Introduction Learning Goals Wind corrections In order to fly a course, whether it's enroute from A to B, a nice aerodrome traffic pattern or a runway approah with crosswinds, you need to understand the effects of crosswinds. Left Headwind : Course : Heading : Wind direction : Wind correction angle : Acute wind angle Right Headwind Left Tailwind Right Tailwind Page of 5
The wind correction angle The wind correction angle () is the angle between the course () and the heading () that is required for the aircraft to track that course when there is wind. The is basically added (when the wind is to the right) or subtracted (when the wind is to the left) to the course. The result of this addition or subtraction is the heading which the pilot must fly to maintainn that course. = + = - for winds from the Right for winds from the Left If we have a perfect cross wind ( =9 ) easily described with some math as: the wind correction angle can be WS Example: Wind : 36 : 27 @ knots : knots ma x= ASIN(/) = 5-6 Now for a Cessna this is easy to remember. Our will usually be around knots and for each knots of crosswind we need a heading correction of 5-6 degrees!. In reality we willl not have a perfect crosswind so what to do now? The WS has to be corrected with a Correction factor in order to get the crosswind component : Page 2 of 5
Now this is getting complicated. For reason of estimation it's easier to use a correction factor CF which is very close to the real value of sin(). 5 2 3 4 5 6 7 8 9 SIN().258.342.5.642.7666.8666.9399.985 Correction factor (CF ) /4.25 /3.33 /2.5 2/3.67 3/4.75 9/.9 example: Wind : 36 : 23 @ knots : knots = asin * (*.5 / ) = 2.6 degrees Page 3 of 5
How to estimate the in practice Use any compass related instrument to visualize the wind. In our example we will use an HSI. head wind correction factor Wind vector cross wind correction factor Imagine you are flying heading 36 / North. winds are 3 / knots = knots. draw a line from 3 down to the X-axis. The blue line from the center to the intersectionn point represents the cross-wind (X-wind) correction factor which is,5 ( half the length of a the red circle) Note: sin(3 ) =,5 2. draw a line from 3 left to the Y-axis. The Red line from the center to the intersectionn point represents the Head-wind (H-wind) correction factor which is approx.,9 Note: cos(3 ) =,87 The wind is knots so: X-wind =,5 * = 5 knots H-wind =,9 * = 9 knots = 6/ * 5 = 2.7 and in practice use 3 Note : Remember that when you are using this imaginary techniquee during a crosswind landing, your reduces from normal maneuvering speed to approach and landing speed. ( from to 8 to 6 ). In practice this means that if the winds remain constant, your changes from 3 to 6!!!! Page 4 of 5
Difficult...well...I admit..it's not that easy to do it perfect but with our estimation technique we will get pretty close. Let me show you why: Cessna Beechcraft 8 A bit more than /2 * Crosswind A bit more than /3 * Crosswind Crosswind = Correction factor * Wind Correction factor 5 2 3 4 5 6 7 8 9 Correction facto /4 /3 /2 2/3 3/4 9/ or (CF.25.33.5.67.75.9 ) So...we fly a Cessna 72 and want to fly a course of 36 when we have winds from 33 @ 2 knots? our will be a bit more than /2 * 2 * /2 = a bit more than 5 so make it 6 Our heading should be : 354 Generally speaking we could say: for a Cessna: use 5-6 degrees of wind correction for every knots of perfect crosswind for a Beechcraft : use 3-4 degrees of wind correction for every knots of perfect crosswind for an Airbus or Boeing...well...just read the wind correction from your display. Page 5 of 5