Wind triangle

The wind triangle is a navigational display method in aviation with which the effect of wind on the course direction and speed of a vehicle can be determined graphically. In shipping , the influence of currents on the course is determined analogously.

Instruments and resources used

Traditionally, the wind triangle is set up graphically. The known vectors are proportionally transferred to a drawing. The unknown quantities can then be taken from the graphic. Mechanical navigation computers such as the Aristo Aviat computer or the slide graphic computer from Jeppesen are also used as aids to avoid the time-consuming drawing . In aircraft and ships with advanced navigation equipment, the calculations are carried out by the on-board computer. This uses data from the inertial navigation system , ground stations and satellites, among other things .

Requirements for creating a wind triangle

A total of six values determine the shape and position of the wind triangle. This can be solved arithmetically and graphically if four of the six values are known. The windward angle results from the difference between the true heading (TH) and the true course (TC).

Directions and angles	Speeds
true heading rwSK , TH	Drive TAS
legal course rwK , TC	Speed over ground V _G , GS
Wind direction TWD	Wind speed V _W , WS
Luvwinkel (wind correction angle) WCA

Graphic process

sketch

The sides of a wind triangle are vectors. Vectors are directed quantities. They therefore contain two pieces of information. The arrowhead describes the direction and the length of the arrow defines the speed. The sides of the wind triangle have the following designation:

Heading vector: Direction information: rwSK or TH ( true heading ): Direction in which the aircraft's longitudinal axis points.; Speed information : V _E or TAS ( true airspeed ): Speed of the aircraft in relation to the surrounding air.; Symbol: −−−>
Course over ground vector: Directional information: rwK or TC ( true course ): Course that the aircraft is traveling over the ground.; Speed information : V _G or GS ( ground speed ): speed over ground.; Symbol: −−− >>
Wind vector W / V ( wind vector ): Wind direction W _R or TWD ( true wind direction ); Wind speed: V _W or WS ( wind speed ); Symbol: −−− >>>

Construction of the wind triangle

Define the yardstick for the speed
(e.g. 10 kn = 1 cm, in order to be able to draw the construction on a DIN A4 sheet of paper)

Set TN ( true north - pointing right Nord ) or true north; true true north - matches N on map

Draw in the TC ( true course ), also known as the true course (rwK): the course that the aircraft actually covers, i.e. the course that is drawn on the map.

Draw the auxiliary meridian in the direction of the course

Enter wind vector (wind with original direction) at the intersection of auxiliary meridian / TC with wind speed

At the starting point of the wind vector, hit the arc with TAS ( true airspeed ) on TC

Connect the intersection of the arc / TC with the starting point of the wind vector (heading vector)

Measure the base speed (V _G ) using the TC (course-over-ground vector) , take the scale into account

Measure WCA ( wind correction angle ) between TC and TH

Computational method

The individual values can be calculated using the sine law :

{\ displaystyle {\ frac {\ text {WS}} {\ sin ({\ text {WCA}})}} = {\ frac {\ text {TAS}} {\ sin ({\ text {WA}}) }} = {\ frac {\ text {GS}} {\ sin ({\ text {WA - WCA}})}}}

WA = wind angle = angle between the course-over-ground vector and the wind vector

WS, WCA, TAS, GS see above under graphic procedure .

The associated cross wind component (cross wind) results from: The associated head / tail wind component (head / tail wind) results from: ${\ displaystyle {\ text {WS}} \ cdot \ sin ({\ text {WA}})}$ ${\ displaystyle {\ text {WS}} \ cdot \ cos ({\ text {WA}})}$

literature

Jeppesen Sanderson: Private Pilot Manual . 2001, ISBN 0-88487-238-6
Walter Air: CVFR textbook , Mariensiel, 2001
FSM, Flight Safety Messages 2/86, Flight Operations Course . Federal Aviation Office (D), Braunschweig, December 16, 1986
Wolfgang Kühr: The private pilot, flight navigation . Verlag Friedrich Schiffmann, Bergisch Gladbach 1979, ISBN 3-921270-05-7