Airplane design #2 - Flight Dynamics

In this video, we’ll be discussing the basics of flight dynamics. 1. Introduction To fly an airplane in a straight leveled line involves a horizontal balance between aerodynamic drag & thrust force and a vertical balance between aerodynamic lift and gravity. To make an airplane take off, follow curved trajectories and land, involves a whole lot more and is the domain of flight dynamics. 2. Roll, Pitch, and Yaw The main parameters used to describe this three-dimensional orientation are the roll, pitch and yaw axes of the plane, all running through the center of gravity. - The roll axis, also called the longitudinal axis, runs from nose to tail. - The pitch axis, also called the transverse axis, runs from left to right. - The yaw axis, also called the vertical axis, runs from top to bottom. Also important is the plane’s orientation with respect to the relative wind vector, which is the combination of the velocity vector of the plane and the wind vector. Around the pitch axis, this is called the angle of attack. Around the yaw axis, this is called the sideslip angle. 3. Leveled flight During a leveled flight, the roll, pitch & yaw orientation stay constant. To achieve this static balance, the moments around all three axes must be zero, otherwise, the plane would start to change its orientation. For example, if the center of lift of the main wings is not aligned with the center of gravity, this can generate a pitch moment causing the plane to tilt its nose upward or downward. To neutralize this pitch-moment, lift or downforce can be generated at the tail. Keep in mind that the location of the center of gravity can change between flights and even during flights due to changes in cargo and fuel for example. 4. Dynamic flight During dynamic flight maneuvers, the airplane changes its orientation. To climb or descend, for example, the elevators at the tail can be lowered or raised. This will cause the angle of attack to change which will affect the lift and drag that are generated on the main wings for example. Mapping & understanding the correlation between angle of attack and lift is crucial to understanding & optimizing flight dynamics. To achieve this, you can perform a wind tunnel test during which you monitor lift & drag values while gradually increasing the angle of attack from the lowest to the highest value of interest. Such a sweep procedure can also be performed digitally by changing the angle of attack over a series of aerodynamic simulations. 5. Horizontal sweep The results are curves that plot the lift and drag values versus the angle of attack. This is quite similar to the 2D airfoil curves we saw in earlier videos, only now it’s the lift & drag of the full plane, taking aerodynamic effects like flow around the fuselage and wingtip vortices into account. Here as well, very steep curves could indicate that the plane is very dynamic but more difficult to fly. Such crucial information can then be used as input for the flight control strategy.  6. Vertical sweep A similar approach can be applied to a yaw maneuver, where the rudder at the tail is used to turn the plane left or right. Sweeping the sideslip angle beta again results in changes in the forces on the plane. In this case, however, the lateral force is of particular interest, as a sideslip angle will generate a sideways push on the plane. 7. This is only the tip of the iceberg in terms of flight dynamics: much of the airplane maneuvers involve a combination of pitch, roll, and yaw. Side winds can have a tremendous impact as well. And the speed of rolling, pitching and yawing also generates additional dynamic forces and moments that play a big role. That was it for this short introduction on flight dynamics. Thanks for liking, sharing and leaving your comments below the video, thanks for watching and see you soon! Bye-bye. ----------------------------------------------------------------------------------------------------------- Wouter Remmerie Wouter is the Founder of AirShaper, an online, virtual wind tunnel. With this tool and these videos, we want to make aerodynamics accessible to everyone! Interested in more content like this on the field of aerodynamics? Make sure to click that subscribe button, we post new videos every week! Looking for a way to test your Aerodynamics projects without all the hassle and the huge costs coming with it? Check out and see how easy it can be!

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