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SIFT (Army Aviation Information)
Practice Test Questions and Answers
The typical structure of a helicopter is a ______ (fill in the blank) with a ____ (fill in the blank) protruding upward out of it. - correct Answer-Fuselage (the body of the craft), Mast. The engine of the craft drives power upward through the ____ (fill in the blank) to the rotor blades, which are controlled by the pilot. - correct Answer-Mast This main rotor is used to generate ____ (fill in the blank). - correct Answer-Thrust. ____ (fill in the blank) is balanced by a second rotor, usually a tail rotor, which is intended to account for the effects of ____ (fill in the blank). - correct Answer-Thrust, Torque. What are the two main types of aircraft? - correct Answer-Rotorcraft and Fixed Wing. The main advantage of a helicopter over an airplane is its ability to takeoff ____ (fill in the blank). It can also ____ (fill in the blank). This means helicopters can be used to takeoff from and land in places that would be impossible for planes. They can also perform tasks such as dropping cargo or troops into challenging positions. - correct Answer-Vertically, Hover. What are the different Helicopter types? - correct Answer-Single Main Rotor, Tandem Rotor, and Coaxial Rotor. This is the most common design for a helicopter- a ____ (fill in the blank) rotor generating power, with a secondary rotor, such as a tail rotor, used to offset the effects of torque. One disadvantage of this design is that some power is used for countering ____ (fill in the blank), rather than being used solely for lift. - correct Answer-A Single Main Rotor, Torque. This helicopter design features two main rotating blade sections: front and rear. Each set of blades rotates counter to the other, meaning that torque is automatically offset. There is no need for additional measures, such as a tail rotor, to deal with torque. Because of this, all of the power from the engine can be used to lift. Consequently, ____ (fill in the blank) helicopters are some of the fastest and most powerful in existence. - correct Answer-Tandem Rotor Helicopter.
This type of helicopter features two sets of blades rotating above and beneath each other. The two sets of blades are mounted to the same mast, but rotate in opposite directions to each other. This has the advantage of reducing ____ (fill in the blank) and allowing for greater cargo and passenger capacity as a result. - correct Answer-Coaxial Rotor Helicopter, Payload. ____ (fill in the blank) is created by the engine, or engines, of the helicopter. It is transferred into motion via the ____ (fill in the blank) and ____ (fill in the blank). Sufficient ____ (fill in the blank) is needed to overcome the drag and the weight of the helicopter and keep moving it forward. - correct Answer-Thrust, Mast and Rotors, Thrust. ____ (fill in the blank) is a force which acts against thrust. In the case of helicopters, drag is caused by the shape and size of the aircraft disrupting the flow of air as it travels. There are several types of ____ (fill in the blank) which impact helicopters. - correct Answer-Drag What are the 4 different types of Drag? - correct Answer-Profile Drag, Induced Drag, Parasite Drag, Total Drag. ____ (fill in the blank) is caused by the frictional resistance of helicopter blades passing through the air. - correct Answer-Profile Drag. What are the two subcomponents of Profile Drag? - correct Answer-Form Drag and Skin Friction. ____ (fill in the blank) increases as the speed of the helicopter increases. - correct Answer-Form Drag. ____ (fill in the blank) is caused by microscopic roughness of the helicopter blades. Any roughness on the surface causes air to become trapped and drag to increase. - correct Answer-Skin Friction. ____ (fill in the blank) is caused by airflow circulation around the blades creating vortices. This type of drag increases when the helicopter is flying at lower speeds, and decreases when it is flying at higher speeds. During low speed flight, ____ (fill in the blank) is the main cause of drag for helicopters. - correct Answer-Induced Drag, Induced Drag. ____ (fill in the blank) is the drag created by the helicopter components that are external to the fuselage. For example, the landing gear, cowlings and doors can all create ____ (fill in the blank) drag. ____ (fill in the blank) drag slows down the speed of a helicopter by opposing thrust. - correct Answer-Parasite Drag. ____ (fill in the blank) are achieved through manipulation of the collective. Moving the collective manipulates the amount of lift, causing the helicopter to rise or fall as the pilot desires. - correct Answer-Climbs and Descents
For example, a regular helicopter blade that revolves counterclockwise generates a maximum airflow velocity at its 3 o'clock position and minimum at its 9 o'clock position, Therefore, it can be said that airflow meeting each blade varies with the position of the blade in its circular motion cycle, gen - correct Answer-Air Flow in Forward Flight ____ (fill in the blank) is a surface that contributes to airlift generation by regulating airflow over its upper and lower surface. In helicopters, horizontal stabilization is achieved by this ____ (fill in the blank) and maintained by the revolving blades of the rotating main rotor and the tail rotor. Design of ____ (fill in the blank) is a critical and precise task that is governed by angle of incidence and angle of attack. - correct Answer-Airfoil. ____ (fill in the blank) is a relative angle depending on the direction of motion of the blade with respect to air and the chord line of an airfoil. For example, the angle between the rotor blade and net wind passing through it. - correct Answer-Angle of Attack (AOA) ____ (fill in the blank) is a mechanical angle between the chord line of the blade and the circular plane it is rotating in. The blades are tilted to regulate the direction of wind they are cutting through during their circular motion. - correct Answer-Angle of Incidence (AOI) ____ (fill in the blank) is the sum total of the profile, induced and parasite drag acting upon the helicopter at any given time. The point at which the ____ (fill in the blank) drag is lowest is the preferable point for maximum endurance, best rate of climb, and minimum of descent in autorotation. - correct Answer-Total Drag. ____ (fill in the Blank) is a force which results from the combined mass of the helicopter being acted upon gravity. It is a downward force which acts through the center of gravity of the helicopter itself. When a helicopter is flying a curved flight path, the angle at which the helicopter banks has an impact upon the total weight. The total weight at any given time is also impacted by the g force acting on the craft. When the helicopter is flying a curved path, requiring the pilot to bank the vehicle then then g force increases. Weight results from mass multiplied by negative g force. The more severe the banking, the greater the rate of g force. As a result, if a helicopter is banking, or flying into unexpected gusts, the weight acting on the craft increases. More thrust is therefore needed to overcome this increase in weight and keep the craft flying as the pilot intends. Weight acts counter to thrust. - correct Answer-Weight. ____ (fill in the blank) is the upwards force created by the spinning of the helicopter blades allowing air to pass over them. Lift is necessary to give the helicopter by overcoming the weight acting upon it. Angle of attack is a description of the angle at which a helicopter blade's direction of movement is relative to the air. The angle of
attack is sometimes manipulated by the pilot, by moving the cyclic and collective; but is also impacted by factors outside the control of the pilot, such as blade flapping and flexing and turbulent conditions. When the angle of attack is favorable, more lift is produced. Conversely, when the angle of attack is not optimum, the amount of drag increases. The angle of incidence, also known as the blade pitch angle, is the intersection of the chord line with the plane of rotation. This is a mechanical angle, rather than an aerodynamic angle, as is the case with the angle of attack. - correct Answer-Lift. What are the 3 Scientific principles? - correct Answer-Bernoulli's principle, Venturi Flow, and Newton's Third Law of Motion. Explains how a helicopter achieves its lift. Basically, when lower pressure occurs over a wing blade under it, lift is achieved. This happens because airflow is traveling faster above the blade than underneath. - correct Answer-Bernoulli's principle. States that the amount of energy within a closed system, a tube, does not change, but can change form. In the case of helicopter aviation, this applies to the top of the blades. Think of them as a 'half tube'- a tube with the top half removed. Despite this removal, the flow of air still accelerates over the curved area of the blade. This creates a needed pressure differential caused by an imbalance of static and dynamic pressure. - correct Answer-Venturi Flow. Is often expressed as the idea that 'for every action there is an equal reaction.' In the case of helicopter aviation, it relates to the downward deflection of air causing an equal opposing reaction, pushing the blade upward. Combined with Bernoulli's Principle, ____ (fill in the blank) is a key element of how a helicopter generates lift. - correct Answer- Newton's Third Law of Motion What are the 4 types of Flight Controls? - correct Answer-Cyclic, Collective, Anti-Torque Pedals, and Throttle. Usually resembles a joystick. It is typically in front of the pilot's lap, although some cyclics descend from the roof of the cockpit. By moving the cycling, the pilot is able to alter the pitch of the main rotor blades, which causes thrust in a particular direction. - correct Answer-Cyclic. Is located to the left side of the pilot's seat and serves the purpose of simultaneously moving the pitch angle of the main blades. This impacts upon the total level of lift or thrust. As a result, the collective is used to increase or decrease altitude or airspeed. - correct Answer-Collective. Are located at the pilot's feet, in an equivalent position to where rudder pedals would be found on an airplane. By using the pedals, the pilot is able to adjust the pitch of the tail rotor, altering the amount of thrust produced. This changes the direction the nose of the helicopter is pointed. - correct Answer-Anti-Torque Pedals.
The number of rotor evolutions per minute, the blade pitch, and the rate of descent influence the size of the driving region. Therefore, the driving region can be altered by changing any of these features. TAF in this region is slightly tapered, pointing toward the forward axis of rotation. This generates an acceleration force responsible for thrust. Stall region of a hovering helicopter is the circul - correct Answer-Autorotation on While Hovering ____ (fill in the blank) is caused by greater airlift during hovering. The blade angle is designed in such a way that during hovering, air lift is balanced by the centrifugal forces of the spinning wheel. The blades move faster to balance the lift that is increased by airflow, or spin of the blades, during autorotation while hovering. - correct Answer-Blade Flapping. ____ (fill in the blank is) is the distance between the tip of the blade and the drive shaft on the rotor it is attached to. - correct Answer-Blade Span. ____ (fill in the blank) is a design feature of a helicopter to distribute air lift evenly throughout the surface of the airfoil. Blade twist is attained by generating greater pitch angles toward the blade root on low rotational velocities, and vice versa. - correct Answer-Blade Twist. ____ (fill in the blank) occurs during helicopter takeoff. It is caused by the difference in amounts of forces experienced by the advantage and the retreating blades of the helicopter on either side of the rotor disc. Due to forward motion, the wind speed on the advancing is more prone to create unbalance, which eventually causes the helicopter to crash. This ____ (fill in the blank) is countered by blade flapping, which is when the retreating blade flaps down and the advancing blade flaps up, and vise versa. - correct Answer- Dissymmetry of Lift. The airstream around the spinning rotor blades provides an extra lift to the helicopter when it is close to the ground. This is called the "____" (fill in the blank). At this stage, the lift acts vertically, reducing induced drag and creating optimized conditions for maximum efficiency of the rotor system. Maximum ____ (fill in the blank) is noticeable when a helicopter hovers above a smooth, hard surface at a height equal to the diameter of the circular path of the revolving blades. - correct Answer-In Ground Effect. ____ (fill in the blank) is that state of a helicopter's flight when it descends vertically downward, at about a rate of 5 feet per second and low forward speeds. It is a state of stall when, even though, the main rotor system is using 20% up to 100% of the power generated by the engine, the downflow produced by the spinning blades is used to overcome the upflow caused by the drastic descent, leading to turbulence. Since maximum power is used by the rotor, minimal or no power is available for the pilot to
stop this descent. This state is also known as ____ (fill in the blank). - correct Answer- Settling with Power, Vortex Ring State.
