# ATAT101 Theory of Flight > # [[T101 Week 3| ◀️ ]]  [[T101 Home| Home ]]  [[T101 Week 5| ▶️ ]]               [[QR T101 Week 4| 🌐 ]] ># [[T101 Week 4#ATAT101 Theory of Flight|Week 4]] >- [[T101 Week 4#Fixed Lift Devices|Fixed Lift Devices]] >- [[T101 Week 4#Anti-Lift Devices|Anti-Lift Devices]] > [!jbPlus|c-blue]- Lesson Intro >### What > >In this lesson we will learn about fixed lift and anti-lift devices. > >### Why > >These fixed devices round out your knowledge of the various devices around an aircraft, and how they all contribute to controllable safe flight. You will encounter these devices in your work as a technician. Understanding their function may help you to be diligent and aware in your work around aircraft. > >### Testing > >You will be tested on this material on Assignment 3 and the final test, as per the [[T101 Intro#Testing and Grades|testing strategy]]. > >#### Approach and Objectives By understanding the following topics, you will have achieved the learning outcome for this lesson. Consult your course outline for the learning outcomes and other details of this course. > >##### Course Learning Objectives CLO 3 Explain theory of flight applicable to fixed and rotary wing aircraft. CLO 5 Explain flight controls including primary, secondary and auxiliary controls ## Fixed Lift Devices %%==[[Master QB1#Q00751|Q]]==%% %%Ref A p. 5-47%% A lift device, also known as a high-lift device, or supplemental lift-modifying device, or lift augmentation device, or auxiliary lift device is a component or mechanism on an aircraft's wing that increases the amount of lift produced by the wing. These devices can be fixed or moveable. We already saw moveable lift devices such as the flap being used as secondary controls. Common fixed devices include leading edge slots, leading edge root extensions and boundary layer control systems. Common examples of moveable devices are flaps and slats. As we will see, these devices alter the shape of the wing and therefore affect the wing's lift characteristics. ### Boundary Layer Control One of the characteristics of the wing that can be altered by secondary lift devices is the boundary layer. Remember that the boundary layer is most effective when it flows smoothly, or exhibits laminar flow. #### Blown Flaps %%==[[Master QB1#Q00752|Q]]==%% - Engine air over the flap The high pressure airflow in the engine can also be used to reenergize the boundary layer. Blown flaps refer to redirecting high pressure airflow from the engine over the upper rear surface of the wing and flap, reducing turbulence and therefore reducing stall speed. We include this in the fixed lift device section, because even though the surface being blown may be movable, the forced air is usually not. #### Boundary Layer Suction %%==[[Master QB1#Q00753|Q]]==%% Let's review and expand a little on the boundary layer before we go on. The air molecules at the surface of a wing are effectively stationary. If the flow is smooth, known as [laminar flow](https://en.wikipedia.org/wiki/Laminar_flow "Laminar flow"), the velocity of the air increases steadily as measurements are taken further away from the surface. However, the smooth flow is often disturbed by the boundary layer breaking away from the surface and creating a low-pressure region immediately behind the [[airfoil]]. This low-pressure region results in increased overall drag. Attempts have been made over the years to delay the onset of this flow separation by careful design and smooth surfaces. Boundary layer suction attempts to remove the boundary layer from the surface before it can separate, preventing the turbulence that separation causes. It appears to be pulling the boundary layer closer to the wing. The technology was first developed by Werner Pfenninger in the Second World War and has been researched almost continuously since. In the 1960s, NASA experimented with this concept with the Northrop X-21, a converted Douglas WB-66D. In the 1990s tests were done by NASA with an F-16XL.  [[T101_4_001.png|➡]] #### Leading Edge Slots %%==[[Master QB1#Q00754|Q]]==%% %%==[[Master QB1#Q00755|Q]]==%% %%==[[Master QB1#Q00756|Q]]==%% A leading edge slot is a duct or opening that allows air to flow from the bottom of the wing to the top surface at high speed, helping to reduce turbulence of the boundary layer. On some aircraft, this slot is permanent and fixed, on others, the use of a slat allows the slot to be variable to be optimized for various angles of attack. In either case, the use of a slot keeps the boundary layer intact at higher angles of attack, and thus increasing the range of motion of the wing before a stall condition occurs.  [[T101_4_002.png|➡]] Another description: Leading edge slots are gaps just aft of the leading edge of a wing that allow air to be ducted from the higher-pressure lower surface of the wing to the less dense upper surface air. This high velocity air ensures the boundary layer stays intact and smooth, and attached to the wing, rather than turbulent and tending to separate from the wing. These slots do not change the camber of the wing, but improve its lift capabilities, especially at higher angles of attack when the boundary layer tends to separate from the wing surface. Leading edge slots are often found on the leading edge of the wing corresponding to the location of the aileron on the trailing edge. This is intended to maintain airflow over the ailerons, keeping them functional, even if the rest of the wing is in a stall condition. #### Vortex Generators %%==[[Master QB1#Q00757|Q]]==%% A vortex generator is an aerodynamic device, consisting of a small vane usually attached to a lifting surface, but sometimes also attached to the fuselage. When the [[airfoil]] or the body is in motion relative to the air, the VG creates a vortex, which, by removing some part of the slow-moving boundary layer in contact with the [[airfoil]] surface, delays local flow separation and aerodynamic stalling, thereby improving the effectiveness of wings and control surfaces, such as flaps, elevators, ailerons, and rudders. Vortex generators are also useful when controlling airflow in engine intakes, especially those that are longer, such as jet fighters.  [[T101_4_004.png|➡]] ### Changing the shape of the [[airfoil]] #### Leading edge cuffs %%==[[Master QB1#Q00758|Q]]==%% ![[T101_4_003.png|400]] [[T101_4_003.png|➡]] Leading edge cuffs are fixed aerodynamic devices that extend the leading edge down and forward. This causes the airflow that hits the leading edge to attach better to the upper surface of the wing, especially at higher angles of attack. This effectively lowers the aircraft's stall speed. #### Fixed Induced Drag Because leading edge cuffs are fixed, the drag that is induced is not adjustable, and thus the maximum cruise airspeed of the aircraft is lower than if they were not there. However, like most areas of aviation, design and technology are always improving, and new developments have reduced the drag penalty of leading edge cuffs. ### Airflow Control #### Strakes/Fences %%==[[Master QB1#Q00759|Q]]==%% %%==[[Master QB1#Q00760|Q]]==%% %%==[[Master QB1#Q00761|Q]]==%% - Directing airflow - Dividing the wing into sections A strake, also known as a fence, is an aerodynamic surface mounted typically on the fuselage of an aircraft to improve flight characteristics, mostly by controlling airflow around the aircraft. Generally, strakes are long and narrow, unlike winglets or other protrusions. Strakes can be applied to the nose, wing, engine nacelles, on the belly of the aircraft (ventral), as well as the wings. Generally speaking, strakes help to direct airflow at high speed along the surface in question to preserve boundary layer flow and lift at higher angles of attack. Sometimes it does this by dividing the wing into sections, helping performance in specific areas.  [[T101_4_005.png|➡]] #### LEX, LERX %%==[[Master QB1#Q00762|Q]]==%% %%==[[Master QB1#Q00763|Q]]==%% Leading Edge Extensions, or Leading Edge Root Extensions are triangular extensions to the inboard leading edge connected to the fuselage. These are also sometimes called wing strakes.  [[T101_4_006.png|➡]] ##### F-18 LEX  [[T101_4_007.png|➡]] For normal straight and level flight, the effect of the LEX is minimal, contributing little to lift, and causing little drag. However, at high angles of attack, the LEX generates a high speed vortex that attaches itself to the top of the wing. This helps to maintain smooth airflow over the rest of the wing well past normal stall points, thus improving lift, and lowering stall speed. This graphic shows a rather large LEX on a CF-18. Its use for high performance aircraft allows for advanced flying maneuvers that would normally place an aircraft outside of its safe flight envelope. #### Canards %%==[[Master QB1#Q00764|Q]]==%% %%==[[Master QB1#Q00765|Q]]==%% ![[T101_4_008.png|400]] [[T101_4_008.png|➡]]  [[T101_4_009.png|➡]] ##### Stall before main wing A canard is a small wing that is mounted on the fuselage of the aircraft forward of the main wing. Its angle of incidence is typically higher than that of the main wing, meaning that its critical angle of attack is reached earlier than that of the main wing. This causes the canard to stall earlier than the main wing, causing it to fall, and thus helping to keep the main wing from stalling. This helps improve the overall performance of the aircraft in high angles of attack. It also has the purpose of reducing overall wing loading, by sharing some of the forces. This may make it possible to have a smaller main wing. ## Anti-Lift Devices %%Ref E p. 6-10%% ### Flight Spoilers %%==[[Master QB1#Q00766|Q]]==%% %%==[[Master QB1#Q00767|Q]]==%% %%==[[Master QB1#Q00768|Q]]==%%  [[T101_4_010.png|➡]] - Reduce lift In certain circumstances, the aircraft has too much lift, or not enough drag. For instance, a pilot coming in on final must make many adjustments to ensure he is on the correct glideslope. By deploying flight spoilers, he can descend quicker without having to increase the speed. You can remember the terminology by remembering that spoilers spoil lift. In other circumstances, it can help to improve roll control when used differentially. By deploying spoilers more on one side than the other, roll characteristics can be improved in flight. Deploying spoilers generally has an immediate effect on airspeed, and so they are often used and referred to as air brakes. This is not quite correct however. ### Air Brakes/Speed Brakes %%==[[Master QB1#Q00769|Q]]==%% While the terminology is sometimes flexible, air brakes, or speed brakes are different from spoilers in regards to lift. Spoilers work by changing the shape of the upper camber, effectively destroying lift. They reduce the lift to drag ratio and require a higher angle of attack to maintain lift, which results in a higher stall speed. - Increase drag Speed brakes, however, are designed to increase drag while having less of an impact on lift. This is why you will often see them mounted on the side of the fuselage. ![[T101_4_011.png|400]] [[T101_4_011.png|➡]] ### Ground Spoilers %%==[[Master QB1#Q00770|Q]]==%% %%==[[Master QB1#Q00771|Q]]==%% - After touchdown: - Decrease lift - Increase drag Ground spoilers are used to drastically decrease lift and increase drag on the aircraft immediately after touchdown. This shortens the braking distance needed, reducing the load on the brakes, preserving their life, and reducing the need for larger and heavier brakes. Ground spoilers can only deploy on the ground, and typically work together with the flight spoilers. - Prevent takeoff Because the ground spoilers drastically reduce lift, they also prevent the aircraft from taking off again once on the ground due to bounce or wind gusts.  [[T101_4_012.png|➡]] #### Many devices working together As you can see in this graphic, the primary controls, secondary controls, lift and anti-lift devices can take many forms, and all work together for safe efficient flight. ![[T101_4_013.png|400]] [[T101_4_013.png|➡]] %% ## AutoFlight %% %%==[[Master QB1#Q00772|Q]]==%% %%==[[Master QB1#Q00773|Q]]==%% %%  [[T101_4_014.png|➡]]%% %% ### Advantages of AFCS An aircraft autopilot with many features and various autopilot related systems integrated into a single system is called an automatic flight control system (AFCS). These were formerly found only on high-performance aircraft. Currently, due to advances in digital technology for aircraft, modern aircraft of any size may have AFCS. AFCS capabilities vary from system to system. Some of the advances beyond ordinary autopilot systems are the extent of programmability, the level of integration of navigational aids, the integration of flight director and autothrottle systems, and combining of the command elements of these various systems into a single integrated flight control human interface. #### Superhuman Automatic flight control systems fly the aircraft more accurately than a pilot can. AFCS can use inertial guidance systems as well as GPS or radio to correct flight path errors. #### Lower Fuel consumption. %% %%==[[Master QB1#Q00774|Q]]==%% %% Autoflight systems have access to the main computing power of the aircraft and can calculate flight paths that use the minimum amount of fuel, calculating altitudes, climb rates and other key parameters to optimize the flight. #### React faster Again, because AFCS is connected to many key systems in the aircraft, it can react faster and better to any atmospheric disturbances than the pilot. It can also see farther than the pilot, thanks to the terrain avoidance systems that you will learn more about later in the program. #### Reduce pilot workload. %% %%==[[Master QB1#Q00775|Q]]==%% %% Modern AFCS can take-off, ascend, level out, descend, approach, & land. And they do all of this optimized for the best efficiency and effectiveness. Another part of pilot workload is reduced by the automatic control of trim in many flight profiles. ### Categories of AFCS #### Category IIIb Category IIIb landing capability guides the plane's automatic pilot through landing and rollout. #### Category IIIc Category IIIc does all that Category IIIb does, but also taxis the plane to the terminal. This requires 3 autopilot systems. #### Important Safety Feature AFCS is an important safety feature of modern aircraft, because it can prevent the pilot from getting into trouble: - Provides flight control travel limiting. - Control lock out at different speeds. Given the widened flight envelopes enabled by advanced flight controls, the pilot must not be allowed to control the aircraft into problems. The AFCS will prevent the pilot from using controls at inappropriate phases of the flight. - Lift dump capability on landing. With everything else a pilot needs to control on landing, AFCS lightens the load by deploying anti-lift devices automatically when the aircraft touches down. #### Basic Basic autopilots have few functions - Heading or horizontal hold - Altitude or vertical hold #### Advanced %% %%==[[Master QB1#Q00776|Q]]==%% %% Later ones added - Auto throttle to maintain a constant speed - Climb/descent hold - Track following Modern AFCS can be set to follow a track over the ground, a heading, or a radio beacon. - Pilot guidance The AFCS can also display "command bars" to indicate to the pilot where to fly when not engaged. - Go around indicator For cases when a pilot must touch and go, most AFCS include a "GA"or go-around button on the throttles which will raise the command bars to indicate the best climb angle. - Stick shaker/pusher As we saw in the section on stall warnings, modern aircraft give tactile information to the pilot in the form of stick shaking or stick pushing. This is also controlled by the AFCS. In the future collision avoidance, by way of the TCAS that you will learn more about, may be done automatically. ### Components of an AFCS As you learn more about aviation systems, you will see common architectures. Since most avionics systems are really just computers, you can expect to see controls, inputs, processors and indicators. #### Control head  [[T101_4_015.png|➡]] A typical control head is shown. The main purpose of the control head is to accept pilot input. Sometimes displays are incorporated, but most modern aircraft use electronic displays to handle the amount of information available. #### Amplifier/computer  [[T101_4_016.png|➡]] The many processes required by the AFCS are all computer controlled. Some analog signals may require amplification or boosting before processing, and these functions will take place in the amplifier/computer as well. #### Gyroscope(s) One important category of equipment that tells the autopilot about the aircraft's situation is gyroscopes. You will learn about these in more detail in this program, but for now, know that the principles of precession that you learned about help to determine the aircraft's position on several planes.  [[T101_4_017.png|➡]] #### Radio Advanced AFCSs can track a preselected radio course (VOR, LOC or GS) and in some cases these radio nav aids are dedicated for use with the AFCS. Others have radios for automatic transponder functions. Some com and nav functions can be controlled by AFCS as well.  [[T101_4_018.png|➡]] #### PFD or ADI Displays vary widely in respect to AFCS, but very simply put, in modern aircraft AFCS is displayed by the [[EFIS]] (Electronic Flight Information System). Especially if you pursue an avionics route, you will learn more about this later.  [[T101_4_019.png|➡]] #### Connection Small aircraft use electromechanical servos, connected by cables to the regular aircraft control system. Large aircraft use the existing hydraulic flight controls, which are electrically controlled. You will learn more about AFCS in later courses in the program. %% ### Conclusion In this lesson we covered the following topics: - [[T101 Week 4#Fixed Lift Devices|Fixed Lift Devices]] - [[T101 Week 4#Anti-Lift Devices|Anti-Lift Devices]] %%[](T101%20Week%204.md#AutoFlight)]]%% You can demonstrate your understanding of the material in this lesson by answering the questions in the corresponding weekly practice quiz correctly. > # [[T101 Week 3| ◀️ ]]  [[T101 Home| Home ]]  [[T101 Week 5| ▶️ ]]     [[QR T101 W4| 🌐 ]]    [[FB T101|Please Help]]