|WikiProject Transport / Maritime||(Rated Start-class, Mid-importance)|
I doubt if the definition is precise enough
Course is the intended path of an airplane over the ground; or the direction of a line drawn on a chart representing the intended airplane path, expressed as the angle measured from a specific reference datum clockwise from 0° through 360° to the line. The reference can be true north or magnetic north and called true course or magnetic course respectively. —The preceding unsigned comment was added by Natasha2006 (talk • contribs) 17:41, 25 April 2007 (UTC).
The differences in interpretation of "course" are noted in the Pilot Training Manual of a major European airline, which recommends that the term be avoided because it has different meanings depending on the part of the world one is in. It does not appear in ICAO documentation, which only defines track and heading.
In the past it was simple - the vectors course/true airspeed, wind direction/wind-speed, and track/gound-speed made up the triangle of velocities used in dead reckoning navigation and illustrated in the <RAF Pilots Flying Manual AP 129 1941 edition>.
However in 1967 this illustration was changed to show "required rack", "track made good", and "heading". The term course disappeared <RAF AP 1234 2nd Edition 1967>).
For an idea of the confusion over this term see these:
<GARMIN Internet site: (2009)> Course - The direction from the beginning landmark of a course to its destination (measured in degrees, radians, or mils), or the direction from a route waypoint to the next waypoint in the route segment. Track - Your current direction of travel relative to a ground position (same as Course Over Ground). [too many courses!!]
<AMERICAN PRACTICAL NAVIGATOR (HYDROGRAPHIC DEPARTMENT, US NAVY, BOWDITCH (1938)> Course - the angle which the centreline of the vessel makes with the meridian [looks more like heading, they do not mention compass correction!!]
<MATHEMATICS AND AIR NAVIGATION (1941) H. T. H. Piaggio, The Mathematical Gazette, Vol. 25, No. 264 (May, 1941), pp. 66-71> The drift is the difference between the course and the track. [correct, but hardly a definition of course!!]
- Currently ground track is written mainly for satellites while it could also serve for air navigation. A link to wind triangle has been provided to improve the description of a key navigational requirement. Currently track (navigation) redirects to this article. Given that course is going out of use, with track in its place, a switch in titles may be considered.Rgdboer (talk) 02:29, 8 December 2014 (UTC)
Is crab angle the negative of drift angle?
"Crab angle is the amount of correction an aircraft must be turned into the wind in order to maintain the desired course. It is equal in magnitude but opposite in direction to the drift angle."
I believe that this is true only approximately and for small angles.
Consider an airplane traveling east at 100 knots with a 70-knot wind from the north. The drift angle is atan(70/100) ~= 35 degrees. But, to counter that 7-knot wind, the airplane must be crabbed -asin(70/100) ~= -45 deg.
Increase the wind to 100 knots. Then the drift angle is 45 degrees and the crab angle must be -90 degrees; that is, the airplane must head directly north, just to stand still against the wind.