maneuversflight notes.pdf

Maneuvers and Flight NotesCopyright Flight Emergency & Advanced Maneuvers Training, Inc. dba Flightlab, 2009. All rights reserved.

For Training Purposes Only

General Briefing

Anxiety!!!

If youve never flown aerobatics (or have hadsome bad experiences in the past), anxiety isnatural. Sometimes people are anxious aboutsafety, sometimes about how well theyllrespond when the instructor places the aircraft inan upset condition. Anxiety disappears as youlearn to control the aircraft. We wont take youby surprise (well, not immediately). Well teachyou how to follow events so that surprisesbecome manageable.

Even so, there may be times when you feel thattoo much is happening too fast. Thats notentirely bad: it shows that youre pushing theboundaries of your previous training. As yougain practice youll find that the aircraftsmotions become easier to follow and tracking thehorizon becomes less difficult. Your comfortlevel then quickly rises.

But if you feel confused or unsafe at any time, letus know.

Airsick?

The same goes if you begin to feel airsick. Youprobably dont learn well with your head in abag, so dont hesitate. Let us know immediatelyso that we can modify the program and flightschedule for your comfort. If youre new toaerobatics, youll discover that airsickness hasnothing to do with the previous number oftrouble-free hours in your flying career.Resistanceor habituation, depending on yourtheoryusually arrives, but it takes time.

Most of our maneuver sets call for repetitions,but we can easily stretch those out over severalflights, if you prefer. Thats easier on theinstructor, as well. If youre concerned aboutairsickness, a good resistance-building techniqueis to fly somewhat aggressive lazy-eights (whichyou might remember from the CommercialFlight Test) in a light aircraft a few days beforeyou fly with us. Lazy-eights supply the pitchingand rolling motions and variations in g forceyour body must adjust to. But stop at the first

feelings of discomfort. Becoming sick does nothelp you adapt faster.

Dont fly aerobatics on an empty stomach. Eat!You look thin! Drink plenty of water, especiallywhen the outside temperature is high.Dehydration reduces g tolerance.

Research done with persons subject to motionsickness suggests what youve perhaps alreadyobserved: People who report that theyverecovered from feelings of nausea can remainhighly sensitized to vestibular disturbance forhours afterwards. Thats why those airsickpassengers who announce with relief that theyrenow feeling much better often spontaneously re-erupt as you start to maneuver into the trafficpattern. The temporary disappearance ofsymptoms doesnt necessarily mean the battle isover.

What to Read: Ground School Texts

The texts youll receive (or download) alongwith the Maneuvers and Flight Notes cover awide range of subjects, giving backgroundmaterial you can go into, more or less deeply,according to your interests. Our program is bestfor pilots who not only want to gain aerobaticand upset recovery skills but who also have abroader curiosity about the principles of aircraftresponse. Skills can be learned quickly, butsatisfying curiosity takes timebecause, ideally,curiosity grows. (And the subject of airplanes isvast.) You may find it helpful to read at least theground school selections Axes and Derivativesand Two-Dimensional Aerodynamics beforethe first flightdont worry if you dont have atechnical background; theyre not as nerdy asthey sound. Treat the ground school texts as along-term resource, not a short-term burden.

What to Think About

Think about searching out the basic relationshipsthat determine aircraft behavior. At very least,you need to examine two areas. The two ground

Maneuvers and Flight Notes

Bill Crawford: WWW.FLIGHTLAB.NET2

school selections mentioned above provide anintroduction.

You need to understand how an aircraftresponds to its own velocity vector, and to its liftvector. If you know where the velocity vector ispointed (relative to the aircrafts fixed axes), andwhere the lift vector is pointed (relative to thehorizon), you know how a stable aircraft is likelyto behave. This is the core of our presentation ofstability and control.

You also need to understand the nature of thepressure patterns over the surface of the wing:how those patterns originate and how theymigrate as angle of attack changes. This isespecially important as the aircraft approachesthe stall, because pressure patterns determine theavailability of control.

Where to Look

Unusual-attitude training should take bothoutside and inside attitude references intoaccount. Aerobatic pilots look outside first. Wefly in reference to the real horizon, not theartificial one. Of course, thats because we flyaerobatics only in VFR conditions; but even ifwe have an aerobatic-friendly attitude indicator,the real horizon provides much betterinformation.

Unlike aerobatic pilots, many IFR pilots tend tolook inside first, even in good weather. If controlof aircraft attitude is a reflexive, heads-in activityfor you, you may need to reacquaint yourselfwith the information out the window. Partlybecause of the essential role peripheral visualcues play in spatial awareness, thats where theinformation is best during unusual attitudes.Physiological correlation between what yourbody feels and what your eyes see also happensmuch faster when youre looking outside. Thenbegin to connect what youve learned aboutaircraft behavior from looking out with thesymbolic attitude information available withinthe cockpit. Youll find that the symbolicinformationwhich unfortunately lacks theperipheral cues we primarily rely on to perceiveour motion within the worldbecomes easier tointerpret when you can associate it with attitudesand flight behaviors youve already seen outside.

One of the drawbacks of simulator trainingprograms for unusual attitudes is that this

valuable building block, outside/inside-learningprocess may not occur with sufficient repetitionfor the benefits to sink in. Pilots mightdemonstrate maneuvering proficiency in specific,directed tasks, but still have limited attitudeawareness.

Rudder Use

We want you to experience and understand theeffects of rudder deflection on aircraft responseat high angles of attack. While the same basicaerodynamic principles apply in swept-wingaircraft as in our straight-wing propeller-driventrainers, in practice large aircraft and swept-wingdynamics are different, and more limited rudderuse is recommended. On matters concerningrudders, search the Internet for BoeingCommercial Airplane Group Flight OperationsBulletin, May 13, 2002. Also Airbus FCOMBulletin, Use of Rudders on Transport CategoryAirplanes, March 2002.

Standard Procedures

Clear the airspace before eachmaneuver.

Acknowledge transfer of control.

Dont hesitate to apply your own CRMprocedures and call-outs as you thinkappropriate to the safety of the flight.

Dont fret about your mistakes.Mistakes are your best source ofinformation. Bracket your responsesuntil you zero-in on the correctprocedure.


Bill Crawford: WWW.FLIGHTLAB.NET 3

Maneuver Sets and Lesson Plan

Because certain maneuvers use up motiontolerance more rapidly than others, and personaltolerance varies, your maneuver sequence mightbe different than the standard schedule. Youllalso repeat some maneuvers when you fly thesecond aircraft.

The core lesson is upset recovery, but we teachmuch more than recovery procedures, as youllsee when you begin reading. The Flight Notesbelow each maneuver description coverfundamental aerodynamic principles. Togetherwith the ground school presentations andsupporting texts, they describe aircraftcharacteristics youll observe and techniquesyoull learn. They attempt to expand your frameof reference with examples drawn from differentaircraft types. Theyre part narrative, partexplanation, and sometimes a warning.

The information in the Flight Notes is obviouslymore than an instructor could give during aflight, and much more than a student could beexpected to take in. Chances are we wont havetime to cover every detail, nor will every detailapply to your type of flying. Dont let thematerial overwhelm you. Familiarize yourselfwith the relevant Flight Notes before each sortie,as you think best. When you review the notesafter the flight, youll find them much easier toabsorb, because you can connect them with whatyouve just done. The ground school textsreinforce the Flight Notes and add furtherinformation.

We use boldface italics to emphasize importantconcepts. (Boldface in the procedure descriptionreminds instructors of points to emphasize insetting up and carrying out maneuvers.)

Heres how the maneuvers break down intogeneral categories:

Natural Aircraft Stability Modes, Yaw/RollCouple:

1. Longitudinal & Directional Stability, SpiralDivergence, Phugoid

2. Steady-Heading Sideslip: Dihedral Effect &Roll Control

High Angle of Attack (Alpha):

3. Stall: Separation & Planform Flow (Wing tuftobservation)

4. Accelerated Stalls: G Loads & BuffetBoundary, Maneuvering Stability

5. Nose High Full Stalls & Rolling Recoveries6. Roll Authority: Adverse Yaw & Angle of

Attack, Lateral Divergence7. Flap-Induced Non-convergent Phugoid

Roll Dynamics:

8. Nose-Level Aileron Roll: Rolling FlightDynamics, Free Response

9. Slow Roll Flight Dynamics: ControlledResponse

10. Sustained Inverted Flight11. Inverted Recoveries12. Rudder Roll: Yaw to Roll Coupling

Refinements and Aerodynamics:

13. Rudder & Aileron Hardovers14. Lateral/Directional Effects of Flaps15. Dutch Roll Characteristics16. CRM Issues: Pilot Flying/Pilot Monitoring17. Primary Control Failures

High-Alpha/Beta Departures:

18. Spins

Additional Basic Aerobatic Maneuvers:

Loop, Cuban Eight, Immelman, Hammerhead,Slow Roll, Point Roll



First Flight

1. Longitudinal & DirectionalStability, Spiral Divergence,Phugoid

2. Steady-Heading Sideslip:Dihedral Effect & Roll Control

3. Stall: Separation & PlanformFlow (Wing tuft observation)

4. Accelerated Stalls: G Loads &Buffet Boundary, ManeuveringStability

5. Nose High Full Stalls &Rolling Recoveries

6. Roll Authority: Adverse Yaw& Angle of Attack, LateralDivergence

7. Flap-Induced Non-convergentPhugoid

8. Nose-Level Aileron Roll:Rolling Flight Dynamics, FreeResponse

Possible:

9. Slow Roll Flight Dynamics:Controlled Response

On Return:

17. Primary Control Failures

Second Flight

9. Slow Roll Flight Dynamics:Controlled Response

10. Sustained Inverted Flight

11. Inverted Recoveries

12. Rudder Roll: Yaw to RollCoupling

13. Rudder & Aileron Hardovers

14. Lateral Effects of Flaps

15. Dutch Roll Characteristics

Possible:

19. Spins

Basic Aerobatic Maneuvers

On Return:

17. Primary Control Failures

Third Flight

Review Maneuver Sets 9-12

16. CRM Issues: PilotFlying/Pilot-Not-Flying

18. Spins

Basic Aerobatic Maneuvers

On Return:

17. Primary Control Failures (asnecessary)

Fourth Flight

Review and additional aerobaticmaneuvers to be determined.

These maneuvers are for training purposes in appropriate aircraftonly. Follow the procedures and obey the restrictions listed in

your pilots operating handbook or aircraft flight manual.



Trimming for Airspeed in Level Flight

We usually trim an aircraft in climb for VY, best rate of climb, or perhaps a bit faster to preserve the view overthe nose and to keep engine temperatures from rising. In descending from altitude for landing, we might trimfor a comfortable descent rate. In the pattern we trim for pattern speed based on habitual power settings, andthen for our landing reference speed.

But we usually dont trim for a particular airspeed in cruise. Instead, we level off at a certain altitude,accelerate a little while nudging the trim forward, and then pull back the power to cruise setting. Last, wefinal-trim to zero out the control force necessary to maintain level flight. Then we take the airspeed we get.

Sometimes in flight-testing, or in our program, youll want to start a maneuver from a specific, trimmed,level-flight airspeed. Heres what you do:

Bring the aircraft to the required altitude

Set the power to the approximate value dictated by experience. Of course, dont chase airspeed withlarge power changes. Just get close.

Use pitch control to bring the aircraft to the desired airspeed.

While holding airspeed constant, use power to center the VSI at zero climb/descent rate.

Trim out the control force.

Note that pitch controls airspeed, power controls the aircrafts flight path angle relative to the horizon.



1. Longitudinal & Directional Stability, Spiral Divergence, Phugoid

Flight Condition: Upright, free response in roll/pitch/yaw.

Lesson: Aircraft behavior when disturbed from equilibrium flight.

Procedures:

Longitudinal Stability: Stick force, Phugoid

Static stability: On the climb to the practice area, trim for VY. Observe longitudinal (pitch axis) stickforces needed to fly at airspeeds greater than or less than trim. Assess force gradient. Look forcharacteristics due to friction.

Simulate the effect on longitudinal stability of moving center of gravity aft: Trim, pitch up to fly 10knots slower than trim, hold speed while instructor slowly trims nose up. Note how stick forcedecreases (simulating a decrease in stability), disappears (simulating neutral stability), and thenreverses (simulating static instability).

Dynamic stability: Use pitch up and stick release to demonstrate phugoid. Observe period, amplitude,damping.

Directional Stability:

Low cruise power, airspeed white arc.Enter flat turn with rudder, while keeping wings level with aileron. Observe build up of pedal forcesto full deflection.Quickly return pedals and ailerons to neutral; observe overshoots and damping.Look for characteristics due to friction.

Lateral Stability: Spiral Mode

Power and trim for low cruise.Enter a 10-degree bank angle, return controls to neutral and observe response in roll. Note appearanceof phugoid. Repeat bank with additional 10-degree increments until onset of spiral departure.Look for asymmetries by repeating to the opposite side.

Allow spiral mode to develop as consistent with comfort and safety.Roll wings level; release controls; observe recovery phugoid.

Reduce entry airspeed and observe the increase in roll amplitude versus time.

Knife-edge recovery:Low cruise power, airspeed white arc.Roll knife-edge.Immediately release controls and observe response.



Flight Notes

Well start by exploring how an aircrafts inherent stability determines its free response when disturbedfrom equilibrium. Free response is what happens when the pilot stays out of the control loop. Its easier tounderstand the sources of an aircrafts complex, self-generated motions when you can break them downinto simpler, free response modes around each axis. Usually, a moment generated around one axisproduces some form of response around another. From the standpoint of unusual-attitude training, if youunderstand and can anticipate an aircrafts basic moves, managing the control loop properly to maintainor to re-establish control becomes closer to second nature.

In aircraft with basic cable-and-pushrod reversible controls, like our trainers, free response can depend onwhether the stick and rudder pedals are held fixed or literally left free so that the control surfaces areallowed to streamline themselves to changes in airflow. Irreversible, hydraulically powered controls arealways effectively fixed. See FAR Parts 23 & 25.171-181 for stability requirements.

Longitudinal Static and Dynamic Stability

Well use some maneuvers borrowed fromflight test procedures to look at basic aircraftcharacteristics. Were going to adapt theprocedures to our own purposes, take a generalapproach, have fun, and not worry about alwaysdoing things with the real precision thatsrequired to gain accurate data points in actualflight test. A rough narrative follows.

Heres the deal on longitudinal static stability,as required by Part 23.173: with the airplanetrimmed the characteristics of the elevatorcontrol forces and the friction within the controlsystem must be as follows: (a) A pull must berequired to obtain and maintain speeds below thespecified trim speed and a push required toobtain and maintain speeds above the specifiedtrim speed.

On the way to the practice area well observethe Part 23.173 requirement. Well trim theaircraft and then observe the stick forcesnecessary to fly at slower and faster airspeeds(a.k.a. angles of attack) without retrimming.When we release the force, the nose initiallypitches toward the trim angle of attack. Thisinitial tendency is what we mean by positivestatic stability (static refers to the initialtendency, dynamic refers to the tendency overtime). The more force we have to apply todeviate from trim, the greater the stability. Wecan increase static stability (and thus the stick

forces needed to deviate from trim) by movingthe center of gravity forward. We decreasestability (and decrease the forces) by moving itaft. We can fake the effect using trim, asdescribed in the Procedures, above.

Youll observe that the push force required tohold the aircraft 10 knots, say, faster than trim isnoticeably greater than the pull force needed tohold it 10 knots slower. Thats because thedynamic pressure generated by the airflowyoure holding against is a function of velocitysquared, V2. The illustration below suggests howstick forces vary with speed. The force is zero attrim speed.

Con

trol F

orce

, FS

0

Pull

Push

Airspeed

Stick Force Gradient

Trim Speed



Phugoid: Next, well pitch up about 45 degreesor more, slow down and nibble at the stall, thenreturn the stick to its trim position and let go.(This is a more aggressive entry than actuallyrequired to provoke a phugoid, but its a goodattention-getter during unusual-attitude training.)The nose will start down, again indicatingpositive static stability, but then go below thehorizon. Velocity will increase past trim speed,and the nose will begin to rise. Although theaircrafts attitude varies, its angle of attackremains essentially constant. The aircraft willpitch up, slow, pitch down again, speed up, andthen repeat this up-and-down phugoid cycle anumber of times. It will gradually converge backto its original trimmed state. (Had we simply letgo of the stick instead of carefully returning it tothe original trimmed position, control systemfriction might have produced a different elevatorangle and a different trim. That, in turn, couldsuperimpose a climb or a dive over the phugoidmotion.) Your instructor will point out that theamplitude of each pitch excursion from leveldecreases (indicating positive damping and thuspositive dynamic stability) while the period (timeto complete one cycle) remains constant at agiven trim speed. The period is quite long, so thephugoid is also referred to as the long periodmodeand the faster you fly the longer theperiod. Damping in the phugoid comes from thecombined effects of thrust change and dragchange as the aircraft alternately decelerates andaccelerates as it climbs and descends.

Youll need right rudder at the top of thephugoid to counter the slipstream and p-factorand keep the nose from yawing, and maybe someleft rudder at the bottom. You might need aileronto keep wings-level, as wellbut dontcontaminate the phugoid with inadvertentelevator inputs.

Positive Longitudinal Dynamic Stability

Dis

plac

emen

t

Time

Period

Amplitude

Period/Time to subside = damping ratio,

Time to subside

Equilibrium



Directional Stability

Flat Turn: The next maneuver is the basicflight test for static directional (z-axis) stability.When you depress and hold a rudder pedal,causing the nose to yaw along the horizon, yougenerate a sideslip angle, . Sideslip creates aside force and an opposing moment. Notice theincreased pedal force necessary as rudderdeflection increases. For certification purposes,rudder pedal force may begin to grow lessrapidly as deflection increases, but must notreverse, and increased rudder deflection mustproduce increased angles of sideslip. The ruddermust not have a tendency to float to and lock inthe fully deflected position due to a decrease inaircraft directional stability at high sideslipangles as the fin begins to stall. If it did, theaircraft would stay in the sideslip even with feetoff the pedals. (Things could be dicey if thepedal force needed to return a big rudderexceeded the pilots strength. Many well-knownaircraft had rudder lock problems during theirearly careers, including the DC-3 and the earlyBoeing 707, and the B-24 Liberator bomber.)

A given rudder deflection produces a givensideslip angle, but the force required rises withthe square of airspeed. So we wont have to workas hard if we pull the power back to keep thespeed down.

When you release or quickly center the pedals,the now unopposed side force causes the aircraftto yaw (weathervane) into the relative wind. Inour jargon, the directionally stable aircraft yawsits plane of symmetry back into alignment withthe velocity vector. This initial tendencydemonstrates positive static directional stability.Weve entered a dynamic state, as well.Momentum takes the nose past center, whichgenerates an opposing side force that pushes itback the other way. The nose keepsovershooting, but the amplitude of thedivergence decreases each time. This timehistory indicates positive dynamic directionalstability. You might notice an increase indamping when you return the rudders positivelyto neutral and hold them fixed, instead of lettingthem float free. However, this behavior alsodepends on the amount of friction in the ruddercontrol circuit.

Notice that the aircraft tries to roll in thedirection of the deflected rudder, and that youhave to apply opposite aileron to keep the wingslevel. This is caused by a combination ofdihedral effect (an aircrafts tendency to rollaway from a sideslip angle, , a response wellexamine presently), and roll due to yaw rateinwhich one wing moves faster than the other andproduces more lift. An aircraft with reduceddirectional stability may yaw faster in responseto rudder deflection than will a more stable type,and go to a higher , and consequently needmore opposite aileron. (Youll see a differencebetween the Zlin and the SF 260 in this regard.)

Finally, note that when you apply aileronagainst the roll, youre also applying anadditional pro-rudder yaw moment, this timecaused by the adverse yaw that occurs when theinto-the-turn aileron goes down. (Therere othermoments in the mix we wont worry about.)

Stabilizing yaw moment.

V

v v is the Y-axis component of the aircrafts velocity vector, V. v = V sin

X

Directional Stability



Spiral Mode

When you enter a shallow bank and positivelyreturn the controls back to neutral (so thatunintended deflections or control system frictiondont taint the result) the aircraft should slowlystart to roll level after a few moments. Theaircrafts velocity vector (for a definition, seeground school text Axes and Derivatives) has acomponent of motion (sideslip) toward the lowwing, which leads to a wings-level rollingmoment due to dihedral effecta responsereferred to as lateral stability. The aircraftslateral stability provides positive spiral stability.Sideslip also produces a yawing tendency, butdihedral effect predominates at smaller bankangles.

The outside wing in the turn is moving fasterthan the inside wingthats a yaw rate. As youadd bank increments youll find a pointif theatmospheres not too turbulentwhere bankangle remains constant (neutral spiral stability).The rolling moments produced by dihedral effectand roll due to yaw rate are now equal andopposite. (Again, therere other moments in themix, but their contribution is minor.)

At some point the aircraft will likely begin abanked phugoid, just like the phugoids weveobserved, but tipped on its side. The aircraft willbring its nose up and down as it turns. Hands off,the aircraft retains a constant angle of attack,according to trim, regardless of pitch attitude orbank angle.

When we raise the bank angle further, but dontincrease lift by adding back stick, the aircraftslips increasingly toward the low wing. The yawrate builds due to the greater side force againstthe tail. Directional (z-axis) stability causes thenose to weathervane earthward in a descendingarc. Now roll due to yaw rate predominates overthe opposite rolling moments, and sends theaircraft into the unstable spiral mode

Test pilots typically place an aircraft in a givenbank angle, center the ailerons (or bank theaircraft with rudder while holding the aileronsfixed), and then time the interval required toreach half the bank angle for the spirally stablecondition, or double the bank angle for theunstable. Its important that control surfaces are

positively centered during these tests, becauseany residual deflection caused by control systemfriction can create an apparent difference inspiral characteristics. (Friction confuses thepicture when youre trying to figure out how anaircraft behaves. Friction in the elevator systemmakes you think longitudinal stability is differentthan it is; friction in the ailerons that preventsthem from returning to center automaticallywhen released gives you a roll rate that shouldntbe there. Normally, youd accommodate to suchthings without really being aware of the extracontrol inputbut here were paying attention!)

The coefficient of roll moment due to yaw rate,Clr, goes up with coefficient of lift, CL, so itsmore pronounced at low speeds, where andcoefficient of lift are high. And for a given bankangle, yaw rate goes up as airspeed goes down.So youll double your spiral bank angle morequickly at lower entry speeds.

Finally, note that the ball stays essentiallycentered during a spiral departure. Thatsdirectional stability doing its job, unto the last.

Z axis

Effective lift less than weight results in a sideslip velocity component, v, and sideslip angle, .

v

Resulting yaw rate, r.

Roll moment due to yaw rate, Lr, greater than opposite roll moment due to sideslip, L.

Lr

L.

Sideslip Becomes a Spiral Dive When Dihedral Effect x Yaw Damping < Directional Stability x Roll Due to Yaw Rate



Phugoid Again

Recover from spiral dives by first rolling thewings level with the horizon. Now were back inthe more familiar wings-level phugoid. Noticehow the aircrafts positive static longitudinal (y-axis) stability initially brings the nose back tolevel flight. Youd normally push to suppress thephugoid as the nose comes level with thehorizon, but well again allow the aircraft to gopast level and progress through the first cycles ofthe phugoid mode.

Again, youll need right rudder at the top of thephugoid to counteract the slipstream and p-factorand keep the nose from yawing, and some leftrudder at the bottom. Jets and counter-rotatingtwins dont have this problem.

An aircrafts longitudinal stability comes fromits tendency to maintain a trimmed angle ofattack. As you ride through it, the attitudes,altitudes, and airspeeds change, but in a phugoidthe angle of attack, , remains basicallyconstant. The attitude excursions of ourconstant- phugoid remind us again that anaircrafts angle of attack and its attitude are twodifferent things. When displaced, aircraft returnto their trimmed attitude and airspeed by virtueof maintaining their trim angle of attackthroughout a cycle of phugoid motions. Inessence, pilots keep altitude pegged by keepingahead of the phugoid and damping its cyclethemselves. A power change provokes aphugoid, unless the pilot intervenes to smoothout the transition.

Well experience an increased g load asairspeed exceeds trim speed at the bottom of thephugoid. At a constant angle of attack, lift goesup as the square of the increase in airspeed. If wetrim for 100 knots in level flight (1 g) andmanage things so as to reach 200 knots (whichwe wont!), airspeed will be doubled and loadfactor will hit a theoretical 4 g. If we accelerateto 140 knots, thats a 1.4 increase in speed. 1.42= 2; thus a load factor of 2 g. (The actual factorcan be affected by the mass balance of theelevator, or the presence of springs or bobweights.) Well experience less than 1 g over thetop.

The phugoid shows us how a trimmed,longitudinally stable aircraft normally maintainsits speed if left to its own devices. After adisturbance, it puts its nose up or down, tradingbetween kinetic and potential energy, until iteventually oscillates its way back to trim speed(or to its trim speed band if control friction isevident). But the trade becomes solely potentialto kinetic when a bank degenerates into a spiraland, as weve seen, the bank angle becomes toosteep for the phugoid to overcome. Think of aspiral departure as a failed phugoid, in whichthe nose cant get back up to the horizon becausethe lift vector is tilted too far over.

What if an aircraft trimmed for cruise rollsinverted for some reason and the befuddled pilotjust lets go? Left unattended, the inverted aircraftwill pursue its trim by dropping its nose andreverse-phugoiding itself around in a rapidlyaccelerating back half of a loop (a split-s).Speed will rise until the structure maybe quits, orthe dirt arrives. Inverted, hands-off survivalprospects improve in the unlikely situation thatthe aircraft is at altitude but trimmed for slowflight. Trimmed for 70 knots with power forlevel flight, and then rolled inverted while thenose is allowed to fall, the Zlin will pull a 4-gsplit-s, hands-off on its trim state alone, using upsome 1,300 feet of altitude. Then it will playfullyzoom right back up into a normal but initiallyhigh-amplitude phugoid.



Knife-edge Free Response

After youve observed spiral characteristics,and learned to expect divergence following ahigh bank angle, knife-edge behavior mightsurprise you. Starting at knife-edge with the noseon the horizon, when the controls are released anaircraft with positive dihedral effect willgenerally roll upright and pitch nose-down (andthen eventually pitch up into a phugoid if youdont touch the elevator). The roll response hasbeen associated with the amount of keel areaabove the aircrafts c.g. Acting at differentlocations and in opposite directions,aerodynamic side force and gravity produce aroll couple. This wings-leveling couple, added tothat generated by dihedral effect, overcomes theopposing spiral tendencies caused by directionalstability and roll due to yaw rate.

If you enter knife-edge flight, or even just asteep bank angle, in a nose-high attitude,however, spiral tendencies will often dominate.Its fun to examine this by flying aggressivelazy-eights (linked wingovers) and observing

which moments win out when you let go of thestick and/or rudder at various points. Note thephugoid embedded in the maneuver as theaircraft climbs and descends.

Side force producesboth wings-level rollmoment and nose-down yaw moment.

Gravity actingthroughaircraft c.g.

Resulting roll.

Keel Effect



2. Steady-Heading Sideslip: Dihedral Effect & Roll Control

Flight Condition: Upright, crossed controls, high .

Lesson: Lateral behavior during sideslips.

Flight Notes

A directionally and laterally stable aircraft yaws toward but rolls away from its velocity vector whenthe vector is off the plane of symmetry. Those characteristics are the basic moves of directional andlateral behavior. In our steady-heading sideslips, well apply cross-controlsrudder in one direction andaileron in the othercausing the aircraft to fly with its velocity vector displaced from symmetry. Thecontrol forces necessary to prevent the aircraft from yawing and rolling in response to that displacement arethe reflection of its inherent stability. They tend to change with angle of attack, especially in the buffetboundary, where aileron effectiveness often deteriorates and the rudder takes on increasing importance forlateral control. In that regime, a pilot often displaces the velocity vector on purpose, to assist roll control.(He may not know thats what hes doing, but nevertheless...)

Pilots of flapless (usually aerobatic) aircraft are accustomed to using sideslips to control the descent tolanding. Its how they show off in front of the aircraft waiting at the hold line. If you rely on flaps fordescent, you may be rusty on aggressive cross-control slips. A little practice with them will improve yourability to respond to control system failures. You counter the rolling moment generated by anuncommanded rudder or aileron deflection by entering an opposing sideslip, modifying the sideslip asnecessary for turns.

Test pilots use steady-heading sideslips toevaluate an aircrafts lateral stability. That meansits tendency to roll away from the direction of asideslipin other words, to roll away from the

direction the velocity vector is pointed when thevelocity vector is not on the plane of symmetry.(The mechanics of lateral stability, or dihedraleffect, are explained in more detail in the ground

Procedures:

Power for speed in the white arc.Apply simultaneous aileron and opposite rudder to rudder stop.Aileron as necessary to maintain steady heading with no yaw rate.Maintain approximate trim speed. Aircraft will descend.Hold rudder/ release stick.Repeat in opposite direction.

Hold stick/ release rudder. Observe sequence of yaw and roll.

Hold sideslip. Pitch up and down to demonstrate y-wind-axis pitch/roll couple.

Possible Maneuver: Hold the sideslip and demonstrate over the top spin entry, with immediate, controlsneutral recovery.



school text Lateral-Directional Stability.)Steady-heading sideslips are also used to assessdirectional stability and rudder effectiveness bymeasuring the rudder deflection and pedal forceneeded to produce a given sideslip angle, .They can also be used to evaluate controlharmony and to set up the conditions forobserving Dutch roll. Wing-low crosswindlandings are steady-heading sideslips, so anaircrafts behavior in sideslips can limitcrosswind capability.

Pressing the rudder and yawing the aircraftcreates a sideslip angle between the aircraftsvelocity vector and its x-axis plane of symmetry,as illustrated to the right, below. This in turnproduces a rolling moment due to dihedral effect.Well evaluate the strength of this yaw/rollcouple at various sideslip angles by observingthe aileron deflection needed to counteract theroll and fly the aircraft at a constant, steadyheading, although sideways and wing-low.

Youll enter a steady-heading sideslip byapplying crossed controls: deflecting the rudderwhile adding opposite aileron to keep the aircraftfrom turning. Notice how the forces anddeflections increase as you move the controlstoward the stops. Under FAR 23.177(d), theaileron and rudder control movements and forcesmust increase steadily, but not necessarily inconstant proportion, as the angle of sideslip isincreased up to the maximum appropriate to thetype of airplane. the aileron and rudder controlmovements and forces must not reverse as theangle of sideslip is increased.

Do you notice any differences sideslipping tothe left or right, possibly caused by p-factor orslipstream?

Dihedral effect can depend on aircraftconfiguration. It can diminish with flapextension. This is important in connection withrudder hard-overs, because flaps lowercrossover speed, as youll see later.

When you release the stick while holdingrudder, the low wing rises due to dihedral effectand to roll due to yaw rate. Dihedral effect,strongest at first, decreases as the sideslip anglegoes to zero. Roll due to yaw rate, weak at first,increases as the yaw rate rises; then suddenlydisappears when the yaw damps out. Thecapacity to raise a wing with rudder alone, incase ailerons fail, is a certification requirementfor non-aerobatic aircraft, and this stick release isa standard flight-test procedure.

Aerobatic aircraft without much dihedral effect(such as the Great Lakes, or the Yak-52) oftentend not to roll toward level but to pitch down atstick release. An aircrafts pitching moment dueto sideslip may be nose-up or down, minimal orpronounced, different left or rightdependingon how propeller slipstream, fuselage wake, andthe downwash generated by the wing and flapsaffect the horizontal stabilizer. The combinationof longitudinal (pitch) and lateral (roll) forcesyou find yourself holding helps you anticipatehow aggressively the aircraft will respond onrelease. The Zlin is a great trainer in this respect.

X body axis

Angle of Attack () and Sideslip Angle ()

Angle of velocity vector, V, to xbody axis gives aircraft angle ofattack. Angle of velocity vector towing cord gives wing angle ofattack.

X-Z planeLift vector

Z body axis

Velocity vector, V, andsideslip angle, . Sideslipto the right.

V

V

X bodyaxis

Y bodyaxis

Left rudderproduces rightsideslip.



When the stick is released in a sideslip to the left(right rudder down, left aileron), the Zlin canaggressively pitch-up and roll right, thecombined motions leading to a sudden increasein the angle of attack of the right wingtip, and apossible tip stall. Much fun!

Swept-wing aircraft can build up large rollingmoments during sideslips, and mishandling canput even a large aircraft on its back. Sideslipangles are generally restricted to around 15degrees during flight test for transport aircraft.FAR 23.177(d) says that a Rapid entry into,and recovery from, a maximum sideslipconsidered appropriate for the airplane must notresult in uncontrollable flight characteristics.Rapid is a key word here, since a slow entry toand recovery from a sideslip keeps the aircraftsangular momentum under control.

Things get a little complicated now, and weapologize. Notice that when you first release therudder, while holding aileron deflectionconstant, the aircraft doesnt respond to theailerons and immediately start rolling. Watchhow the nose yaws and reduces the sideslipbefore the roll begins. The vertical stabilizerscenter of lift is above the aircrafts center ofgravity. As a result, the rudder deflection in asteady-heading sideslip actually produces anadded roll moment in the same direction as theailerons. (See Figure 17 in the ground school textLateral-Directional Stability.) Releasing justthe rudder eliminates this rolling momentcontribution, but replaces it briefly by a rollingmoment due to yaw rate as the aircraftstraightens out. (Did you get that?) Theimportant point is that only after the aircraftsdirectional stability substantially eliminates thesideslip will the ailerons start to dominate andthe aircraft roll. This really is less confusing witha hand-held model for demonstration, or in theaircraft where you can see things unfold.

Our trick of holding the ailerons in place whilereleasing the rudder allows us to keep the rollmoment due to aileron deflection fixed. We canthen observe the yaw as the aircrafts directionalstability realigns the nose with the velocityvector. We can observe the ramp-up in rollresponse and properly attribute it to thevanishing sideslip. This gives us a way to use a

steady-heading sideslip to demonstrate therelationship between sideslip and aileroneffectiveness. A sideslip can either work for aroll rate, or against it. For a given ailerondeflection, in an aircraft with dihedral effect,roll rate goes down when rolling into a sideslip(right stick, right velocity vector, say, as in thesideslip seen from above, illustrated on theprevious page). Such an adverse sideslip couldtypically happen in an aircraft with adverse yawand not enough coordinated rudder deflectionwhen beginning the roll. On the other hand,stomping on the rudder too hard while rollingwith aileron will skid the airplane anddemonstrate that a proverse sideslip, oppositethe direction of applied aileron, increases rollratein addition to sliding your butt across theseat. That stomp could be a useful trick foraccelerating roll response in an emergency, butin swept-wing aircraft could lead to a severeDutch roll oscillation. The fundamentalrelationship between sideslip angle (angle of thevelocity vector versus plane of symmetry) androll rate is something many pilots never reallygetmaybe because instructors think that therudder affects only yaw. But in a laterally stableaircraft, yaw just about always provokes a rollingmoment.

Roll couple for a given sideslip angle, , andaircraft configuration varies in directproportion to the coefficient of lift, CL. Thatscertainly the case with swept-wing aircraft, andat least apparently the case with straight-wing,although not to the same degree. (See groundschool text Lateral-Directional Stability.)

Roll due to yaw rate also varies directly withCL, as noted when we observed the spiral mode.When we fly steady-heading sideslips, we try toisolate dihedral effect by keeping the headingsteady and eliminating yaw rate. But theresalways a yaw rate when we enter and leave themaneuver, and of course sideslips and yaw ratesoccur together in turbulence. Their individualcontributions at a given moment can be difficultto sort out.

You can think of the deflected rudder (or anexisting sideslip) as setting the direction andinitial rolling tendency, and of the elevator asmodulating the rate through its control of CL.



This is easy to remember, because when youraise CL by pulling back on the stick, toward therudder, roll moment produced through dihedraleffect and roll due to yaw rate increases. Whenyou lower CL by pushing, the contributiondecreases. This relationship holds for bothstraight and especially for swept wings, althoughthe mechanisms and some details are different,as the ground school illustrates. It also worksupside-down; as long as you have positive g.You will see this when we do rudder rolls.

Or, if you prefer a more visceral terminology,put it this way: Hauling back and loading anaircraft increases yaw/roll couple; unloadingdecreases it. And thats not all unloading does,as well note more than once. Imagine thatyoure operating at an angle of attack highenough to reduce aileron effectiveness throughairflow separation, and high enough to disruptflow over the tail such that yaw-axis stability isreduced and a sideslip develops. Putting the stickforward and unloading will reattach the flow,bringing the ailerons back while also reducingthe sideslip-generated roll couple by reducingcoefficient of lift, CL. (Examples might be duringan immediate recovery from an initial stall/spindeparturedeveloped spins are handled withrudder firstor during a recovery from a rudderhardover.)

With a swept wing, the dihedral effect derivedspecifically from sweep actually disappears atzero CL. A sideslip then no longer produces arolling moment, unless the wing also hasgeometrical dihedral (tips higher than roots),which does work at zero CL. (Again, see groundschool text Lateral-Directional Stability.)

Wind-Axis: In this maneuver set we pushedand pulled on the on the stick while sidesliping.We watched the motion of the nose relative tothe horizon, and discovered that the aircraft waspitching about its y wind axis, not its y bodyaxis. Because of the displacement of the y windaxis from the body axis, a pitching moment alsoproduces a rolling moment, as described in theillustration to the right. This geometrical effectworks in the same direction as the CL effectdescribed above. In other words, pulling willgeometrically produce a rolling moment oppositethe velocity vector; pushing will produce a

rolling moment toward the vector. This isanother effect thats tough to visualize, but if youspend a few minutes fiddling with a smallaircraft model you just might have a revelation.

Aircraft Pitch Around Y Wind Axis

V

x bodyaxis

y body axis

y windaxis

The y wind axis remains perpendicular to and moves withthe velocity vector, V. The aircraft pitches around the ywind axis. Geometrically, this also produces a roll. So in asideslip to the right, as above, pulling the control backcauses a roll to the left; pushing forward causes a roll to theright.



Steady-Heading Sideslip Spin Departure:More confusing stuff, sorry again: Heres whathappens when we stall the aircraft during asteady-heading sideslip, by holding crossedrudder and aileron while increasing aft stick. In asteady-heading sideslip to the aircrafts left, asillustrated here, right rudder is deflected; aileronsare left. The horizontal component of lift createdby the bank angle pulls the aircraft to its left andthus generates a nose-left aerodynamic forceagainst the tail. We counter the resulting left yawmoment with right rudder to maintain our steadyheading. At the stall, as lift goes down so does itshorizontal component and the resulting yawingmoment to the left. This allows the rightwardyaw moment generated by right rudder to

dominate. If we hold control positions theaircraft yaws and rolls to the right in an over thetop entry into a spin.

Going over the top is the most congenial wayfor the aircraft to behave, because the wings firstroll toward level and theres more time forrecovery. Bringing the stick forward andneutralizing the other controls should keep theaircraft from entering a spin. Opposite ruddermight also help. Remember that aircraft alwaysdepart toward the deflected rudder (opposite thedisplaced velocity vector). So you wont breaktoward the low wing in a sideslipit just feelslike you might because thats the direction inwhich youre sliding off your seat.

Note that in a side-slipping spin departure to theaircrafts right, for illustration, the left aileron weoriginally hold to maintain a steady heading, andthen for demonstration keep in at the stall,doesnt arrest the rightward roll off. Theres toomuch airflow separation by that point for theailerons to generate much opposite roll. But thedown aileron still produces lots of adverse yaw,which pulls the right wing back and encourages aspin entry.

W

W sin

Y

L

The horizontal component of liftincreases as the stick is pulled backand CL rises. This component rapidlydecreases at stall, as lift drops(dashed arrow).

Roll moment due tosideslip/dihedral effect

Roll moment due to ailerons,here shown in equilibrium withthe opposing moment due tosideslip, quickly drops off asthe aircraft stalls and airflowseparates over the ailerons. Butadverse yaw increases andhelps drive the aircraft into aspin to its right.

Steady-headingSideslip SpinDeparture



3. Stall: Separation & Planform Flow (Wing tuft observation)

Flight Condition: Upright, power-off 1 g stall, high .

Lesson: Stall anatomy.

Flight Notes

Well cover boundary layers, adverse pressure gradients, and wing planform effects in the ground schooland supporting texts. Then, as an accomplished aerodynamicist, youll be able to interpret the sometimes-surprising motions of the wing tufts and the accompanying separation of the airflow from the wing as rises or the aircrafts configuration changes. FAR Parts 23 & 25.201-207 cover stall requirements.

On the way to the practice area, note theturbulence in the boundary layer as shown by themovement of the wing tufts. Note the increasedmovement as the turbulent layer thickensdownstream.

Dont make our stalls a minimum-altitude-loss,flight-check-style exercise. Give yourself time toobserve the full aerodynamic progression. Playaround. But remember: This is not proceduretraining. Follow the recovery techniques inyour aircrafts AFM or POH.

For FAR Part 23 and 25 certification, stallspeeds are determined for the aircraft configuredfor the highest stall speed likely to be seen inservice. In part, this means at maximum takeoffweight and forward center of gravity limit, trimset for 1.5 anticipated stall speed, and using anairspeed deceleration rate of 1 knot-per-secondstarting at least 10 knots above stall. Well try tomaintain this deceleration rate for latercomparison to a 5 knot-per-second decelerationentry. Up to a point, increasing the deceleration

Procedures:

Clearing turns.Power idle.Trim for 1.5 times anticipated stall speed.1-knot-per-second deceleration below 70 knots.Note buffet onset airspeed and stall speed.Full stall before power-off recovery.Power as required for recovery and climb.

Repeat with 5-knot-per-second deceleration below 70 knots.

Stalls while watching the wing tufts.

Provoke secondary stall in recovery.

Repeat with flaps. (Is there a difference in break?)



rate beyond 1 knot-per-second usually drivesdown the stall speed, but then the load factorstarts to rise and stall speed increases. Thedecrease in stall speed that comes with asomewhat increased deceleration occurs becauseof the delay in pressure redistribution as rises.This delays separation and allows the wing tofunction briefly at a higher angle of attack andcoefficient of lift than normal, a phenomenoncalled dynamic lift to differentiate it from the liftconditions at static angles of attack measured ina wind tunnel. Lift normally creates a downwashover the horizontal stabilizer, and thus a nose-uppitching moment. The nose pitches down whenthe downwash disappears at the stall. Dynamiclift delays this to a higher angle of attack.

Its important that a rapid deceleration producedby a high pitch rate doesnt compromise controlauthority. Thats not an issue with our aircraft,but can be with large aircraft in which pitchingmomentum can carry and momentarily hold theaircraft past stall angle of attack, withinsufficient airflow available for positive control.On the other hand, a deceleration rate below 1knot-per-second may not produce maximum .

Watch the tufts. The trainer has the root-firststall progression typical of its wing shape. Incontrast, swept wings naturally stall first at thetips. Theyre coerced to behave more in a root-first manner by the use of stall fences, vortilons,vortex generators, and changes in airfoil fromroot to tip.

Notice the definite relationship between airflowseparation at the wing root, as evidenced by thetufts, and the buffet onset in our training aircraft.Do you feel the buffet in the airframe, mostly inthe stick (as in the L-39 jet trainer), or in both?In our aircraft the buffet provides plenty ofaerodynamic stall warning. Compare this to a T-tail design where the turbulent flow largelypasses beneath the stabilizer and stall warninghas to be augmented by a mechanical stickshaker, or to planform designs where the wingroot separation happens too late to provide muchaerodynamic warning. In the MiG-15, forexample, theres no real buffetthe stick getslight and lateral control goes to mush.

You might want to do a couple of stalls with theinstructor assisting in directional control whileyou concentrate on the wing and play the stick tomodulate the full tuft stall progression from rootto tip. If youve done the relevant ground school,visualize and manipulate the adverse pressuregradient in the chordwise direction, and thechange in local coefficient of lift in the spanwisedirection. Note the change in airflow over theirsurfaces (as shown by the tufts) when the flapsor ailerons go down. When the flaps go down,note the vortex that forms on the outboard tip.Acting on the tail, the increased downwash fromthis vortex causes the pitch-up that follows flapdeployment.

The secondary stall we provoked on purpose,by pulling too hard on recovery, reminds us of

Adverse pressure begins earlier as increases.

Favorable pressure gradient

Adverse pressure gradient resists airflow.

Location of minimum static pressure

Adverse pressure strips the airflow from the wing.

Boundary layer separation at stall

Favorable pressure



the absence of positive (nose-up) pitch authorityat maximum lift coefficient, CLmax, regardless ofaircraft attitude. We can run out of elevator(and aileron!) authority in any attitude whentheres no angle of attack in reserve. Theabsence of positive pitch authority, in the formof an uncontrollable downward pitchingmoment is one of the ways the FAA defines astall for certification purposes under FAR Part23.201(b). Well revisit this loss of pitchauthority when we fly loops, and during the pull-up recovering from spins.

Part 23.201(d) states, During the entry into andthe recovery from the [stall] maneuver, it mustbe possible to prevent more than 15 degrees ofroll or yaw by the normal use of the controls. Incoordinated flight, our trainers tend to stallstraight ahead, without dropping a wingat leastnot initially. If you hold the stick back during thestall oscillation, a wing may drop. Many aircraft,like the sultry Siai Marchetti SF260, willannounce a stall more by a wing drop than by anose-down pitch-break (also called a g-break).Some airfoil and planform arrangements can bedemanding, no matter how carefully the pilotkeeps the ball centered. A venerable T-6 Texanor SNJ will generally drop to the right. The rightwing stalls first, reportedly, because its set at ahigher incidence. Our ground school video of aT-6 wing shows how the stall pattern leads toearly flow separation in the aileron region. Ourvideo of the Giles G-200 aerobatic aircraft showsa rapid trailing-to-leading-edge stall, which gives

no buffet warning, and in this particular aircraftproduces a sudden drop to the left.

Stall separation can also begin at the leadingedge, and aircraft with leading-edge stallstypically misbehave. The stall break, perhapscaused by the sudden bursting of the laminarseparation bubble, is abrupt and usually happensasymmetrically due to physical differencesbetween the leading-edge spans. A wing drop islikely. On various Lear models, if the leadingedge has been removed for repair, a test pilotwill come out from the factory to do a stall testbefore the aircraft goes back in service.

Even if meant to be, aircraft often arentaerodynamically symmetrical in behavior. Inpractice, manufacturing tolerances simply arentthat tight; and a life of airborne adventure takesits toll. The PA-38 Piper Tomahawk became aparticular offender when the production aircraftwere built with fewer wing ribs than theprototype used for certification tests. Thisallowed the wing skins to deformoroilcanunder changing air loads.Unfortunately, the performance of its GA(W)-1wing is very sensitive to airfoil profile. Thedeformations led to rapid and unpredictable wingdrop at stall. Prompt, proper recovery inputswere necessary. The Tomahawk has about twicethe stall/spin accident rate per flight hours as theCessna 150/152.



4. Accelerated Stall: G Loads & Buffet Boundary, Maneuvering Stability

Flight Condition: Banked, high .

Lesson: Flight behavior under turning loads.

Flight Notes

Earlier, we increased the airspeed deceleration rate to lower the book stall speed. Here we use load factorto raise it.

Stall speed goes up by the square root of theload factor, n. (n = Lift/Weight).

Induced drag goes up by the square of the loadfactor.

Thus whenever you raise the load factor (pullg), stall speed and drag also rise. You cantfeel the latter two directly; you have to learn theassociation. The increasing stick force is one cuethat the numbers are ascending. The forcedriving you into your seat is another.

Of course, hangar wisdom holds that a wingsstalling angle of attack remains constant for agiven configuration (high-lift devices in or out).Thats a small fiction, but also a profoundworking truth because it emphasizes angle of

attack as the essential stall determinant, not just anumber on the airspeed diala number thatitself changes with weight and load factor for agiven configuration. If you want to be picky,stalling angle of attack depends on ReynoldsNumber, which is the ratio between inertia forcesand viscous forces in the boundary layer on thesurface of the wing. For a given airfoil, stallangle of attack rises with Reynolds Number.

Notice the increased buffet intensity in theaccelerated stalls compared to those at 1 g.Theres more energy in the turbulent airflowshed by the wing at this higher buffet speed (theinboard wing tufts tend to capitulate and blowoff after repeated accelerated stalls), and moreenergy in the surrounding free stream flow.

Procedures:

Power low cruise.Trim.Using instrument or outside reference, roll to bank angle specified by instructor.Keep the ball centered with rudder.Apply stick-back pressure to buffet, reducing power or increasing bank angle as necessary.Note buffet speed, stall speed, buffet margin as compared to 1-g stall.

Repeat at higher bank angles. Note exponential rise in buffet speeds and stick force.

Explore aileron effectiveness in buffet by rocking wings 15 degrees left and right.



At higher g, does the buffet margin changecompared to a 1-g stall? The comparison shouldbe made at the same knots-per-second airspeeddeceleration rate to be valid. Often stall warningvaries inversely with knots-per-second, morerapid entry producing less warning. A rapid entryis probably typical of pilot technique in anaccelerated stall.

The accelerated stall and the 1-g stall bothoccur at the same angle of attack, but theaccelerated stall requires a heftier pull. Theaircraft exhibits an increase in pitch stability asthe g load rises (meaning a stronger tendency toreturn to trim speed, which is the tendencyyoure pulling so hard against). Thats becausethe angular velocity of the tail, caused by thepitch rate in the turn, produces a change in tailangle of attack, as illustrated to the right, andthus an opposing damping moment. Increasingthe g load means increasing the pitch rate, andups the damping. The additional elevatordeflection needed to overcome more dampingrequires more force. This effect leads to whatscalled maneuvering stability (which we cover inthe ground school text LongitudinalManeuvering Stability). Damping is a functionof air density, and goes down as you climb.

The geometry is such that, for a given g, anaircraft has a higher pitch rate (thus higherdamping) in a turn than it does in a wings-levelpull up. As a result, youll pull harder in a 2-gturn than in a 2-g pull up, for example.

At a given density altitude, in aircraft withreversible control systems, like ours, thenecessary stick-force-per-g is independent ofairspeed (although Mach effects may increaseforces at higher speeds). In other words, theforce required to pull a given g doesnt increasewith airspeed, as you might naturally think. (Ofcourse, its a bit more complicated. See groundschool text Longitudinal ManeuveringStability.)

The table farther on shows how load factorincreases exponentially with bank angle in aconstant-altitude turn. It follows that stick forces

also increase exponentially, rather thanuniformly, with bank angle. A pilot banking intoa steep turn has to increase his pull force at afaster and faster rate. Stick force rises slowly atlesser bank angles. Past 40 degrees or so, theincreasing force gradient starts becoming moreapparent. Theres a surprising difference in theforce necessary for a 55-degree versus a 60-degree bank. Steep turns might get a little easier(maybe) once you figure this out.

Notice the instant transformation in controlauthority at recovery due to the increasedairspeed in the accelerated stall. Watch the wingtufts to see how quickly the airflow reattacheswhen you release some aft pressure. Thedamping you generate in the turn pushes the noseright down. At 2 gs theres a 40 percent increasein stall speed. Because dynamic pressure goes upas the square of the airspeed increase, that meansdouble the dynamic pressure (1.42 = 2) availablefor flight control compared to a recovery from astall near 1 g. More dynamic pressure meansmore control response for a given deflection.You can recover from an accelerated stall whilethe wing is still loaded (pulling more than 1 g).You only have to release enough g to get the stallspeed back down.

Tail arm, lT

cg.

Pitch Damping

qlT (pitch rate times arm)

, Change in tail angle of attack

VT

Pitch rate, q

Tails aerodynamic center

VT



But releasing g may not always be equivalent toreleasing your aft pressure on the stick. In someaircraft (often former military) you may have topush to expedite things. You may find that thegradient of stick force rises more slowly as gincreases, as it does in the L-39 jet trainerbecause of the bungee cord boost within theelevator circuit. Or the aircraft may have an aftc.g., which increases maneuverability at theexpense of stability, and thus reduces thetendency to pitch the nose down when aftpressure is released. Early swept-wing fightershad a tendency to stall at the tips first. Becauseof the sweep, a loss of lift at the tips shifted thecenter of lift forward and caused the aircraft topitch nose-up and dig in during acceleratedstalls.

The higher dynamic pressure whilemaneuvering can lead to higher rolling momentsif the wings stall asymmetrically. Any wing-dropping obstreperousness an aircraft might hintat during 1-g stalls can intensify at the higherairspeeds of an accelerated stall. Our rectangular-wing trainers stall root-first, and resist roll-off ifflown in a coordinated, ball-centered manner.But accelerated stalls in other aircraft can bedefined more by a wing drop than by a pitchbreak or a stolid, straight-ahead mush.

As the load factor increases, the stall speedstarts coming up to meet your airspeed. At thesame time, if you didnt or cant increase power(thrust-limited), your airspeed starts headingdown because of the increased induced drag.Eventually, if you pull hard enough, the twospeeds converge. If an aircraft is thrust-limited,test pilots will perform descending, wind-upturns to explore its behavior at higher g, byturning altitude into the increasing airspeednecessary to attain increasing g levels.

Because stall speed rises in a turn, yourcalibrated airspeed above 1-g stall dictates yourbank-angle maneuvering envelope. The closeryou are to the 1-g (wings-level) stall speed in agiven configuration, the less aggressively youcan bank and turn an aircraft while keepingout of buffet and maintaining altitude. You cancertainly enter a steep bank without stallingwhile flying slowly, since stall speed is not

directly related to bank angle. Stall speeddepends on load factorin this case on the loadfactor required to make a turn happen at a givenbank angle without altitude loss. For a constant-altitude turn, load factor goes up exponentiallywith bank angle, as the table illustrates. Youcant generate the necessary load factor unlessyoure going fast enough for your bank angle. Ifyoure too slow, but nevertheless try to arrest adescent by hauling back on the stick, youll stall.Level the wings first. If you have excessairspeed, you can haul back and turn and climb.The relationship between airspeed, attainableload factor, and turning performance is discussedin the ground school text Maneuvering Loads,High-G Maneuvers.

Pilots have it drilled into them that an aircraftcan stall at any attitude. Stall speed is alsoindependent of attitude. At a given weight andconfiguration, an aircraft pulling two g, for

Deg.bank

Load factorrequired forconstant-altitudeturn

Stall speedfactorincreaseover 1-g Vs

60 ktstalltimesincrease

30o 1.15 1.07 64.3

35o 1.22 1.10 66.3

40o 1.30 1.14 68.4

45o 1.41 1.19 71.2

50o 1.55 1.24 74.7

55o 1.74 1.32 79.1

60o 2.00 1.41 84.8

65o 2.37 1.54 92.4

70o 2.92 1.71 102.5

75o 3.86 1.96 117.9

80o 5.76 2.40 144



example, has the same stall speed regardless ofits attitude relative to the horizon.

An aircraft constantly rolls toward the outsideof a climbing turn. It constantly rolls toward theinside of a descending turn. (Youre right. This isdifficult to visualize.) The rolling motion createsa difference in angle of attack between thewings, with the down-going wing operating at ahigher angle of attack. As a result, climbingaircraft tend to roll away from the direction ofthe turn at stall break. This is favorable becauseit decreases the bank angle. When descending,they tend to roll into the direction of the turn atstall break. But propeller effects, rigging, andpoor coordination can gum this up. Watch wherethe skid/slip ball is and see what happens.

Prop-induced gyroscopic precession can affectcontrol forces in turns. Precession creates amoment thats always parallel to the axis of theturnthe axis typically being perpendicular tothe horizon. On aircraft with clockwise-rotatingpropellers, as seen from the cockpit, precessionpulls the nose to the dirt in a turn to the right,and to the sky in a turn to the left. If the forcesgenerated are large enough (heavy prop, highrpm, high turn rate, long moment arm from propto aircraft c.g.) more up-elevator will be needed

when turning to the right. And the rudderbecomes more involved as the bank angleincreases and precession moves closer intoalignment with the aircrafts y axis. Greaterrudder deflection may then be needed forcoordination. The WW-I pursuits equipped withrotary engines (engine and prop turned together)were famous for their gyroscopicbehaviorsquick turning to the left but awkwardand vulnerable to the right. If the nose pitcheddown gyroscopically in a right turn, the pilotcould spin out trying to counter with oppositerudder and up elevator.

Finally, notice the greater rudder forcenecessary to stop or reverse a steep turn,compared to the coordinating rudder forcenecessary when beginning the turn. One reasonis the higher angle of attack in the turn and thusthe greater adverse yaw accompanying ailerondeflection. Also, the aircraft has picked upangular momentum, which the rudder has to helpoppose. So more rudder deflection is required forcoordination coming out.



Stick-force-per-g test procedure: wind-up turn.

Fly the test at a constant, trimmed airspeed. Airspeed variations introduce additional forces, as describedin the ground school Longitudinal Maneuvering Stability. At a constant airspeed and power setting, youwill descend during the maneuver as bank angle increases.

Establish trim speed in level flight at test altitude. Record pressure altitude, temperature, and power setting.

Climb with increased power to 1,000 above test altitude. Reset trim power.

Bank as required to obtain desired load while descending as necessary to remain at trim speed.

If equipped, measure stick force when airspeed and g-meter readings stabilize. Establishing a stable state,even briefly, isnt always easy it takes practice, especially as bank angle increases! If youre notequipped for measuring, a subjective assessment of stick force and gradient is still a useful exercise.

If the aircraft does not have a g-meter, use bank angles to establish approximate load factors. As 60oapproaches, you might find it easier to control airspeed with your feet: for example, top rudder if speedexceeds trim.

Trim speed: Pressure altitude: Temp: Power setting:

Bank angle 30o 1.15-g 45o 1.41-g 60o 2-g

Actual g-meterreadingStick force



5. Nose-High Full Stalls, Lateral Control Loss & Rolling Recoveries

Flight Condition: Wings level, high , nose-high, limited lateral control.

Lesson: Exposure to nose-high attitudes, limited visual references, lateral control loss.

Flight Notes

Nose-high recoveries are practiced in simulators as a standard element in upset training. The AirplaneUpset Recovery Training Aid gives a procedure based on a pushfollowed by a roll, as required to get thenose back down. Well explore the dynamics of recoveries done badly. We want you to lose lateral control,see why, and see what it takes to get it back.

The first maneuver gets you familiar with nose-high attitudes and pitch breaks. The pitch break(or g-break) in a 1-g nose-high stall is muchmore pronounced than in the 1-g stalls done fromclose to normal pitch attitudes. The aircraftrapidly sinks and the nose will swing well belowthe horizon before its possible to recover a

flyable angle of attack. The initial nose-upattitude will block the horizon ahead and forceyou to use the wingtips for roll, pitch, and yawreference. (The attitude indicator will be off,unless we forget.) Dont just stare at onewingtip. We have two! Compare them.

Procedures:

Full Stall: Nose-High Pitch Break

25/2,500 rpm.Clearing turns.Pitch up + 60 degrees (use wingtip reference).Power idle.Hold wings-level attitude as possible, keeping the ball centered with rudder.Allow full stall with stick held back.

Pitch up + 60 degrees.Hold necessary power, with stick back, aileron neutral and feet off the rudder pedals.Allow a yaw rate to develop (aircraft will yaw left due to prop effects).Observe lateral control divergence.Recover aileron effectiveness with nose down pitch input.Recover aileron effectiveness with opposite rudder.

Rolling Recovery from Nose High

Recover nose-below-the-horizon.

Recover nose-to-thehorizon.



We want you to experience lateral controldivergence and loss of roll damping. We set thisup by holding a nose-high attitude with poweron, stick back, feet off the rudders, and aileronsinitially neutral. We let the aircrafts naturaltendencies in this configuration take over. P-factor and slipstream will yaw the aircraft to theleft. Well try to recover from the resultingcoupled roll with ailerons alone (stick still heldback). Lateral control will be lost.

Notice that, while you can retain some aileroneffectiveness into a stall buffet and break, athigh, aileron effectiveness disappears if theairplane starts to yaw opposite the direction ofintended roll, as we let it do above. Instead ofrolling the aircraft as we intend, the aileronsgenerate more adverse yaw than lift, whichsimply makes things worse. Once the stick goesforward, however, or the pilot uses rudder to stopthe yaw, the ailerons regain authority.

The Airplane Upset Recovery Training Aidrecommends recovery from a nose-high attitudewith a push, followed by a roll if necessary(2.6.3.2-5). Pushing starts the nose in the rightdirection and unloads the wing so that theaircraft accelerates and the ailerons retaineffectiveness. Rolling tilts the lift vector andallows the aircrafts z-axis directional stability toassist in bringing the nose down. Confining theroll to less than approximately 60 degrees keepsthe wing lift vector above the horizon and makespitch control easier in the recovery back to levelflight. During the time it takes to roll the liftvector back to vertical, the buildup in angularmomentum in a heavy aircraft can carry the noseunnecessarily below the horizon if the initialbank angle is too steep.

In a delayed rolling recovery, if you hold thenose in the buffet and apply ailerons, you wonthave much roll authority. The reduced rollcontrol at low airspeeds and high angles of attackcan increase the difficulty of a rolling recoveryfrom a nose-high attitude. This underscores theneed to push and unload the airplane if theailerons arent working.

The nose below horizon and nose to thehorizon rolling recoveries demonstrate theproblem of flight path control at high angles ofattack. Because nose-up authority disappears athigh , stopping the nose on the horizon isdifficult without encountering a buffet.

In a jet, power application in a nose-highrecovery will depend on the aircrafts thrust lineand the resulting pitching moment when poweris applied. Aircraft with engines mounted onpylons below the wings can pitch up in a mannerpossibly difficult to control when thrust isincreased at low airspeed. In addition, a jet has toaccelerate and build up speed before controlsurfaces regain authority. With a prop, horizontaland vertical stabilizers start to regain authorityonce the slipstream returns. But ailerons stillrequire airspeed. In an extreme case, if you slamthe power forward on a go-around in a P-51 orsimilar warbird while flying slowly, the torqueeffect can be more than the ailerons can handle.



6. Roll Authority: Adverse Yaw & Angle of Attack, Lateral Divergence

Flight Condition: Upright, power-off 1g stall, high , varying , pro-spin.

Lesson: Lateral/directional control at increasing .

Flight Notes

In the previous maneuver set we observed the loss of aileron effectiveness during delayed nose-high rollingrecoveries. In this set well continue to examine changes in lateral control. We wont intentionally spin theaircraft at this point in the program, but the aircraft will be bopping around pretty aggressively, with thevelocity vector wagging left and right, and these are potential spin entries (high angle of attack plus sideslipand yaw rate). Just centering the rudder and ailerons and releasing aft pressure is enough for recoveryfrom an incipient spin departure in our aircraft. (As the spin develops, however, recovery techniquebecomes more critical, for reasons well cover in spin training.). That saiddont be timid. Challenge theaircraft to the point where lateral control is lost, and then get it back.

Procedures:

Spin recovery briefing as required.

Power idle.1-knot-per-second deceleration below 70 knots.Instructor demonstrates initial task.

Sample aileron authority: Decelerate toward stall while rolling 15 degrees left and right at a constant roll rate.Alternate between rudder free and coordinated rudder as necessary to hold nose on point.Note: 1. Change in aileron deflection needed to maintain roll rate.

2. Change in aileron forces.3. Increase in adverse yaw.4. Contribution of coordinated rudder to roll rate.5. Lowest speed for aileron authority.

Continue rolling inputs through stall break. At wing drop, hold opposite aileron. Observe aileron reversal.Hold aileron deflection and recover using forward stick to demonstrate return of aileron authority. Instructorwill demonstrate if required.

Sample rudder authority: (Instructor demonstrates initial task.) Establish constant rate left/right yaw temposufficient to assess rudder authority during stall entry. Note: 1. Change in required rudder deflection.

2. Change in rudder forces.3. Lowest speed for rudder authority.

Observe lowest speed for lateral control using coordinated aileron and rudder.



The subject of this maneuver set is mostly the rudder. Rudder-induced sideslips can accelerate a rollingmaneuver and contribute to maximum-performance upset recoveries. Proper rudder use is essential forcoordination at high : but misuse of the rudder at high can also cause spin departure, or severe yaw/rolloscillation (Dutch roll), especially in swept-wing aircraft. Following the November 12, 2001 verticalstabilizer failure and crash of American Airlines Flight 587, an Airbus A300-605R, attention has focusedon the structural loads generated on a vertical stabilizer when the rudder is deflected to opposite sides inrapid succession. Rapid rudder reversals, even below maneuvering speed, VA, and even with rudderlimiters, can result in loads in excess of certification requirements. FAR Part 25.351 rudder and fin loadrequirements are based on the demonstration of a sudden full rudder deflection (either to the stop or until aspecified pedal force is reached) at speeds between VMC and VD (design dive speed) in non-acceleratedflight. This is followed by a stabilized sideslip angle, and then the sudden return of the rudder to neutral,not to a deflection in the opposite direction.

The American Flight 587 accident also raised fears that unusual-attitude training that overemphasizesrudder can in fact provoke an upset if a pilot overreacts with rudder to an otherwise non-critical event, oruses it at the wrong time. Although well demonstrate the effects of rudder and sideslip on rolling momentsas increases, for all the reasons above we wont define the rudder as the primary high- roll control,especially not for swept-wing transport aircraft (historical jet fighters are a separate issue). Reduce theangle of attack if necessary to regain lateral authority, and use ailerons or spoilers for unusual-attituderoll recoveries, along with the rudder required for coordination, not roll acceleration. This is consistentwith both Boeing and Airbus philosophy, but can be applied to any aircraft. Aggressive rudder use is animportant part of aerobatic training, and of course aerobatic training is the basis of unusual-attitudetraining. But aggressive rudder use doesnt always carry overpartly because of concern the rudder will beused at the wrong moment and partly because, even with an experienced aerobatic pilot at the controls, thedynamics following a nominally correct aerobatic input may be different in a swept-wing aircraft than in astraight-wing trainer.

In the golden days, when tail-wheel aircraftwith lots of adverse yaw were standard, andpilots could still be seen wearing jodhpurs, flightinstructors often had students perform back andforth rolls-on-point, which instructors in jeanstoday often mistakenly call Dutch rolls. (In areal Dutch roll the nose wanders.) The idea wasto wake up the feet for directional control duringtakeoffs and landings, and especially to teach therudder coordination necessary to counteractadverse yaw. This maneuver set is similar, butthe dynamics are more complex and revealingbecause we roll the aircraft while simultaneouslyincreasing its angle of attack (and thus itscoefficient of lift, CL).

Pay attention to how control authoritydeteriorates: Youll need to increase your controldeflections to maintain rolling and yawingmoments as airspeed (dynamic pressure)diminishes. The down aileron will beginproducing proportionally less roll control andmore induced drag as the angle of attack rises(induced drag increases directly as the square of

lift), and therefore more adverse yaw. Youll seethe result in the movement of the nose. Keepingthe nose on point with rudder will demonstratehow the rudder becomes increasingly necessaryfor directional control when using ailerons forroll control at higher angles of attack, and thenincreasingly dominant for roll control as theailerons lose authority and roll damping beginsto disappear.

Rudder-induced roll control doesnt decline asmuch as aileron control typically does, becausethe yaw/roll couple that the rudder provokes goesup in proportion to coefficient of lift. Aileronauthority, however, goes down as airspeeddiminishes and as flow separation begins toaffect the outboard wing sections.

Ultimately, at aircraft stalling angle of attackthe ailerons can (legally, see below) begin toreverse (not to be confused with wing twisting,aeroelastic reversal). This happens whenadverse yaw begins to dominate, and theopposing roll moment the yaw produces (through



sideslip and yaw rate) overcomes the rollmoment generated by the ailerons. The airplanethen rolls toward the down aileron. This is calledlateral control divergence. Its natural prey is anairplane with lots of adverse yaw and lots ofdihedral effect, when flown at high angle ofattack by pilots who dont use their feet to keepyaw under control (and thus the velocity vectoron the plane of symmetry).

Adverse yaw goes down and aileroneffectiveness returns when you apply forwardpressure to reduce : Push to recover aileroneffectiveness. As in the nose-high stalls doneearlier, youll see how quickly a reversedaileron regains its appropriate authority once thenose comes down.

After the flight, compare the trainers stallbehavior to the requirements in FAR Part23.201-203 (for aircraft under 12,500 pounds)and to the requirements for transport certificationunder FAR Part 25.201-203. (See the Summaryof Certification Requirements.) The wording isdifferent, but 23.201(a) and 25.203(a) say thesame thing. According to the latter: It must bepossible to produce and to correct roll and yawby unreversed use of the aileron and ruddercontrols, up to the time the airplane is stalled.[Italics ours] Did we demonstrate capabilities atstall beyond those explicitly required?

Weve demonstrated the continuing authority ofrudder, compared to aileron, for roll control inthe high- region of the envelope. Nevertheless,in general, dont rely on the rudder for primaryroll authority at high , if you can avoid it. Thebest course is to push the stick forward and causenormal control authority to return. Certificationrequirements assume a pilot will do just that. Wedont want our demonstrations to turn into whatthe airlines call negative learning, so remember:These lateral and directional control exercisesare not procedure training. Recover roll controlat high by pushing to reattach airflow and torestore aileron effectiveness as required. Usecoordinated, ball-centered rudder to enhanceroll rate by checking adverse yaw. This iscorrect for any aircraft, but particularly so forswept-wingin which yaw/roll couple is morepronounced than for straight-wing aircraft andthe gyrations of the real Dutch roll are moresevere, and in which the high-/ corners of theenvelope may not have been explored duringflight test because operational encounter wasnever intended.



The illustration below puts things in velocityvector terms.

X body axis

Velocity Vector, V

Velocity vector, V,projected onto x-zplane gives aircraftangle of attack, . X-Z plane of symmetry

Lift vector

Z body axis X-Y plane

Velocity vector projectedonto the x-y plane givessideslip angle, .

V V

Velocityvector

z bodyaxis

x body axis

X-axis

Y-axis

A directionally stable aircraft yaws in the direction the velocity vector is pointed, returning the vector to the x-z plane of symmetry asit does. A laterally stable aircraft rolls away from the velocity vector when the vector becomes displaced from the plane of symmetry.In the illustration, the second aircraft wants to yaw right but roll left.

As an aircraft slows, and angle of attack and thus adverse yaw increase, aileron deflection will increasingly shift the velocity vectoroff the plane of symmetry, unless the pilot uses coordinated rudder deflection to counter the yaw. If present, P-factor andslipstream will also increase, tending to shift the velocity vector to the right unless the pilot compensates with right rudder.

So as speed goes down, the tendency of the velocity vector to wander goes up. The resulting rolling moments away from the velocityvector increase with , and also increase with angle of attack.

Rolling an aircraft with rudder is a matter of pointing the velocity vector to generate a rolling moment in the desired direction. Thedangers of aggressive rudder use at high angle of attack are that the aircraft enters a spin, or enters a Dutch roll oscillation the pilotinadvertently reinforces while trying to correct.



7. Flap-Induced Phugoid

Flight Condition: Longitudinally unstable, varying lateral/directional control.

Lesson: Downwash/horizontal stabilizer interaction, control practice.

Flight Notes

A dynamically stable phugoid motion is convergent. We can produce a non-convergent phugoid bylowering the flaps, but we dont retrim. The flaps increase the downwash angle over the horizontalstabilizer and, with the stick free, the nose pitches up in response. As the wing roots stall and the downwashdisappears, the nose pitches down. When lift then returns, the downwash reappears, driving the nose backup for the next stall. Your job, during this stall-and-recovery roller coaster, is to keep the aircraft underdirectional and lateral control, using aileron and rudder only.

The center of lift moves rearward along thewing chord when you lower the flaps. Thisproduces a nose-down pitch moment. (The dragyou create below the aircrafts center of gravityalso contributes.) But watch the tufts when theflaps go down and note the vortices that formaround the flaps outboard tips. These vorticesincrease the angle of the downwash affecting thehorizontal stabilizer. This down flow produces anose-up pitch moment. The pitch-up from thedownwash on the stabilizer is greater than thepitch-down from the reward shift in lift. As aresult, the aircraft pitches up at flap deployment.

Anytime you (or a gust) raise the angle ofattack of a wing you also increase the downwashangle. Typically, the downwash angle changesmore rapidly with AOA when the flaps aredeployed. Because the change in downwash

angle reinforces rather than opposes a change inwing angle of attack, flaps generally reducelongitudinal (pitch axis) stability. One reason forT-tails is to raise the stabilizer out of the area ofdownwash (and propwash) influence.

As the aircraft stalls and recovers, youllexperience changes in lateral and directionalcontrol, already familiar from earlier nose-highmaneuvers. Propeller and slipstream effects willbe more pronounced, however, because of theneed to maintain power to keep the maneuvergoing.

Procedures:

Speed for white arc in level flight.Students hands in prayer position (palms facing inward but not touching stick, rudder/aileron control only).Instructor lowers flaps approximately 15 degrees.Student maintains directional and lateral control. No pitch input.Instructor manipulates flaps as required, monitors flaps-extended speed.

Observe the effect of lowering the landing gear.



8. Nose-Level Aileron Roll: Rolling Flight Dynamics, Free Response

Flight Condition: Knife-edge & inverted, free yaw/pitch response.

Lesson: Free response behavior in rolling flight, attitude familiarization.

Flight Notes

We tea

maneuversflight notes.pdf

Documents

dont fly aerobatics

previous training

thats easier

light aircraft

aircraft inan

abroader curiosity

butsatisfying curiosity

youprobably dont