Where is the Wind? How to find out where the wind is coming from .... Easily! . Barry C. Lloyd © 2005

Typical ways of determining the direction of the wind: Blowing Smoke Blowing Dust Waves On Water Wind Lines On Water Flagging of Trees

What is Flagging? Wind Direction

What is Flagging? Wind Direction

First, some elementary principles of wind and motion: An aircraft makes relative wind opposite to the direction of travel. Equal to the forward velocity of the aircraft.

Forward velocity of the aircraft Creates relative wind opposite the direction of travel

So, flying North at 80 knots on a no-wind day, where is the relative wind for the aircraft? Off the nose of the aircraft at 80 knots.

But, what if the wind is really from the East at 15 knots? No problem! We just visualize its vector! Vector? What’s a vector? In simple terms, a vector is a physical quantity such as force, velocity or acceleration, that has magnitude and direction.

Oh No! You’re not going to give me math are you? No! But we are going to cover some elementary principles of motion.

The vector of the wind made by your motion through the air adds to the vector of the ambient wind to make the relative wind that the aircraft actually feels in flight. But, how do we add vectors? Sounds like math to me!

A simple rule to remember: to add vectors, put the tail of the little vector on the head of the big vector. Vector of wind caused by flight Northbound at 80 knots. Vector of the ambient wind (from the East at 15 knots) Resultant vector of wind that the aircraft feels in flight.

Adding vectors is exactly what your E-6B does!

When we fly an aircraft in trim, the nose of the aircraft points directly into: The resultant relative wind; which is the sum of the relative wind caused by the motion of the aircraft through the air, and the ambient wind caused by Mother Nature at that time.

Resultant relative wind that is a sum of the ..... Direction of Travel (Course ) Wind caused by your motion on your course, and ....... The ambient local wind. This is called your “crab” angle or wind correction angle.

Now, the story of Billy and Bob

Billy and Bob are flying Northbound to the hills to do some pinnacle landing practice. They both notice that the heading of the aircraft is a little to the right of the course across the ground (ground track). From this, they both decide that the wind must be coming from somewhere on the right side of the aircraft.

Billy and Bob agree that the wind could be from: the right front (right quartering headwind) directly on the right (right crosswind) right rear (right quartering tailwind). They further agree that ambient wind from anywhere on the right side would make the aircraft crab to the right. Billy thinks the wind is from the right front and decides that for his final approach to the pinnacle or in the event of a forced landing, he will turn to the right front. (Billy) Course If Billy does this, and the wind really had been from the right rear, he would be landing with a quartering tailwind. This could be a problem.

Bob thinks the wind is from the right rear Bob thinks the wind is from the right rear. He decides that for his final approach to the pinnacle or in the event of a forced landing, he will turn to the right rear. Course Of course, if Bob turns to the right rear and the wind really had been from the right front, he also would be doing a downwind landing This could also result in an undesirable conclusion! (Bob)

So, if Billy and Bob can’t agree on whether the wind is from the right front, directly from the right, or from the right rear, which way should they turn in the event of a forced landing? Course They could turn directly to the right. That way, they would have at least some headwind component (direct, left or right) in the event of an emergency landing.

But this isn’t good enough But this isn’t good enough! They want to more closely resolve where the ambient wind is really coming from while enroute. This is quite easy. All they have to do is pick a reference point to the right of the aircraft and turn directly toward that reference point and maneuver the aircraft so that the course (ground track) is directly toward that reference point.

Now, all the pilot has to do is make sure that they are flying in trim, and compare their heading to their ground track. Actual wind Heading Course Ref. pt. Upon roll-out with the ground track (course) going toward the reference point that had been to the right of the aircraft, if the aircraft is now crabbing to the left, then when previously flying Northbound, the wind had really been from the right front, or Northeast.

Conversely, if upon roll-out the pilot now finds the aircraft crabbing to the right of the course, then the pilot knows that the wind is now coming from the right of his ground track and had been from the right rear, or Southeast, when flying Northbound. Course Ref. Pt. Heading Actual wind

And, if the pilot rolls out and now finds the aircraft with no crab angle, then he knows that the wind is directly off the nose and is coming from the East. Heading Ref. Pt. Course Actual wind

1. Fly the aircraft in trim. So, the steps are easy: 1. Fly the aircraft in trim. Some pilots believe that if you take your feet off the pedals in forward flight the wind will “blow” the nose of the aircraft in the direction of the wind. This is incorrect. If the aircraft is in trim, it is directly into the wind that is the sum of the wind caused by the aircraft’s movement and the ambient wind. If you take your feet off the pedals in forward flight, the aircraft will eventually yaw out of trim, indicating an imbalance between torque/anti-torque. 2. Carefully notice the “crab” angle, the difference between your heading and ground track.

3. If you notice crab to the right, then the wind is coming from somewhere on the right side of the aircraft. 4. If you notice crab to the left, then the wind is coming from somewhere on the left side of the aircraft. 5. Want to know which quadrant the wind is coming from? Turn 90 degrees right or left in the direction you were crabbing, roll out and notice your new crab angle, if any.

With your new crab angle, you will be able to judge the wind direction to within 10-20 degrees! Don’t want to fly around making 90 degree turns? Then just make the first turn of your high reconnaissance a 90 degree turn and roll out level for a few moments (in trim, of course) to observe your new crab angle and to perceive the wind direction. It works every time! Easy, wasn’t it?

But Wait! There’s More ..........

What if you are making an approach, in trim, and the crab angle is increasing as you slow down?

This can be caused by two things: Either the ambient wind is...... Coming more from the right than anticipated...

Greater velocity than anticipated. Or, the ambient wind is...... Greater velocity than anticipated. Merely readjust your final approach direction to accommodate the wind direction!

So, while it’s nice to have some ground-based ways of determining the direction of the wind such as: Blowing Smoke Blowing Dust Waves On Water Wind Lines On Water Flagging of Trees

We don’t always have such tell-tale ground-based indicators of wind available. However, our helicopter is an excellent “wind sock” and when flown in trim, will always indicate the direction from which the ambient wind is coming!

We just need to fly in trim and pay attention to that slight difference between our heading and our ground track!

E-mail: fltpro@mindspring.com That’s All, Folks! Thank You! E-mail: fltpro@mindspring.com