Propwash
The air flow from a propeller swirls like a corkscrew around the fuselage of the plane. It curls across one wing differently than the other and into the vertical stabilizer and rudder from only one side unless there is one below the fuselage. In a C-150 the left wing will have a higher angle of attack than the right. Higher angles of attack create drag. The propwash hits the left side of the vertical tail components. Because of propwash the rudder is the first on your controls to become effective. In low speed high power situations your rudder is the most effective control you have. Both of these effects contribute to the left turning tendency of an aircraft. The pilot must counter these effects by anticipating use of the right rudder.
Propeller
The propeller has 80% efficiency. This efficiency exists only at the designed cruise speed, which is often faster than the L/D and fuel efficiency speed. A constant speed propeller is most efficient as RPM is at or slightly below manifold pressure. A propeller is most efficient if the leading edge is rounded smoothly and the trailing edge is squared.
P-factor
The arc that a propeller makes can be considered as a variable pitch disk. In a vertical plane to the horizontal the pitch of the entire disk is the same and it pulls equally side to side and top to bottom. Pitching the nose up causes the blade pitch angle on the left descending blade to increase and the rising blade on the right to decrease. The descending blade takes a larger cut than the rising blade. It is working harder and exerts more pull on the right side. The net effect of this is to turn the aircraft to the left. Some aircraft engine installations point the engine slightly to the right. The right thrust effect is used to offset the p-factor of the descending blade. Usually the pilot must anticipate P-factor with applications of right rudder.
Torque
I have always demonstrated torque using a rubber-band powered model while using only the fuselage with no wings or tail. Wind up the propeller and let it go. As the rubber-band unwinds the propeller turns in one direction and the fuselage turns in the other. On the ground the landing gear prevents your airplane's fuselage from turning but it does cause the left tire to exert more ground pressure than the right. This causes a left-turning tendency. Additionally the left wing can be set (twisted) to provide the additional lift that counters the torque effect of the propeller while in the air. This wash-in amount is most effective at cruise. In low-speed-high-power situations the pilot must add right rudder.
The Gyroscopic Propeller
Pitching of the nose causes yaw, and yawing of the nose causes pitching. As mentioned before the propeller is a spinning disk and has all the effects of the toy gyroscope you see in stores. Just by pitching up you can cause the plane to yaw to the left. Yawing the aircraft back and forth with the rudder will cause the nose to vary in pitch.
Level Dynamics
When a pilot has his aircraft flying so that the amount of propeller thrust is equal to the drag and the wing lift equals the weight plus the negative lift of the tail surfaces he is in level flight. The weight will always be focused to the center of the earth. Up to the wing's critical angle of attack an aircraft and power available will be able to maintain level flight over a wide range of speeds. When the aircraft is flying slowly drag is mostly induced drag. At high speeds drag is mostly parasitic drag.
Turns Lesson
Enter successive 20, 30 or 45 degree banked turns. Reduce power during the turn. Hold altitude. Stabilize turn at reduced power with trim. Note increased rate of turn at lower airspeed. A one-third reduction in airspeed will reduce your 30-degree bank turn radius by over 50%.
Leveling Off from Climb
An old saying among pilots is, "How long does it take a student pilot to level off?" Thirty-five hours is the answer. It should not take that long if the instructor is on the ball. The student should know for leveling off from a climb at Vy will require a certain amount of anticipation, a certain amount of trim, a certain amount of acceleration, changing amounts of yoke pressure, a power adjustment, changing sounds and some fine tuning. The trick is to put the aircraft into the desired attitude and leave/keep it there.
Demonstrate how pushing forward on the yoke will both lower the nose and level the bottom of the wing's surface with the distant horizon. Have the student perform. Have the student watch the wing and hold it locked level with his arm against the door. Have him note the pressure required. Have him swing his eyes to measure the space between the nose and the horizon. Have him touch the bottom most button on the trim wheel and move it full up while keeping the nose in position. Have him note the gradual change in pressure as the plane accelerates. Power should be reduced when reaching 85 kts. Instructor might make any fine changes needed. If the student needs to search for level flight and is carrying control pressure then he's doing something wrong.
Level Cruise #1
As you reach a desired altitude sight on the horizon under the left wing and move the yoke forward until the wing tip is level. Immediately bring your vision to the nose and hold the yoke so that the nose does not change position relatively to the horizon. Trim to relive pressure but according to the final trim condition desired. If you continue to adjust the trim while the aircraft is still accelerating you will create problems to yourself. Let the aircraft reach its cruise speed (85 kts) and power set before making final trim adjustments.
Level Cruise #2
By going high and then diving to acquire cruise speed you can get to speed faster. Some aircraft actually get on a 'step' like a speed boat and will maintain a higher than normal speed until the condition is disrupted. The reason for not reducing the power initially to 2450 is that some deceleration occurs during leveling off. This causes a 100 decrease in RPM.
Level Cruise #3
The actual reason for having the student to look at the bottom side of the wing for the nose level attitude is because the student does not yet know where to look over the nose. The use of the wing can be substituted by a
marker on the windshield once level for the particular person has been determined. Each persons 'level' will be slightly different. Level flight is established and maintained by positioning the nose. Repetition in positioning the nose is the best way for a student to learn where level is. The more often you trim for hands off level the better able you will be able to discern just where level is. With constant power there is one point on the windshield that keeps the plane level, every rate climb or descent has a specific position for placement of that point based on constant airspeed. Airspeed is a relatively coarse way of nose adjustment. It takes & makes a proficient pilot who uses the nose position for level flight. The pilot who trims for his climb and descent airspeeds soon develops a set of constants for the aircraft. With repetitive practice the pilot will learn to feel, hear, and SEE just where a particular configuration and attitude will position the nose.
Unable to fly level
After you have been flying a while either with the instructor or solo a common phenomenon seems to occur where the new pilot is suddenly having difficulty in leveling off. This is normal. As we have trained and practiced we have developed along with the procedures for leveling a set of references. We may have started with the wing on the horizon and gradually been able to reference the nose to the horizon. Now, it doesn't seem to work. We may oscillate in altitude, airspeed and trim for several minutes and still not get it right. It is going to happen.
The reason it this occurs may be due to one factor or a combination of factors. If the weather changes so that your usually clear horizon is blocked by haze or cloud formations you have lost an essential reference. Flying in mountains where the horizon cuts through the mountains can be a causal factor. Perhaps due to a distraction you forget to trim. Power control can cause the aircraft to fail to accelerate or to exceed cruise speed. Any one of these or a combination can cause leveling off problems. You might practice making deliberate errors in your leveling off procedure to ascertain the corrective procedure that works for you.
Most of the small movements evade detection of the eye but are sensed subconsciously by the peripheral vision, dangerously so. In certain pattern turn conditions the peripheral vision can deceive your brain as to the true attitude of the nose.
On Making Turns
In the very beginning of flight instruction and any proficiency check I review the four basics. Of these, the making of turns require the most attention. A properly performed turn is a thing of beauty with just the right amount of aileron, rudder and pitch. Just the other day, I had a student reviewing for her second solo in the pattern. She had what I call an 'a-ha' experience. She had performed the cross wind turn from entry to rollout at exactly 65 knots in the C-150. Such a turn is not easy. The use of rudder must be anticipated along with feather-light pitch pressures.
The aileron into the roll in and out must be smooth and blended with the use of rudder. I want my students to use 30-degree banks, no more, no less. Such a bank is unique in that when reached and held there the yoke will be parallel to the cockpit panel just as in level flight. the 30-degree bank is very stable and can be held there with light rudder pressures. There is only .15 G difference between level and the bank G-forces. The 30-degree bank feels good when done right and held there.
There are distinct differences between left and right 30-degree banked turns. In a Vy climb a turn to the left may well not require any additional rudder pressure except when rolling out. The entry into a right bank from a Vy climb will require leading with the rudder, holding it into the turn and relaxing it during the roll-out. These uses of the rudder are not intuitive and exist to a slight degree even in level and descending flight.
Practice doing the Dutch roll will sensitize the student to the sensations of a slip, skid, and coordinated flight by creating the discomfort of uncoordinated flight. The rigging of the aircraft is a variable factor that accounts for the need of pilots to adjust to each aircraft. The making of 30-degree banks is useful as a maximum limit in the pattern because it makes the turn quickly into the cleared area. A more shallow bank is useful if a higher rate of climb is required as in making a 270 departure. ATC prefers the 30-degree bank to the 20-degree bank because it is less likely to be confused with a wing wobble. 30-degree banks can be checked with both the attitude indicator and the Cessna wing strut being parallel to the ground or horizon.
In making turns there are two criteria that are used around the pitch axis. In level flight it is the altitude and in climbs and descents it is airspeed or rate of descent. The indicator in both cases is the nose and sound. 30-degree banks do not require much pressure but the application an removal of that pressure must be done in anticipation of what is going to be happening.
On rolling into the turn you apply pressure with the forefinger and hold it until beginning to roll out. At this point you apply thumb pressure because the increased lift in level flight always causes a pitch-up unless anticipating counter pressure is applied. The usual rule for rolling -out on a heading is to begin at half-the-angle-of-bank. Students should be encouraged to watch the nose during turns with only quick glances at the heading indicator for the lead-in heading used for rollout. The final heading should be initially acquired by watching the nose. Any fixation on the heading indicator prior to or after roll-out will generate wing wobble. Precise turns are a matter of consistency in the roll-in and the rollout.
Why Turns Turn
A turn is a combination of several aerodynamic factors. Individually each factor has both positive effect and negative effect. Beginning with the ailerons the inside aileron goes up and decreases lift that lowers the wing while the outside aileron goes down and increases the lift that raises the outside wing. We now have roll. Along with raising the wing the outside aileron just by increasing the lift also creates drag. Parasitic drag that is. This drag is a negative that tends to swing the nose away from the turn. This is yaw... Adverse yaw, that is. The combination of roll and drag is called coupling. With roll you get yaw. The speed or rate of your roll entry, by affecting the relative winds of the two wings, causes additional but slight adverse yaw.
Without coordinating rudder to counter any adverse yaw the aircraft is in a slip. The lower wing is faster and moving forward and rising with the increased lift. The relative wind weakly moves the vertical stabilizer away from the turn effectively moving the nose into the turn and reducing the slip.
Coordinated rudder solves all the dynamic equations of the turn. It eliminates adverse yaw and all the forces that reduce roll effectiveness. the rudder must be applied or even anticipated at the beginning of the roll and then pressure reduced once the aileron deflection is reduced. The roll-out to heading reverses the roll-in process. Turns are more enjoyable when the proper rudder forces are applied.