Army Aviation Digest - Jun 1971

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UNITED RMY VI TION..,, 1GESJDIRECTOR OF ARMY AVIATION ACSFORDEPARTMENT OF THE ARMY

BG Will iam J . Maddox Jr .COMMANDANT U . S. ARMY AVIATION SCHOOL

MG Allen M . Burdett Jr .ASST COMDT U . S ARMY AVIATION SCHOOL

COL Hubert S. Campbell Jr .DIGEST STAFF

Richard K Tierney EditorCPT Edward A . Bickel2lT Kenneth G . Kitzmiller2lT John H. ZwarensteynCW2 Mike lopezWil l iam H . Smithl inda McGowanBrenda R. HarpBetty S. Wallace

GRAPHIC ARTS SUPPORTHarry A . PickelDorothy l CrowleyAngelo A . Akin

DIRECTOR U . S. ARMY BOARD FOR AVIATIONACCIDENT RESEARCH

COL Eugene B. ConradUSABAAR PUBLICATIONS AND GRAPHICS DIV

Pierce l Wiggin ChiefWill iam E. CarterJack DeloneyTed KontosCharles MobiusPatsy R. ThompsonMary W . Windham

BOUT THE COVERThis month as Army aviationcelebrates its 29th birthday ,we salute the pioneers in heli -copter armament and tactics .Cover photo is one of the firstCH -3 4s to be experime ntallyarmed at the aviation school atFt . Rucker , Ala., in the late1950s . Armament includestwin .50 caliber machine guns

and 4 .5- inch rockets

JUNE 1971 VOLUME 17 NUMBERViews From ReadersWe Armed The HelicopterFog Dissipation QuestionnaireOH-58 Kiowa Power MarginHover DownAeromedic-Oh Say, Can You See?Instrument CornerCharlie And Danny s Write-InIt Could Be They ll Get You TooMission Of Mercy: PakistanAnother First (And We Hope The Last)Hover SenseMaster Of The Sky?Army Aircraft Mishap ReportingViolators Gamble And LoseVisibility Restrictions Demand Clearing

Turns and AlertnessHow Do You Get The Ball Rolling?USAASO SezPresidential Helicopter Retired At Rucker Inside Ba

The miss ion of the U. S. RMY AVIATION DIGEST is to provide information of on operationol or funct ional noture con ce rning safety and aircraft occident prevent ion, train ing ma intenance, operat ions , research and de velopment, av iat ionmedici ne , o nd other reloted data .The DIGEST is on o fficial Department of the Army period ica l pu b lished monthly under the supe rv ision of the Comman da nt, U. S. Army v iat ion School. Views expressed herein are not necessarily those of Department of the Army or the U. S.Army v iation School. Photos are U. S . Army unless otherwise spe ci fied . Material may be re p rinted provided credit is g ivento the DIGEST and to the author, unless otherwise indicated .Art icles, photos, and items of interest on Army av iat ion ar e invited . Direct communication is authorized to : Editor. U. S.Army v iation Digest , Fort Rucker, Ala 36360 .Use of funds for p rinting th is publicat io n has been ap p roved by Headquarters , Departme nt of the Army, 1 October1970.

Active Army un its receive distribution under the pi npoint dist ri but ion system as out li ned in R 310 - / . Comple te D Form12-4 and send d irectly to CO , AG Pub lica tions Cente r. 2800 Eastern Boulevard , Baltimore , Md . 21220 . Fo r any change indistri but ion req u ire ments , init iate a rev ised D Fo rm 12-4 .Nat ional Guard and Army Reserve units under pinpo int d istribution also should submit D Form 12-4 . Oth e r Nat ionalGuard un it should submit requests through their state adjutants generalFor those not elig ible fo r officia l distribut ion or who de s ire personal copies of the DIGEST, paid subscript ions , 4 .50domestic and 55 .50 overseas , ore avai lable from the Superintendent of Documents, U. S. Government r int ing Office ,ington , D. C. 20402 .


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R

JEWSROE DERS

Sir :I wish to thank you for publishing theletter which appeared on page 19 of theApril 1971 edition of AVIATION DIGEST.There are many of us junior warrant officers (we were all junior as far asGeorge T . was concerned) who remember and were associated with SuperChief. There were many who swore athim and many a 34 driver who oweshis life to lessons learned from George.As a retired nonrated maintenance type,I would like to add my thanks to ColonelMillett for his fine letter telling us abouta crusty Super Chief that Army aviationowes so much to.

Sir :

CW3 Leo Rodden (Ret.)830 Carneal RoadLexington, Ky. 40505

CW2 Hesket's article on refueling theCH-47 [AVIATION DIGEST , March 1971,page 32J makes a lot of se nse , althoughmost of his procedures are SOP in allunits of the First Aviation Brigade inVietnam . The units I have been in (the243d ASHC Freight Trains and the178th ASHC Box Cars ) learnedthrough experience that the safestmethod of operating this aircraft is toshut down at least every other refuelingstop for a quick maintenance check. taccomplishes several things :I . You don't fallout of the sky because some problem has developed inflight. In most cases the check catchesproblems while they are still minor andallows on-the-spot tightening, adjustmentand minor repairs. t also finds suchitems as hangar bearing failures which, ifnot repaired promptly, will cause moresevere damage to the aircraft if loads arebeing carried externally.2 It actually increases rather than decreases the productive time of the aircraft. especially when long distancesfrom home stations are involved .3 t increases crew responsibilitiesand, at the same time , increases crewconfidence in the aircraft, a valuable as-JUNE 1971

set in training new crew members . Witha little assistance from the pilot and copilot. this check can be accomplished ina very short time. We felt that with theage of the CH-47 As this was the mostimportant routine to follow. even thoughit occasionally increased our work dayby a short amount of time .

Sir:

M AJ Donald W. ReckU. S. Army Aviation SchoolElementHunter AAF. Ga. 31409

While flying in RVN and now in Europe the following question has arisenand no one has been able to find an answer; consequently, I thought that perhaps it could be answered by one ofyour research specialists. At any ratehere it is: While flying in air space designated as a flight level (either IACO or U.S. jurisdiction) does one introduce theK factor to the standard altimeter setting of 29 .92?I have been told both ways; however,no one is able to provide a reference . Ipersonally never use the K factor due tothe fact that none of our sister servicesuses it while flying at an altitude designated as a flight level.CPT Stan W. King2d M. I. Flight SectionSembach Air BaseAPO New York 09103

Your letter was forwarded to the U. S.Aeronautical Services Office, CameronStation, Alexandria, Va., which providedthe following answer to your question:

We recommend the use of the K factor adjustment whenever the error doesnot exceed the 70 feet maximum permitted(.07 inches Hg). f the error exceeds thisfactor you should consider the instrumentunreliable. Basis reference for this function is found in TM 1-225, paragraph 2-37.

The following logic may help in understanding this practice. Suppose you takeoff from a sea level airfield for which the

current altimeter setting is 29.92 (Hg) andthe altimeter reads minus 60 feet. Youwould set the altimeter to read 00 feet andnote the Hg difference (K factor) in theKollsman window. When cruising where29.92 is normally used as a standard, youwould accordingly maintain the samecorrection (K) factor. This correctionwould also be applied to any subsequentcurrent altimeter setting required and willcom pensate for the inherent 60foot error .DOD FLIP describes altimeter settingprocedures but does not address the erroradjustment. It's good to remember thatyou've set the 29.92 only after you've adjusted for the known error.We trust this will help clear the issuefor you. Your letter has identified a needto clarify the procedures contained in reference manuals. With thanks to you, wehave brought this to the attention of reosponsible offices.Sir:Due to the fact that I am a supplyofficer for Company E, 42d Aviation Battalion . New York Army National Guard.and trying to keep our pilots suppliedwith the latest safety equipment. I aminterested in the di spos ition of Nomexsuits in CONUS.Through our normal supply procedureshere and at higher levels we have beenunable to obtain Nomex flight suits,gloves, SPH-4 helmets , etc . We do havethe same problems with flying safety asthe active Arm y

However. there is a surplus store inNew York City which is presently sellingthe Nom ex flying uniform for 14.00 perset. Some of this equipment is new andsome used . If they can get this equipment so fast and we cannot, how come?

Sir:

CW2 William L. SeymourNew York Army National GuardAmityville, N. Y. 11701I am writing in regard to a letter whichappears in the Views From Readerscolumn of the March 1971 issue of AVIA

TION DIGEST .Continued on page 5


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e rmed The HelicopterThe helicopter was the ugly duckling of aviation in the mid1950s. But there were a few who dared to think of i t as a weaponssystem and the key to successful airmobile operations. Today thereare few who would think of going into combat without the helicopter

HELICOPTER armament wasinevitable. The requirementwas generated by the historicNational Security Act of 1947which established the U. S.Army and U. S. Air Force asseparate departments. The AirForce retained the responsibilityfor close air support; the Armywas allowed to retain light observation aircraft with Army pi-lots.The nex t decade saw anational military doctrine dictated by strategic nuclear weapons. The strategic air commandheld first priority on the AirForce budget. The tactical air

Colonel Jay D VanderpoolU S Army, Retired

command directed its limitedfunds primarily to intercept andinterdiction functions, with littleleft for close support. As jet air-craft flew higher and faster theybecame less responsive to theground commander.

Meanwhile, the helicopter wasbattle-tested during the KoreanWar. t was then that I first be-came acquainted with this amazing f ly ing m a c h i n e Myorganization was a cloak anddagger outfit engaged in militaryoperations behind enemy lines inNorth Korea. t was a joint andcombined command. As a contribution from our theater Air

Force commander we were assigned a squadron of SikorskyUH-19s, primarily I think be-cause no one knew what else todo with them.

The value of the helicopterwas soon recognized in the rolesof air-sea rescue and aeromedical evacuation. Not many peoplehad the time or inclination tostudy this new vehicle but thenature of my job forced me tolearn how to use it

One mission profile demonstrates what the helicopter couldreplace in that war. Normally,when I visited one of our off-shore island bases behind enemylines I would go by jeep to aport or beach. There I d take aNavy landing boat out to deepwater where I d board a Britishlight cruiser escorted by destroyers. We d steam at 25 knots tothe island where we offloaded ina landing craft. Another jeepwould take me to the base. Thattied up a lot of hardware andtime to move one officer aroundthe battlefield

Lft: Colonel Jay D Vanderpool di-rected and sparked the develop-ment of the Army s airmobility andarmed helicopter programs in the1950s. He was not an aviator but hisWorld War II and Korean War experi-ences made him uniquely aware of thehelicopter s potential on the battlefield


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Rght: Brigadier General CarlI Hutton triggered develop-ment of the armed helicopter whenhe was the commandant of the US Army Aviation School at Ft Rucker Ala. in the mid 19505

When we received the helicopters we would fly from our headquarters in Seoul direct to theisland ba e refuel and return.One helicopter two pilots and acrew chief relieved a large combat force for other missions.However one thing disturbedus: we were unarmed. When wedid not have a fighter escort weflew well out to ea over the iceflow where survival in the Yellow Sea in winter was estimatedat less than 8 minutes.In 1955 I was assigned to theU. S. Army Aviation School atFt. Rucker Ala. and took aninterest in helicopter armamentsystem experiments which werebeing conducted within theArmy but unfortunately did notprove conclusive . Then in June1956 Brigadier General Carl I.Hutton commander at Ft. Rucker, was determined to prove thefeasibility of arming helicopterand developing a 100 percentarmed, airmobile force. I wasgiven the mission and later, asChief of the U. S. Army Aviation School's Combat Developm e n t s Office, gu i e theprogram through its early years.

Our basis or excuse for actionwas a training memorandumfrom General Willard Wyman inthe Continental Army Commanddirecting the development ofhighly mobile task forces withan improved ratio of firepowerto manpower for employment onthe nuclear battlefield. GENWyman did not tell us to usearmed helicopters but neitherdid he tell us not to. We went towork using our local resources.On 3 July 1956 GEN Wymanformally approved our experimentation providing we coordi-4

nated with the U. S. ArmyInfantry School at Ft. Benning,Ga.

We deliberately started with amall cadre of five people andselected the OH-13 as our firsttest vehicle. We decided to startwith caliber .50 machine gunsand antitank aerial rockets. Wepicked the caliber .50 reasoningthat if we could handle it smallerweapons would not pose seriousproblem . We chose the antitankrocket because we consideredthe tank to be the most difficulttarget on the battlefield to hitand kill.

The most promising antitankrocket available wa the Swis -made Oerlikon, 8 centimeter,fixed-fin weapon de igned fordelivery by fixed wing aircraft.The rocket was launched with azero travel rail which was easy

to install and had very little deadweight after firing. The weightpenalty for four rocket , rail,gunsight and station distributorwas 146 pounds. We wired thesy tem for single rounds or aripple at 100 milliseconds.

The machine gun installationcost us 150 pound plus theammunition which was about 35pounds per hundred. We were of course crowding our weightlimitation . The machine gunrecoil thrust was softenedwith edgewater adapters.There were many unknownsthe first day we went out towhat i now Matteson Range: Would the machine gunrecoil shock do structural damage to airframe? Would the muzzle blastbreak the plastic bubble anddoors?

U. S. ARMY AVIATION DIGEST


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Would the machine gunrecoil thru t cause a eriouspitching attitude in flight?

Would the recoil generate aseriou decrea e in air peed?

There were al orne realque tions concerning the aerialrocket ystem which was designed for launch speeds of 180knot or more. Rail travel wasonly about an inch from theshear pin and we were to try azero air peed launch with azero travel guide rail:

Would the rocket tumble? Would the helicopter rotordownwa h on the big fixed finsdeflect the trajectory?The rapid ignit ion of therocket motor , re trained by a12G shear pin , gave hope thatthe shear pin would hold untilwe had enough thrust to give ua stable flight. We bore-sightedour sy terns in orne 800 yardsdown range and were ready totes t fire f rom an e leva tedwooden platform on which thehelicopter was securely anchored (see back cover). We hadnot invited a large gallery onlyGEN Hutton , the test team anda few others.

We tested the machine gunsfirst singly and then in pairs withincreasingly long bursts. Westopped frequently to in pectvisually for structural damagebut found none. In later tests themuzzle blast and/or vibrationunlocked the door which wereriddled . We removed the dooras an unnecessary luxury .

We next test fired a rocket byremote ignal. It impacted downrange on line for azimuth andslightly short of the bore-sightpoint. We could hardly believeit , so we fired orne more singlyand in ripple . The dispersion

Rght: Machineguns are fired froman OH-13 during helicopter armament tests in the early 1950sat Ft. Rucker s Matteson Range

JUNE 1971

pattern wa much mailer thanwe had even hoped it would be.We were close to an antitanksy tern.

The next tep wa to crank upthe helicopter to crui e rpm, pullorne pitch to generate a good

downwa h and fire more rocket . With our telescope andbinocular we could not detectany appreciable increase in thedispersion pattern.

After a final check for structural damage we fired both gunsand rockets from a low hover.We had no problems except thatthe dispersion wa gr ea t e r -whether due to the pilot or thesy tern we were not then sure.

After another examination forstructural damage the pilot tookthe hip around and fired machine gun and rockets downrange from about 00 feet alti-tude. We reloaded and madeeveral more firing passes. Accu

racy wa increased with eachpass. We had had no problems... we were a mighty excitedand happy group.

We knew we did not have theoptimum air vehicle nor an optimum weapons system, but we

had proven the fea ibility andpracticality of arming the helicopter. We were particularlyelated over the surprising accuracy of our weapon . Most previou tudies had concluded thatthe helicopter wa too un tableto be employed a a weaponpla t form The s tudie werewrong.

The next step was to tudyarmed airmobile tactical organizations or formations-our realobjective. GEN Hutton directedon a Friday afternoon that wedevelop a conceptual ky caval ry-an airmobile tactical forceof company size; determine theaircraft requirements; determinetroop and pilot requirements ;sketch a troop maneuver scenario; a emble the pilot , troopsand ai rcraf t on the paradeground Sunday morning forbriefi ngs; and conduct a maneuver Sunday afternoon. We werepretty busy that weekend.I drafted the organization thatnight. The doctrine was till inour minds. I leaned heavily onthe Duke of Wellington concept of cavalry, dragoon andartillery employment. Hi caval-

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rymen fought from their mount .The dragoons were hor emounted infant ry who dismounted to fight. They wereupported by hor emobile artil

lery. His trains moved by horsedrawn wagon. Wellington haddone well with this type organization; we would try it.

We employed the helicopteravailable in 1956 and our pilotwere selected in tructor pilotsfrom the aviation choo ' Theinfantrymen were drawn fromschool troop . Helicopters weretaken from the school trainingfleet. They were unarmed ofcourse.

That Sunday GEN Hutton andI experimented with commandand control of the airmobileforce. My biggest problem wasgrasping how quickly the forcecould respond. It could convergeon a point in moment or disperse over miles of area in min-utes. The cavalry platoon couldcover dozens of square miles in amatter of minutes

Our early scenarios assumedthat the enemy had a radar detection and antiaircraft capabili ty . We s t r essed that the6

helicopter must take advantageof covered approaches and useits inherent speed and agility toachieve surprise. This requiredcareful terrain analysis and treetop flying. We flew just abovethe trees or between them whenwe could. Although we werefreed from terrain and vegetation, we wanted to use them forconcealment. We wanted to besneaky.The profes ional instructorpi lo t , mostly civilians, weregood-very good. The new tactical flying was a welcome changefrom their routine training misions. Each pilot tried to find

better technique for low alti-tude maneuver. We were alllearning together.

During 1956 and early 1957 weworked on experimental weapons systems during weekdaysand experimented with tacticsand techniques on weekendswhen the school was closed. Werecognized requirement forweapons sy tern for specificmis ions as defined by Wellington. We needed weapon forhard targets and soft targets, forpoint targets and area target .

Lft: OH-13 helicopters were avail-able at Ft. Rucker in the 50s. Thusthey were used both for armamenttests s depicted on page 5 andalso s seen here for the develop-ment of airmobile tactical concepts

The "cavalryman" would fightfrom hi mount. He needed allthe firepower hi reconnaissancehelicopter could lift and stillaccomplish the mi sion.

The dragoons would dimount to fight. The primary air-craft mission was to delivertroops. Some defen ive or suppre ive fire was de irable toensure safe delivery and evacuation of the infantry.Artillery or weapon hipswould support the entire force,whether airborne or in groundmaneuver. Maximum firepowerwithin lift capabilities was e ential.

Trains would require someprotective or suppressive fire topermit mission accomplishmentwith minimum cavalry or artil-lery support.

With these principles in mindwe extended our testing withinour own resource of men andmateriel. We didn't have anymoney but we did have ideas,helicopters, maintenance andfuel from the aviation center.We scrounged everything elsefrom Air Force, Navy, Armyordnance and industry. It was allcondoned and encouraged atlower levels of command andgenerally ignored at higher lev-els.

We knew we had to prove ourconcep t , obtain recognition,r esearch and deve lopment(R&D) money, machines andmanpower before we were hotdown in flames. Dozens of y -terns were fabricated in our shopand tested.

Continued on page 4U. S. ARMY AVIATION DIGEST


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FOG DISSIP TION QUESTIONN IRENumerous experiments have been carried outwith helicopters in attempts to dissipate warmfog Many of these experiments have been suc-

cessful while others have failed There are atpresent several documented cases of rotary wingaircraft being used to dissipate fog; however it isbelieved that other experiences that might providevaluable information on the subject may havegone unreported or undocumented.

In order to expand the data base on the subjectit is requested that anyone with personal experi-ences or knowledge of the downwash of rotarywing aircraft being used to dissipate fog pleasesupply the information on the questionnaire. In-formation pertaining to the fog dissipation projectat Ft. Rucker Ala. during 1 to 28 February 97may be omitted.

Please cut out this page fold and mailI. a. NAME: _

b RANK: ________________________________________________________________c. SSAN: _d. UNIT, DUTYPHONE: ____________________________________________________

II. a. Location/Date/Time of Fog Dissipation Experience:

b. Type Terrain:

c. Visibility on ground and on top of fog:

d. Aircraft type/gross weight:

e. Flight Posture hover, slow forward flight, etc. and any additional flight information youconsider pertinent to the experience:

III. Summarize what was done and what resulted from that action:

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Cut along line at right fold and mai I postage free

FOLD

DEPARTMENT OF THE ARMYHEADQUARTERS

UNITED STATES ARMY AVIATION SCHOOLFort Rucker Alabama 36360

OFFICIAL BUSINESS

POSTAGE AND FEES PAIDDEPARTME NT OF THE ARM

U. S Army Aviat ion SchoolA ttn: A TSAV -DL-DDFort Rucker Alabama 36360

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taple t


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OH 58 iowa

Dan Ti.dal. Jr.

Dan Ti.dale Jr. a .ale.engineer with Bell HelicopterCo. explain. the powercapabilitle. of the Kiowa

IF Y U H VE never flown a your technique for the characturbine-powered hellcop- teristics of each helicopter areter, the rules you have I.arned different. In either case you,about using manifold pressure the professional pilot, mustfor power management will understand how the Kiowa'shave to be unlearned when performance Is affected by theyou start flying the OH-58A power margin-the exceKiowa. If you have flown other power available over the powerturbine-powered helicopters, you demand. (The power v il-you may stili have to modify ble for use is limited by the

engine and/or airframe ratln,and power m. .ln do.. notimply an engine pow.r re v.above this maximum ratln. )L.t s look then at thl. powermargin, how you determine Itand why you n.ed to know It,and abllsh .ome auldeUne.for evaluating the Kiowa .capability.


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Basis for Power Margin-Power Available

To understand how an aircraftperforms under various operating conditions, it is necessary tocomprehend the effects of theseconditions on the engine ratingand power output. The OH-58AKiowa is powered by an AllisonT63-A-700 turbine engine thatproduces 317 horsepower at sealevel on a standard day. Whenthe altitude and/or temperaturediffer, so does the power outputfigure I).

At ll combinations of temperature and altitude within theshaded area in figure I, 317 horsepower are available. At greateraltitudes and temperatures, however, the power available wil1 bereduced. The line at 35 degreesC. shows how the power available is reduced as altitude is increased at that temperature. Atemperature change alone has aneven greater impact on poweravailable. For example, a 10-degree increase in outside airtemperature reduces the poweroutput by approximately 10 per-

10

u

10000

I 8000wC;:j : 6000ICwa:;:

4000wa:

2000

o-50 -40 -30

cent. This is not so in a reciprocating engine. Less than 2percent of power is lost with theto-degree change in outside airtemperature or an equivalentcarb-air temperature adjustment.It is because of these variationsin power with altitude and temperature that power availablecharts are so important to theaviator, and therefore, they areprovided in the operator s manual. But there is another veryimportant factor: time. If youtake the power available foryour conditions from the TAKEOFF POWER chart, you can useit for 30 minutes without exceeding the engine limitations. Values taken from the NORMALPOWER chart have no timelimit; they are maximum-continuous ratings.

Power IndicatorsThe torque meter and the tur

bine-outlet-temperature TOT)gauge are both power indicatorsbut ambient temperature and altitude affect their use. Whenconditions are such that thepower output is somewhat less

-20

FIGURE I

TEMPERATURELIMITEDAREA

-10 o +10

than the sea level standard rating, TOT wil1 reach the redlinewhile torque is still within theoperating range below the torqueredline. In this case the TOT isthe power limiter; therefore,TOT margin represents thepower margin.

At sea level on a cooler day,when power is applied thetorque limit is reached beforeTOT hits the redline. Nowtorque is the power Iimitee. TheOH-58A is designed so that thistorque limit occurs when theengine is producing full-ratedpower, 3 t7 horsepower. In otherwords, the transmission is ratedat 317 horsepower so that thetotal output of the engine can beutilized if necessary. In somehelicopters the transmission israted below the engine s maximum output , so there is atorque limit at some value lessthan the engine s peak power.But, the torquemeter in the OH-58A reaches the redline onlywhen maximum power is beingtransmitted to the transmissionand under these conditions the

+20 +30

} 175HPy 92 HPI

Y 2 1 0 H P

Y 2 3 0 HP

+40 50OUTSIDE AIR TEMPERATURE - c



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torque margin I indicative ofpower margin. It is evident thatoperating conditions have a substantial effect on the engine spower output and , con equently,on the limit that the pilot mu tabide by figure II).

Figure II indicates when eachof the two indicators (TORQUEor TOT) should be used . At allaltitude and temperature combinations within the haded area317 horsepower are availableand torque is the limiting factor.In effect , in this torque-limitedarea power margin is of littleconcern becau e performancecapability is more than ample ,even at maximum gross weight ,but you must monitor torque toprevent exceeding the limits inaccordance with the o p e ~ a t o r smanual.

TOT i the limiting factor outside the shaded area. Since lessthan 317 horsepower are available the helicopter cannot reachthe torque limit. In effect , youreach red line TOT at the poweravailable for those conditions. Inthe temperature-limited area ,performance capability is not aswell defined as when full poweris available. For this reasonpower margin in terms of TOTcan be a useful aid to predictperformance capability.

The TOT gauge is shown belowwith the operating limits

9 10 TURS8 OUT5 TEMP4

~ :3 2

MAX CONTINUOUS .. 693 C30MIN LIMIT .. 749 C

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FIGURE II10000 T63 A 700POWER LIMITATIONS

I BOOOw0;:j: 6000..Jwa:;: 4000wa:Q.

2000

50 40 30 20 10 +10 +20 +30 +40 +50OUTSIDE AIR TEMPERATURE _ c

Some rules of thumb for predicting performance capability forthe OH-58A can be drawn interms of hover capability inweight and altitude), speed andrate of climb. This informationis to supplement the operator s

manual and help the pilot better understa nd a nd interpret theKiowa s c p bi l i ty within theoper t ing l imitat ions . WhenTOT is above 600 degrees C.the following rules of thumb

pply under most conditions

HOVER

SPEED

RATE OFCLIMB

RULES OF THUMBo For each degree of TOT remaining, approximately 10 pounds

rnay be carried , or :200C TOT one Increment = 200 poundson the gauge

o For each degree of TOT remaining the OH 58 A can hove rapproximately 50 feet higher , or:

120C = 1000 feet Io For each 10 degrees of TOT remaining peed can be increased

by approxima tely 2.5 knots o r:120 0c TOT = 5 knots I

o For each degree of TOT remaining, the rat e of climb at 54knotTA can b increa ed by approximately 10 feet per minute, or:120 0 TOT = 150-200 feet per minute I*Depend on gross weight

NOTE: Each of the Rule of Thumb is also true for a 5-psi increment on the torquemeter.

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It took only a few seconds toconfirm that they did have aserious line 2 that needed tobe medevaced immediately. Iwas also informed that theRTO was new on the job andwas just a bit confused as towhat was happening.My crew and I decided toat tempt a hover down, although one of my crewmenwould have to remain behindwhile the medevac mission wasbeing performed due to theweight problem.As I made my last reconpass I noted that the aircraftwas now down to 160 poundsof fuel full load for an LOH is400 pounds) which gave us anextra 240-pound margin. Thewind was light and variable,again Lady Luck was smiling atus. One factor not in our favorwas that only about 1 hour ofdaylight remained. However,this was ample time i f the mission went more or less asplanned.With this in mind and myheart in my throat I advisedmy high bird and the commander of our decision andbegan to hover down .For the first 30 feet downthings looked pretty easy. Mycrew chief, standing on theright skid, was giving instructions for positioning the aircraft. At about 30 feet downhe advised me to move forward3 feet to keep from connectingwith a branch of mahogany.After moving forward we continued down another 20 feetand again had to move forward this time approximately8 feet. With a 30-degree heading change we were now about80 feet above the ground.

ta r t ing down again Iglanced overhead and was horrified to see nothing but trees,limbs and very little blue sky.A go-around at th is point

JUNE 97

would have probably provenfatal due to excessive weightwe were between 2,200 and2,300 pounds due to missionrequirements.

By now the crew chief wasgiving directions as fast as hecould. The next 30 feet wentby rather easily with only one5-degree heading change.I was beginning to feel a litt le more relaxed when sudden ly I n o t i c e d a ve rydistasteful looking tree about5 feet under my chin bubble. Iinformed the crew chief of thenew problem and was thenadvised that we could possiblymove to the rear 10 feet ,which would just clear us ofour forward obstacle. The onecatch was the tail rotor clearance only about 1 foot oneach side. We were still 50feet from touchdown and a tailrotor failure would probablyhave meant disaster. Withsweat dripping from my forehead we finally managed tobypass the tree.As we neared the ground Ispot ted about 12 smi l ingtroops crouched in their defensive positions. One of themjumped up and guided us therest of the way in. With theskids on terra firma blownaway bamboo) we all breatheda sigh of relief. I glanced at mywatch and saw that our hoverdown had taken approximately8 minutes .I elected to keep my crewchief on board for directionssince he was experienced sothe observer unstrapped andtook the M-60 machine gunand the rest of the ordnanceoff. This reduced the weightabout 200 pounds. The l ine 2was loaded aboard, apparentlythe victim of a mine which hadreally done a job on his back.You could tell that he was inextreme pain, but he did man-

age a slight smile of thanks.Just prior to takeoff I no-ticed we were down to 130pounds of fuel. As we lifted offi t was readily apparent thatthe bird was much more re-sponsive due to the decreasedweight. I also noticed my observer was now dug in on theground.

The f l ight out seemed atleast three times as easy asthe one coming in . Our intended fire base with a doctorwas only 10 minutes away sothings were going pretty well.After dropping the l ine 2 offwe proceeded to the ammodump and started loading theO had requested as many

smokes and grenades as possi-ble). Afterwards I made ahover check and found that Icould almost hover at 1 footusing 3 pounds of torque under the redline.We quickly unloaded twocases of smokes and one caseof grenades. This t ime thehover check was acceptableand as we lifted off there was100 pounds of fuel remaining,just enough to complete themission with a little to spare.This was another lucky breakbecause now the sun was al-most down and it would havebeen impossible to get in afterdark.As we again approached theLZ the crew chief positionedhimself to vector us in. It wasvery gratifying to see that ourletdown was much easier thistime due to our knowledge ofthe area.

The unloading of the M-79rounds and smokes was uneventful. Our observer happilycl imbed aboard and we departed with much relief.As we were on short final the10-minute warning light cameon. Things h d really workedout just right

]


16/68

14

Provided by the Society of U S rmy light Surgeons

Major Nicholas E. Barreca, M. D.

The 1970 edition of Accident Facts, a magazine published bythe National Safety Council says that during 1969 about 20 per-cent of the automobile accidents were caused by failure to yieldthe right of way. Some of these were the fault of drivers who forsome reason or other, did not heed the Stop or Yield signs.But many were caused by drivers who came up to the intersec-tion, stopped or slowed looked both ways to see if somethingwas coming and proceeded through right in the path of an on-coming vehicle. Why? The answer is that they did not see theother car. In some ways each of us is a l i t t le bit bl ind

U S ARMY AVIATION DIGEST


17/68

Oh Say anYou SeeTo the air crewman: Did youever look for something andfinding it right "under your nose" wonder how you misseds ing it? Perhaps t w s "behind" your nose Occasionallyanother might say, "What areyou, blind or something?"-notrealizing how true that statementmight be. Actually, each of us isa little bit blind This condi tion,while certainly a frail humanlimitation, is nevertheless anormal and necessary consequence of the eye's structuralmakeup.

The anatomy (structure) of theeye is simple, but unique. Theinner surface of the eyeball islined with a light sensitive layerof nervous tissue called the ret-ina. This layer is much the sameas the film in a camera and con-tains specialized light receptorscalled rods and cones. The rodsand cones are the cells responsi-ble for sending light images tothe brain. They send their mes-sages through avenues caIJednerve fibers. The fibers cross theretina and exit the eye on theirway to the brain. This point ofJUNE 1971

exit is caIJed the optic disc.Light enters the pupil or keyholeof the eye and is projected to afocus on the retina by the cor-nea and lens. f one was to peekthrough the keyhole (pupil), inmuch the same way as a flightsurgeon using an ophthalmoscope, he would see the curioussight in figure 1

To one side, the pale yellowoptic nerve head (optic disc) isseen, from which a network ofarteries and veins radiate outand stream across the retina.The optic disc and blood vesselsare not sensitive to light, thusthey are projected into our fieldof vision as blind spots, knownmedically as scotomas. Luckily,the most sensitive portion of theretina, known as the macula andfovea centralis, are not inter-fered with in this way. A con-centration of cones at themacula is responsible for 20/20visual acuity and central vision.The visual blind spots are pro-jected into our peripheral (side)fields of vision where visual acu-ity becomes as poor as 20/200*.Thus, our most sensitive vision

is not usually obscured whenboth eyes operate together pro-viding us with binocular vision.This is because the blind spot inone eye is covered by vision inthe other eye.Under certain conditions ofsloppy viewing or scanning it ispossible for our potential blindspots, especially the one result-ing from the optic disc, to ob-scure vision. This can be vividlydemonstrated by the examplesbelow:First, looking at figure 2 holdthis page about a foot in front ofyour eyes. Close your left eyeand look steadily at the pedestrian while moving this pageslowly toward you. The car dis-appears Now close your righteye and look steadily at the carwhile moving this page slowlytoward you. The pedestrian dis-appears

Next, pick a point across theroom. Extend your right armwith the thumb extended up-ward. Close your left eye andplace your thumb so that it sup-ports the visual point of regard(like a target on a rifle sight).

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Now continue to look at thepoint with your right eye aloneas you move your thumb slowlyto the right. Your thumb disap-pears

As your blind spot s pro-jec ted in the dis tance , itbecomes larger and larger interms of the size object that itmight conceal in the distance.The blind spot is a circle about

Figure

6

1 2 inch in diameter at 8 or 9inches. This circle of blindness ,when extended to a distance of200 feet, s about 6 feet in diameter. Thus, at 200 feet it couldswallow a car or small aircraft.At 100 meters it could conceal aUH-1D /H.All very interesting , but howcan you , the two-eyed ogglingman , get into trouble? Well ,

some of us are endowed per-haps burdened) with prominentnoses. The bridge of the nosecan prevent the opposite eyefrom covering the blind spot ofthe other. In addition, the eyehas other limitations, particularlywhen it is rapidly scanning.

First , retinal images do notregister sharply when the eyesare moving. The image isBLOOD

V SS LS

M CULND FOVE

CENTR LISU. S. ARMY AVIATION DIGEST


19/68

blurred. This is why spinningdancers or skaters snap theirheads a full turn for a split-second focus on a point to preventnausea and dizziness.

Next, the eyes can only focusclearly on points about 45 degrees from central fixation (eventhough our binocular field of peripheral vision is 180 degrees ormore). Thus, clear, sharp imagesare received only when we arelooking directly at an object ofregard and dwell on it for a fewinstants.

I ~FigureHere's how your scotoma(blind spot) and other limitationscan blank out an oncoming caror aircraft at 200 or 300 feetfrom your left or right. You pullup to an intersection and stop.Hurriedly, without moving yourhead and neck , you glance to theleft and- right. An oncoming car200 to 300 feet away would notregister while your eyes aremoving. You momentarily focuson a point about 45 degrees tothe side. At this point the bridgeof the nose prevents the opposite eye from covering the blindspot n which an oncoming vehi-cle could be hidden Thinkingyou are clear you start throughthe intersection. The oncomingvehicle is seen in your peripheralvision as you move into the intersection. By then it may beimpossible to prevent an accident because the vehicle, whichwas hidden in your blind spot,will need 243 feet to stop at aspeed of 50 miles per hour.BLAM You've done boughtyourself an accident

So there you have it You toohave a blind spot. Your flightsurgeon can easily demonstrateit for you if you must be shownmore dramatically. He uses aJUNE 197],

device called the tangent screento measure an indivudual centralfield of vision . This test is performed with one eye patchedand the individual seated onemeter away from a fixation pointon a black background . A smallwhite target, usually one to twomill imeters in diameter , ismoved through the predetermined meridians on the screen.The flight surgeon can thus determine the position and size ofboth normal and abnormal"blind spots" of the examinee.

The normal blind spot wasdiscussed above. There aremany causes of abnormal blindspots. Some result from abnormal enlargement of the "normal" blind spot. This can becaused by an increase in the intraocular (inside the eye) pressure, such as from glaucoma.Many types of blind spots canbe caused by abnormal pressureor certain inflammatory diseasesand toxic agents. Injury to theeye can sometimes result in scotomata. The amount of visionlost depends on the location andthe degree of overlap from thenormal eye.

These blind spots and thenormal one should not be confused with the "night blindspot." As mentioned before , theretina is composed of rods andcones. The cones are the specialized receptor cells that areresponsible for the very acutevision necessary for reading.They are also responsible forcolor vision. The problem withcones is that they are unable to"see" in low or dim illumination(starlight). Since the cones arecrowded and concentrated in asmall area on the retina (themacula) along the central visual

axes of the eye , darkness willproduce a blind spot whereverthe macula is projected into ournight visual field. The normalblind spot, due to the optic disc,is present all the time. The nightblind spot occurs only when westare at an object under verylow illumination. Thus, at nightwe have two blind spots.

As an old pilot adage goes,"Keep your head on a swivel."With all of our limitations it's awonder we see at all. The use ofsome precautionary steps willincrease your seeing ability anddecrease the likelihood of catastrophe.

Under daylight conditionslook in the direction you wish toclear visually. Turn head andneck as well as eyes so that binocular vision covers the blindspot.

Establish a consistent andmethodical scanning pattern indaylight. Scan from left to right,top to bottom in overlappingareas , hesitating at each pointand looking for several seconds.

Avoid a sweeping "radardisc" scanning pattern. All youwill see is a blur which mayconceal the small discrete imageof a distantly approaching aircraft.

At altitude there may benothing within view to visuallyfix upon. This can cause a condition called space myopia ornearsightedness due to overaccommodation. To void this oneshould look at the ground fromtime to time or at a distant cloudor even a wing tip (provided it isas much as 20 feet away). Thus,your eyes will be focused fordistance when an aircraft comesinto your scanning pattern .

At night a different scanning pattern must be adopted. Itmust still be consistent and methodical from left to right, top tobottom in 10-degree overlappingcircles. The major difference is

7


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the avoidance of staring or looking for more than an instant.Staring causes the night blindspot to cover the area to beviewed. Once a target is acquired by silhouette in the peripheral or side fields of vision,it can be followed by looking 10degrees to the right , left, aboveor below it to avoid the nightblind spot as well as bleachingout the rods.

Finally, if blind spots inyour visual field become apparent under other than the "normal" condi t ions descr ibedabove, seek the advice and examination of your flight surgeon.The life you save may be yourown

o th flight surgeon: In a previous issue of AVIATIONDIGEST ( Aeromedic," April1970) the combined use of theclear plastic helmet visor and N-15 sunglasses was recommendedfor dual protec t ion againstbrightness and injury. Some inquiring minds have wonderedabout the extent of reduction intransmitted light resulting fromthis practice and the impact ofthis limitation of flying safety.Light transmission through thewindscreen of UH- 1 aircraftapproximates 87 percent. Sincelight transmission through the N-15 sunglasses is approximately15 percent, the ultimate lightreaching the eye would be 13percent of that incident upon theaircraft windscreen. This figureis well within the desired limitsfor light transmission throughsunglasses, the range which isgenerally given to be between 10to 15 percent. Even under conditions in which the combinationof the clear polycarbonate helmet visor and N- 15 sunglasses isused, an ultimate light transmission of 11.35 percent would berealized. Again, well within thesuggested limits for conditionsof bright sunlight.18

A t night the use of a clearvisor would ultimately re sult inthe transmission of approximately 80 percent of the lightincident upon the aircraft windscreen. Thus , at night the clearvisor is best used on takeoff,landing or when the risk of hostile fire is evident. A number ofincidents have been reported inwhich the only injury sustainedby an air crewman was to hisvisual apparatus. These occurredunder hostile fire conditionswhere the air crewman , failingto use his helmet visor for protection , was struck by extremelysmall, but damaging, metal fragments. For the simple lack ofeye protection these air crewmen sustained serious eye injuries, many with visual loss sogreat as to preclude flying.

Occasionally through misappropriation air crewmen willacquire and use helmet sun visors intended for arctic or desertconditions. These visors willtransmit only 5 to 7 percent oflight incident upon them. Theother military services frequently issue them for extremelybright environments (snow,sand, etc .) , but they are notmeant to be used routinely.

Looking at already existingcharts for visual acuity plottedagainst illumination , it was estimated that on an average brightn e s s d a y , e v e n if l i g h ttransmission were reduced to 0.1percent , one would still have20/20 visual acuity. A n experiment was performed using theVT A near and distant visual acuity test. Two N -IS sunglass filters were placed over each eye(yielding a 2 .25 percent lighttransmission). This resulted inno reduction in the observer'svisual acuity. The light availablein this situation was equivalentto 10-foot candles. An overcastday provides about 500-footcandles.

The contrast illumination of atarget will ultimately determineour ability to see with 20/20 visual acuity. Under relativelybright days, reduction in lighttransmission normally will notinterfere with visual acuity.However , when total illumination is decreased and contrastbetween objects of regard andbackground is diminished, theuse of sun visors, particularlythose with low transmission 5percent), might become a hazardto flying safety.

Since sunglass filters are beingdiscussed, another potentialproblem area is worthy of consideration by the flight surgeon.f there is a 25 to 30 percent

difference in light transmissionbetween one side of a visor andthe other, it is theoretically possible for disruption of true stereopsis to occur . This waspreviously described as the Pulfrich stereo phenomenon, andgenerally applies to the individual lenses of sunglass spectacles.When there is a large differencebetween light transmission fromone eye to another , a swingingpendulum , rather than havingpendular motion will insteadappear to have elliptical motiona change in apparent depth).This is what Pulfrich originallydescribed.

This phenomenon was alsotested using the VTA stereopsistest. A flight surgeon viewed thestereoptic circles with an N -ISfilter over one eye and no filterover the other, thereby creatingan 85 percent difference in transmission. This did not interferewith his ability to identify stereoptic circles. He then testedhimself with a 12 to 13 percentdifference between spectaclelenses , and again there was nodisruption of stereopsis. However, this is a static test of stereopsis . The resul t s underdynamic conditions were not



21/68

tested. It is under conditions ofmovement that Pulfrich described his illusions of depthproduced by differences in lightt ransmission between eyes.Thus, this phenomenon remainsa potential hazard when air crewinadvertently mix sunglass lenses indiscriminately.

Standard issue sun visors areuniformly tinted to military specifications. They are seldom asource of the above phenomenon unless altered by the aircrewman (i.e. , application ofcommercial sprays or films). Theaccidental combination of sunglass filters of differing transmission is possible though remote.Flight surgeons should be alertto the accidental occurrence ofthis situation and warn air crewof the potential hazards createdby the misutilization of otherwise useful and necessary eyeprotection.

There are a few abnormalconditions of the eye that canproduce the Pulfrich stereo phenomenon as well. Monocularpupillary constriction is one, butthis condition would usually bedrug induced or t raumaticHowever, perhaps an individualwith Horner's syndrome couldpresent with depth perceptiondifficulties. Other types of unilateral pathology can potentiallycause the phenomenon. Opacification of the cornea or vitreousand early cataract might causesufficient reduction in unilaterallight transmission, while stillpermitting relatively sharp vi sion.

In summary, the followingrecommendations are offered foreye protection:

Under bright sunlightedcondi t ions all a i r c rewmenshould use sun visor or sunglass(N -15) eye protection.

For general usage the combined use of the clear helmetvisor and sunglasses providesJUNE 97

I

ideal protection in sunlight, withthe availability of alternativeprotection for night flying.

At night the use of the clearvisor will permit adequate lighttransmission for most conditions. However , it is recommended that risks versuslimitations be weighed, choosingonly those times when the potential risks are increased , i.e.,takeoff, landings (normal andemergency) and when hostile fireis anticipated.

Use only standard issueequipment for this protection.Avoid the use of scroungedequipment , which may havebeen intended for special purposes. The Army air crewmen'ssun visors and sunglasses havetransmission values of 5 percent.

Refrain from applying comercial sprays or plastic films tosun visors or sunglasses. Thiscould create a situation where

difference in light transmiSSIOnresults in disrupted stereopsis.In addition, intolerable distortionresults. Do not jerry-rig sunglassspectacles. Have them repairedwith standard filters from authorized sources.* Visual acuity or one's abilityto see sharply and distinctly istested with the use of a visiontesting device called the Snellineye chart. The letters on thischart are of such a size that the

20 line can be easily readwith one eye, by a person withnormal visual acuity, from a distance of 20 feet. Thus , when anindividual reads this line from 20feet he is said to have 20/20 visual acuity. f he can only readthe big E (the 200 line' ) hisvision is poor, for he must cometo a distance of 20 feet to read aletter the normal eye can seeclearly at 200 feet. Thus, he issaid to have 20/200 visual acuity.

INSTRUMENT ORNERQ. At what point is an aircraft considered to be in the holdingpattern?A The aircraft is considered to be in the holding pattern atthe time of initial passage of the holding fix. Reference: DODFLIP, 1 Apr 71, section II, page 11-77.)Q. When a pilot has been informed by ATC that his aircraft isin radar contact, and then is later handed off to another con-troller, is i t necessary that the new controller advise that hehas radar contact?A No, this fact will not be repeated to the pilot when handedoff to another controller. At times the aircraft identity will beconfirmed by the receiving controller.Reference: Airman s Information Manual, February 71 page

1-55, TB AVN, 24 Feb 71 1-761.)Q. Is there a requirement that an ATC clearance be read backeven when not requested to do so?A No, however, controllers may request that a clearance beread back whenever the complexity of the clearance or anyother factors indicate a need. The pilot should read back theclearance i f he feels the need for confirmation .Reference: Airman s Information Manual, February 71, page1-42.)

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22/68

i l 1Hl MON>I

~ ' 1 3 ~

Dear Danny: I noticed while reading the OH-58A manual, it recommends avoid operatingin the 172 to 2 6 rotor rpm range. I understandwhy this range needs to be heeded in the OH-13or UH-1 series with the stabilizer bar. The OH-58A does not have one, so what is the reason?There is no explanation in the manual.

lLT F. E. T.Danny's answer: Man, did you give me a beaut t2

took a long while, but here's what was explained tome. t seems this is a carry-over from the originalLOH program (OH-4 manual) when they suspecteda harmonic vibration in the tail rotor drive shaftsystem. However, the engineers I've talked to seeno reason for this statement in the OH-58A manualsince it has an entirely different type of tail boomand power train system; consequently, this cautionrange is not valid. Thanks to your query a DAForm 2 28 is being submitted to correct this error.



23/68

ehorlie ona DonnY s Write InYou know, there are times you can't see the forestfor the treeesDear Danny: On page 4-2 , paragraph 4-118 of theCH-54A dash to, it refers you to a figure 10 1 inreference to different types of bell mouths installed on the aircraft. How does an instrumenttakeoff chart, which figure 10 1 does display , giveyou this information?

CW4 T. B. D.Danny's answer: Thank you for your sharp eyes. twas either an oversight or misprint. The correctchart made reference to in paragraph 4-118 of TM55-1520-217 -10/1 is figure 10-5, located on page 10-9. Just the other day we received a DA Form 2028on the same matter. Say, if you run into any moreitems of this nature, how about submitting a DAForm 2028 as well as writing us a letter? We certainly would appreciate both.Dear Danny: I've sent in some suggestions and2028s on the CH-34C and haven't seen anychanges lately. What is the story on this aircraftand when can we expect some of the recommended changes?

ILT O. H. D.Danny's answer: As you know this aircraft is nolonger on the active list of aircraft; consequently,changes and reviews are controlled by availabilityof funds and criticality of the proposed changes or2028s. This aircraft has such a good reliability factor that few changes were submitted. But to answeryour question, the manual is in the process of beingrevised to incorporate all recommended changes,including the dash CL. t is my understanding thatunless funds or some unforeseen situation appearsthe proposed changes should be printed and in yourhands in approximately 4 months.Dear Danny: In the OH-6A what are the capabilities of the attitude indicator? We are unable tofind it in the manual.

WOI H. B. A.JUNE 1971

Danny's answer: The information you desire is onpage 2-25, paragraph 2-94 of TM 55-1520-214-10.t says the attitude indicator has a 360-degree azi

muth and roll capability but only a 50-degree pitchrange both upward or downward. Hope someonedidn't remove that page from your manual by mistake.Dear Danny: Since it is required that an aircraftbe started with external power to conserve aircraft battery , why were the steps for connectingand disconnecting the external power unit omittedfrom the U-6A prestarting procedures?

2LT M. H. R.Danny's answer: t is common practice to use theaircraft battery to start small aircraft engines likethe one used in the U-6A. An external power unit isrequired only when the battery is dead or whenoperating in extremely cold climate. Informationfor the use of external power is given in paragraphs2-72, 10-31 and 10-33 of the U-6A operator's manual (TM 55-1510-203-10 .Dear Danny: On the CH-54B it states when icingconditions are encountered , to open the bypassdoors with EAPS installed. In our hangar flyingsessions some people disagree with the manual.Who can we write to and obtain the correctinformation?

CW3 G. B. P.Danny's answer: You came to the right place forthe answer. I just returned from a manual reviewand the same subject was brought up. Testing theEAPS under icing conditions in the laboratory revealed that the EAPS bypass doors should not beopened and to land as soon as possible. Once icedevelops on the bypass doors it may not be possibleto open them. Change 6 to TM 55-1520-217-10/2,which was reviewed, will correct this erroneous information. t also contains other valuable information on the functioning and limitations of the EAPSunder icing conditions. Hope this change, when itarrives , will clear up your hangar flying question.

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25/68

They ll et You Toowould like to recreate the conditions in the cockpit. The AC wasa warrant officer about a yearout of flight school and rated forabout 1 months, though he hadless than 250 hours in the aircraft. His pink card had justexpired. I was a brand new captain with considerably more timebehind a desk than in an aircraft. Though I had been ratedfor the same amount of time, Ihad less than 200 hours in theaircraft. However, I had justrenewed my tactical ticket.Though the automatic directionfinder was inoperative in the aircraft, airport surveillance radarand precision approach radarwere available from an AirForce base about 1 miles pastour home base.As we flew north the sky became darker and a few minuteslater, while flying level at 2 200feet, 120 knots over mountainous terrain, we entered a densewhite cloud. The AC, who wasflying entered an abrupt cyclicclimb. I went immediately to mymaps and IFR Supplement inpreparation for an IFR flight.

After a short period I returnedmy attention to the instruments.The air speed indicator was atzero, the attitude indicator wasindicating 15 degrees nose high the ball of the turn and slip indicator was on the far left end ofthe race and the turn needle wasindicating a right turn. The vertical s peed ind ica to r as Iwatched, went from 1 000 feetper minute (fpm) climb to 200fpm descent.I realized that the AC was at-JUNE 1971

tempting a 180-degree pedal turnwith the intention of flying backout. I glanced down to my mapto see what minimum obstruction clearance altitude would beto the south when I felt a sudden swinging sensation to theright. When I looked up the faceof the attitude indicator wassolid black. I looked over to theleft seat attitude indicator and italso was indicating a steep dive.I looked back at my attitude indicator, incredulously waitingfor the AC to react. After several seconds in this attitude Itold the AC to get some aft cy clic and then asked for the aircraf t . He made no reply. Ilooked down at the air speedindicator and watched the needleaccelerate from 120 through 150knots. I put my hands on thecontrols and began to apply aslight aft pressure on the cyclic,attempting to bring the horizontal bar on the attitude indicatorinto sight. Then we broke out ina valley between two mountains.

The tops of the mountainswere well up into the cloud. Ientered a violent deceleration,leveling the aircraft and decreasing thrust to keep from climbingback into the cloud. The aircraftshook violently and the rotorrpm must have gone extremelyhigh. The aircraft leveled, heading directly toward a mountainside at an extremely high rate of

The views expressed herein are theauthor s and do not necessarily reflectthe views of the Department of thermy

closure. I put the aircraft over tobetter than a 70-degree leftbank, pulled more aft cyclic andpulled in thrust. When I cameout of the turn I leveled the aircraft at about 300 feet above thevalley floor. The AC then tookthe aircraft and landed it in afrozen rice paddy.

Without shutting down thecrew checked the aircraft andlearned that the only apparentdamage was to five side windows which had popped out.Since the damage was minor andwe were unable to detect anyabnormalities, we flew the aircraft 5 miles back to the basecamp we had just passed.

The next morning I went outto inspect the aircraft in thelight. I couldn t believe it. Oneof the aft rotor blades had acord wise crack in it so bad thatthe only thing holding the bladetogether was the spar, whichwas clearly visible. Several ofthe tunnel covers on the top ofthe aircraft were missing andothers had been punctured bythe flex packs of the drive shafting. The shelf the battery sits onwas bent at approximately a 30-degree angle. I had picked upthis aircraft and flown it 5 miles.In the pas t yea r I havethought of many things I couldand should have done to preventthose few seconds of impendingdeath, but they all work out toone common mistake: poor priorplanning and complacency.You ve heard them so manytimes before; they go in one earand out the other. Keep it u p -they ll get you too someday .

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1


27/68

sonable area fire accuracy ofsome 1 to 12 mils. But the warhead was too small for antitankand the weight and bulk penalties were considered excessivefor antipersonnel. We soon expended the limited stock ofrockets at Redstone Arsenal.

As we expended all availableR D and limited productionrockets in the national inventory, we looked for other sourcesof weapons. There were two:the 2.75-inch folding fin aerialrocket and the 4.5-inch spin stabilized artillery rocket.The 2.75 was a lightweightstandard Air Force air-to-airweapon with a dispersion patterncomparable to a sawed-offg u n s o m e 50 mils when

launched at low or zero speeds.The warhead had a limited killradius, but the rocket was easyto mount on the helicopter. Byincreasing the launch tube lengthfrom 4 to 12 feet we reduceddispersion from 50 to 25 mils butproduced an awkward package.The characteristic of the 2.75that we really liked was the na-tional inventory f igure- therewere some 8 to 1 million available.

The 4.5-inch artillery rocketwarhead had a good kill radiusand dispersion appeared acceptable for area fire. We riggedtwelve 4.5-inch rocket tubes tothe nosewheel strut of a CH-21.The machine guns were used toadjust rocket range. The tandem

The need for a weapons system tobe used against hard point targetssuch as tanks resulted in the arming of an OH-13 helicopter upperleft) with the SS-10 wire-guidedmissile which was obtained fromFrance. Tests were conducted bythe U. S Army Aviation Boardtoday known as the U. S ArmyAviation Test Board) located at Ft.Rucker. Interest then evolved tothe newer 5S-11, also a wireguided missile upper right). Thisbecame the M-22 system which isfired below in a test conducted ata Redstone Arsenal, Ala., range


28/68

Major General Bogardus S. Cairns right), com-mandant of the aviation school and a cavalryman,located the last field manual written in 1936 for horsecavalrymen. Cavalry tactics such as those used above)by the 102d Cavalry Battalion in 1941 maneuversheld in the Carolinas are the basis for today s air-mobile tactics. The 1936 manual was rewritten in-corporating air cavalry tactics learned at Ft. Rucker

rotor CH-21 appeared to be areasonably stable platform forthe artillery rocket.

Rock Island Arsenal, Ill., andthe Ft. Rucker maintenance contractor installed machine gunsand twenty-four 4.5-inch artilleryrockets on the CH-34. Stationaryfiring from the ground indicatedno structural damage to the aircraft although rocket blast andvibration did pop out some ofthe porthole windows. Once airborne, we fired pairs of twowithout appreciable change inattitude. When we tried to ripplethree or more pairs we encountered a severe pitch problem anda slight yaw reaction. We didnot experiment enough to determine precisely what our problems were because the 4.5-inchrocket was also being droppedfrom the Army inventory.

We were wary of the recoiland vibration of the 20 millimeter machine gun. Also, our analysis of the 5-inch high velocityaerial rocket 's motor ignitiontime curve made it doubtfulwhether the rocket could safelybe launched from zero air speed.The systems were tested and noone was hurt. However , ma-

chine gun vibrations shatteredthe firewall when the 5-inchr o cke t s were f ired. Onegrounded about 1,000 yardsdown range; the other was stillclimbing when it went out ofsight.

Our earliest machine gun androcket systems were mounted tofire straight ahead without elevation or traverse. We knew, ofcourse that some weaponswould require inflight e v a l u ~ t i o ndepression and traverse controls.But incorporating these controlsexceeded our blacksmith shopcapabilities. Also, we did nothave R D money and if wewent through formal channels itwould take years to obtain anyhardware so we turned to industry.

The General Electric Corporation plant in Burlington, Vt.,agreed to help us at its own expense. General Electric developed a helicopter pod for twoM-60 7.62 machine guns andeight of the 2-inch T-290 Redstone Arsenal rockets.

We ran out of 2-inch rockets,so we converted the pod for four 2.75-inch weapons. The podgave us a + 1 to -15 degree ele-

vation capabili ty. The weightpenalty was 270 pounds. Anelectric switch on the controlstick activated a motor on thekit and for the first time wecould alter weapon elevationwithout changing aircraft attitude.

Our friends with General Electric and the Air Force picked upa B-29 gun turret, which GeneralElectric attached under the forward fuselage of a CH-21.

Now we had elevation, depression and traverse. The copilot was the gunner . Thepackage with two caliber .50guns and 500 rounds of ammunition cost 650 pounds. The kitworked better for General Electric engineers than it did for ourcopilots. Malfunctions were dueprimari ly to an inadequatesource of electrical power in theCH-2 I. We were real proud ofthe system but a bit cautiousabout showing it. When we werealone it worked beautifully;when we had a packed gallerywatching, it would malfunction.

One other weapon systemshould be noted. While we couldprovide area fire against soft targets, we still did not have a

26 U. S. ARMY AVIATION DIGEST


29/68

weapon for hard , point targetssuch as tanks or bunkers. Wejoined with the U. S. ArmyAviation [Test] Board also located at Ft. Rucker) to send ateam to France to study wireguided missile gunnery employedby the French Army .Bell Helicopter Company,Fort Worth, Tex., installed theFrench SS-IO on an OH- 13 Weconducted tests here and {stablished the feasibility of the system. Of course, the French hadalready used it on the Alouette.They were then adopting thenewer 1 1 later designated M-22). Despite the disadvantages ofa wire-guided system, we saw apotential antiarmor weapon forhelicopter use the only onethen in sight.

On 5 March 1957 our teamwas augmented by a permanentsky cavalry platoon of I 1 officers, 16 enlisted men and 10 helicopters the personnel and thehelicopters were taken from theaviation center resources).JUNE 1971

A irmobile tactics and concepts spread throughout the Army and upwardin military channels. As commandant of the U. S Army Aviation Schoolin the early 1960s, Major General Ernest Easterbrook above left) continued the practice of opening training exercises to the public and highofficials to familiarize as many as possible with the potential of Army air-mobile concepts. Here he chats with Assistant Secretary of the Army PaulIgnatus during an exercise in 1961 at Ft. Rucker. Colonel Dutch Williamscenter) was assistant commandant of the school. A year later the ArmyTactical Mobility Requirements Board under Lieutenant General Hamilton

H. Howze below) recommended division-sized air cavalry forces


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We graduated from R D tomass production. Each pilot andcrewman became a machinist.The post machinist along with 27enthusiastic, yet inexperienced ,assistants worked day and nightuntil we had an armed platoonflying. Army aviators flew acrossthe country to locate weapons ,solenoids, gunsights and metalstock.

The new platoon, includingthe R D weapon ships, wasofficially unveiled on 6 June 1957

at Ft. Rucker before an industrial-military group in a sympos i um s pon so r e by t heAssociation of the United StatesArmy.

In November 1957 the unitwas redesignated the AerialCombat Reconnaissance (ACR)Platoon Provisional (Experimental . Then in March 1958 the pla-toon was expanded to a fullcompany or troop size unit andthe title was changed to the7292d Aerial Com bat Recon-

CH-47 ehinooks played key roles in the 1 hAir Assault Division s test of airmobile concepts

Fr left: Major General Harry Kinnard who commanded the 11th AirAssault Division (T) at Ft. Benning, andlater took it to the Republic of Vietnamas the 1st Cavalry Division (Airmobile).Left: Brigadier General Robert R Williams who commanded the Test Evaluation and Control Group, ProjectTEAM, which evaluated the 11thand wrote up the afteraction reports

naissance Company (Experimental .By 1958 we had our own

machine shop. We had collectedover 1,000 guns and hundreds ofbits and pieces of rocket pods,gunsights, intervalometers, etc.With 100 blacksmiths we soonhad an armed helicopter company ready to fight.

The airframe people, Armyarsenal specialists and industrypersonnel monitored, listened toour problems and went home todesign something more sophisticated.

The development of our tactical doctrine is a long story, but asimple one. The most obviousassets of the helicopter were notalways readily understood. The


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vertical f1slng machine couldoperate in confined areas of theforward battlefield. It is an agile ,re sponsive device . It has a highbattlefield speed ratio comparedto trucks and tanks. But mostimportant of all , a ground com-mander could be divorced fromthe obstacles of terrain that haverestricted him for centuries. Welearned that a former barrierbecome s an avenue of approach.Freedom of maneuver in theX and Y coordinate domi-

nates air cavalry force tactics.While our task organization

followed Wellington , the Navyinfluenced our tactics. SurfaceNavy forces are also free tomaneuver in any direction on thehorizontal plane.

There is a grey area betweenst ra tegy and tactics , and anothergrey area between tactics andtechniques. To avoid years ofresearch of cavalry tactics we incombat developments adopted acowardly approach. We plagia-rized the last field manual writ-ten for horse cavalrymen in1936. The younger people hadnever seen it; the older ones hadJUNE 1971

forgotten it. Major General Bo-gardus S. Cairns , then com-manding Ft. Rucker , was acavalryman . He located themanual for us.Chapter by chapter we re-wrote horse cavalry tactical doc-t r i ne i n to i r c v l r yincorporat ing our lessonslearned. When finished, we pub-lished the New Tactical Doc-trine as a training text. Wemodestly refrained from adver-tising our source of genius.Some time later when a fieldmanual had to be written onshort notice our air cavalrytraining text was available andused, including some passagesthat I would have preferred torewrite.

Concurrent with our tacticaltests and hardware exploration ,we demonstrated our ideas formilitary and civilian scientificand industrial leaders at Ft.Rucker , Ft. Benning , Ft. Knox ,Ky., Ft. Bragg, N. C., and Ft.Bliss , Tex.

With the constant movementof military leaders our ideaswere tran sferred to Europe and

Left: An AH-1G HueyCobra gunshipof the 2d Battalion, 20th Artillery sARA) B Battery joins a Nighthawksearchship in 1st Cavalry Division Airmobile) operations in the Republic ofVietnam. The helicopter armamentconcepts of the 1950s were provenvalid in the 1960s in Southeast Asiathe Far East where others begantheir own tests. As our pilotsmoved to other stations , theycarried the ideas with them.Thousands of ideas and theorieswere tested.

The revolution from the bot-tom spread upward in militarychannels. By 1960 the Army wasspending R&D money on heli-copter weaponry. Then in 1962the Secretary of Defense RobertS. McNamara called for a quan-tum jump in Army mobility. TheArmy Tactical Mobility Require-ments Board , under LieutenantGeneral Hamilton H. Howze ,was convened at Ft. Bragg todevelop and recommend coursesof action to take. The boardmet , s tudied , analyzed andtested the problems and recom-mended division size air cavalryforces.

With the Department of De-fense's blessings, money , peopleand equipment became available.Major General Harry W. O.Kinnard moved a cadre to Ft.Benning and organized the 11thAir Assault Division T) for air-mobility tests. Later his divisionbecame the 1st Cavalry Division(Airmobile) which he took to theRepublic of Vietnam for the realtest. The airmobile divisionproved to be an undisputed suc-cess and justified the faith thatthe late GEN Hutton had placedin armed helicopters and airmo-bility just 1 years earlier.Next month the DIGEST continuesits coverage of the history of thearmed helicopter with Part I of' The Armed Helicopter Storyby Lieutenant Colonel Charles O.Griminger

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rotor to warn the populace. Itwas printed both in Bengali,Pakistan s predominant language, and English. In the 30days the Americans flew in Paki-stan, we did not have one inci-dent with Pakistani nationals

an outstanding safety record for any mission but evenmore so considering the extremeconditions under which the heli-copters had to fly.Maintenance personnel atCaveman International Heliportpulled all aircraft inspectionsand daily maintenance with superior speed and accuracy andenabled the 182d Aviation Company to fly missions 7 days aweek during the entire month.The only outside work not doneat the heliport was an enginechange which necessitated aflight to the East Pakistan capitalto complete. Major William A.Hall III, the 182d AviationCompany commander and themission commander, had nothing

but praise for the fine efforts ofhis maintenance people in keeping all aircraft available duringthose first critical weeks.

Some aviation personnel weresent to Dacca to act in liaisonwith the Pakistani governmentand the small American colonyliving there went all out to makethe aviators feel at home. Foodavailable to Americans in Pakistan calls for a drastic change ofdiet and a liberal outlook on justwhat a gastric delight includes.Wives of American embassypersonnel worked hard to bringan American touch to the dietand the U. S. Informat ionAgency provided films andbooks to the aviation group forentertainment.Initially the helicopter company was expected to stay untilthe Pakistani government felt theworst of the crisis was over.Due to the intense effort putforth by all concerned, it wasdecided that the aviation contin-

gent could depart after only 30days, far short of original estimates.

Missions continued to beflown up until the final departuredate using a gradual phaseout toensure that at least one helicopter would be available on thelast day of flying. Final statisticsfor the 30-day period were exceptional. Over 17,300 passengers were airlifted in Americanhelicopters alone. In 1,259 sorties an astounding 1,111,295pounds of blankets, food, medical supplies and clothing werecarried. A total of 663 hourswere placed on the eight air-craft. The aviators and theirequipment returned to the continental United States over a spanof 4 days and were welcomedback to Ft. Bragg by LieutenantGeneral John J. Tolson, Commanding General, XVIII Airborne Corps and Ft. Bragg, witha hearty and sincere, "Welldone "


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ANOTHER IRSTAnd e Hope The Last)

Occasionally a near miracle occurs however it ismost often attributed to a lot of forethought andlabor. The impossible is made possible by Armyaviation. It will be recorded in the annals ofhistory but hopefully will never need repeating

I T WAS A HOT sultry Sundayafternoon in the MekongDelta in the Republic of Vietnam. The rainy season wasdrawing to a close yet the canals rivers and rice paddieswere still swollen.A CH-47B Chinook from the271 st Assault Support HelicopterCompany was performing a se-ries of resupply sorties to aSouth Vietnamese infantry unitlocated on Nui Dai Mountain atthe northwest corner of MilitaryRegion IV. One sortie in particular generated great anxietyamong the crews. As the Chinook turned toward the mountain on its final approach with 35troops aboard and a 5 000-poundexternal load of concertina wireand fence pickets a .30 caliberround tore into it just aft of theright forward cabin window. I tcont inued through the roofwhere it cut 14 wires of an electric wire bundle.The number 2 engine lostpower and number 1 went to fullpower. A right turn down themountain slope to friendlier territory was made. The externalload was released after it wasapparent that the aircraft could

32

Mo jor Joh n L Wood

not maintain altitude.With the number engine

operating at full power the air-craft could not be slowed below110 knots in straight and levelflight. Either a running landingor an autorotation would be re quired. The former was chosenbecause of the number of passengers aboard and the fact thatthe crew was not certain whatother damage may have beencaused by the hostile fire. Thenthe aircraft commander noted anabnormal increase in the vibration level of the aircraft and decided to land at a nearby asphaltairstrip.

On short final just over therunway overrun the number Iengine was brought to idle andthe aircraft touched down on therunway with a ground speed ofapproximately 125 knots. Rollingonly on the aft gear to effectaerodynamic braking the crewexperienced a feeling of success.Rotor rpm diminished and theforward gear touched down. ButPhoto 1: U S Navy frogmen attached recovery slings to the mastsof the submerged CH-47B Chinookand the operation was underway

when brakes were applied theaircraft skidded off the shortasphalt airstrip through the dirtoverrun and into water at theend of the airfield.

At about 50 meters from theairfield the aircraft came to aturning halt. While it shippedwater rapidly through the opencargo hook hatch and the brokenchin bubbles the crew and passengers made a hasty evacuation. The aircraft with its rotorsystems turning slowly listed tothe left then sank on its side in1 feet of water.


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~}

Here was a challenge for arecovery crew. According toofficial records this recoverywould be the first for a Chinookwhich was in a rolled-over,submerged position. The challenge was to effect a recoverywithout causing further damage.To complicate matters there existed a significant hazard fromthe large amount of IP-4 fuelwhich was seeping from the aircraft's nearly full fuel tanks. Onthe plus side the airfield and itsenvirons were tactically secure,aviation fuel was available at the

Photo : Left the Chinookwas rolled upright and nosehigh enabling water to drain

Photo 3: Right beached butata calculated 30 000 poundstoo heavy for a vertical l ift

field and there was not a pressing deadline to complete therecovery.After viewing the crash scenein the afternoon, the assaultsupport helicopter companycommander, his operations andmaintenance officers, the resident Boeing engineer and theLycoming representative met inthe evening to plan what was tobecome a very successful endeavor. Simply stated, the plancalled for a 2-day recovery operation. On the first day the goalwas to bring the aircraft to anupright position and move it toshore; on the second day itwould be stripped of its heavycomponents and lifted by a CH -54 helicopter to a repair depot.

the aft rotor head and with a 10-foot riser. This would assure anose-high airframe attitude oncethe aircraft was upright. AnotherCH-47B from the 271 st was usedfor the recovery. I t was strippedof its cabin equipment and itsfuel load was kept at less than1,500 pounds.The recovery Chinook was

The first day's operation began when two U. S. Navy frogmen dived through the JP-4 fuelslick, removed the submergedrotor head covers, installed lifting eyes into the masts and attached recovery slings to thelifting eyes. The recovery slingswere made using 20,OQO-poundload cargo slings and 40,000-pound load endless slings. Thesewere fashioned 37 feet to theforward rotor head, 43 feet to

flown by the operations andmaintenance officers who werein radio contact with the groundcrew which controlled the entireoperation with portable radios.A frogman hooked the recoverysling to the helicopter. The recovery pilots were instructed tomaintain a direct vertical pull onthe slings and to increase powerslowly. Because of their smoothtechnique, the submerged helicopter rolled to the upright position (photo 1 . .The configuration of the slingsmade the aircraft rise nose-high.With the helicopter in this position, a large amount of waterwas drained. The next and finalphase for the day was the movement to shore. The aircraft ,though still partially s u m ~ r g e dand resting on the mU(ldy bottom, was towed (photo 2) to

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ontinuedfrom page

JEWSROE DERSI think maybe someone should have agood long look at the priority systemwhich was established for distribution ofthe SPH-4 flight helmets .Not one single instructor pilot in the

Contact Flight Division at Ft. Ruckerwas ab le to obtain an SPH-4 during theentire 2 years that I was stationed there .Some of the students had them. but onlya few .I received orders for RV N back inSeptember 1970. I immediately went tothe issue facility to draw my SPH-4 . Atlast They told me that I would have towait until I arrived at my new unit inRVN . I ha ve been in my new unit forsome time now and I still am not ab le toget an SPH-4 . The y just are not available. Furthermore. current directives will

not allow me to take it out of RVN if Ishould be lucky enough to get one beforemy tour is up .When I ship back to CON US I will beright back in the same old boat-DEAFCW2 Jo se ph G. Wel chAviation Safet y OfficerHHC. 10l st Airborne Di v (Ambl)APO San Francisco 96383

Information received from the NewYork Army National Guard, Army Aviation Support Facility #1, Amityville, N.Y., advised that determination of the sizesneeded in Nomex shirts and trousers forflight personnel at that facility has recently been completed. Requisitioning ofthe items is proceeding normally and noproblem of supply is anticipated.

Stocks on hand of the K-2B coveralls

and the APH-S and APH-5A helmets areto be fully utilized before requisitioning ofNomex shirts and trousers and SPH-4helmets. Stocks of B3A gloves are exhausted; normal requisitioning of Nomexgloves is currently in progress. TheACMA Supply Information Letter No.1-71, dated 1 January 1971 , contains information on these item s. Information onhelmets will be found on page 2 of thisinformation letter and K-2B coveralls andNomex flight clothing are noted in item 22on pages 26 and 27 of the same publication.

The repor ted availability of Nomexflight clothing from a civilian source at aprice of $14.00 per uniform apparentlyrefers to material that did not meet specification standards and was rejected forArmy use. The contractor disposes of th istype of material through non-military outlets. They are not authorized for use byArmy personnel due to deficiencies thatcaused their rejection when produced.

Life support clothing and equipmentthat does not conform strictly to the specification as written and is not approved fordelivery on inspection ma y not give theprotection it was designed to provide.Purchase and use of such substandardequipment ma y well endanger the wearerin the performance of his duties.

N ...............N MonthB nejitsAwaiting he AviatoIn Ttie ReserveComponents

.


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36

F YOU WERE TO take a notion to try tocrossbreed a Missouri mule with a butterflythere s no telling what sort of interesting critteryou might come up with. You could be sure ofone thing-wh a tever it might look like, it wouldhave mo st of the characteristics and personalitytraits you norm a lly ass ociate with an Army helicopter.

Bone stubborn . Strong as Atl a s. Skittish. Delicate as a flower in spring. Temperamental. Andabout as ha rd to ha ndle as a box kite in a whirlwind.

Sp ea king of whirlwinds, that s a good part ofthe problem when it comes to handling helicopters. When you are at the controls of a helicopteryou are quite literally riding the wind a manmadehurricane which can flatten anything in its way.Normally if you have sufficient altitude andplenty of elbow room there s no problem. When ahelicopter hovering close to the ground on takeoffor landing begins to huff and puff it can causetrouble which makes the Big Bad Wolf look like abush leaguer in the big wind department.

The big blow is only a part of the problemwhen it comes to hovering. Here is where the butterfly side of a helicopter s nature swings into action. Treat it wrong hurt its feelings ask it tocarry a few pounds more than it thinks the unionrules allow and it will go into a temper tantrumwhich could do justice to a spoiled Hollywoodactress. When this happens a helicopter will letyou down.

Hard.

--



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JUNE 97

FACTS OF LIFEEvery budding aviator learns at his instructor's

knee that when it comes to flying hovering isonly a mite more tricky than balancing an eel onthe end of his nose while playing' The Stars andStripes Forever on a trombone. Just as we allpick up a lot of other hard facts as we trudgethrough this vale of tears which we promptly for-get or ignore, to our ultimate sorrow.

Well, shucks, maybe hovering isn't all thathard. Few of us can play The Stars and StripesForever, with or without an eel, but we do knoweverything there is to know about the fine art ofhovering.

Or do we?Well, sure we know all right, or at least we

used to. The trouble is we don't always let whatwe know get in the way of what we do. That's asgood a way as any, for example of explainingwhy so many helicopters in Vietnam have been

HOV R S NSMajor hester Goolrick

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HOV R S NSdamaged or destroyed by tail boom strikes in revetments. And this doesn t begin to take in thenumber which have come to grief during hoveringeverywhere because pilots forgot or ignored someof the facts of life like pressure altitude, weightlimitations, NI and N factors, temperature, visi-bility ground conditions, rotor downwash andblade tip vortices. f there is a bright side to thisseamy story it is that at least the pilots involvedsooner or later have ha

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