HP HP-21 - Page 49

Example 2: Convert polar coordinates (8,120°) to rectangular
coordinates.
-
(x,y)
O =120°
r=8
Solution:
Slide oea [[[ljr0 switch to Degrees.
Press Display
120 8 il x-coordinate
D35 6.93 y-coordinate
Example 3: The instruments in fearless bush pilot Apeneck
Sweeney’s converted P-41 indicate an airspeed of 125 knots
and a heading of 225°. However the aircraft is also being buf-
feted by a steady 25-knot wind that is blowing from north to
south. What is the actual course and speed of the aircraft?
Method: Combine the vector indicated on the P-41’s instru-
ments with the wind vector to yield the actual course and speed.
Convert the vectors to rectangular, then combine the x-coordi-
nates in the storage register and the y-coordinates in the stack.
Finally, bring the summed x- and y-coordinates back out again
and convert them to polar coordinates giving the actual vector
of the aircraft. (North becomes the x-coordinate in order that
the problem corresponds with navigational convention.)