An airplane is flying on a compass heading(bearing) of 340 degrees art 325 mph. A wind is blowing with the bearing 320 degrees at 40 mph, how do you find the component form of the velocity of the airplane?

1 Answer
Jun 6, 2016

Below are the formulas for X- and Y-components of the resulting movement as well as the amplitude and angle of this movement (all angles are measured according to trigonometric standard).

Explanation:

In navigation the angle of the course (on a compass) is counted clockwise from the North (so, the direction to the North is 0^o, to the East is 90^0, to the South is 180^o and to the West is 270^o).
The North on most maps is a vertically up direction.
In coordinate Geometry and Trigonometry, which we will use, angles are measured counterclockwise from the positive direction of the horizontal X-axis (the East on most maps).

Let's make a simple transformation into Trigonometric standard using the direction to the East as an X-axis.:
340^o on a compass is 90^o +(360^o -340^o)=110^o counterclockwise from the X-axis.
320^o on a compass is 90^o +(360^o -320^o)=130^o counterclockwise from the X-axis.

This is a problem on addition of two vectors. Each is defined by its amplitude and angle of direction:
airplane (vector A) has amplitude 325 (mph) and angle 110^o;
wind (vector W) has amplitude 40 (mph) and angle 130^o.

To add these two vectors, we represent both as sums of X-component and Y-component:
A_X = 345*cos(110^o)
A_Y = 345*sin(110^o)
W_X = 40*cos(130^o)
W_Y = 40*sin(130^0)

Both X-components act along the same direction, both Y-components act along the same direction. So, we can add X-components to get an X-component of the resulting movement and add Y-components to get a Y-component of the resulting movement.

(A+W)_X = A_X + W_X = 345*cos(110^o)+40*cos(130^o)
(A+W)_Y = A_Y + W_Y = 345*sin(110^o)+40*sin(130^o)

Knowing two components of the resulting vector of movement, we can easily determine the amplitude |A+W| and direction /_(A+W) of the resulting vector:

|A+W| = sqrt((A+W)_X^2+(A+W)_Y^2)

/_(A+W) = arctan[(A+W)_Y/(A+W)_X]

We leave the calculations to the person who suggested the problem.

If it's necessary to express the angle /_(A+W) in compass format (/_alpha) from its standard trigonometric format (/_beta), use the conversion formula
/_alpha = 360^o-(/_beta-90^o) = 450^o-/_beta
(if the result is greater than 360^o, subtract 360^o)