In the be­gin­ning

The XH-40 to the UH-1A

Aviation Classics - - CONTENTS - Words: Tim Call­away

The ex­traor­di­nar y use­ful­ness of the Bell 47 Sioux dur­ing the Korean War, es­pe­cially in the role of med­i­cal evac­u­a­tion trans­port, had been a clear pointer to the fu­ture of bat­tle­field util­ity he­li­copters. The US Army were par­tic­u­larly in­ter­ested in de­vel­op­ing such a ve­hi­cle, an in­ter­est that would lead to the in­tro­duc­tion of a leg­end.

The devel­op­ment of the UH-1 and its even­tual use in an as­tound­ing va­ri­ety of roles be­gan with the lessons learned by the US Army dur­ing the Korean War, which had in­tro­duced a num­ber of new weapons and ve­hi­cles to the United Na­tions forces fight­ing in the coun­try. The Bell 47 Sioux he­li­copter had ful­filled a num­ber of roles and is best re­mem­bered for the evac­u­a­tion of wounded per­son­nel to the Mo­bile Army Sur­gi­cal Hos­pi­tals just be­hind the front line. Around 18,000 ca­su­al­ties were evac­u­ated by air, sav­ing many lives be­cause of the speed with which the wounded reached med­i­cal aid. This les­son was not lost on the US Army, nor on civil­ian med­i­cal or­gan­i­sa­tions world­wide and would re­sult in the devel­op­ment of the med­i­cal evac­u­a­tion (mede­vac) and air am­bu­lance ser­vices we know to­day. The Bell 47s had also op­er­ated in lo­gis­tics sup­port, tak­ing ammunition and ra­tions to the front line and sup­port­ing units cut off from other ground forces. The trans­port of sup­plies and per­son­nel into the bat­tle­field was also seen as a prime re­quire­ment for fu­ture he­li­copters and th­ese two roles be­gan to shape the Army’s think­ing re­gard­ing new air­craft.

POWER RE­QUIRE­MENTS

The ex­pe­ri­ences of the Korean War prompted Bell He­li­copters to write a de­tailed re­port on the use of the he­li­copter on the bat­tle­field, a re­port which also sug­gested the fu­ture im­prove­ments re­quired in he­li­copter per­for­mance in or­der to ef­fi­ciently ful­fil th­ese roles. This sat very well with a US Army Colonel, Jay Van­der­pool, who had al­ready been press­ing for the devel­op­ment of high per­for­mance and armed he­li­copters for close bat­tle­field sup­port. The Key West Agree­ment of 1948 had rigidly de­fined ar­eas of re­spon­si­bil­ity and re­sources be­tween the US Army, Navy and Air Force. While this agree­ment gave the army the abil­ity to de­velop and field re­con­nais­sance and mede­vac air as­sets, there were a num­ber of se­nior army per­son­nel who be­lieved that close air sup­port should also be within the army’s purview. Against this back­ground of grow­ing sup­port for the con­cept of a truly ca­pa­ble mul­ti­role bat­tle­field sup­port he­li­copter, by 1952 the US Army recog­nised a re­quire­ment for a mede­vac and trans­port air­craft which would also have to be ca­pa­ble of op­er­at­ing as a trainer for in­stru­ment fly­ing. The he­li­copters then avail­able were all con­sid­ered but were found to ei­ther lack power and there­fore load lift­ing ca­pa­bil­ity, were too large and un­ma­noeu­vrable, or were too me­chan­i­cally com­plex to be eas­ily main­tained in the field. Re­li­a­bil­ity, ma­noeu­vra­bil­ity and ex­cess power were all go­ing to be vi­tal if the new he­li­copter was to sur­vive on a mod­ern bat­tle­field. The ini­tial re­quire­ment was re­fined un­til it was is­sued in Novem­ber 1953. Twenty com­pa­nies re­sponded to it with new de­signs. The spec­i­fi­ca­tion was ex­act­ing for the time, an 8000lb (3629kg) pay­load had to be car­ried over a range of at least 100 nau­ti­cal miles (185 km) at speeds above 100 kts (185kph). The new he­li­copter also had to have suf­fi­cient power to be able to hover at heights of up to 6000ft (1829m) and yet be able to be car­ried eas­ily in­side a Lock­heed C-130 Her­cules trans­port air­craft. Bell was one of the com­pa­nies that re­sponded to the re­quire­ment, and with Ly­coming had been de­vel­op­ing a novel ap­proach to the power prob­lem in he­li­copters, be­tween them de­vis­ing the air­frame and en­gine which would pro­vide the nec­es­sary per­for­mance. The Ly­coming Tur­bine En­gine Di­vi­sion at Stratford, Con­necti­cut, had be­gun de­vel­op­ing a new tur­boshaft en­gine in 1951 un­der the de­sign lead­er­ship of Anselm Franz. Franz had been the chief designer at Junkers’ en­gine depart­ment in Ger­many dur­ing the Sec­ond World War and had pro­duced the Jumo 004 tur­bo­jet that had pow­ered the Messer­schmitt Me 262 jet fighter. Franz’s de­sign con­cept was to pro­duce a small, light but tremen­dously pow­er­ful en­gine suit­able for op­er­a­tion as a tur­bo­prop or to pro­vide shaft drive for he­li­copters. A sim­ple five stage ax­ial com­pres­sor was mated to a sixth stage cen­trifu­gal com­pres­sor which fed an an­nu­lar com­bus­tion cham­ber be­fore the ex­haust gasses ex­ited over two im­peller tur­bines which drove the com­pres­sors ahead of them. The main drive gear­box and an­cil­lary drives for elec­tri­cal gen­er­a­tors and other air­craft sys­tems were mounted for­ward of the first stage com­pres­sor, cen­tral to the air in­take, re­sult­ing in a very small en­gine, only 58in long (1.48m) and 23in (0.58m) in di­am­e­ter. The lay­out also al­lowed the air­flow through the en­gine to keep the heat gen­er­ated by the com­bus­tion cham­ber away from the gear­box for the pro­pel­ler or ro­tor,

depend­ing on how the en­gine was be­ing used. The most im­pres­sive re­sult of this en­gine devel­op­ment was its power to weight ra­tio, the first ver­sion of the LTC-1, as it was ini­tially known, pro­duced 700hp for a weight of just 655lb (297kg), a tremen­dous leap for­ward over the rel­a­tively low pow­ered and heavy pis­ton en­gines that had been fit­ted to he­li­copters up to this point. The new tur­bine had a num­ber of other ad­van­tages in ad­di­tion to its low weight. Its fuel con­sump­tion was much lower than a pis­ton en­gine, mean­ing less fuel needed to be car­ried to achieve a given en­durance or lift a given pay­load. The high power out­put be­stowed high speed on the he­li­copter, and the sim­plic­ity of the en­gine’s de­sign re­duced the time re­quired and there­fore the costs of main­tain­ing the air­craft. In short, the tur­bine was ex­actly what the he­li­copter in­dus­try had been look­ing for to rev­o­lu­tionise the ca­pa­bil­i­ties of its air­craft.

NEW DE­SIGN

Bell He­li­copters was well aware of the short­com­ings of ex­ist­ing ro­tary winged air­craft and was cer­tain that the new Ly­coming tur­bine could solve the per­for­mance is­sues and meet or ex­ceed the US Army’s re­quire­ment. The de­sign team at Bell started with a blank sheet of pa­per to pro­duce an air­craft that would take best ad­van­tage of the per­for­mance the en­gine of­fered. Yes, there were proven el­e­ments from their ear­lier de­signs in the new air­craft, but the new pow­er­plant al­lowed the de­sign team a de­gree of free­dom hith­erto un­known in he­li­copter con­struc­tion. The he­li­copter they de­signed can be thought of as three sep­a­rate sec­tions. The sec­tion around the cen­tre of grav­ity does all the work as far as the stresses in the he­li­copter are con­cerned. It con­sists of two main beams that run fore and aft from the rear of the cen­tre sec­tion to the nose. Th­ese have lat­eral bulk­heads link­ing them to­gether, but at the cen­tre of grav­ity they are joined by the lift beam, a ver­ti­cal struc­ture that has the trans­mis­sion with its plan­e­tary type gear­box and ro­tor mounted at the top and the hook for sling­ing ex­ter­nal loads at the bot­tom. The main bulk­head at this point forms the rear wall of the cabin. The lower space aft of this com­part­ment is sep­a­rated into three sec­tions. The first, again un­der the cen­tre of grav­ity, housed the port and star­board main fuel tanks, aft of which were the com­bus­tion heater unit then a crew bag­gage com­part­ment which would later be used to house the weapons con­trol elec­tron­ics on the armed ver­sions of the he­li­copter. A deck sep­a­rated th­ese three com­part­ments from those above. Cen­tral above the fuel tank sat the main ro­tor trans­mis­sion and ro­tor head, to ei­ther side of which were the oil and hy­draulic tanks and aft of which was the en­gine. The air in­take for the tur­bine was im­me­di­ately be­hind the main ro­tor trans­mis­sion and drew cool­ing air over the gear­box when the en­gine was in op­er­a­tion. The semi rigid ro­tor head de­sign fea­tured Arthur Young’s sta­biliser bar, mounted above the main ro­tor in this case, a 44ft (13.41m) span two bladed ro­tor with a 14in (35.6 cm) chord to the blades.

For­ward of the main bulk­head was the cabin struc­ture. The two main floor beams and their in­ter­con­nect­ing bulk­heads formed the struc­ture on which the cabin floor sat; be­neath which were two un­der floor fuel tanks and the for­ward at­tach­ment point for the main un­der­car­riage. This con­sisted of two curved trans­verse tubu­lar legs, the rear one of which was just aft of the cen­tre of grav­ity in the cen­tre sec­tion, the legs at­tach­ing to the main skids at ei­ther end. The skids were long, al­most the length of the cabin and cock­pit and sat 8ft 4in (2.54m) apart, giv­ing the he­li­copter tremen­dous sta­bil­ity on the ground. The un­der­sides of the skids were fit­ted with re­place­able metal shoes to pre­vent wear to the skids them­selves. The cabin was in­tended to seat eight armed troops in two rows of four can­vas seats, ahead of which the two pi­lots sat in a tan­dem cock­pit with full dual con­trols. The cabin was 98.5in (2.5m) wide de­lib­er­ately to ac­com­mo­date stan­dard stretch­ers across its width. The side cabin doors slid aft, fully open­ing to al­low up to four of th­ese stretch­ers to be loaded quickly and eas­ily. For­ward of th­ese, the pi­lots each had a car type door on ei­ther side of the cock­pit. The in­stru­ment panel and avion­ics bays were sup­ported by the front ends of the two main floor beams, ei­ther side of which the lower nose was glazed to af­ford the pi­lots the best pos­si­ble view while land­ing. The pi­lots’ doors were ex­ten­sively glazed, in ad­di­tion to which a large split wind­screen ran the full width of the cock­pit and a large win­dow was set into the roof above each pi­lot’s head. The last sec­tion of the de­sign bolted onto the rear end of the cen­tre sec­tion struc­ture with just four bolts, and com­prised the semi­mono­coque tail boom, tail ro­tor and drive, the fin and el­e­va­tors. The tail ro­tor was large, 102in (2.6m) in span and mounted on the top of the fin on the port side. The shaft drive to the tail ro­tor ran along the top of the tail boom un­der its own protective shroud then up the lead­ing edge of the fin via a bevel gear­box at its base. The twin el­e­va­tors were all mov­ing fly­ing sur­faces mounted on ei­ther side of the tail boom un­der­neath the base of the fin. Th­ese were linked to the pi­lots cyclic con­trol col­umn and pro­vided pitch sta­bil­ity in the cruise as well as in­creas­ing the air­craft’s al­low­able cen­tre of grav­ity range while loaded. A great many of th­ese de­sign fea­tures have be­come stan­dard on he­li­copters, but it must be re­mem­bered that at the time Bell was at the cut­ting edge of ro­tary winged

devel­op­ment and this de­sign would be­come the world’s first tur­bine pow­ered he­li­copter to en­ter pro­duc­tion. To learn more about the use of tur­bine en­gines in he­li­copters, Bell had taken a Model 47 and fit­ted it with a 425hp Con­ti­nen­tal CAE XT-51 tur­boshaft. This sin­gle ex­am­ple first flew on Oc­to­ber 20, 1954, and was used to test com­po­nents for the new de­sign, even­tu­ally be­ing des­ig­nated as the XH-13F and used by the US Army as a tur­bine test­bed from April 1955 on­wards. Mean­while, the Bell en­try for the US Army’s mede­vac and util­ity he­li­copter com­pe­ti­tion had been se­lected as the win­ner on Fe­bru­ary 23, 1955, Bell be­ing con­tracted to pro­vide three pro­to­types of its Model 204 as it was known un­der the des­ig­na­tion XH-40.

FIRST FLIGHT

As men­tioned ear­lier, Bell’s chief test pi­lot, Floyd Carl­son made the first flight of the XH40 pro­to­type on the day Larry Bell died, Oc­to­ber 20, 1956. The he­li­copter had been built at Bell’s Hurst plant on the out­skirts of Fort Worth and was pow­ered by an early devel­op­ment model of the Ly­coming LTC-1 tur­boshaft en­gine, des­ig­nated YT53-L-1 in its mil­i­tary guise, which pro­duced 700hp. Only 16 months had elapsed since the ini­tial de­sign work had be­gun and even be­fore the first flight the US Army had or­dered six more devel­op­ment pro­to­types for ser­vice testing, des­ig­nated YH-40S. The ur­gent re­quire­ment for the type and the prom­ise the de­sign showed even from this early stage meant that the other two XH-40S joined the flight test pro­gramme in 1957 and all six YH40s were de­liv­ered by Au­gust 1958. The XH-40S had proved to have a max­i­mum speed of 138mph (222kph) and a ser­vice ceil­ing of 17,500ft (5334m), but there were a num­ber of changes the army re­quired in the de­sign. The cabin was too short to com­fort­ably carry the en­vis­aged load of troops or stretch­ers and had to be stretched by 1ft (30.48cm) in length. For­tu­nately, in bas­ing the de­sign on the two floor beams as the main struc­tural el­e­ment, such a stretch was eas­ily ac­com­mo­dated. The main cabin slid­ing doors also had to be stretched by the same amount and the en­gine cowl­ings needed to be re­designed to im­prove cool­ing and ease of ac­cess for main­te­nance. The el­e­va­tors were in­creased in span to 9ft 4in (2.84m) and moved for­ward on the tail boom to about two thirds of the way along its length. Lastly, the ground clear­ance was in­creased by 4in (10cm) by in­creas­ing the length of the two main skid sup­port tubes on the un­der­car­riage. This last change was to al­low ground crew to more eas­ily at­tach un­der-slung loads and to pre­vent the fuse­lage ‘bot­tom­ing’ on rough ter­rain. All of th­ese changes were in­cor­po­rated in the six YH-40S, which were also fit­ted with the first pro­duc­tion ver­sion of the new en­gine, the Ly­coming T53-L-1A pro­duc­ing 860hp, but de­r­ated to 770hp to ex­tend en­gine life and re­li­a­bil­ity.

While the con­struc­tion of th­ese first batches of he­li­copters was go­ing on, the army had in­tro­duced a new des­ig­na­tion sys­tem in 1956, which meant the he­li­copter be­came the HU-1, the tri­als air­craft be­com­ing the XHU-1 and YHU-1. The six YHU-1S were fol­lowed by a pre-pro­duc­tion batch of nine HU-1S, which be­gan to be de­liv­ered for ser­vice tri­als from June 30, 1959. The new des­ig­na­tion quickly gave rise to the nick­name the air­craft is known by the world over – Huey. So popular was this name that the cast­ing of the rud­der ped­als was changed to in­cor­po­rate the word into the face of them, a prac­tice con­tin­ued to this day.

INTO SER­VICE

The tri­als with the pro­to­type air­craft were still on­go­ing when the US Army is­sued its first pro­duc­tion or­der on March 13, 1959, th­ese be­ing des­ig­nated HU-1AS to dif­fer­en­ti­ate them from the pre-pro­duc­tion air­frames. A to­tal of 173 HU-1AS were built, and were in­tended to give the US Army ex­pe­ri­ence of op­er­at­ing the type as it was the first tur­bine pow­ered he­li­copter in both pro­duc­tion and in gen­eral ser­vice. Four­teen of th­ese he­li­copters were de­liv­ered equipped for blind fly­ing train­ers as the TH-1A, en­ter­ing ser­vice with the US Army Avi­a­tion School at Fort Rucker in Alabama and be­ing used to teach in­stru­ment fly­ing on Army he­li­copter pi­lot cour­ses. The first op­er­a­tional units to re­ceive HU1As were the 82nd Air­borne Di­vi­sion at Fort Bragg in North Carolina and the 101st Air­borne Di­vi­sion (AD) at Fort Camp­bell in Ken­tucky, along with the 57th Med­i­cal De­tach­ment (MD) of the Brooke Army Med­i­cal Cen­tre at Fort Sam Hous­ton in Texas. The 57th MD was the first to use the air­craft in its in­tended mede­vac role, but the first to be de­ployed over­seas were two HU1As from the 82nd AD who took part in an ex­er­cise in Panama in early 1960. The fol­low­ing year, the first HU-1AS to be per­ma­nently based out­side the US were de­liv­ered to the 55th Avi­a­tion Com­pany in Korea, from which time the HU-1A be­gan to spread across the world, sev­eral Euro­pean based units re­ceiv­ing the type from the end of 1961 on­wards. With the in­tro­duc­tion of the pro­duc­tion vari­ant came the of­fi­cial name, Iro­quois, but in prac­tice this has al­most never been used as the nick­name Huey was al­ready both wide­spread and popular. A num­ber of changes hap­pened to Bell dur­ing this pe­riod. In July 1960, Bell Air­craft and Bell He­li­copters were bought by Tex­tron In­cor­po­rated of Rhode Is­land. The Bell Aerospace Cor­po­ra­tion was founded to cover the ex­per­i­men­tal, fixed wing and rocket mo­tor ac­tiv­i­ties of the group, while the Bell He­li­copter Cor­po­ra­tion was re­named the Bell He­li­copter Com­pany. Things changed for their he­li­copter too, not least of which through the in­ter­est aroused by it set­ting six Fédéra­tion Aéro­nau­tique In­ter­na­tionale (FAI) recog­nised world records in 1960. Th­ese in­cluded climb­ing to 19,686ft (6000m) in just eight min­utes 7.1 sec­onds and sus­tain­ing a speed of 142.22mph (228.9kph) over a 100km (62 miles) closed course. One fi­nal change was made as the Huey be­gan to en­ter large scale ser­vice. In 1962 the US armed forces in­tro­duced a new stan­dard­ised des­ig­na­tion sys­tem which meant that the HU-1 be­came the UH-1, the des­ig­na­tion we know it by to­day.

INTO BATTLE

De­spite the in­ten­tion only to use the first pro­duc­tion HU-1AS as eval­u­a­tion air­craft, five of the air­craft of the 57th MD were de­ployed to Viet­nam in April 1962, the first Hueys to ar­rive in theatre.

They were tasked with evac­u­at­ing wounded Army of the Repub­lic of Viet­nam (ARVN) sol­diers from bat­tle­fields, and for the next 10 years, the thud­ding of the Huey’s ro­tor was to be a familiar sound over the war torn coun­try. The next group of UH-1AS to ar­rive in Viet­nam were with a new tri­als and eval­u­a­tion unit, the US Army’s Util­ity Tac­ti­cal Trans­port He­li­copter Com­pany (UTTHCO) based at Tan Son Nhut air­port. Fif­teen UH-1AS had ar­rived on Oc­to­ber 9, hav­ing been fer­ried from Ok­i­nawa via a workup pe­riod in Thai­land, dur­ing which the he­li­copters had been ex­ten­sively mod­i­fied. It is worth ex­plain­ing that by this time, the forces of other coun­tries had found more mil­i­tary uses for the he­li­copter. A small num­ber of Sioux were armed with ma­chine guns by the French Army and pro­vided fire sup­port to ground forces on counter in­sur­gency mis­sions dur­ing the Al­ge­rian War be­tween 1954 and 1962. Th­ese proved par­tic­u­larly use­ful in coun­ter­ing dis­persed guer­rilla forces in the moun­tain re­gions, and were soon joined by more heav­ily armed ver­sions of other Siko­rsky and Pi­asecki types fielded by the French Army and Navy. The US Navy and Royal Navy had al­ready be­gun de­vel­op­ing armed anti-sub­ma­rine war­fare he­li­copters to track and attack sub­marines with sonars and depth charges, while in the Soviet Union, Mil-8s had been fit­ted with rocket pods in an ex­per­i­ment to pro­vide air sup­port to ground forces dur­ing air­borne as­saults. Th­ese lessons were not lost on the US Army, who had be­gun to ex­pe­ri­ence losses to ground fire among the trans­port he­li­copters de­ployed to Viet­nam. The Pi­asecki CH-21C Shawnee twin ro­tor cargo he­li­copters based at Da Nang and Tan Son Nhut with the 8th, 33rd, 57th and 93rd Trans­porta­tion Com­pa­nies (Light He­li­copter) had been fly­ing troop trans­port and sup­ply mis­sions with ARVN units since Fe­bru­ary 1962. Th­ese trans­port he­li­copters were in­creas­ingly com­ing un­der attack by North Viet­namese Army and Vi­et­cong units who were be­gin­ning to field more anti-air­craft weapons, par­tic­u­larly heavy ma­chine guns, shoot­ing down a CH-21 near the Lao­tian bor­der in July and killing its four man crew.

In or­der to pro­tect the trans­port he­li­copters, the UTTHCO was formed us­ing 15 UH-1AS taken from the 53rd Avi­a­tion De­tach­ment on Ok­i­nawa. The Hueys were ex­ten­sively mod­i­fied with weapons to en­able them to act as an armed es­cort to the trans­ports and to en­sure the in­tended land­ing zone was clear of en­emy ac­tiv­ity and an­ti­air­craft weapons. Ex­per­i­ments be­gan with var­i­ous free swing­ing door mounted ma­chine guns aimed and fired by the crew in the cabin. The best way to mount th­ese was found to be on bungee cord, elas­ti­cated rope slung from the cabin roof, which ef­fec­tively sta­bilised the weapons prior to the in­tro­duc­tion of fixed pin­tle door mount­ings later in the con­flict. Mount­ings were also de­vised by the UTTHCO se­nior en­gi­neers to al­low rocket packs to be car­ried on the skids, th­ese con­tain­ing seven or eight of the 2.75in Fold­ing Fin Aerial Rock­ets (FFARS). Along­side th­ese were a .30 cal M-37 or 7.62mm M-60 ma­chine gun, again in im­pro­vised mounts on the skids, both th­ese and the rock­ets be­ing fired by the pi­lots. Two of the unit’s en­gi­neers, Chief War­rant Of­fi­cers Cle­muel Wo­mack and Clea­tus Heck were to be re­spon­si­ble for the devel­op­ment of a stan­dard­ised mount for rocket pods which would be adopted through­out the Huey fleet. Back in the US, a sin­gle UH-1A, 58-2038, had been re­des­ig­nated as the XH-1A and used for a va­ri­ety of weapons tri­als, in­clud­ing the fit­ting of a grenade launcher in a tur­ret on the nose. Mean­while, us­ing the im­pro­vised mounts, the UH-1AS of UTTHCO un­der the com­mand of Ma­jor Robert Reuter be­gan fly­ing mis­sions on Oc­to­ber 16, 1962, their task be­ing to pro­tect the trans­port he­li­copters and ARVN forces en­gaged in Op­er­a­tion Morn­ing Star, aimed at clear­ing Tây Ninh prov­ince of en­emy per­son­nel. From th­ese small be­gin­nings, the armed ver­sion of the UH-1 grew in com­plex­ity and ca­pa­bil­ity and would even­tu­ally de­velop into an en­tirely new de­sign, but that he­li­copter will be cov­ered in an­other is­sue of Avi­a­tion Clas­sics. The UH-1A had proved it­self a quan­tum leap for­ward in per­for­mance over the ear­lier pis­ton pow­ered he­li­copters and was al­ready prov­ing in­cred­i­bly adapt­able de­spite still be­ing un­der eval­u­a­tion from its re­cent en­try into ser­vice. The early ex­pe­ri­ences of Huey crews in Viet­nam showed that the air­craft was more than rugged enough to take the stresses of op­er­a­tional fly­ing and sim­ple enough to eas­ily main­tain in the field. How­ever, the US Army had also recog­nised that the per­for­mance of the UH-1 would have to be in­creased still fur­ther in fu­ture model in or­der to fully en­able it to meet their needs in all en­vi­ron­ments, es­pe­cially the hot and high con­di­tions to be found in southeast Asia. Th­ese re­quire­ments had been put to Bell and an or­der placed for an im­proved ver­sion as early as July 1959 while the UH-1AS were still be­ing de­liv­ered. This would lead to the UH-1B, and a plethora of sub-types as will be de­scribed next.

USAF

The Bell H-13 had proved the value of the he­li­copter in the mede­vac and bat­tle­field lo­gis­tics roles dur­ing the Korean War.

Three views of the pro­to­type XH-40 on a test flight in front of the staff at the Bell plant. Note the doors, en­gine cowl­ings and tail ro­tor drive shaft cover have not been fit­ted for th­ese flights.

Bell

The sec­ond pro­to­type Bell XH-40 with the all fly­ing el­e­va­tors in the full down po­si­tion. Note that a sta­biliser bar has been added to the main ro­tor, but be­low the blades.

Bell

A rare colour shot of the pro­to­type Bell XH-40. Note the orig­i­nal po­si­tion of the all fly­ing el­e­va­tors at the end of the tail boom and the low mounted sta­biliser bar on the main ro­tor.

Bell

Bell

The pro­to­type Bell XH-40 with the en­gine cowl­ing and other cov­ers re­moved on a early test flight shows the ar­range­ment of the en­gine, gear­boxes and main ro­tor trans­mis­sion clearly. It also shows how the air­craft was built in three sec­tions, cabin, cen­tre sec­tion and tail­boom.

Bell

The first pro­to­type Bell XH-40, 55-4459, dur­ing field tri­als with the US Army. Note how low on the ground the fuse­lage is sit­ting, which led to an un­der­car­riage mod­i­fi­ca­tion on the pro­duc­tion air­craft.

Bell

A close up of the early Ly­coming YT53-L-1 tur­boshaft en­gine in­stalled in the pro­to­type Bell Xh-40.this small, light en­gine pro­duced 700hp.

Left: The pro­duc­tion line at Fort Worth, show­ing short and the later long bod­ied UH-1S and the way the air­craft was built in three dis­tinct sec­tions.this bril­liant de­sign al­lowed rapid changes to be in­cor­po­rated into pro­duc­tion and be­stowed its fa­mous fle

Bell

Two views of the third pro­to­type Bell XH-40, 55-4461, show­ing the in­creased span of the all fly­ing el­e­va­tors and their changed po­si­tion, fur­ther for­ward on the tail boom and that the sta­biliser bar has moved to above the main ro­tor.

Above: A pro­duc­tion Ly­coming T53 tur­boshaft.this pow­er­ful light­weight en­gine was one of the keys to the UH-1’S suc­cess, and was to dou­ble in power dur­ing its devel­op­ment. Cliff Ar­ling­ton

US Army US Army Avi­a­tion Mu­seum US Army Avi­a­tion Mu­seum

The first tur­bine he­li­copter in pro­duc­tion and ser­vice un­der­went ex­ten­sive testing in all en­vi­ron­ments, such as this Bell HU-1A seen dur­ing cold weather tri­als. The 57th Med­i­cal De­tach­ment (MD) of the Brooke Army Med­i­cal Cen­tre at Fort Sam Hous­ton in Texas were the first to re­ceive the Bell HU-1A in the mede­vac role. An early Bell HU-1A at Fort Rucker, the Army Avi­a­tion School in Alabama.

The 57th MD was the first unit to deploy the Bell UH-1A, as it was now known, to Viet­nam in mede­vac sup­port to ARVN forces in April 1962.

The cabin of the Bell UH-1 was 98.5in (2.5m) wide de­lib­er­ately to ac­com­mo­date stan­dard stretch­ers across its width.

US Army

The Pi­asecki CH-21C Shawnee was be­ing used in air as­sault and lo­gis­tics sup­port mis­sions in Viet­nam from Fe­bru­ary 1962 on­wards.

US Army Avi­a­tion Mu­seum

Fif­teen UH-1AS were de­ployed to Viet­nam in Oc­to­ber 1962 with the US Army’s Util­ity Tac­ti­cal Trans­port He­li­copter Com­pany (UTTHCO) based at Tan Son Nhut air­port. Th­ese were the first UH-1S to be armed to act as es­corts to the CH-21C trans­port he­li­copters.

US Army Avi­a­tion Mu­seum

Two .30 cal ma­chine guns were mounted on the skids of the UTTHCO UH-1AS, the ammunition feed run­ning from boxes in the cabin through slots cut in the floor and sides of the cabin.

US Army Avi­a­tion Mu­seum

US Army Avi­a­tion Mu­seum

US Army Avi­a­tion Mu­seum

Three views, in­clud­ing two rare colour shots, of the weapons pack­age im­pro­vised on the skids of the UTTHCO UH-1AS. On each side of the air­craft are eight 2.75in Fold­ing Fin Aerial Rock­ets (FFARS) and a .30 cal Brown­ing M-37 ma­chine gun.

US Army

Right: A Bell UH-1A of the US Army Avi­a­tion Board, the test and eval­u­a­tion unit be­hind much of the devel­op­ment of the he­li­copter in ser­vice.

Mu­seum US Army Avi­a­tion

One of the in­no­va­tive se­nior en­gi­neers re­spon­si­ble for suc­cess­ful fit­ting of weapons to the UTTHCO UH-1AS was Chief War­rant Of­fi­cer Clea­tus Heck who was killed dur­ing his sec­ond tour in Viet­nam.

Ma­jor Robert Reuter was the com­man­der of the UTTHCO in 1962 and took th­ese rare shots of armed UH-1AS in flight in Viet­nam from their base at Tan Son Nhut Air­port. His pho­to­graphs are now part of the US Army Avi­a­tion Mu­seum’s ar­chive.

US Army Avi­a­tion Mu­seum

US Army Avi­a­tion Mu­seum

An­other of the US Army weapons tri­als on the Bell UH-1A was fit­ting six AGM-22 wire guided mis­siles.th­ese were a li­cence built ver­sion of the French Nord S.11 anti-tank mis­sile and were used in Viet­nam from Septem­ber 1965 on­wards.

US Army Avi­a­tion Mu­seum

One of the US Army Test Board air­craft used in de­vel­op­ing the ar­ma­ment sys­tems of the UH-1, seen here with the M-21 weapons sys­tem of mini­guns and rocket pods on the uni­ver­sal fuse­lage mounts and an M-5 grenade launcher in a tur­ret in the nose.the M-5 was first tested on a UH-1A.

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