lift on the glider is mainly generated by the wings. It is an aerodynamic force produced by the motion of air flowing through the glider. Lift acts through the centre of the pressure of the glider and is in the direction which is normal to the flow of air.

Lift occurs when a flow of air is turned by the glider. According to Newton’s 3rd law of motion the flow of air is turned in one direction, and the lift is generated in the opposite direction. Since air is a gas and its molecules are free to move about, any solid can deflect its flow. For an air foil, both the upper and lower surfaces plays part in turning the flow of air.

There can be two types of lift static and dynamic lift.

Static lift

according to the Archimedes principle whenever a body is immersed in a fluid it experiences an upward force called the buoyant force.

The factors on which the buoyant force depends are:

The volume of the fluid displaced and; the density of the fluid.

If the area of the wings increases the magnitude of the lift should also increase and the net force acting on the glider should also increases which in turn should decrease the net acceleration and hence increase the flight time.

Dynamic Lift

According to Bernoulli’s principle; the dynamic lift is due to the difference in pressure on the two sides of the body which is due to the difference in the speed of the air on the two sides of the body.

There are various factors that affect lift, these are:

Aircraft wing geometry has a large effect on the amount of lift generated. The shape and size of the wing will have a significant impact on the amount of lift generated.

In order to generate lift there must be some velocity; hence if the object is moved in air then lift will be generated. Lift also depends on the mass of the flow.it also depends in a major way on the viscosity and compressibility of air.

## Viscous force or Drag

Viscous force is a mechanical force. The drag, like lift, is also produce by the interaction and contact of a solid body with air. For drag to be produce, the solid body must be in contact with the air. If there is no air, there is no drag. Drag is generated by the difference in the speeds of the solid object and the air. There must be relative motion between the object and the air. If there is no relative motion, there is no drag. Viscous force always opposes the motion, hence it will be opposite to the motion of the glider.

The most of the factors affecting drag is same as that affecting the lift.

The viscous force can be taken as the aerodynamic friction, and one of the sources of this force is the skin friction between the molecules of the air and the solid surface of the glider. Since the skin friction is an interaction between a glider and the air, the magnitude of the skin friction depends on properties of both glider surface and air. The smooth, waxed surface of glider will produces less skin friction than a rough surface. And for the air, the magnitude of skin friction depends on the viscosity of the air.

The relative magnitude of the viscous forces to the motion of the flow of air is called the Reynolds number.

Also the drag can be taken as the aerodynamic resistance to the motion of the object through the air. This source of drag depends on the shape of the glider and is called form drag. When air flows around a body, the velocity and pressure around the glide are changed. The pressure is a measure of the momentum of the air molecules and a change in momentum results in a force, a change in pressure will produce a force on the body. This component of the aerodynamic force that is opposed to the motion is the drag.

Viscous force directly depends on the mass of the air flow going past the glider.

## Effect of Height on Flight time

In this experiment there will be 4 heights taken but the height intervals will not be uniform in order to check the trend and see if there is a clear distinction in readings of flight time. As the height increases the flight time should increase as there is more distance to cover for the glider and since there are no forces acting as mentioned above, it is only the height that acts as a factor to change flight time.

## Wing area

In this experiment the wing area should effect the flight time of the gliders as seen earlier, lift has a direct connection with wing area. As the lift increases the glider goes higher in the air thus increasing the flight time.

Every glider has a different wing area and this makes a clear distinction between the flight times for the gliders.

## Wing position

The wing position whether towards the front or back determines the stability of the glider while its flight. The more it is to the front of the socket it tends to do be more unstable and has a very loopy flight which increases the flight time.

The further behind the wing is in the socket the more stable the glider is as the weight is more towards the centre of mass, making it more stable and also increasing the flight time however whilst a straight and balanced there are other forces acting on the flight that might pull it down to the ground.

## Gliders

In the initial stages the glider used were made by hand using a template to cut out the parts of the gliders. However these gliders lacked perfect stability and the edges had to be rubbed and smoothened in order to use make them completely aerodynamic. Even after doing so they lacked perfect specification and the material used to make them was not the right material hence they did not glide as required to.

The gliders used in the later stages were bought online from amazon.com. These gliders are laser cut and ready to fly. They are made out of balsa wood. There were 3 types of gliders that were used, the parts of the gliders were precisely cut and well balanced in order to obtain a decent flight. The 3 gliders varied differently in shape, size, and weight and wing area.

## Area

The experiment was conducted in a closed environment. The length of the place was approximately 35meters and width approximately 12meters. The wind factor was controlled as all doors and windows were shut and it was an enclosed area.

## Method:

There were various steps that are involved in this experiment.

The glider was first flown in an outdoor environment to check the flight. Since the wind factor cannot be controlled in an outdoor environment it was not possible to conduct the experiment outside as this affects the flight time. Hence an indoor area was chosen.

## Measuring Wing Area

The gliders that will be used which each have different shape, size, and wing area. The first variable wing area cannot be measured by a given formula as it is not a uniform shape and cannot be broken into smaller shapes.

The wing area will be measured by keeping the entire wing on a graph sheet whose each square area is known and the outline of the wing shape will be sketched out on the graph sheet. After having done this the number of complete squares of the known area that are enclosed by the outline of the wing will be counted. After this the number of incomplete squares and an approximation will have to be made as it is not feasible to calculate area of a fraction of the square. This will be done for each of the three gliders and will be noted down.

In order to make sure that the gliders, glide properly without any hindrance and technical difficulty a test flight will be done. If there seem to be any technical problems with any of the three gliders they shall be fixed at first in order to provide accurate and legit readings. If any parts seem to be broken they will be fixed by the special adhesive which is used to stick balsa wood.

## Launching and Measuring Flight Time

Keeping in mind that there are no holders or launching devices provided with these gliders they will have to be launched by the free hand as it is not possible to devise a launch method. This is so because making any alterations to the glider might distort its stability and will cause unequal weight balance.

Although launching from the hand will have uncertainties such as different launch force and height it will be controlled as much as possible.

In order to make sure the height is constant a plumb line will be taken and held from the comfortable launch height. This plumb line will then be measured in accordance with a metre scale. Every time a glider is launched it will be launched from the same height as the thread will be held at that height while launching the glider. The second height from which it will be launched will be after standing on top of a dining table. The height of the table will be measured by using another plumb line and will be measured in accordance to the metre scale. This height of the table will be added to the initial launch height and then a plumb line of that height will be held while the launch.

The fourth height will be from approximately the first floor. The vast interval difference is taken so that there can be a clear trend that can be observed for the flight time. The height of the wall will be measured and then the initial height of the launch will be added to this. The fourth height will be from above a table on the first floor, in order to obtain this height the same step as the one for the table height on the lower level will be used.

Taking the readings of the flight time will be done by using a stopwatch. It is not possible for me to do this alone as starting the stopwatch and launching the glider is not possible at the same time hence a little assistance will be required to measure the flight time. The assistant will start recording the flight time as soon as the glider leaves contact with my hand and will stop as soon as the glider touches the ground. These readings will then be recorded in a table. There will be 5 readings taken for each glider at each height.

There are two wing positions possible either at the front of the socket or the back. Each glider’s wings will be adjusted as front and back and for each position there will be 5 readings taken.

## Glider A

Height (meters)

Flight time

(± 0.01s)

Average(±0.13s)

t2(sec2)

1.5

1.64

1.78

1.84

1.81

1.74

3.03

2.24

2.21

2.45

2.53

2.28

2.38

5.68

5.3

3.83

3.94

4.04

3.72

3.91

15.29

6.04

4.81

4.63

4.79

4.84

4.75

22.54

As the height was increased the flight time also increased. Since the glider used was the same and the speed with which it was projected also remained same the lift experienced by the glider did not change. The increase in the time was only due to the increase in height from which the glider was projected.

## Glider B

Height (meters)

Flight time

(± 0.01s)

Average

(±0.13s)

t2(sec2)

1.5

1.25

1.5

1.28

1.3

1.32

1.75

2.24

1.54

1.68

1.61

1.59

1.61

2.60

5.3

2.19

1.94

2.4

2.33

2.24

5.02

6.04

2.78

3.01

2.92

2.84

2.87

8.26

The trend between the time of flight and the height of launch was same as in the case of glider A.

## Glider C

Height (meters)

Flight time

(± 0.01s)

Average

(±0.04s)

t2(sec2)

1.5

0.93

0.90

1.01

0.94

0.94

0.88

2.24

1.16

1.21

1.24

1.19

1.19

1.43

5.3

1.57

1.59

1.55

1.6

1.57

2.45

6.04

2.1

2.12

2.11

2.15

2.11

4.47

The trend between the time of flight and the height of launch was same as in the case of glider A and B. hence in all the 3 cases it was found that the lift experienced by the gliders did not depend upon the height of projection or the height at which the glider was flying.

As seen above in the graph the flight time of the glider is directly proportional to the height from which it has been released i.e. as the height increases the time taken by the glider to touch the ground also increases.

According to the equation of motion 2

If we are considering the vertical motion then the initial speed in the vertical direction will be taken as zero then 2. The three forces acting on the glider that is the weight (mg), the drag and the lift are all constant. Since the drag and the lift depend on the speed of the glider it is not changing as the speed in all the cases are constant.

The above relation can be made linear by plotting a graph between t2 and h from this graph the net acceleration acting on the glider can be calculated by measuring the slope of the graph.

Since:

2.

## Calculation

Net acceleration = 2/slope of the curve.

Net acceleration in glider A= = 0.51 m/s2

## Calculation

Net acceleration = 2/slope of the curve.

Net acceleration in glider B= = 1.62 m/s2

## Calculation

Net acceleration = 2/slope of the curve.

Net acceleration in glider B= = 3.1 m/s2

The Glider C has the maximum acceleration and Glider A has the least. This also means that Glider C comes to rest much more quickly than Glider A, Glider A also has a longer glide time and this is because of the light weight and wing span that makes it more stable while in flight. Whereas when compared to Glider C the weight is much more and the glider isn’t stable enough to stay in air for a long time. The wing area also has a significant impact on this as the more wing area means more lift however when we check Glider C has more wing area but it yet doesn’t get enough lift; this explains that this glider needs more thrust when launched in order to stay in air longer than the others.

## Glider A

Wing Position for A

Position

Flight time

(± 0.01s)

Average

(±0.11secs)

Front

1.72

1.85

1.9

1.68

1.77

1.78

Back

1.56

1.59

1.72

1.6

1.52

1.60

As seen above when the wings of the glider are moved forward the flight time of the glider increases.

## Glider B

Wing Position for B

Position

Flight time

(± 0.01s)

Average

(±0.11secs)

Front

2.13

2.06

2.24

2.17

2.26

2.17

Back

1.66

1.59

1.63

1.82

1.74

1.69

As in the case of Glider A when the wings of the glider are moved forward the flight time of the glider increases.

## Glider C

Wing Position for C

Position

Flight time

(± 0.01s)

Average

(±0.12secs)

Front

1.47

1.59

1.61

1.53

1.42

1.52

Back

0.84

0.79

0.94

0.75

1.03

0.87

As in the case of Glider A and B when the wings of the glider are moved forward the flight time of the glider increases.

As we can see in the graphs above the time taken for the flight when the wings are in front is more than the flight time for when the wings are pushed backward. This is because the forward wings make the flight of the glider much more unstable and cause it to loop more. The looping increases the time to touch the ground as it causes sudden immediate lift and this also increases the horizontal gliding time.

Whereas on the other hand when the wings are pulled back in order to make the flight more stable but there are still other factors like weight, lift and drag that are constantly affecting the flight and causing it to descend.

## Conclusion:

In the first part of the experiment it was found that the flight time increases as the height from where the glider was launched increases. I each of the 3 gliders the lift acting on the glider did not change as the area of the glider remained same. The change in the flight time was only due to the change in the height of the launch. The graph between the height of launch and the square of flight time gave the measure of the net acceleration in case of the 3 gliders which in turn could be interpreted in terms of net force acting on the glider. The measure of net acceleration showed that the lift produced in case of the gliders increased with the wing area. The lift in the case of Glider A was found to be maximum, as it had the maximum wing area.

In the second experiment the flight time increased as the wing position was shifted towards the front of the glider. The trend obtained in all the three gliders was the same. The increase in the flight time was due to the increase in lift that made the glider shoot up and loop in the air. As the glider looped in the air the height also increased which in turn increased the flight time. The increase in the loop made by the glider was due to the instability produced by shifting the weight of the wing to the front of the plane.

## Limitations:

There were several limitations while doing this experiment. The first and what can be considered as the most important is the launching technique. This is the most crucial part of this experiment and all the readings depend on this. Due to the fragile bodies of the glider there could be no launching technique devised that would make sure the force on each launch is the same. The lift acting on the glider depends on the speed of the glider; if the launching speed varies it can affect the lift experienced by the glider.

Since it is not possible to neither control the force used for each launch nor measure it, it was the biggest drawback.

When the experiment was conducted in the open the wind factor had a great impact on the flight of the gliders. The gliders being light and very fragile, the wind outdoor was drifting the gliders into different directions and also slowing them down. This change in path and time was random and unpredictable. Since it was not possible to control the wind the experiment was carried out in a closed environment, yet there was some wind that affected the flight and caused slight deviation in path which could have possibly increased the flight time or even decreased it.

Since the gliders were launched several times and had not landing mechanism as well, the rough landing chipped quite a few parts of the gliders that made the flight for the later readings relatively unstable and defective.

## Unresolved Questions:

The effect of projection velocity on the flight time was not clear as the gliders were launched with almost same velocity and force.

The speed with which the glider moves effects both the lift on the glider and the drag acting on it. The two forces are very important in deciding the flight of the gliders.

By designing a proper launch mechanism the effect of speed or the launch force would had been studied.

Also the efficiency of the flight could have been studied by measuring glide ratio i.e. the ratio of the horizontal distance travelled and the loss of height travelled in a given time.

## Books:

Giancoli, Douglas C., Physics Principles with Applications, 6th Edition, Pearson Education Limited, NJISBN: 0-13 -184661-2-1.

Nelkon, M., and Parker, P., Advanced level Physics, London, Heinemann Educational Books Limited, ISBN 0-435-68636-4

Tsokos, K., A., Physics for the IB Diploma,5th Edition, Cambridge University Press, ISBN 978-0-521-13821-5

## Websites:

http://en.wikipedia.org/wiki/Gliding_flight

http://www.grc.nasa.gov/WWW/k-12/airplane/glider.html

http://www.skysailing.com/pages/theory.htm

http://web.mit.edu/16.00/www/aec/flight.html

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