06. Frames of Reference Summary
Longitudinal Frames of Reference
There are three frames of reference we care about when discussing longitudinal flight.
1. Inertial Frame
The inertial frame is just the N,E,D frame you've seen before. The origin is fixed relative to the earth and the x, y, and z axes point north, east, and down respectively.
2. Body Frame
The body frame is rigidly attached to the aircraft. The origin is the center of mass of the vehicle. The x axis points through the nose, the y axis points out over the right wing, and the z axis points down through the belly of the plane.
3. Stability Frame
The stability frame (or wind frame), is similar to the body frame: the origin is the center of mass and the y axis points out over the right wing. The x, and z axes differ.
The x axis points into the incoming airstream. The z-axis still points "downwards" but it's perpendicular to both the x and y axes, so it won't generally go directly through the belly of the plane.
This plane is moving rightwards and slightly downwards through still air. The relative airstream is shown as a red arrow. The gray dotted line gives "horizontal" in the inertial frame and the blue line is aligned to the x-axis of the vehicle's body frame.
As shown in the picture above, we can define three angles which relate these three frames of reference.
- Pitch angle \theta
- Flight path angle \gamma
- Angle of Attack \alpha
The reason we define all these frames of reference (and the associated angles) is to make it easy to keep track of the various forces that we care about.
SOLUTION:
- Weight
SOLUTION:
- Thrust
SOLUTION:
- Lift
- Drag