Imagine you intend to swim across to the other side of a river where a cute young lady is sunning herself, but as you swim, the current is pulling you down stream. You're swimming straight but your track will actually take you downstream to where a gator also happens to be sunning itself. Not exactly your planned destination, huh? To end up with the tan and lovely versus toothy and hungry would have required you to angle the path you swam a bit upstream, into the current. By what degree varies with the speed of the current and the speed at which you swim. The same thing happens when we don't take the currents of the air into consideration. We call these currents WIND.

Wind is every pilot's constant companion; it affects every aspect of flight and must be a constant consideration. Its effects vary with the wind's velocity and its angle to your helo's flight path and speed. Once we decide to sprout wings we have to understand and accommodate these effects if we want to successfully navigate to our destination. If the wind is coming from anywhere but our desired heading or it's reciprocal we need to apply a Wind Correction Angle.

But how do you know the angle???

Ah, Grasshopper, read on.

Okay, before we get ahead of ourselves there are a few things we need to understand because the rest of this won't mean squat if we don't know how to apply it so learn to visualize this:

The compass with 360 and our aircraft's course line superimposed on it. Now divide the circle into quarters with left and right halves oriented to the left and right sides of our aircraft and head and tail halves oriented ahead and behind our aircraft. Now we visualize where the wind is coming from. This will quickly let us know whether we need to correct to the right or left and whether we should expect an increase or decrease in groundspeed. The closer it is to direct right or left (perpendicular to our flight path) the greater the effect on our course. The closer it is to direct head or tail (parallel to our flight path) the greater effect it has on our speed. This way you can at least know the direction of your correction. In the helo we have a handy-dandy device that will help us visualize this, the HSI. Set your heading bug to the course heading and then look to see where the wind would be coming from in relationship to the heading bug. Now we can better utilize the two following methods to get our WCA (wind correction angle). Tan and lovely, here we come!


Method #1         Estimation       (the easy way)


Instead, once established on the leg, turn a bit into the wind. The correction angle will be determined by the strength of the crosswind (which is a product of its angle and speed). Let's start off with 5 into the wind and check the progress in 15 or 30 seconds. The idea is to fly a heading that keeps the ADF needle a constant number of degrees from the heading indicated by the moveable card; this is your estimated WCA. If this doesn't remain constant (heading constant, needle moved) you will have to adjust your estimated WCA by adjusting your heading by few degrees (needle moved left, adjust heading left; needle moved right, adjust course right) Once the relationship is constant (heading constant, needle constant) you've got it!

Procedure in the aircraft:
1. Turn to course (per plan leg).
2. Set Heading bug on HSI.
3. Set moveable card on ADF to same heading as HSI.
4. Estimate correction angle into the wind and execute.
5. Monitor every 15 seconds, then as your estimate proves out monitor at 30 seconds, then minute intervals.
6. If the relationships between heading and ADF needle changes make adjustments to your heading a couple of degrees till you make that relationship constant.
7. Don't make any drastic corrections when within 2 miles of navaid.


Method #2       Calculation       (for you retentive types)

For calculating the WCA we need a formula and some abbreviations.

First the abbreviations:

TAS = True Airspeed                   WCA = Wind Correction Angle
WD = wind direction                    WV = wind velocity
X-wind = crosswind component     (%) = the calculated percentage

Important:  A) All wind corrections calculations are based on acute angles. If the wind angle (WD-COURSE) is obtuse subtract 180
                  B) Max percentage in formula is limited to 100%
                  C) All negatives are dropped

First find the crosswind component of the forecast wind velocity by estimating the (acute) angle at which the wind meets the course, multiplying that by 1.5 and applying the result as a percentage (to maximum 100%) of the wind speed.


We will use these formulas to help us estimate our wind correction angle

Unless otherwise stated these are the numbers for these examples:

    Desired Course= 60     the direction to the next checkpoint
    TAS= 100                                 airspeed of the helicopter
    Wind Forecast   120/15      or       wind from 120 at 15 kts

Now we plug the figures into our first formula to find our crosswind component:

WD COURSE x 1.5 = (%) x WV = x-wind
(120 � 60) x 1.5 = (90%) x 15 = 13.5 kts

Now this figure gets plugged into the next formula:

x-wind / TAS x 60 = WCA
13.5 / 100 x 60 = 8.1         WCA= 8

You add this figure to your course if the wind is from the right, and subtract it if the wind is coming from your left.

Heading needed is 60 + 8 = 68 degrees  

This will get you real close without giving yourself an aneurism
My whiz bang electronic flight computer says 7.5, so we're that close!!

Another example, but we'll change the wind direction to 200:


WD � COURSE x 1.5 = (%) x WV = x-wind
(200 � 60) x 1.5 = (60%) x 15 = 9   (Remember 200 � 60 = 140, so subtract 180 = -40)
(-40) x 1.5 = (60%) x 15 = 9                    (Negatives are dropped)

Then:

x-wind / TAS x 60 = WCA
9 / 100 x 60 = 5.4             WCA=5

Flight computer says 5.5, cool.


Try this one, with the wind from 200� and desired course 320:

WD � COURSE x 1.5 = (%) x WV = x-wind
(200 � 320) x 1.5 = (60%) x 15 = 9   (200 � 320 = -120, drop the negative and subtract
                                                           180 = -60, drop the negative)                          
(60) x 1.5 = (90%) x 15 = 13.5 kts                    

And:

x-wind / TAS x 60 = WCA
13.5 / 100 x 60 = 8.1         WCA= 8  just like in the other example.

Yes and no. Remember this time the wind is from your left so you'd subtract the WCA of 8 from your desired course to get your new heading of 312.


This can apply to both NDB and VOR but explaining it for NDB will serve both.
For the VOR just use the estimated or calculated WCA to make it easier to keep the CDI centered. As long as the needle is centered you are on course. Good Job!