Types of Drag in Helicopters скачать в хорошем качестве

Types of Drag in Helicopters

Welcome back to Helicopter Lessons in 10 Minutes or Less! Check out my ebook covering this and more! Get your copy on iBooks: http://itunes.apple.com/us/book/id144... or on Kobo for Android, Windows and Desktop users: https://www.kobo.com/us/en/ebook/heli... This video's topic is covers the types of drag in helicopters. We know from basic aerodynamics that thrust and drag are opposing forces. But what exactly is drag? Drag is the force that opposes or resists the motion of an object as it travels through the air. An easy way to show this visually is to compare drag is relation to airspeed. Drag can be briefness down into 3 types. The first one being Parasite drag. Parasite drag is probably the easiest to understand because to everything moving through the air whether it be a helicopter, plane , a car, or even you hand out of the window of a car. This type of drag is the air resistance on an object as it moves. It increases with both surface area and speed. This is why you see streamlining in high speed cars and planes. In order to achieve higher speeds, the surface area must be reduced. In relation to airspeed, parasite drag increases rapidly and exponentially because drag is a product of Velocity squared in the drag equation. This means that if speed doubles, drag quadruples. The next type of drag is Profile drag and this specifically deals with drag caused by the frictional resistance of the blades as they travel through the air. This is generally affected by airfoil shape and skin friction. To illustrate this imagine a non-efficient airfoil shaped like a block compared to the typical streamlined airfoil. When airflow impacts the block-shaped airfoil it becomes turbulent and very disturbed as it tries to pass around the airfoil. This turbulent airflow is what causes profile drag. Now consider the streamlined airfoil where air passes more efficiently over it. This type of airfoil creates less drag due to its efficiency. Keep in mind that parasite drag and profile drag are different in that parasite drag applies to total drag of the aircraft while profile drag specifically deals with the airfoil itself. Since the airfoil travels so much faster than the actual aircraft due to its relational velocity, it's drag is varies drastically. Profile drag increases gradually with speed because it's based mostly on shape and skin friction. So profile drag is higher than parasite drag at lower airspeeds but eventually gets surpassed as speed increases. Lastly there's induced drag. Simply put, induced drag is the result of producing lift. It is higher with higher Angles of Attack (AOA) in the blades because more lift generates greater downward velocities / vortices which increase drag. Think back to my videos on Airflow at a Hover (   • Airflow at a Hover in Helicopters  ), Effective Translational Lift (   • Effective Translational Lift (ETL) in...  ), and Aerodynamics of a Takeoff (   • Aerodynamics of a Takeoff in Helicopters  ) videos where it takes more power required to fly the helicopter less than ETL and especially at a stationary Out of Ground Effect (OGE) hover. With these higher AOA's at lower airspeed flight profiles, stronger induced flow and vortices form. These decrease drastically as airspeed increases. When you combine all 3 types of drag together you get a total drag line. This important to understand because it is what performance planning is based on. Each helicopter operator's manual should break down performance charts you that are specific to that aircraft. It from here you get things like: Max Endurance / Max Lift to Drag Airspeed: this is the least amount of total drag on the aircraft. This speed has the greatest power margin available and can be used to obtain the max time aloft. Max Range Airspeed: this is the most distance per unit of fuel or simpler put, the most miles per gallon. Best Climb Angle Airspeed: the best climb rate for the least amount of forward distance covered. This is helpful when you want to takeoff from a confined area. Fuel burn rates: you can calculate exact fuel burn for each power setting / flight profile. It's important to understand drag because it is the foundation for performance charts/ planning. And by understanding more about drag, you have a better grasp on helicopter performance in different flight profiles. More specifically, you understand what you can and cannot affect as a pilot. That wraps up the types of drag in helicopters. Thanks for watching! As always, safe flying! If you enjoyed the video or have any questions or comments, hit the like button and comment below.