While travelling from an aircraft it must have been observed many a times that during a flight and after touchdown of aircraft a part of the wing in between the leading and trailing edges of the wing is deployed. This part of the wing is called the spoilers. Especially after the touchdown, it can clearly be observed that the spoilers are extended upward into the airflow.
Spoilers as the name itself explains, it means to spoil. The spoilers, spoils the airflow over a wing and decreases the lift of an aircraft. Here by spoiling the airflow means to disturb the airflow and decreasing the lift by increasing the drag. Spoilers can be used to slow an aircraft, or to make an aircraft descend, if they are deployed on both wings. Spoilers are also used to generate a rolling motion for an aircraft, if they are deployed on only one wing. Spoilers are used for multipurpose; they are sometimes used when descending from cruise altitudes to assist the aircraft in descending to lower altitudes without picking up speed.
An increased rate of descent could also be achieved by lowering the nose of an aircraft, but this would result in an excessive landing speed. However, when spoilers are used along with the thrust reversers they also help in considerably decreasing the runway distance required by an aircraft to land safely and enable the approach to be made at a safe speed for landing. In a descent without spoilers, air speed is increased and the engine will be at low power, producing less heat than normal. The engine may cool too rapidly, resulting in stuck valves, cracked cylinders or other problems. Spoilers alleviate the situation by allowing the aircraft to descend at a desired rate while letting the engine run at a power setting that keeps it from cooling too quickly.
Spoilers are hinged, rectangular plate-like structures installed flush along the top of an aircraft wing, just forward of the flaps. When the pilot activates the spoilers, the plates pivot up on their center hinge fittings into the airstream. By doing so, the spoiler creates a carefully controlled stall over the portion of the wing behind it, greatly reducing the lift of that wing section, as a result, the airflow over the wing is disturbed (spoiled) and lift is decreased with the increment in the drag. This can be observed from fig.1 below.
Fig. 2.1: Spoilers on a wing.
The spoilers works in different conditions of the flight as per desirable by the pilot. All these conditions are discussed in the underwritten sections of the report.
On landing, however, the spoilers are nearly always used at full effect to assist in slowing the aircraft. The increase in form drag created by the spoilers directly assists the braking effect. However, the real gain comes as the spoilers cause a dramatic loss of lift and hence the weight of the aircraft is transferred from the wings to the undercarriage, allowing the wheels to be mechanically braked with much less chance of skidding.
Fig.2.2: Spoilers in action
In the above Fig.1.2 we can clearly observe the disturbance i.e. the turbulence that is caused in the flow when the spoilers are deployed. This turbulence which is created in the flow is the major cause for decrement in lift along with the increase in the drag.
The spoilers may also be differentially operated to provide roll control. On landing, however, the spoilers are nearly always used at full effect to assist in slowing the aircraft. The increase in form drag created by the spoilers directly assists the braking effect. However, the real gain comes as the spoilers cause a dramatic loss of lift and hence the weight of the aircraft is transferred from the wings to the undercarriage, allowing the wheels to be mechanically braked with much less chance of skidding. Reverse thrust is also often used to help slow the aircraft on landing. The spoilers may also be differentially operated to provide roll control.
The spoilers are used in multiple conditions such as:
When the pilot deploys the spoilers, the plates flip up into the air stream. The flow over the wing is disturbed by the spoiler, the drag acting on the wing is increased, and thus as a result lift is decreased. During the mid air i.e. when an aircraft is airborne and spoilers are deployed by the pilot the aircraft descend from cruise altitudes to assist the aircraft in descending to lower altitudes without picking up speed. This is very helpful in decreasing the altitude of the aircraft, without the use of propulsive or any other power.
Fig.3.1: Spoiler up position.
On landing, however, the spoilers are nearly always used at full effect to assist in slowing down the aircraft. The increase in form drag created by the spoilers directly assists the braking effect. However, a major advantage is that the spoilers cause a dramatic loss of lift and hence the weight of the aircraft is transferred from the wings to the undercarriage, allowing the wheels to be mechanically braked with much less chance of skidding. By the use of spoilers at the time of landing after touchdown gives efficiency to the brakes. Reverse thrust is also often used to help slow the aircraft on landing along with the spoilers (consider Fig.3.2).
By use of spoilers along with thrust reversers effectively stops the aircraft on landing and also helps in reducing the required ground distance for landing.
Fig.3.2: Spoilers being used after touchdown.
They are useful on gliders to vary the lift-to-drag ratio for altitude control and on airliners on landing to reduce lift quickly to prevent the airplane from bouncing into the air. During the time of landing the aircrafts needs to have least lift, if there is a little misbalance and lift is produced on the wing then instead of landing the aircraft will bounce back in the air. To avoid this situation spoilers are very helpful in dumping the lift acting on the aircraft.
A single spoiler is used to bank the aircraft; to cause one wing tip to move up and the other wing tip to move down. The banking creates an unbalanced side force component of the wing lift force which causes the aircraft's flight path to curve.
Fig.3.3: Roll motion caused by spoilers.
If the airplane's right wing spoiler is deployed, while the left wing spoiler is stored flat against the wing surface (as viewed from the rear end of airplane) consider Fig.3.3. The flow over the right wing will be disturbed by the spoiler, the drag of this wing will be increased, and the lift will decrease relative to the left wing. The lift force is applied at the center of pressure of the segment of the wing containing the spoiler which in result creates a torque about the center of gravity. The net torque causes the aircraft to rotate about its center of gravity.
The resulting motion will roll the aircraft to the right (clockwise) as viewed from the rear. If the pilot reverses the spoiler deflections (right spoiler flat and left spoiler up) the aircraft will roll in the opposite direction.
The aircraft rolls because one aileron is deflected downward while the other is deflected upward. Lift increases on the wing with the downward-deflected aileron because the deflection effectively increases the camber of that portion of the wing. Conversely, lift decreases on the wing with the upward-deflected aileron since the camber is decreased. The result of this difference in lift is that the wing with more lift rolls upward to create the desired rolling motion. Now, Consider Fig.3.4.
Fig.3.4: Adverse Yaw.
Unfortunately, drag is also affected by this aileron deflection. The induced drag and profile drag, are increased when ailerons are deployed. Thus, the wing on which the aileron is deflected downward to generate more lift also experiences more induced drag than the other wing. The profile drag increases on both wings when the ailerons are deflected, but the increase is equal. However, the induced drag on each side is not equal, and a larger total drag force exists on the wing with the down aileron. This difference in drag creates a yawing motion in the opposite direction of the roll. Since the yaw motion partially counteracts the desired roll motion, we call this effect adverse yaw.
When used in coordination with ailerons, a spoiler can be used to reduce the lift and increase the profile drag on the wing with the up aileron. As a result, the wing with the down aileron experiences a large increase in lift and a small increase in drag while the wing with the up aileron experiences a large decrease in lift and a large increase in drag. These effects combine to create the desired roll motion and a complimenting yaw motion that is called proverse yaw.
By the use of spoilers a rapid descents may be made without having to reduce power, thereby maintaining engine temperatures at a comfortable level, and eliminating the risk of engine "shock cooling." In time of a descent without spoilers, i.e. by simply reducing the throttle the air speed is increased and the engine will be at low power, producing less heat than in normal. Thus as a result the engine may cool too rapidly, resulting problems such as, stuck valves, cracked cylinders or other problems. Spoilers alleviate the situation by allowing the aircraft to descend at a desired rate while letting the engine to run at a power setting that keeps it from cooling too quickly.
Wood is used to make the solid wing as per the coordinates; Steel plate is used to show the spoiler on the wing, nuts and bolts.
The experiment was conducted in the aerodynamics lab at the university. Wind tunnel is used for the testing of solid wing. This is a low speed and low turbulence wind tunnel. The experiment was performed at tunnel velocity of 30m/s. Lift and drag on the solid wing was calculated before and after the spoilers were deployed.
A NACA 0015 symmetrical airfoil with a 25% thickness to chord ratio was analysed to determine the lift and drag. The chord of the airfoil is 15 cm; using the NACA 0015 symmetric airfoil coordinates the solid wing was made. The coordinates of NACA 0015 are:
1
0.95
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.15
0.1
0.075
0.05
0.025
0.0125
0
0.0125
0.025
0.05
0.075
0.1
0.15
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0.95
1
0.0012
0.01027
0.01867
0.0332
0.0448
0.0532
0.05827
0.06
0.05827
0.05293
0.04867
0.0424
0.03813
0.03267
0.02453
0.01813
0
-0.01813
-0.02453
-0.03267
-0.03813
-0.0424
-0.04867
-0.05293
-0.05827
-0.06
-0.05827
-0.0532
-0.0448
-0.0332
-0.01867
-0.01027
-0.0012
Fig.4.1: NACA 0015 airfoil
The wind tunnel testing of solid wing was performed, first with normal condition i.e. when spoilers are not deployed. The following results are:
1
0°
0.164 N
0.377 N
2
5°
20.23 N
0.725 N
3
10°
33.02 N
1.54 N
4
15°
16.2 N
6.525 N
Now, for the second case i.e. when the spoiler is deployed. The values obtained are:
1
0°
-0.034 N
0.549 N
2
5°
12.94 N
6.45 N
3
10°
24.05 N
13.37 N
4
15°
9.85 N
20.58 N
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