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Archives for January 2013

Ground reference maneuvers – Turns around a Point

Turns Around a PointGround Reference Maneuvers are low-altitude maneuvers designed to get you to understand the effects that wind has on your airplane while it is in flight.

The point of ground reference maneuvers is not just so that you understand the effects of winds, but that you can correct for the winds effect and make the plane do what YOU want it to do instead of just what it wants to do.  In these maneuvers, you truly become a  pilot, not just someone along for the ride.

For these maneuvers, your goal is to maintain a constant altitude and a constant airspeed.  You should perform these maneuvers at an altitude between 600 & 1000 feet above ground level (AGL), and maintain the entry altitude you chose within 150 feet.  Your airspeed goal is to maintain your entry airspeed within 10 knots indicated airspeed (KIAS).

There are three ground reference maneuvers you will do for your Private Pilot Certificate (or Sport, or Recreational, if that's your thing):

  1. Turns Around a Point
  2. S-Turns
  3. Rectangular Course

This series will talk about all three of these maneuvers, and to kick it all off, we'll start by talking about Turns Around a Point.

Turns around a point is, simply, a circle with a constant radius from a central point.  Your job as the pilot is to correct for the wind and make sure that you maintain a constant distance from the selected point so that the airplane flies a perfect circle around it.

There are 4 "critical" points, but this maneuver is really about finesse and a constantly changing bank angle and wind correction.  If you understand what each of the four critical points should look like and why, the rest of this maneuver will fall together pretty easily.

So let's take a look at those critical points, shall we?  Reference the image at the top:

Point 1: This is the beginning, or "entry" to the maneuver.  It is "downwind," meaning the wind is directly behind you, pushing you.  You'll choose a point to use, and then when the plane is "abeam" (to the side of) the point, you will start your turn.  The reason this maneuver is generally started on the downwind leg is because your "ground speed" (actual speed over the ground) is fastest when you are downwind, so your rate of turn needs to be highest to maintain your distance from the point.  This also (and most importantly) means that your bank angle will be steepest here.  Keep in mind that "steepest" in regard to bank angle is relative - all this means is that your bank for the rest of the maneuver will never be steeper than at this point.  It does not mean that you will be in a "steep turn," which is a totally different maneuver!

 

Point 2: The next point is 90 degrees further around the circle, and is a direct crosswind.  Here, your ground speed is slower than at point 1, and faster than it will be at point 3, so you will have a "medium" bank here, and you will have the airplane "crabbed" into the wind to maintain the track of the circling maneuver. You should have been slowly changing your bank and your crab angle the whole time from point 1 to point 2, and you will continue to slowly change them between point 2 and point 3.

 

Point 3: At point 3, you are 180 degrees from where you started, which means you are now pointed directly "upwind" (or into the wind).  This means you will have the slowest ground speed, and commensurately, the "shallowest" bank angle relative to the rest of the maneuver.  Also, notice that during upwind - point 3 - (and downwind - point 1), you have no "crab angle" like you do at points 2 & 4.  This is because there is no crosswind at these points for you to correct for - you are flying directly into (or directly with) the wind.  Point 3 is like the opposite of point 1 as far as ground speed and bank angle are concerned (point 1 = highest ground speed & steepest bank; point 2 = lowest ground speed & shallowest bank).

 

Point 4: At point 4 you have nearly completed the maneuver - you are again in a direct crosswind, so your ground speed will be faster than at point 3 (but still slower than point 1), meaning you will be in a medium bank here.  You will also be crabbed into the wind here, similar to point 2.  Notice that in point 2, however, you were crabbed toward the inside of the circle, but in point 4 you are crabbed toward the outside of the circle.  Your crab angle will always point the nose of the plane into the wind.

The main thing to remember here is that your bank and crab angles are constantly changing to do this maneuver correctly... you don't hold your steepest bank until you reach point 2, then change to a medium bank and add crab, then hold that until point 3, etc.  Essentially, you will be thinking ahead of the plane and making slight, minute adjustments to get you from the configuration you need at point 1 to the configuration you know you will need at point 2, and so on.

There also is no "secret recipe" to getting this maneuver perfect every time.  Each day you fly, the winds will be a little different - they may be higher or lower speed than they were last time, or they might be gusty, or you might be in a different plane than you were in last time you did turns around a point... the moral of the story is, you're the pilot!  You'll need to estimate and correct to get it right - so if you find that the bank angle or crab angle you choose is too much or not enough, make the change and fix it!

There is at least one modification / alternative to this maneuver that I want to discuss, but that will have to wait for another post, so keep an eye out!


Do you have any tricks or suggestions on how to execute a perfect turn around a point every time? Turn them out in the comments, below!

Andrew Hartley is a certificated flight instructor in Columbus, Ohio.

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The Three Axes of an Airplane

Three axes of an airplaneAn airplane has three (3) axes about / around which it can move in flight.

In the image above, you are seeing all three of these axes:
Longitudinal axis: from the nose to the tail of the airplane
Lateral axis: from wingtip to wingtip
Vertical axis: from the bottom of the airplane to the top of the airplane

Each of these three axes meet at the center of gravity (CG) of the plane. The CG is the point at which the airplane would balance if you could lift it up by an imaginary string that attached at that exact point. You can think of the CG also as a kind of fulcrum (like on a teeter-totter) that the plane rolls and pitches around.

Anyway, back to the axes of the plane. Here's what you need to know about them and why they are important.

The Longitudinal axis (the one that runs the length of the plane from nose to tail) is the axis that stays fixed when the airplane "rolls" or "banks" - such as in a turn. In this case, the plane is rotating "about" or "around" the longitudinal axis. This is caused by the airplane's ailerons, which change the camber of the wing and increase its lift on one side,making the wing climb, and spoil the lift on the other side, making the wing drop.

The Lateral axis (the one that runs from wingtip to wingtip) stays fixed when the plane "pitches" - raising or lowering the nose (such as for a climb or a descent). The plane pitches about the lateral axis. This is done using the airplane's elevators. The elevators change the shape of the horizontal stabilizer, causing it to decrease lift (tail goes down, nose goes up) or increase lift (tail goes up, nose goes down). Some aircraft have "stabilators," where the entire horizontal surface moves instead of just the elevator, but the concept (and result) is still the same.

The last one is the Vertical axis, which runs vertically (up and down) through the fuselage. This one stays fixed when the airplane "yaws" - meaning the nose moves left or right. When the plane yaws, it is turning about the vertical axis. This is like turning a car (the car doesn't roll or pitch, it just turns, or "yaws"). This can be done by moving the rudder, which is the movable control surface on the vertical stabilizer (the upright portion of the tail). Moving the rudder right puts it into the airflow and pushes the tail to the left (and the nose to the right). Generally, the rudder is used in tandem with the ailerons to coordinate an airplane's turns, because when an airplane banks, there is a change in drag, making the nose want to move away from the turn initially. the rudder is used to "yaw" the nose the right way and keep the whole plane moving in the direction the pilot (you) want it to go.

It is possible to move an airplane about all three axes at one time, and rarely does an airplane move about just one at a time. You, as the pilot in command, will use all the control surfaces to move the plane about all of its axes and make it do what you want it to do.


Do you have any questions about the three axes of an airplane, or do you have any hints or tricks or stories to share that relate to them? Leave a comment and tell us all about it!

Andrew Hartley is a Certificated Flight Instructor in Columbus, Ohio.

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