Army Flight Warrant Officer SIFT Test Study Guide with Complete Solutions

Army Flight Warrant Officer SIFT Test Study Guide with Complete Solutions Helicopter Structure - Answer-The typical structure of a helicopter is a fuselage (the body of the craft) with a mast protruding upward out of it. The engine of the craft drives power upward through the mast to the rotor blades, which are controlled by the pilot. This main rotor is used to generate thrust. This thrust is balanced by a second rotor, usually a tail rotor, which is intended to account for the effects of torque. In the USA, UK and Germany, it is conventional for the main rotor to rotate counterclockwise. The opposite is true in other countries. Throughout this book, reference will be made only to counterclockwise main rotors. Single Main Rotor Helicopter - Answer-This is the most common design for a helicopter -a single main 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 torque, rather than being used solely for lift. Co-axial Rotor Helicopter - Answer-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 payload and allowing for greater cargo and passenger capacity as a result. Tandem Rotor Helicopter - Answer-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, EMILLYCHARLOTTE 2024/2025 ACADEMIC YAER ©2024 EMILLYCHARLOTTE. ALL RIGHTS RESERVED FIRST PUBLISH SEPTEMBER 2024 Page 2/10 all of the power from the engine can be used for lift. Consequently, tandem rotor helicopters are some of the fastest and most powerful in existence. Thrust - Answer-Thrust is created by the engine, or engines, of the helicopter. It is transferred into motion via the mast and rotors. Sufficient thrust is needed to overcome the drag and the weight of the helicopter and keep it moving forward. Drag - Answer-Drag 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 drag which impact helicopters. Profile Drag - Answer-Profile drag is caused by the frictional resistance of helicopter blades passing through the air. It has two components: form drag and skin friction. Form Drag - Answer-Form drag increases as the speed of the helicopter increases. Skin Friction - Answer-Skin friction is caused by microscopic roughness of the helicopter blades. Any roughness on the surface causes air to become trapped and drag to increase. Induced Drag - Answer-Induced drag 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, induced drag is the main cause of drag for helicopters. Parasite Drag - Answer-Parasite drag 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 parasite drag. Parasite drag slows down the speed of a helicopter by opposing thrust. EMILLYCHARLOTTE 2024/2025 ACADEMIC YAER ©2024 EMILLYCHARLOTTE. ALL RIGHTS RESERVED FIRST PUBLISH SEPTEMBER 2024 Page 3/10 Total Drag - Answer-Total drag is the sum total of the profile, induced and parasite drag acting upon the helicopter at any given time. The point at which the total drag is lowest is the preferable point for maximum endurance, best rate of climb, and minimum rate of descent in autorotation. Weight - Answer-Weight is a force which results from the combined mass of the helicopter being acted upon by gravity. It is a downward force which acts through the center of gravity of the helicopter. Weight is reliant upon more than just the mass 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 flight path, requiring the pilot to bank the vehicle, then the 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. Lift - Answer-Lift is the upwards force created by the spinning of the helicopte