L03 Teaching Aerodynamics

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Teaching AerodynamicsObjective: At the completion of this lesson, you will have an understanding of the major theoretical and practi-cal elements of aerodynamics relevant to the flight operations/maneuvers presented.

IntroductionGiving your students a basic understand-ing of how an airplane flies is only thebeginning.

What about:

• knowing the techniques that helpyou get the most cruise airspeedfrom your airplane?

• intuitively making the right recov-ery efforts during a spin becauseyou understand why an aircraftspins and the aerodynamic forcesthat perpetuate the motion?

• discovering how the parts of the air-plane function together, and inspir-ing the desire to learn more aboutaircraft design?

Aerodynamics can be one of the most complex and important subjects you teach. When discussing this subject,you are giving your students better tools with which to fly. Your students will be more in tune with the aircraftand its limitations, and be able to operate safely within those limits. In this lesson, we'll explore lesson planningfor basic aerodynamics, stability, stalls,spins, and maneuvering speed.

Lesson Planning forAerodynamicsBy referring to 14 CFR part 61, you candetermine the aeronautical knowledgeareas that involve aerodynamics. Youmay also want to refer to the AirmanKnowledge Test to review the ques-tions the FAA will ask your studentson the written exam. From these begin-nings, form your lesson plan.

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REVIEW: Lesson Planning for Aerodynamics

To determine how to approach a given aerodynamics subject, gauge the:

• level of knowledge demanded on the Airman Knowledge Test.

• need to understand how aircraft components work together.

• aerodynamic limitations of the airplane.

• student’s need of the information to become a safe pilot.

Lesson plan review:

• The parts of a lesson plan may include: objective, elements, com-pletion standards, ideas for further study, references, and notes.

• Start with the objective or goal for the lesson and plan your lesson from this point.

• Make sure the completion standards complement the objective.

• Consider your intended audience carefully when planning lessons on aerodynamics.

�Most gulls don�t bother to learn more than the simplest facts of flight � how to get from shore to food and back again.�� Richard Bach, Jonathan Livingston Seagull

3-2 Teaching Aerodynamics

Have you ever noticed how a bird lands on the water?

• The bird begins with a glide to slow down and losealtitude, similar to reducing power in an airplane.

• The bird then increases the angle of attack by puttingits tail down.

• At the same time it curls its wings to change theirshape or camber, as flaps do for an airplane. Thisgives the bird lift at slower speeds.

• The tail fans out like speed brakes to slow the birdfurther.

• Finally, the bird puts out its legs, like floats thatskim the water, and it settles into the water at mini-mum speed and rate of descent.

• If the descent rate is too great, the bird flaps itswings to soften the touchdown, as a pilot might add power in a similar situation.

Your student, Jan, is beginning work on her private pilot certificate, and you need to introduce her to basic aero-dynamic concepts. Jan is college-educated, and works as an information technology professional, so you knowthat she can grasp higher-order concepts.

Although you don't want to overwhelm her with aerodynamic theories right away, you need to be able to delvemore deeply into any topic if she understands the basics easily. Therefore, before you prepare your lesson plan,you decide to review your own aerodynamics texts to make sure you understand the material.

You might begin your discussion by explaining how manycomponents on an airplane are based on airfoils. There arereally three surfaces on an airplane in addition to the wingsthat produce lift: the propeller, the horizontal stabilizer,and the vertical stabilizer.

• The prop is a moving airfoil that produces lift in a forward direction.

• The horizontal stabilizer is designed with a negative angleof attack, which produces a downward force, or negative lift on the tail.

• The same thing happens when the rudder is moved one way or the other on the vertical stabilizer. It provides a shape that causes lift to be produced on one side or the other, resulting in yaw around the vertical axis.

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Here’s an example of a lesson plan you may create for an average student. If the students grasp the concepts eas-ily, the plan allows for the expansion of several key elements.

Fundamentals of Lift

Objectives: To introduce the student to the four forces as they apply to the fundamentals

of flight, to introduce principles of lift production, and to incorporate these

concepts with a flight lesson.

Elements:

• lift, drag, thrust, weight

• balance of forces in steady flight

• how lift is produced

• definitions of terms: airfoil, camber, chord line, center of pressure,

planform, angle of attack, relative wind, flight path

• Newton's Relative Laws of Motion

• Bernoulli's Principle

• coefficient of lift vs. angle of attack

• how lift is controlled by airspeed and angle of attack

Completion

Standards: The lesson is completed when the student demonstrates understanding of the

four forces of flight and the basic principles associated with the production of lift.

Further

Study: Jeppesen Guided Flight Discovery Private Pilot Manual (3-1 to 3-6)

Pilot's Handbook of Aeronautical Knowledge AC 61-23C (FAA-H-8083-25)

References: Jeppesen Guided Flight Discovery Private Pilot Manual (Chapter 3)

Pilot's Handbook of Aeronautical Knowledge (AC 61-23C) (FAA-H-8083-25)

Aerodynamics for Naval Aviators

One tool that you may find useful is an application provided on line by NASA’s Glenn Research Center. FoilSimis a simulator that allows you to manipulate parameters like airfoil thickness, camber, airspeed, and angle ofattack. The FoilSim presents these changes graphically to show how they affect relationships involving the pro-duction of lift. You can use this simulation to demonstrate these relationships to your students. On the same website, you’ll also find several lessons that may help you find new ways to discuss these concepts.

You can use the following technique to teach basic aerody-namic principles:

1. Take a flexible straw and a Ping-Pong ball.

2. Bend the straw up at a 90° angle and place one end inyour mouth.

3. Hold the ball over the open end of the straw and beginto blow.

4. Slowly let go of the ball and see what it does.

You can find other experiments on the National Air andSpace Museum web site in their interactive presentation onHow Things Fly. Though this site is designed with kids inmind, the principles of aerodynamics are explained in anapproachable, logical manner that is useful to adults aswell.


You are looking for an interesting way to teach your student, Bob, about the various forms of drag, and how theyinterrelate. You explain the different forms of parasite drag and how it is part of the total drag created by the formor shape of airplane parts. But, induced drag is a little bit more challenging for Bob to grasp.

Since Bob is working on his private pilot certificate, during the first few hours he really only needs to know thatinduced drag is a by-product of lift, and increases with reduced airspeed. You can give Bob a more detailed expla-nation later on in his training, once he has had hands-on experience from which to draw. Then, you can discussthe total drag versus the power curve, and reinforce these concepts by demonstrating slow flight.

1. Reduce power, and gradually applyback pressure on the yoke.

2. When your student reaches thedesired airspeed, increase power tomaintain altitude.

3. During turns, your student mustcoordinate pitch and powerincrease to maintain airspeed.

4. Have your student add full powerto return to cruise flight.

An important aspect of teaching isensuring your students understand andcan use the material. Asking good ques-tions is a simple way to determine whatyour students have learned.

A good question is one that:

• forces your students to think criti-cally about a given situation.

• requires your students to applytheory and proper procedures to come up with a sound answer.

• can't be answered with a simple yes or no.

• takes thought and practice to create.

Questions are especially helpful when you’re ready toexpound upon a given subject. For example, once you havediscussed the power curve and induced drag with your stu-dents, you can ask them how these concepts help explainthe behavior of an airplane flying in ground effect. Thiswould lead to a discussion of wingtip vortices.

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For more advanced students, you can begin with a review of the power-required curve. Then, elaborate to showhow thrust and power relate and taper off with airspeed, indicating the maximum level flight speed.

You may use the following lesson plan as a template for designing your own session on drag basics for a studentworking on a private certificate.

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Drag Basics

Objective: To introduce the student to induced and parasite drag, how drag is

affected by airspeed, and to relate the concept of the power curve

to a flight lesson on slow flight.

Elements:

• parasite drag; how it varies with airspeed

• induced drag; function of angle of attack; how it varies with airspeed

• total drag; drag curve

• power curve

Completion

Standards: The lesson is completed when the student demonstrates understanding

o f how drag varies with airspeed by proper power management when

transitioning through all speed regimes.

Further




Pilot's Handbook of Aeronautical Knowledege (AC 61-23C) (FAA-H-8083-25)



StabilityMany airplanes are designed to maxi-mize the positive elements of stability,maneuverability, and controllability.In order to teach these concepts to yourstudents, you should first point out theaxes of the airplane and then describethe stability of, or around, each axis.

REVIEW: StabilityStatic stability — the tendency for an object to initially return to equilib-rium when displaced• Most airplanes are designed to demonstrate positive static stability.

• If an airplane displays negative static stability, we refer to it as unstable.

Dynamic stability — the tendency of an object to return to equilibrium over time when displaced, also referred to as damping

• If an airplane returns to equilibrium immediately, it displays non-oscil-latory dynamic stability.

• If an airplane returns to equilibrium through a series of oscillations, itdisplays oscillatory dynamic stability.

• If an airplane initially returns to equilibrium, but then continues tooscillate further away, it displays negative dynamic stability, ordynamic instability.

Longitudinal stability — refers to stability about the lateral axis, also known as pitch stability

Lateral stability — refers to stability about the longitudinal axis, also known as roll stability

Directional stability — refers to stability about the vertical axis, also known as yaw stability.

�The machine does not isolate man from the great problems of nature but plunges him more deeply into them.�� Antoine de Saint Exupe´ry, Wind, Sand, and Stars, 1939

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dynamic stability

Positive static, neutral dynamic

stability in an oscillatory mode

Positive oscillatory dynamic stability

Positive static and negative

dynamic stability

Yaw Pitch

Roll

Vertical AxisLateral Axis

Longitudinal

Axis

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Your student, Ed, is learning about stability. It can be helpful to use props and other objectsin your lesson that Ed can manipulate to learn these concepts. Think for a moment how

you might use each of the following in a lesson:

Since a hat stand, much like an airplane, is heavier at one end than the other, youcan use a hat stand to show how a downward force is necessary on the tail. This

points out the need to place the horizontal stabilizer in such a way as to createthis downward force. From here, you can discuss how the result leads to a

balance of forces.

A pendulum displays positive, oscillatory dynamic stability in a sim-ple, elegant way. When the pendulum is displaced, it returns to its

starting position through a series of oscillations.

A rocking chair displays both positive static and dynamic sta-bility — unless rocked past a certain distance. Then, the

chair essentially crashes. You may be able to apply thissimilarity in stability, up to a point, to the airplane you

fly with your students.

A pen can be used to demonstrate positive, neutral,and negative static stability, depending on how

it’s placed on the table. If you lay it on thetable, it’s neutrally stable. If you stand it on oneend, it’s unstable. And, if you balance it in themiddle, on your finger perhaps, it’s positivelystable.

You may also want to apply principles of stabil-ity to the kinds of flying your students plan ondoing after they get their certificates. Let’s sayone of them, Karen, tells you she wants to enteran air race. Make sure you point out to her thatplacement of the CG can have an effect on themaximum TAS she can expect from the airplane.If she plans the weight and balance so the air-plane’s CG is toward the rear end of the envelopeduring the race, the airplane may fly a couple ofknots faster. Explain to her the tradeoff will be aslightly less stable airplane than she may be usedto.

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Several features incorporated into common air-planes help you demonstrate the links betweenstability and design.

You can show how elevator trim design aids thepilot in maintaining longitudinal stability.

1. In straight-and-level flight, have your stu-dent trim the airplane to a normal cruiseairspeed.

2. Then, have your student displace the noseby pitching down.

3. Tell your student to release the controls. Asthe airplane begins an oscillation back toequilibrium, discuss how the trim tabworks to keep the airplane at a particularairspeed.

There are four common design features that influence lateralstability:

• weight distribution

• dihedral

• sweepback

• keel effect

You may have no control over the design features that helpmaintain lateral stability, but you can show your student howto control the distribution of weight and improve lateral sta-bility. For example, most training airplanes have two fueltanks, one inside each wing. By using fuel from only one tank,your student will soon notice that the airplane wants to rolltoward the wing with the full tank. The distribution of weightis uneven and lateral stability is affected. Discussing proper

fuel management with your student by switching tanks, can prevent the lateral imbalance caused by a significantdifference in weight between fuel tanks.

The training airplane you use may have a certainamount of dihedral built in to increase its lateral stabil-ity. You may want to go out to the airplane with yourstudents as you discuss how an airplane with dihedralbehaves in a sideslip. It may be easier for them to under-stand how the lower, upwind wing creates more liftfrom the relative wind if they have the actual wing infront of them.

Sweepback, which is more commonly used on corpo-rate jet aircraft, has a lateral stabilizing effect.

Lateral stability also is provided by the vertical fin andside area of the fuselage reacting to the airflow verymuch like the keel of a ship. Keel effect is the steadyinginfluence exerted by the side area of the fuselage andvertical stabilizer.

When the trimmed airplane pitches up, reduced tail-down force allows the airplane to pitch down.

If the airplane pitches down,increased tail-down forceraises the nose.

Roll Force

Yaw Force

Relative Wind

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You may also find it easier to discuss the weathervaning tendency built into many airplanes if you are out on theramp. Show how the greater surface area of fuselage and vertical stabilizer behind the vertical axis increase thedirectional stability. Weathervaning can be demonstrated nicely on final approach in a crosswind.

StallsA student pilot may simply need to know howstalls occur and how to recognize and recoverfrom them, or avoid them altogether. However,a CFI student must become more intimatelyfamiliar with stalls in order to teach them in away that promotes a high level of stall aware-ness.

Andy has started lessons again after severalyears. He mentions that his first instructor intro-duced stalls to him on the first lesson. Aftersome questions, you find out that this instructordidn't spend much time on the ground explain-ing stalls to Andy, and so his grasp of the con-cepts involved was poor from the beginning.You get the feeling stalls startled Andy, and thatmay be why he didn’t solo. However, he’s obvi-ously excited about learning to fly. The way youintroduce stalls to students affects not only theway they view stalls, but how often they prac-tice them before the test, and whether they con-tinue to stay current in stall recovery after theybecome certificated. Therefore, it’s important togive them the details about stall aerodynamicsbefore you get in the airplane.

1. During stall practice, your student will pitch the nose of the airplane above the horizon to induce a stall. Besure to point out that stalls can occur at any attitude.

2. To recover, your student needs to release back pressure to reduce the angle of attack.

3. If a wing drops, your student can pick up the dropped wing using the rudder. Demonstrate how the aileronsmay not be effective in recovering from a wing drop.

You can use the following as a template for your own lesson plan on stalls. This lesson plan can easily be adaptedfor any level of student, from private to commercial. Be sure to emphasize that the nose does not have to be abovethe horizon in order for an airplane to stall. You will need to add some additional points to cover stalls for a CFIstudent.

REVIEW: Stalls

Private pilot aeronautical knowledge — stall awareness, spinentry, spins, and spin recovery techniques for the airplane andglider category ratings

Flight instructor aeronautical knowledge — the aeronauticalknowledge areas for a recreational, private, and commercial pilotcertificate applicable to the aircraft category for which flightinstructor privileges are sought

�Keep the aeroplane in such an attitude that the air pressure is always directly in the pilot�s face.�� Horatio C. Barber, 1916

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Rather than just teaching your students how to recover from stalls, you should also teach them how to avoid stallsby recognizing common situations that lead to their development. Here are three exercises you may conduct withyour students to ensure they develop good stall avoidance skills.

Wing Pick-Ups

1. Have your students start at or above 2,000feet AGL to ensure you recover from anyunintentional stall above 1,500 feet AGL.

2. Establish a typical approach speed for thetraining airplane.

3. Set the flaps in the same position as for ashort-field takeoff.

4. Lower the right wing with the ailerons to a30° bank.

5. Pick the wing up using the left rudder.

6. Have your students practice until they cansmoothly bring the wings level with thehorizon.

Stalls

Objective: To familiarize the student with the aerodynamic properties, the causes of,

and the proper recovery procedures for stalls; to incorporate this

information with a flight lesson which introduces stalls and stall recovery.

Elements:

• coefficient of lift vs. angle of attack; critical angle of attack

• independent of airspeed, attitude

• airflow; flow separation

• aircraft reaction; sensory inputs

• recovery: angle of attack, power, flight controls

Completion

Standards: The lesson is completed when the student demonstrates understanding

of the cause of stalls and proper recovery techniques.

Further



Airplane Flying Handbook FAA-H-8083-3 (5-2 to 5-11)


Airplane Flying Handbook (FAA-H-8083-3)


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Some may recognize the next maneuver as“Dutch rolls.”

Coordination Maneuver

1. Have your students start above 1,500 feetAGL.

2. Establish a typical approach speed for thetraining airplane.

3. Put the nose of the airplane on a point nearthe horizon.

4. Bank the airplane left and right, usingsmooth and prompt rudder inputs to keepthe nose on the point.

5. Have your students start with shallowbanks; steeper banks are harder to coordi-nate through the maneuver.

Realistic Distractions

This is a structured way of covering the use ofrealistic distractions mentioned in the PracticalTest Standards.

1. Have your students start at or above 2,000 feet AGL to ensure you recover from any unintentional stall above 1,500 feet AGL.

2. Establish an airspeed 10 - 15% below a normalapproach airspeed.

3. Begin a 20° banked turn, as though turning from base to final.

4. Tell your students an aircraft just called on final and have them look over their shoulder.

5. Return to straight-and-level flight at the initial airspeed.

6. Have your students change the radio frequency, as though the tower handed them off to an altenate tower frequency.


8. Instruct your students to reset the heading indicator, as though they forgot to check the compass until afterthey passed the outer marker on an approach.


10. Tell your students to reach back and grab a chart or A/FD out of the back seat to check the pattern altitude.

11. Recover to normal cruise airspeed, and straight-and-level flight.


SpinsNo matter what level your students are, theyneed to understand spin entries, how spinsdevelop, and the proper recovery procedures.However, many training airplanes are notapproved for spins.

Many students mistakenly believe that somenormal and all utility category airplanes areacceptable for spin training. This concept isfalse. No normal category airplane is approvedfor spins, and an airplane certificated in theutility category is not necessarily approved forspins. This is another good reason to alwaysreview the AFM or POH prior to conductingspin training in a particular airplane.

REVIEW: Spins

Spin entries and spins are taught on the aeronautical knowledgelevel to those applying for recreational, private, and commercialcertificates. This training normally is conducted in a classroom.

CFI applicants must show a logbook entry attesting that theypossess instructional proficiency in stall awareness, spin entry,spins, and spin recovery and have completed this training com-petently with an authorized instructor.

Unless the CFI applicant fails any portion of the practical testrelating to stall awareness, spin entry, spins, and spin recovery,the endorsement is normally accepted in lieu of performingspins on the checkride.

According to 14 CFR 91.307, a parachute is not required whenperforming spins and other flight maneuvers required by the reg-ulations for any certificate or rating.

�Do not spin this aircraft. If the aircraft does enter a spin it will return to earth without further attention on the part ofthe aeronaut.� � first handbook issued with the Curtis-Wright flyer

Randy is a private pilot. On one of his recent cross-countryflights, he ended up returning later than he expected, aftersunset. Although he was in VFR conditions, he became dis-oriented and put the airplane into an unusual attitudebefore regaining control. He approaches you, shaken by theexperience, and he asks if you would be willing to give himpractice in more unusual attitude recoveries, includingspins. You have a Cessna 172 available in which you canperform spins if it's loaded within the utility portion of theenvelope.

If you start Randy’sspin training bygoing out to thepractice area andputting the airplane

into a two-turn spin with no preparation, you may only frighten Randymore. Begin the training with a ground discussion on spin entries andrecovery procedures. You should add to this some discussion of spin aero-dynamics as well, depending on how long it has been since Randyreceived his private certificate.

When Randy has a clear understanding of spin entry, spins and spinrecovery techniques, start the flight with slow flight and power-on andpower-off stalls before progressing to incipient spins, and finally, fullydeveloped spins. Do not wait until evening to simulate the conditionsRandy encountered on his recent flight. Even though he may gain somebenefit from flying again in similar conditions, actual spin practice atnight, though legal, may not be prudent.

A progression from known to unknown maneuvers builds upon theknowledge that Randy already has and lays a solid foundation for skill development.

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As you teach spins, much of your emphasis should be on spin avoidance. Unintentional spins may occur becausethe pilot is distracted from flying the airplane — that is, failing to pay attention to the airplane’s attitude and air-speed. Most of these occur in the base to final turn. Pilots will attempt to recover from an overshoot of theextended runway centerline with the rudder. When the airplane begins to overbank as a result of the use of therudder, the pilot reacts with opposite aileron. When the nose drops as a result of these actions, the pilot reactswith back elevator. The result: a crossed-control, stall-spin accident that is usually fatal due to the airplane’s prox-imity to the ground. Because a stall must occur before a spin develops, many of the same distraction exercisesused for stall-avoidance training can be used in spin-avoidance training.

The following step-by-step procedure can serve as your basis for demonstrating the aerodynamic principles ofslow flight to your students.

1. Assign a heading and an altitude. Have your student reduce power and slow to an airspeed just above thestall speed, using trim as necessary.

2. Have your student maintain heading and altitude with the stall warning device activated.

3. Demonstrate the effect of elevator trim, using neutral and full nose-up settings, and rudder trim.

4. Point out the left-turning tendency and rudder effectiveness.

5. Emphasize how right rudder pressure is necessary to center the ball in the turn coordinator and maintainheading.

6. Release the rudder and advise the student to observe the left yaw.

7. While at the low airspeed, have your student enter left and right turns without using the rudder pedals, todemonstrate adverse yaw.

8. Demonstrate flap extension and retraction, and point out the changes in stall speed.

According to Stall and Spin AwarenessTraining (AC 61-67C), spin avoidancetraining should consist of stalls andmaneuvering during slow flight usingrealistic distractions. Performance isunsatisfactory if you must take control ofthe aircraft in order to avoid a fully devel-oped spin. Several scenarios for providingrealistic distractions to your students havebeen covered in this lesson. For moreideas, consult AC 61-67C.

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"Where would you landif the engine failed?"


Your student, Jenny, asks you why the air-plane she flies isn't approved for spins, but asimilar one that a friend flies is approved.You decide this is a great opening to discusshow airplanes are designed for different pur-poses, as well as how minor differences indesign can have a great impact on why oneairplane can recover predictably from spins,and others cannot.

Most Cessna 172s may be used for spin train-ing if certain conditions exist. The airplanemust be loaded so that its CG falls within theenvelope reserved for operations in the util-ity category. The airplane typically must beloaded so there are no passengers in the rearseat, or baggage in the aft compartment.

Pitts are widely known as high-performanceaerobatic airplanes. Various Pitts are availablefrom the factory, or as home-built kits. Bothare the result of a long history of growth fromCurtis Pitts’ original designs in the 1940s.Incredibly light power loading (6.4 lbs./hp.)and a sturdy biplane configuration, combinedwith symmetrical airfoil wings and invertedoil systems, make this airplane capable of per-forming complex aerobatic maneuvers.

The Cirrus SR20 has not been tested or certified for spins orspin recovery characteristics, nor has it been certified as spin-resistant. However, the stall characteristics of theSR20 make accidental entry into a spin extremely unlikely. The CAPS (Cirrus Aircraft Parachute System) was usedfor certification to FAR part 23 as an Equivalent Level of Safety.

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If you listen to pilots hangar fly, you may hear a number of differentstories regarding how to recover from a spin. If you look in an air-plane's POH, you'll find a definitive answer. In the absence of a man-ufacturer's recommended procedure, the FAA has outlined a basicspin recovery procedure that can be followed.

The FAA recovery procedure is:

1. Reduce the throttle to idle.

2. Position the ailerons to neutral.

3. Apply full opposite rudder against the rotation.

4. When the rotation slows, briskly move the elevator forward toapproximately the neutral position.

5. After the spin rotation stops, neutralize the rudder.

6. Begin applying back-elevator pressure to raise the nose to levelflight.

Exercise caution when applying aft elevator pressure during therecovery, to avoid a secondary stall. Also, be careful to avoid exces-sive airspeed buildup which could cause you to exceed the designlimit load factor during recovery.

All of these steps have their basis in how an airplane tends to reactto certain control inputs during a spin. Full power, for example, maybring the nose up and flatten the spin. In general, using oppositeaileron also flattens the spin, while aileron into the turn tends totighten the spin. Full rudder deflection should be used, and the air-plane may not stop rotating for a couple of turns. Recovery from thestalled condition occurs last, as elevator input before this point mayalso tighten the spin.

CG location is also important in spinrecovery. An accident involving a BeechBaron is a good example. The Baron wasloaded four inches aft of the CG limit.When the Baron's pilot flew into heavyturbulence at altitude, the airplane stalledand spun in. Investigators theorized thepilot could not recover from the flat spinthat developed due to the aircraft loading.

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Maneuvering SpeedYou can build in basic concepts to help yourstudents understand maneuvering speed (VA)and apply it to flight operations.

Maneuvering speed (VA) is often poorly under-stood. To help ease the learning process, youmay want to begin by covering the basics ofload factor then segue into a discussion of howit relates to maneuvering speed. Below is anexample of how you can model your lesson:

Have your students consider an airplane fly-ing in straight-and-level flight at 97 knots.Then ask the students what would happen ifthe pilot abruptly pulled back on the yokeand induced a severe load on the airframe.Your students should note that as the loadincreases so does the stall speed, and as the load approaches two Gs, the airplane nears a stall.

Ask them what would happen if the loadwere increased further. If they do notknow, show them how the airplanewould stall causing the load to decrease,and allowing the airplane to unloaditself. The stall would prevent the pilotfrom inducing a load greater than two Gs.

Now, take the discussion one step fur-ther. Talk about the maximum structurallimits for airplanes, and have your stu-dents consider an airplane with a maxi-mum load of four Gs. Ask them if itwould be possible for the airplane flyingat 97 knots to exceed the four-G loadlimit. Because the airplane would stall attwo Gs, they should note that the loadlimit could not be exceeded at this air-

speed.

Many students get confused when considering how maneuvering speed varies with aircraft weight. Point out thatthe above discussion was based on the published stall speed of the airplane, which is given at maximum certifi-cated weight. If an airplane weighs less, it will stall at a lower than published stall speed and thus have a lowermaneuvering speed.

One relationship that you need to thoroughly explain to your students is that between gross weight andmaneuvering speed. Though some of your students will easily digest this relationship by studying the formu-las involved, many students have difficulty with math. For them, you can describe the theory using non-math-ematical concepts and examples. These students may understand the mathematical processes better if theycan visualize that the more an aircraft weighs, the higher its stall speed, and, therefore, the higher its maneu-vering speed.

REVIEW: Maneuvering Speed

Design maneuvering speed (VA) — the maximum speed at whichyou can use full, abrupt control movement without overstressingthe airframe

• Maneuvering speed is based on the aircraft’s gross weight. Generally, VA indicated in the POH is for the aircraft’s maxi-mum gross weight, and the value decreases as aircraft weight decreases.

• A full, abrupt control movement at VA generates the maxi-mum amount of lift possible without exceeding the limit load factor. The aircraft stalls rather than incurring structural damage.

• Though VA is not marked on the airspeed indicator, you’ll find it on a placard in the cockpit, or listed in the POH.

�The course of the flight up and down was exceedingly erratic, partly due to the irregularity of the air, and partly due tolack of experience in handling this machine.� � Orville Wright

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An airplane’s stall speed varies according to its weight.

First find the ratio of the aircraft's current weight to itsmaximum gross weight. If max gross weight is 2,400 lbs.,and you’re flying at a weight of 1,800 lbs., you’re at 75%of max gross weight.

Stall speed is equal to the published VS multiplied bythe square root of the current weight's ratio to max grossweight.

For example, if your C-172 has a VS of 51 knots, multiply51 by the square root of .75 to get the new stall speed atthe given weight. In this case, the stall speed is 44.2knots.

Maneuvering speed equals this stall speed multiplied bythe square root of the limit load factor.

If you take 44.2 knots, and multiply it by the square rootof 3.8, which is 1.95, this equals 86.2 knots, which is themaneuvering speed for the C-172 at 1,800 lbs. You mayalso take the square root of the weight ratio and multi-ply it by the published VA.

Though you may introduce maneuvering speed as aspeed for turbulence penetration, as well as one forperforming maneuvers, you may find some pilots haveforgotten this concept. They may remember maneuver-ing speed as a factor only in performing maneuvers forthe practical test. Therefore, it may be worthwhile toreview other situations where this airspeed is impor-tant, and help them make their flights safer and morecomfortable.

The application of VA for turbulence penetration is to:

1. Disconnect the autopilot.

2. Slow to below VA.

3. Maintain a level flight attitude to the extent possible.

Max is flying his airplane IFR through an area wherethere have been reports of embedded thunderstormactivity. Though he has lightning detection and radarequipment on board, he still manages to find himselfinside a cell. At this point, he could panic, and lockhimself on the controls, fighting to stay upright. Or, hecan prevent a control input which might overstress theairplane, by keeping the controls unloaded.

Simply reacting to unusual attitudes by forcing the air-plane immediately in the other direction can impose structural loads severe enough to cause damage or airframefailure if maneuvering speed is exceeded. However, most airplanes can survive encounters with severe and evenextreme turbulence, but this depends, in part, on the actions of the pilot.


Brenda is taking some friends on their first ride in asmall airplane. One of them expresses some anxietyabout turbulence. Brenda tells them that the afternoon iswarm, and the ride might get a little rough. She couldplan, however, on cruising at a reduced speed, such asmaneuvering speed. You can teach your students to slowthe airplane to give passengers a smoother ride. If youhave them imagine the airplane as a boat, and the airthey fly through as a body of water, they can visualizehow slowing the airplane down can cause them to ridethe air with fewer jolts.

SummaryYou can accomplish this goal by having well-developedlesson plans and a variety of examples in your repertoireto engage your students. By applying concepts immedi-ately to the flying they do every day, you can help themgain insight into why they are learning about aerodynamics.

�Aeronautics was neither an industry nor a science. It was a miracle.� � Igor I. Sikorsky

Activities

I. Select the choice(s) that complete the sentence or answer the question for the following items:

1. A good question is one that:

A. requires a simple yes or no answer.

B. forces your student to think critically about a given situation.

C. should not take much thought and practice to create.

D. requires your student to apply theory and proper procedures to come up with a good answer.

AOPA

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2. What factors affect lateral stability?

A. Dihedral

B. Keel effect

C. Horizontal stabilizer

D. Weight distribution

3. Under what conditions should you not exceed VA?

A. Turbulent air penetration

B. Steep turns

C. Takeoff

D. Chandelles

4. What surfaces on an airplane, in addition to the wings, produce lift?

A. Propeller

B. Spoilers

C. Horizontal stabilizer

D. Vertical stabilizer

II. 5. Indicate the correct order the procedure for recovering from a spin.

A. When the rotation slows, briskly move the elevator forward to approximately the neutral position.

B. Begin applying back-elevator pressure to raise the nose to level flight.

C. Reduce the throttle to idle.

D. Apply the full opposite rudder against the rotation.

E. After the spin rotation stops, neutralize the rudder.

F. Position the ailerons to neutral.

III. 6. Which realistic distraction might you use that could cause your student to stall the airplane while on the departure leg of the traffic pattern?

A. Have your student call for a weather briefing.

B. Have your student change the radio frequency, as though he was just called by the tower.

7. Which realistic distraction might you use that could cause your student to stall the airplane while on thecrosswind leg of the traffic pattern?

A. Instruct your student to reset the DG.

B. Instruct your student to reprogram the GPS waypoints.

8. Which realistic distraction might you use that could cause your student to stall the airplane while on thedownwind leg of the traffic pattern?

A. Tell your student to reach back and grab the A/FD to check pattern altitude.

B. Tell your student to reach back and check the A/FD to see what airport you're on downwind for.

9. Which realistic distraction might you use that could cause your student to stall the airplane while on thebase leg of the traffic pattern?

A. Instruct your student to perform the final landing checklist.

B. Instruct your student to grab the airplane’s landing distance performance chart.

10. Which realistic distraction might you use that could cause your student to stall the airplane while on thefinal approach leg of the traffic pattern?

A. Let your student know they’re on final.

B. Have him identify an aircraft on the taxiway.


The Exam

Log in to CFI Renewal Online and review the lesson. Complete online the exercises that you just studiedhere. Then, you can take the exam for Teaching Aerodynamics. Make sure you are familiar with theserequirements before taking the exam.

Activity Answers

1. B, D

2. A, B, D

3. A, B, D

4. A, C, D

5. C, F, D, A, E, B

6. B

7. A

8. A.

9. A

10. B

L03 Teaching Aerodynamics

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Transcript of L03 Teaching Aerodynamics