Wind and Groundspeed
Turning as low levels from a crosswind path to a downwind path can be hazardous. It leads to the terrible downwind turn stall accident. When the aircraft turns from a crosswind to a downwind direction at low altitudes, all at once the ground seems to go by much faster. In actuality, it is, but the reaction to the sensation-illusion is that the airspeed has changed as well. It has not and should not. The wind speed added to your airspeed has caused an increase in your ground speed. Close to the ground fly the airspeed not the ground speed. To allow for student errors in this regard all ground reference should be flown a cruise power in trainers. The downwind turn illusion will be exacerbated if the pilot has developed a (bad) habit of trying to look around the cockpit window post during the turn. (See material on peripheral vision.)

As a private pilot you are expected to perform a turn about a point. This means a circle at a constant altitude, of a constant radius with ground speed a variable as affected by the wind. As a commercial pilot you are expected to do a turn on a point. The turn on a point has a constant radius but you are expected to keep the wing tip on the point while flying the circle. This can only be done if you fly a constant ground speed. You should know the difference between the two.

Every ground speed has a critical altitude at which a given radius circle will allow the pilot to keep the wingtip on a point. As the circle is flown the wind affects the ground speed differently at every point. To keep the tip on the point the pilot must vary his altitude. Changing altitude will vary the ground speed. Enter a slight dive when the point moves ahead of the wingtip (tailwind component) and a slight climb when the point moves behind the wingtip.

Practicing turns on a point at about 640' in a C-150 will give you an idea of how the wind affects ground speed. With this knowledge you will be better prepared to cope with the sensations present in the downwind turn. The best defense is to fly a wide downwind if the wind direction is forcing you toward the runway. When you slow the aircraft on the downwind add some more wind correction.

Thinking Through Patterns
Depending on the student or airport weather conditions I will use paper diagrams and walk through the patterns on the ramp. I will illustrate turns about a point, rectangular patterns, course reversals, 8's, and S-turns. I will explain the ground track as flown in calm conditions in both left and right turns as well as though in a strong wind with steep and shallow banks and crab angle. All closed patterns will be initiated in left turns with right turns to follow.

Once I have covered the turns about a point in both left and right turns by both diagram and a walk through with course reversal, I will diagram a rectangle. The bank required throughout each of the four corners in left and right turns will be the same as the banks required in the four quadrants of the circles. The only difference is that the crab angle along the crosswind straight legs of the rectangle will be held corner to corner. This will be the same crab angle held at top and bottom of the circle. From the diagram I will go to a walk through with emphasis upon entry and exit from each corner. The paper diagram will indicate the crab positions of the nose best. The walk through with arms extended for bank will best indicate the bank required to adjust for ground speed changes due to wind.

It is best that the first full ground reference lesson of the required patterns be in calm winds. I find that calm winds are more likely in the early morning. At least one full session should be in flying the patterns under winds of 15 knots or greater. Given the choice, I find that calm wind instruction is best in the morning with stronger winds occurring later.

Turns About a Point
Some students do better if the point is selected at the intersection of to right angle roads. This, instead of a lone tree helps maintain orientation. It is important that the student not try to see under a wing or around the windshield to see the point. The student must learn to give the wing a quick flip for a look and then put the wing back down for the turn. Keeping the circle with a 1/4 mile radius works well.

I help the student select a point and plan the downwind entry. Water is a good way to tell if any wind exists. I suggest to him that it is easiest to stay a constant distance by selecting points to make the desired circle. In the beginning I help with altitude problems but otherwise let the first left turn or two go by without comment. Turns to the left are easier because of pilot position.
Draw your own diagram using the words.

Left turns about a point entry
Shallow banks going upwind
Steep banks going downwind
Aircraft headings to make circle instead of ellipse.

We always (New exception is now rectangles that are entered on 45) try to enter ground reference maneuvers on a downwind leg since the first turn will have the fastest roll rate and steepest angle. If you do not bank quickly and steeply for the fastest rate of turn the wind will extend your flight path out of the desired pattern. Going upwind, the opposite concerns exist, do not hurry either the roll rate or the angle of the bank. You must fly into the wind to counter its effort to keep you inside the desired turn radius. The intent is to keep a constant-altitude, quarter-mile circle. It helps if you can select radii points that form the circle.

With a wind, the first turn will require more than a 90-degree angle of turn. The angle beyond 90-degrees is used to set up the crab required by the crosswind. The upwind turn will be gradually decreased so that when directly upwind the wings will be most nearly level. This is where the ground speed is slowest. The bank is gradually increased but crab must be held into the crosswind to keep the circle from flattening on the top. Once across the top of the circle, the bank must be gradually increased to make the circle conform to the added ground speed caused by the tail wind. The steepest bank is held when we are directly downwind. All banks are gradually increased and gradually decreased.

Often the student will try to look under or around the wing while in the turn. Any such tilting or twisting of the head may disrupt the fluids in the inner ear and often affect altitude control. I will suggest that a quick flip of the yoke to momentarily raise the wing is a better way to stay oriented. Once we have flown left turns we must reverse to fly right turns.

Turns about a point have an airspeed and altitude combination that keeps the wing tip on the point. In this situation the turn about a point becomes a turn on a point. The difference is one of focus. The turn about a point is at a constant altitude while the turn on a point is made at a constant ground speed.

In a dead calm condition both turns can be the same only if the pivotal groundspeed and altitude are matched. A between the wingtips should intersect the desired ground point and stay there throughout the 360 turn. A coordinated turn will balance all the factors of speed, angle of bank, radius of turn and altitude. At a constant ground speed there is an altitude that keeps the sight angle on the point. If the point moves forward or back because of wind variations, then the altitude becomes the variable to modify the ground speed. Any change of radius will require that the angle of bank be modified.

Chart of ground speed in knots and altitude in feet AGL for Turns On A Point.(Commercial Maneuver)
70 kt 433 ft
80 ---565
90 ---716
100 --883

The turn about a point can occur in tower controlled situations as when ATC might require a 360 on downwind or as in a SVFR arrival clearance which might require reporting over a specific checkpoint while remaining clear of the airport Class D surface area. The turn about a point should be basic to many uncontrolled airport arrivals which require circling over the field at twice pattern altitude while determining active runway and traffic patterns.

There are two different kinds of turns related to a point. The private level is 'turns about a point'. in this instance the turns are to be constant in radius. In this case you can visualize points at a constant distance from the point and use these to fly your circle. Wind affects your ability to maintain this circle. The first lesson is best done in a calm wind. Subsequent flights require constant adjustment of bank to maintain your wind correction for flying the circle.

The commercial level is a turn on a point'. The turn on a point requires that you fly around the point with a constant ground speed. To fly this constant ground speed you must dive lower in a head wind and climb in a tailwind. The C-150 has a critical pivot altitude of about 620 feet. This means that in calm conditions you can fly a turn on a point which keeps the wing tip on that point. You know where you are flying too fast, slow, or just right by the tip position relative to the point. Every plane will have a different critical altitude at any given speed. Find the critical altitude for the speed you select and then vary your altitude to keep the tip on your selected point. Climb if the point falls behind the tip and dive if the point gets ahead of the tip. How much you vary your altitude will depend on wind velocity.

Turns around a point
--Selection of altitude
--Speed from approach to cruise
--Entry from downwind with maximum bank
--Angle of bank from 30 to 45
--Angle of bank to vary with ground speed

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