Several years ago I witnessed thewreckage of a Piper Cub which crashedwhile circling a coyote at a low altitude.Two pilots, father and son, were killed.The major contributing factor was a stallresulting from a steep turn maneuver.Since then, I have heard and read aboutother similar incidents. "AviationSafety", September 1985 issue, by Bel-voir Publications, Inc., Riverside, CT,refers to an Alaskan conception of thistype of mishap as the "moose hunter'sstall". This type of stall occurs becauseof a differential of lift between the twowings. A hypothetical case would be anairplane in a left steep turn at a lowairspeed close to the ground. This man-euver is usually done with full flaps(e.g., Super Cub) and the aircraft canbe caught in its own wake turbulenceduring the turn. Once the stall occurs,the pilot will react instantly by applyingabrupt back pressure to the stick, result-ing in a secondary stall. Now we are inan unusual attitude with the nose downwhile banking steeply (45 degrees) andcontacting the trees or ground. In theJuly 1985 Cockpit Classroom article,I mentioned that any stall at a low al-titude results in little or no chance forrecovery even by the pro-pilot. From ourCockpit Classroom viewpoint, let'slook at some of the important facts,causes and results of Overbanking insteep turn maneuvers.

In those cases where pilots were for-tunate enough to survive the crash, theyadmitted that attempts to recover weremade by "back pressure" on the stick oryoke, resulting in a secondary stall tooclose to the ground for recovery. Thisbrings up an interesting point. While incoordinated (steep) turning flight (45 to55 degrees bank angle), banking ten-dencies are always in the same direc-tion regardless of power or stick forces.For instance:

Action by Pilot and Effect on BankAngle

Addition of power — Bank in-creases

Reduction of power — Bank in-creases

Back pressure applied on stick —Bank increases

Forward pressure applied on stick— Bank increases

The reason for these similar tenden-cies is due to the Overbanking ten-dency in steep (40-55 degree) turns.The pilot will find it necessary to holdsome aileron pressure against the turn

to prevent the airplane from Overbank-ing (see Diagram 1). The Overbankingtendency can cause the plane to entera nose-down "graveyard" spiral if backstick pressure is lax. Furthermore, in-creasing elevator pressure will onlytighten the turn, resulting, again, in asteeper nose-down spiral.

The purpose of steep turns in flighttraining — it is a coordination maneuverused for training purposes to teachpilots that a steep bank produces ad-verse aileron yaw requiring coordinateduse of rudder. Objective of maneuver isto develop smoothness, coordination,orientation, division of attention andcontrol techniques (Maldon Books,Inc.). It is also important from thestandpoint of having student pilots ex-perience the Overbanking tendency.

While in a steep turn, it is necessaryto maintain a fairly constant degree ofbank (plus or minus 5 degrees). Addi-tional power (approximately 100 rpm)and back stick pressure or up elevatoris required to increase the angle of at-tack to counteract lift lost because ofbanking (see Diagram 3).

The newly issued Private Pilot Practi-cal Test Standards (FAA-S-8081-1)emphasizes performing "constant al-titude turns" below the airplane's designmaneuvering airspeed (Va). Perfor-mance of 180 degree or 360 degreeturns while maintaining a bank angle of40 to 50 degrees in coordinated flightmust be evaluated in flight tests.Examiners are to check the applicant's

turn recoveries at plus or minus 20 de-grees and altitude control at plus orminus 200 feet. Applicants must be ableto divide their attention betweenairplane control and orientation. A re-view of load factors, power required andOverbanking tendency must beevaluated. This is a new maneuver in-cluded in the Private Practical TestStandards (FAA-S-8081-1).

The load factor for any airplane,maintaining a constant altitude, in a 60degree bank is two GS, or two times thepull of gravity; i.e., the weight of a 2000lb. airplane increases to 4000 lbs. Thepilot's weight doubles. This will occur atany airspeed at 2 GS.

At a constant altitude coordinatedturn, the load factor is the result of twoforces — centrifugal force and gravity.For any given bank angle, the rate ofturn varies with the airspeed; the higherthe speed, the slower the rate of turn.This compensates for added centrifugalforce, allowing the load factor to remainthe same (FAA).

Diagram 4 indicates the amount of in-crease in stall speed depending on theangle of bank.

Diagram 3 reveals an important factregarding turns. Here we see that theload factor increases at a terrific rateafter reaching a bank angle of 45 or 50degrees. Earlier I mentioned the loadfactor for any airplane in a 60 degreebank is 2 GS. Surprisingly, the load fac-tor increases to 4.00 GS in a 75 degreebank (see Diagram 6). The wing mustproduce lift equal to these load factorsif altitude is to be maintained (FAAFlight Training Handbook 61-21 A).

Load factors are important to the pilotfor two distinct reasons: (1) because ofthe obviously dangerous overload thatis possible for the sport pilot to imposeon the aircraft structures, and (2) be-cause an increased load factor in-creases the stalling speed and, viewedfrom our Cockpit Classroom, makesstalls possible £' apparently safe flightspeeds.

Another important Cockpit Class-room lesson here is the fact that eachairplane has a different wing designwhich not only affects stall characteris-tics in steep banks, but also spin recov-ery techniques. This is vital information,especially for the sport aviator flying air-craft where wing designs vary greatly.Regardless of the shape of the airfoil,once lift is reduced beyond the criticalangle of attack (stalling angle) — (1)

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drag is increased and the center ofpressure moves rearward along the air-foil when the wing is stalled, and (2)stalling characteristics in level flight orin a steep bank vary depending on thedesign of the wing.

The stalling angle of, let's say, theSuper Cub wing is always the same,providing the shape of the wing or anyother characteristics are not altered.The stalling angle will be different withalterations here. Remember, we men-tioned that many of the accidents result-ing from steep banks close to theground occur at low speeds with fullflaps while caught in their own turbu-lence. The stall characteristics can bealtered adversely by using high lift de-vices such as flaps. Flaps change therelationship between the angle of thestall and the stall speed in two ways: (1)high lift devices (flaps) increase the

maximum lift that can be produced atthe stalling angle, and the indicated stallairspeed (IAS) is decreased for a par-ticular weight (check your stall speedcharts), and (2) high lift devices such asflaps change the angle of attack formaximum lift (the stalling angle). Flapsactually decrease the stalling angle.For some airplanes, flaps reduce thestalling angle from 15 to 11 degrees.Flaps will increase the camber of thewing moving the center of pressure aft.

The fact that flaps reduce the stallingangle will make the common stall warn-ing devices, such as the stall warningvents or vanes, practically useless.From my personal flight experiences,most of the inadvertent stalls and/orspins have occurred in a flaps-downflight configuration with no warning.

To summarize important points in thisarticle, a competent sport aviation pilotshould be aware of the following:

1. The danger of inadvertently stallingthe sport plane by increasing the load

factor, as in Overbanking in a steepturn or spiral;

2. That in intentionally stalling anairplane above its design maneuveringspeed, a tremendous load factor is im-posed (FAA).

3. Avoid stalls from steep turns or ex-cessive maneuvering near the ground— the use of flaps will decrease the stal-ling angle and the aircraft could stallwithout a warning.

4. Sport pilots must be aware of struc-tural failures during acrobatics or otherviolent maneuvers resulting in loss ofcontrol; e.g., during a pull-up followingstall recoveries from a steep spiral orturn significant load factors are induced.

5. Most structural failures due to ex-cess load factors involve rib structureswithin the leading and trailing edges ofwings and tail groups. Critical area offabric-covered airplanes is the coveringabout 1/3 of the chord aft of the topsurface of the wing (FAA finding).

6. During a delayed recovery stall, therudder is the most effective flight con-trol used to counteract any tendency ofthe airplane to yaw, or slip. Note: Useof rudder should be coordinated with P'lerons in modern airplanes.

7. An airplane loaded in a mannerwhich locates the CG slightly aft of thewing's center of pressure in flight wouldreduce stall recovery capabilities; e.g.,airplane becomes less controllable at

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low flight speeds as CG moves aft —more pronounced in steep turn man-euver or spiral.

The new Private Pilot Practical TestStandards make CFF's and examinersresponsible for instructing and evaluat-ing steep turns, including the Overbank-ing tendency and load factors. TheVideo Training Aids tapes on flight man-euvers emphasize that knowledge ofsteep turns is important because theyform the basis for many advanced man-euvers, as well as for the principles ofadvanced control effect analysis. Steepturns serve as an introduction to man-euvers requiring varying and coordi-nated control pressures. Perfect coordi-nation in steep turns may be attainedonly with good instruction, followed withmuch practice. Now that constant al-titude turns (bank angles of 40 to 50degrees — see Diagram 5) are a re-quired maneuver for private applicants,possibly we can reduce the number andseverity of accidents involving the over-banking tendency and understanding ofload factors in steep turns.

Check the Following Procedures• Steep turns performed no lower

than 1500 feet AGL.• Greater rudder pressure is required

upon entering right turns than left.• Perform steep turns (bank angles

40 to 50 degrees) both left and right byvisually keeping altitude and using nat-ural horizon as reference — then byusing instruments only.

• Proper execution of steep turns re-quires smooth and constant use of con-trol pressures.

• Less corrective aileron pressure isused to counteract Overbanking ten-dency in right turns.

• From pilot's seat, controls work thesame in a steep turn as at other times.Increased elevator pressure tightensturn.

• Shallowing of bank will help to holdaltitude.

• During steep turn, flight controlpressure errors are magnified.

• Student will experience an approx-imate 2-G load turn during steep turns.

• Practice smooth entry into oppositeturn after each 180 or 360 degrees ofturn.Evaluation:

Altitude plus or minus 200 feetHeading — within 20 degrees (recov-

ery)Airspeed — below Va

(Illustrations by Maldon Books, Inc., P.O. Box 621, Palatine, IL 60067)

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