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Turns About a Point
2010-03-18

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.

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.

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