CARRIER PILOTS'

SBY JAMES B. FRANTZ and

DAVID M.TROUSDALE

Sport aircraft may be designedwith high wing loading for speedor a low wing loading for flightsinto short strips. Both missionsrequire exacting piloting skills. Ifyou're f ly ing ei ther, you maybenefit by unlocking the secretsthat Navy and Marine carrier pi-lots know.

Imagine this scenario. You aref lying home from a stressfulevening of work; it's pitch black;you have about 25 minutes offuel remaining before you startsucking air. The closest landingstrip within 200 miles is a heav-ing aircraft carrier whose deck isas slippery as wet grass, and only600 feet long. To make things evenworse, your approach speed wi l l be166 miles per hour all the way to touchdown. Land just over 120 feet shortand you will crash into the ship's stern.Sixty feet long and you'll bolter (missthe last wire) and have just enoughfuel for one more quick go around andanother landing attempt or an aerial re-fueling. Too slow and you'll stall intothe ocean. A few knots too fast and thetail hook will skip the arresting cables(hook skip). A bit faster than that youcould rip out the carrier's arresting ca-ble (two block the gear) leaving allyour flying buddies in the pattern be-hind you in a world of hurt.

This precision flying requires beingwithin three feet vertically and fivefeet horizontally from the opt imumtouch down point on the carrier deckand within just a knot or two of the op-t imum approach/touch down speed.How do Navy and Marine pilots do it?

Marine and Navy carrier pilotsuse exclusively one onboard aircraftinstrument, angle-of-attack (AOA)!

Angle of a t tack is the angle be-tween the chord line of the wing andthe relative wind. This is not to be con-fused with attitude that we read fromour artificial horizon. To make this108 JULY 1999

Attitude 0°AOA 11°

Attitude 90AOA 11

Attitude OAOA 2.3

AttitudeAOA

-90'

AttitudeAOA 1.

0°8°

Figure ALooping Maneuver

point very clear, a looping maneuveras shown in Figure A could be per-formed by hold ing a fixed AOA of11.0 degrees around the entire loop.The att i tude would be changing be-tween O degrees plus 90 degrees andminus 90 degrees.

Navy and Marine pilots are trainedto make carrier approaches using angleof attack instrumentation exclusively,mostly ignoring the airspeed indica-tor. The m i l i t a r y spin ent ry andrecovery procedure and t ight highperformance maneuvers are all madereferencing AOA. The airspeed indi-cator is just not accurate enough, hastoo much instrument error, and doesnot factor in bank angle, fuel loadand turbulence. AOA instruments onthe other hand are self-compensatingand become more accurate as thespeed decreases and the angle of at-tack increases.

Now back to reality. Let's fly ourpride and joy around the pattern anddemonstrate how and why to fly AOA.

TAKEOFF AND CLIMB

On takeoff (T/O) we rotate to an at-titude referencing the earth's horizonor the attitude indicator. The rotational

pitch att i tude is what we esti-mate wi l l result in the properIAS for climb. Shortly after lift-ing off and whi le holding thisattitude we cross check the indi-cated airspeed ind ica to r andmake fine adjustments to our at-t i tude bracket ing the desiredcl imb IAS. This IAS might bethe best angle of climb, the bestrate of c l imb or some higherspeed depending upon the de-sired climb gradient. Althoughthis method has served most ofus adequate ly in the past, weneed to understand that Vx andVy do not occur at fixed indi-cated airspeeds.

The second drawback is that the at-titude we init ially rotate to on takeoffis only an educated guess of what willproduce the targeted climb speed. Themost common error students make inmountain flying is rotating on takeoffto the same pitch attitude that workedfor them at their home strip in the low-lands. Invar iab ly th i s results in anattitude on takeoff that is near the criti-cal AOA (stall) at these high densityaltitudes. This is called "operating be-hind the power curve" or "operating inreverse command." Using the samepitch a t t i tude for all T/Os ignoringgross weight and density altitude hasresulted in many short flights into thetrees at the end of the runway. All T/Osshould be flown referencing IAS andAOA. Higher density al t i tudes andhigher gross weights will require lowerT/O a t t i tudes . Flying to the properAOA on ro ta t ion w i l l r esu l t in theproper attitude for every departure re-gardless of density altitude or grossweight.

APPROACH AND LANDING

Does your aircraft's operating man-ual suggest a single approach IAS nomatter what your aircraft 's gross

weight and bank angle? Wow, many afatality has resulted from this over-sight! Let's explore why. We'll assumethat your aircraft stalls at 60 mph andat an AOA of 15 degrees when operat-ing at a gross weight of 1,500 poundsin 1 G flight. After loading your air-craft with additional fuel, passengersand baggage, it now weighs 2,200pounds. What is the stalling speed andcritical AOA now?vs(2,20o#) = 60 V2,200/l,500 = 73 mph

The above relationship shows thatthe stalling speed increases from 60 to73 mph due to the increased grossweight but the critical AOA (stallingAOA) remains the same at 15 degrees.

Suppose we turn the aircraft frombase to final using a 45 degree bankangle to compensate for the strongerthan anticipated crosswinds aloftwhich blew us beyond the runway in-tercept. Now what is the stalling speedand critical AOA?

Vs(45«) = 73 Vl/cos45 - 87 mphThe stalling speed increases from

73 to 87 mph but the critical AOA isstill the same at 15 degrees.

Now add a +1.5 (i turbulence bumpwhile in the turn at the higher weight.

Vs(1.JG) = 87Vr5- 107 mphThe stalling speed is even higher,

but, as before, the critical AOA re-mains 15 degrees.

Since any given airfoil always stallsat the same critical AOA, all approachesshould be flown using a fixed AOA re-gardless of G W, bank angle, turbulence,density altitude, etc. This is one of thereasons why flying AOA is worth itsweight in gold. Those base to f ina lbanked turns, turbulence encountersand changes in gross weight are allflown using a fixed AOA and you arerelieved of all the above computations.

Let's go flying with Captain Ace(the local airport legend) using anAOA indexer manufactured by Propri-etary Software Systems, Inc. anddemonstrate how approaches are flown(or not flown in this example) usingthe elevator to control AOA and powerto adjust the rate of descent. Ace is fly-ing the proper approach AOA for thisparticular instrument when the fourbottom lights are lit (Figure 3). FlyingAOA is s imilar to keeping the IASpointer on the reference bug. In thiscase the reference bug would be per-manently affixed to the middle yellow

Flglbest glide,

max endurance

Flglapproach

AOA loo low

figSapproach AOA

Just right

bulb. In Figure 1 Ace is flying the bestglide or maximum endurance AOA,which in some flight regimes would beappropriate. But this is too low anAOA and too high an airspeed for fi-nal approach, so Ace increases theback pressure on the stick/yoke. InFigure 2 the AOA is s t i l l just slightlytoo low for the optimum approachAOA so Ace continues to increase theback pressure. The AOA is perfect inFigure 3 and Ace should trim out theback pressure in 1 G flight so that no

elevator stick/yoke pressures are re-quired. In Figure 4 the aircraft's AOAis getting dangerously close to criticaland way too high for approach. An au-ral warning "angle push" sounds, andAce should increase the forward pres-sure on the stick/yoke, and decreasethe bank angle. The aircraft is at thecritical AOA (starting to stall) in Fig-ure 5. Ace blew this approach big timeand immediately executes a stall re-covery maneuver saving his life. Uponreturning to a lower AOA as depicted

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in Figure 1, Ace collects his thoughtsand wonders how this could have hap-pened thinking that he had plenty ofairspeed. But Captain Ace recalls sometraining from long ago — it's AOA and$$$ that keeps aircraft flying, not IAS.Ace has become another AOA convert.

AOA instruments fall into threecategories: pressure, stagnation andvane. Vane and pressure based unitare often mounted on the side of thefuselage for multi-engine or pusheraircraft and on a wing mounted boomfor all others. Stagnation based unitsare cut directly into the leading edgeof the wing.

A vane (Photo A) is a wedge shapedairfoi l mounted to a rotating shaftsensing the airflow. The vane is free torotate and is precisely counter bal-anced so that the position of the vaneis determined entirely by the air streamdirection. Vanes are subject to ice ac-cumulation and are heated. The vanesmust be located well ahead of the wingto give accurate results and are usuallyquite expensive. The vanes you see onthe nose of airliners and corporate jetsmay cost $4,000 or more not includingthe AOA computer and display.

The typical direct reading two pres-sure device is a probe with pressuretaps drilled at unique angles in relationto the probe. The pressures are used todirectly drive a pressure sensitive indi-cator as shown in Photo B. Thesesystems are generally called reservelift devices because they do not di-rectly measure AOA.

Stagnation based AOA devicessense the stagnation point on the lead-ing edge of the wing and correlate thelocation of the stagnation point withangle of attack. These units use a pro-truding movable vane to locate thestagnation point and look almost iden-tical to the common stall warning tabscommon on Cherokees and lots ofother aircraft. The tab is also subject torime and clear ice accumulation and isusually heated.

An example of a vane based sys-tem is EM Aviation's RiteAngle whichwas developed by an airline pilot, El-bie Mendenhall. The vane is attachedto a potentiometer which regulates theinput to an electronic module. Thevane is mounted on a 12" long boomoutboard of the prop wash. The dis-play is available in two configurationsboth using a ladder of light emittingdiodes (LED) to provide angle of at-110 JULY 1999

Photo A - Safe Flight Instrument's AOA vane used on large aircraft.

tack information. The more LED's lit,the closer you are to the critical AOA.When the top LED's are lit, a buzzerwill sound and/or the green LED'swill flash. There are two models andseveral options.

The Lift Reserve Indicator (LRI) isa two pressure port reserve lift indica-tor. It is sold by Lift Reserve IndicatorCompany. The inventor, Morgan Hunt-ington, died in 1992with more than twentypatents to his name,ranging from the LRIto oil shale and sewertreatment. With about400 units sold, his sonJim is revitalizing theLRI. Jim says, "My fa-ther's dream was toinvent a safety pin, ele-gant and simple, thateverybody would use.This is it!" The LRIuses an aerodynami-cally shaped air streamprobe that providespressure input to thedisplay. The display isanalog with an arc di-vided into three sectors.The red sector indicates

the aircraft is no longer generatingenough lift to sustain level flight. Theins t rument has marks for rotation,liftoff, maximum angle of climb, flareand more. The instrument requires nopower unless the optional probe heateris used.

Stall warning was invented by SafeFlight Instrument Corporation duringWorld War II. Their SC-1500 speed

Photo B - Reserve Lift Indicator and Probe.

control system is based on the stagna-tion principle and uses a lift transducermounted on the lower leading edge ofthe aircraft wing. The transducer vane,which is very similar in looks to thestall tab we are familiar with on manyGA aircraft , protrudes into the airstream and is positioned during flightby local airflow velocity and direction.By correlating lift with airflow charac-teristics at the stagnation point on thewing, the l i f t transducer measureschanges in angle of attack. The outputsignal electrically enters the computerwhich drives a visual analog displaydivided into three colored pie shapedsectors with indexes for best climb an-gle, short f ie ld approach, normalapproach, and stall AOA. This unit hasoptional anti-icing capability. The sys-tem can optionally activate the aircraftstall warning device whenever the lifttransducer signal approaches the stallangle of attack.

If you were to make a wish list forthe perfect AOA, it should be accurateand display minimum lag or hystere-sis. It should be lightweight but ruggedand easy to install. No moving partswould increase re l iabi l i ty and keepcosts down. Protruding parts are proneto damage by airplane enthusiasts withgood intentions. The AOA should notbe affected by aircraft configuration.The display must be easy to read andunderstand. There must be audio andvisual warnings when approaching thecritical angle of attack.

Until recently AOA instrumentationwith these features would not havebeen feasible but there have been newand amazing technological advances.It's now possible to e l imina te theprobes and vanes which results in lesscomplexity and lower cost. The pow-erful microprocessor, voice playbackchips used in your digital answeringmachine and a variety of pressuresensing devices are now available andaffordable.

Proprietary Software Systems ownspatent pending technologies becomingthe only avia t ion AOA ins t rumentmanufacturer with no moving parts orprotrusions. Their products are allsolid state, have color AOA displays(Photo C, Fig. 1-5), and voices auralwarnings and cautions.

The l iqu id crystal display, AOAProfessional (Photo C), has a greendonut shaped target for the optimumapproach AOA familiar to all Navy

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Photo C - Proprietary Software Systems' Professional

carrier pilots and red chevronsindicating when the AOA is dan-gerously high. A green split baris called the performance barwhich may be set to the best en-gine out gl ide, max imumendurance, or best l if t to dragAOA. The AOA Sport (Figures1-5) uses a three color LED lad-der display. Both ins t rumentshave self-testing features thatcheck accuracy and verbalizes,"AOA PASS," when completedsuccessfully. The AOA instru-ments are programmed to talk toyou announcing warnings of highangles of attack,"Angle AnglePush," instrument problems andinstallation errors. It can also beused to drive stick shakers andbuzzers. An aural warning ,"Landing Gear," wil l help pre-vent inadvertent gear up landingswhen the airspeed is slow andthe gear is not down. And if youare into aerobatics, racing or justan aerotechi, the Professionalalso has a TS-232 data portwhich can be connected to yournotebook computer, recording tothe disk airspeed, G loadings,wing pressures and AOAs — all

time stamped for the entire flight.The AOA Sport is in the processof being FAA certified.

The need for affordable angleof attack instruments becameimperative with the increasingnumbers of high performancesport aircraft like RVs, Glasairs,GlaStars, Lancairs, Stallions,Legends, Seawinds, Europas,Velocities, Thunder Mustangs,etc., and the many slower STOLtype aircraft flying into shorterstrips. High wing loaded war-birds and aerial applicators canalso benefit. Carrying unneces-sary speed when landing theseperformance machines is fool-ish. Similarly, the unacceptablefatality rate resulting from lossof aircraft control and contactwith the ground (stall/spin) hastaken too many of our friendsand acquaintances.

AOA instrumentation will in-crease the awareness and thusthe safety of every pi lot . TheNavy cut their fatali ty rate inhalf when switching to exclu-sively AOA for carrier oper-ations. Sport aviation pilotscould do the same.

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AOA and Reserve Lift Instruments

Contact

Bacon Saver618-594-2681troneill@midwest.netEM AviationRiteAngle I and II360-260-0772www.riteangle.com

Lift Reserve Indicator CoJimRHunt@WCO.COMPO Box 643Occidental CA 95465Proprietary SoftwareSystems, Inc.6124744157PSS@angle-of-attack.comwww.angleofattack.com

Safe Flight Instrument CorpSC- 1500914-946-9500

ProtrusionsVanesProbes

moving vanemounted on

boommoving vaneon 12" boom

probe belowwing

noneTwo smallpressure

taps in wing

vane onleading edge

of wing

Weightlb.

N/A

1.0

2.0

0.5 Sport0.9 Pro

.9

CalibrationMethod

severalflights

3 flights

multipleflights to

adjust probe

1 flight

multipleflights to

adjust vane

CockpitDisplay

in.

none

LEDladder

3.9x2.1or 2x3/8

roundanalog

fourcolor

LCD orLED

Ladder1/2x11/4

roundanalog2.375

Outputsand

Warnings

none

buzzer

none

Voice &Open

collector&RS-232

optionalsignaloutput

OtherFeatures

vane onSS

bearingcan be

poweredwith 9V

AAbatterypackicingheat

optional

LandingGear

warning

icingheat

optional

PowerRequired

none

9 or 14V

noneunlessheated

12 to 28V4 Wan

max

14 or 28V0.3 amp50 Watt

Cost

S95

$300to

S475

S750to

$830

$890to

S 1.495

$1.950

Dave Trousdale is a for-mer Navy instructor pilotand fleet aviator. Davetaught carrier landingsin the T-2C Buckeye andserved a nine month tourof duty in Viet Nam fly-ing the A-7E Corsair. Healso flew the bush inAlaska and has workedas a NWA check airman.Jim Frantz is a bush pi-lot, flight instructor,software designer andelectrical engineer, withover 18,000 flying hoursin everything form J-3sto MD-80s. He built hisown award winning Lan-cair 360 and is thepresident of ProprietarySoftware Systems, Inc.which develops and mar-kets AOA instruments.Jim will be giving AOAforums at EAA AirVen-ture '99 and otherairshows. See www.an-gle-of-attack.com forforum dates and times.

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