PPL Skills - Ground Reference Maneuvers and Crosswinds

Introduction

As the name implies, ground-reference maneuvers involve performing maneuvers on the airplane with reference to ground objects. The difficulty comes when wind comes into play. 

Ground-Reference maneuvers are important because they really sharpen a pilot's flying skills. Learning only the 4 fundementals (straight and level, turns, climbs, and descents) is insufficient; mastering ground-reference maneuvers means that the pilot is able to apply the appropriate control inputs to achieve exactly his desired result, and is able to plan and visualize his desired flightpath. He is able to divide his attention between the many demands placed on him - maintaining proper attitude, airspeed, and altitude, scanning for danger, planning and executing the ground reference maneuvers themselves, tracking visual references, etc.

In my opinion, this is really one of the hardest things to master in the flight sim world, simply because it's really hard to look around outside while performing these maneuvers, especially with one hand on the throttle and the other on the stick. Nevertheless, I think it's still important to attempt learning it. Tools such as trackIR or VR will help a great deal, but I'm not about to invest in those just yet.

Some of these maneuvers are part of the PPL syllabus, and others are part of the CPL syllabus, and the maneuvers have been labelled as such.

Ground-reference maneuvering

• Don't just focus on one object
• Switch your focus between multiple objects to accurately judge your ground track
• Pick suitable visual references
• Take into account, colour, shape, size, visibility, the weather, etc, bearing in mind how different objects may cause different illusions
• Try to pick clearly visible objects that are about the same relative size
• Constantly adjust your control surface input to achieve your desired ground track
• While majority of the attention should be outside of the cockpit, periodically conduct scans of the instruments to make sure nothing is amiss
• Always clear the area with either a 180-degree turn, or two 90-degree turns
• In real life, should be well away from groups of people, livestock, or communities
• Should be between 600ft-1000ft AGL
• Pilot should continually keep in mind possible landing sites should there be an engine failure

Crash-Course: the effect of wind on planes

• Similar to the effect current has on a ship
• The resultant velocity of an aircraft is determined by its speed, without any wind, adding the velocity of the wind
• Remember that velocity is a vector, so unless the wind is a direct headwind or a tailwind, it's never a simple addition or subtraction
• If an airplane flies north at 80kts in calm weather, and a wind blows towards the east at 10kts, the aircraft moves 80nm north and 10nm east every hour. The resultant groundspeed is sqrt(10^2 + 80^2) by Pythagoras' Theorem
• It gets a little more complicated of course if the winds aren't perpendicular to the aircraft's flight. 
• If you don't have a Physics background, read this article on vectors
• A vector is basically a variable that has both a magnitude and a direction
• Velocity is a vector - the velocity of an object technically refers to its speed (which is not a vector) and direction
• The speed and direction (ie. velocity) of the aircraft can be represented by a vector, and the velocity of the wind represented by another
• The addition of the two vectors gives the resultant velocity of the airplane
• See here for the different types of speeds a pilot must consider
• Throughout the entire flight of an aircraft, the pilot must take into account and correct for the effect of wind. 
• This is particularly significant during ground-reference maneuvers and navigation

Correcting the effect of wind

• Unless you're coming in for a landing, you would pretty much always crab into the wind
• This involves turning the aircraft into the wind 
• The angle at which the aircraft maintains a constant ground-track is called the wind correction angle (WCA)
• Mentally estimating it
• Using an E6B flight computer
• While this is useful when flying by instruments, or when doing dead reckoning, it is not necessary for ground-reference maneuvers. The point is to constantly make adjustments based on visual cues

Constant-Radius Turns (PPL)

• Involves a constant radius turn (as seen from the ground) around a selected point on the ground
• Establish wind direction and speed 
• Observe flags, lakes, or smoke to determine where the wind might be coming from
• Might also want to use your own drifting tendencies to establish wind direction
• Remember to make clearing turns before beginning the practice
• The maneuver:
• Enter on downwind to the side of the ground reference object
• The intial bank should be done fairly quickly so as to enter the turn in a timely manner while correcting for tailwind
• Constantly vary bank angle smoothly in between to maintain constant radius as seen from ground
• Steepest turn when ground speed is the highest (direct tailwind)
• Shallowest turn when ground speed is the lowest (direct headwind)
• In the downwind half of the circle, as the tailwind becomes a crosswind, the nose of the airplane will need to be pointed (or "crabbed" - similar to maintaing a straight line track) into the turn to maintain the constant radius turn
• Conversely, in the upwind half of the circle, as the headwind becomes a crosswind, the plane needs to be "crabbed" outside of the turn to maintain that constant turn radius
• The maximum crab should be where the crosswind component is the greatest (ie a quarter of a turn after a direct tailwind or headwind)
• But do not yaw the plane any more than is required for coordinated flight
• Make two complete turns
• Exit the turn on the same altitude and heading as when you entered
• Avoid turns greater than 45°
• Keep aileron and rudder inputs coordinated throughout the turn
• Maintain airspeed and altitude
• As bank angle is varied, elevator control must also be varied to keep a constant altitude
• Power may also need to be adjusted as necessary
• Tip: pick a landmark every 90° to aim for, each at a constant distance from the reference point
• If you can't see the ground reference point due to the wing obstructing you, either fly a wider circle or descend
• ERAU video

Rectangular Course (PPL)

Diagram
Basically fly in a rectangular track as seen from the ground

• Prepares you to fly the traffic pattern
• A rectangular ground reference object should be selected. Possibly a large block in a neighbourhood or a field enclosed by roads
• You should fly parallel to each of the boundaries (and not directly above it)
• Fly between 1/2 - 3/4 miles from the boundaries
• Flying too close would require very steep turns - dangerous and difficult
• Should enter the rectangular course downwind
• Enter the course similar to a traffic pattern: 45° angle to the downwind leg
• Apply wind correction to fly parallel to chosen reference
• Remember to vary bank angle as learnt during the constant-radius turns, taking into account the direction of the wind
• Aim to start the turn parallel to the end of one boundary, and complete the turn parallel to the beginning of the next boundary of the chosen rectangle
• Anticipate crab angle before you actually turn
• You have to be able to visualise the ground track you want your plane to take, as well as the planes attitude at each point
• Maintain altitude and airspeed throughout
• ERAU video

S-Turns (PPL)

Diagram
Maneuver flown with reference to a long, straight reference (eg. roads, railway tracks,etc). Make two semi-circles on opposite sides of the reference (hence forming an S-shape).

• Select a reference line perpendicular to the wind and long enough to perform the maneuver
• When you have completed each turn, you should aim to be perpendicular to the reference line
• Enter downwind, perpendicular to the reference line
• Make two 180° turns, each in opposite directions, hence forming an S
• Same concept as in constant radius turns
• Constantly vary bank, pitch, and power to fly each semi-circle as a constant-radius turn
• Maintain proper coordination and constant radius throughout
• ERAU video