Four bladed suc­cess

The Bell 412

Aviation Classics - - CONTENTS - Words: Tim Call­away

One of the de­sign el­e­ments that has made the ear­lier Huey mod­els so use­ful to land and ship based armed forces was the two bladed main ro­tor. This al­lowed the he­li­copter to be car­ried in trans­port air­craft with­out re­mov­ing the blades and min­imised the deck and han­gar space on car­ri­ers and other ships that the Huey re­quired with­out the need to in­clude a blade fold­ing mech­a­nism, com­mon on larger he­li­copters. This meant that Hueys on de­ploy­ment ar­rived al­most ready to go, speed­ing their en­try into ser­vice in any over­seas theatre. The Huey’s two-bladed main ro­tor had steadily grown in chord and in length, from 44ft (13.41m) span on the XH40 to 52ft (15.85m) on the 214ST. This had been for two main rea­sons, to ab­sorb the in­creas­ing power of the de­vel­op­ing tur­bine en­gines fit­ted to the he­li­copter, and in pur­suit of the holy grail of air­craft de­sign, to in­crease the per­for­mance to meet cus­tomer de­mands. The devel­op­ment of the two bladed ro­tor had reached its lim­its, par­tic­u­larly in terms of re­duc­ing noise and vi­bra­tion, prob­lems long as­so­ci­ated with it, which meant that on Septem­ber 8, 1978, Bell an­nounced the devel­op­ment of a new four bladed de­sign based on the Bell 212.

FIRST FOURS

Two Bell 212 air­frames were taken from the pro­duc­tion line and mod­i­fied to be­come the pro­to­types of the 412, re­tain­ing the 1800hp Pratt and Whit­ney PT6T-3B Turbo Twin Pac pow­er­plant driv­ing the new light­weight com­pos­ite ro­tor. The ro­tor head had elas­tomeric bear­ings like those of the late model two bladed ro­tors, th­ese re­mov­ing the need for me­chan­i­cal hinges and dampers, so greatly sim­pli­fy­ing the sys­tem as well as re­duc­ing the weight. The fact that this was a rel­a­tively straight­for­ward mod­i­fi­ca­tion of the ex­ist­ing de­sign meant that the first flights of the two pro­to­types oc­curred less than a year later, in Au­gust and De­cem­ber of 1979, im­me­di­ately show­ing tremen­dous im­prove­ments in the noise and vi­bra­tion lev­els ex­pe­ri­enced in the cabin. Bas­ing the de­sign on an ex­ist­ing he­li­copter also meant that Fed­eral Avi­a­tion Ad­min­is­tra­tion (FAA) cer­ti­fi­ca­tion was swift, Type Cer­ti­fi­ca­tion be­ing ap­proved on Jan­uary 9, 1981, the first de­liv­er­ies of pro­duc­tion he­li­copters oc­cur­ring only nine days later to Alaska based ERA He­li­copter Inc. Aside from the noise and vi­bra­tion im­prove­ments, the Bell 412 proved to have a bet­ter climb per­for­mance and a higher ser­vice ceil­ing than the two bladed 212, as well as a much im­proved max­i­mum cruis­ing speed of 143mph (230kph) over the orig­i­nal model’s 115mph (186kph). The sheer util­ity of the Huey de­sign re­mained in the 220cu ft cabin with its large two piece doors en­abling easy ac­cess, this still be­ing a mas­sive in­ter­nal space for a he­li­copter of this class which could be con­fig­ured with up to 13 pas­sen­ger seats or any com­bi­na­tion of seats and equip­ment depend­ing on the cus­tomers needs. Dur­ing the early 1980s, Bell re­sponded to cus­tomer feed­back by in­tro­duc­ing the Model 412SP or Spe­cial Per­for­mance. This was fit­ted with the PT6T-3BF pow­er­plant with its im­proved sin­gle en­gined per­for­mance and was mod­i­fied to pro­vide an in­creased max­i­mum take off weight and fea­tured new in­ter­nal lay­outs and seat­ing op­tions. The big­gest change was the in­crease in in­ter­nal

The Bell 412 was the first ver­sion of the Huey to re­place the tra­di­tional two bladed main ro­tor with a four bladed one. Although Bell had pro­duced ex­per­i­men­tal vari­ants with more than two blades, this was the com­pany’s first pro­duc­tion he­li­copter with this fea­ture.

fuel ca­pac­ity to ex­tend the range and loi­ter time, which in­creased mil­i­tary in­ter­est in the new ver­sion, at­tract­ing or­ders from Hon­duras and Nor­way among many oth­ers. In 1984, air­frame vi­bra­tion was re­duced still fur­ther with the in­tro­duc­tion of a pen­du­lum damper sys­tem on the ro­tor head of air­craft on the pro­duc­tion line, which was also of­fered as an up­grade kit to ex­ist­ing he­li­copters. In June 1986, an armed ver­sion of the 412SP was pro­posed, a sin­gle ex­am­ple, N412AH, be­ing pro­duced as a demon­stra­tor. Known as the 412AH for Attack He­li­copter, it could carry a 19 round rocket pod on ei­ther side of the cabin and was fit­ted with a Lu­cas Aerospace tur­ret un­der the nose. This housed a .50 cal ma­chine gun with 875 rounds and was slaved to a hel­met mounted Sperry Head Tracker sight from the AH-1S Co­bra which en­abled the pi­lot to ‘look and shoot’. De­spite some in­ter­est in the con­cept, no or­ders for the 412AH were forth­com­ing. As with other Bell types, pro­duc­tion of the 412 was trans­ferred to the Canadian fac­to­ries in Jan­uary 1989 to free up space at Fort Worth. The devel­op­ment of the PT6T en­gines and their im­proved trans­mis­sion led to the 412SP be­ing re­placed on the pro­duc­tion lines by the 412HP (High Per­for­mance) in 1991, the new ver­sion be­ing fit­ted with the -3BG or 1920hp -3D ver­sions of the Pratt and Whit­ney pow­er­plant. Cur­rently, there are two ver­sions of the Bell 412 in pro­duc­tion, the first be­ing the 412EP (En­hanced Per­for­mance), in­tro­duced in 1993 and fit­ted with the -3DF ver­sion of the en­gines. The new model was also fit­ted with a dual dig­i­tal au­to­matic flight con­trol sys­tem which in­cluded both an au­to­mated ap­proach to hover and au­to­mated hover fa­cil­i­ties. This model was the ba­sis of a cus­tomised devel­op­ment for the Royal Canadian Air Force known as the 412CF, des­ig­nated the CH-146 Grif­fon in ser­vice. Or­dered in 1992, 100 of this ver­sion were de­liv­ered to the RCAF be­tween 1995 and 1997, used in the search and res­cue, com­bat sup­port and tac­ti­cal trans­port roles with 10 RCAF Squadrons and not ex­pected to be re­tired un­til at least 2021. The Bell 412EP has also been the ba­sis of two ver­sions ac­quired by the Royal Air Force and var­i­ous ver­sions of the air­craft have been pro­duced un­der li­cence in In­done­sia and Italy, all of which will be cov­ered later in this is­sue. The other ver­sion still in pro­duc­tion is the 412EPI, fit­ted with the 2143hp PT6T-9 pow­er­plant which fea­tures a Full Author­ity Dig­i­tal En­gine Con­trol (FADEC) sys­tem. The other avion­ics and elec­tron­ics have been sim­i­larly up­graded, the 412EPI fea­tur­ing the Bell Basix Pro In­te­grated Avion­ics Sys­tem in a com­pletely mod­ernised glass cock­pit. The air­frame has also been mod­i­fied in as­so­ci­a­tion with BLR Aerospace, the fin chang­ing shape to a much nar­rower chord with a curved trail­ing edge known as the ‘Fast Fin’, which, when cou­pled with the dual strakes fit­ted along the lower faces of the tail­boom of­fer im­proved fuel ef­fi­ciency, han­dling, tail ro­tor ef­fec­tive­ness and cross­wind tol­er­ance by al­ter­ing the air­flow around the rear of the he­li­copter. This aero­dy­namic im­prove­ment has also been in­tro­duced on to the 412EP and is avail­able as an up­grade to ear­lier ver­sions as it sig­nif­i­cantly im­proves the hot and high per­for­mance of the he­li­copter and in­creases the use­ful load in th­ese con­di­tions. The lat­est ver­sions of the de­sign are in­cred­i­bly ad­vanced air­craft and are a fit­ting con­tin­u­ance of the Huey fam­ily line.

Bell He­li­copters

The Bell 412EP sold world­wide, this be­ing a Nige­rian reg­is­tered ex­am­ple equipped with the emer­gency flota­tion de­vices on the land­ing skids.

Era He­li­copter Bell He­li­copters

Left: The first cus­tomer for the Bell 412 was Era He­li­copter Inc, op­er­at­ing in Alaska among other states. The ex­panded per­for­mance of the Bell 412EP made it popular with fire and res­cue de­part­ments through­out the US and Canada, such as the San Diego Fire Depart­ment as seen in ac­tion here.

Edi­tor/bell He­li­copters

An in­ter­est­ing com­par­i­son be­tween the early in­stru­men­ta­tion, in this case as fit­ted to an RAF Grif­fin HT.1 of the Search and Res­cue Train­ing Unit, a type based on the 412EP, and the lat­est ad­vanced glass cock­pit of the Bell 412EPI.

Above: USMC

Eigh­teen Bell 412SPS were pur­chased by the Royal Nor­we­gian Air Force, all of which are still in ser­vice in 2014. Here a flight in­serts a team of US Marines at the port of Orkanger dur­ing NATO ex­er­cise Strong Re­solve 2002.

RCAF

The Royal Canadian Air Force CH-146 Grif­fon was based on the Bell 412SP and is used in the com­bat sup­port, trans­port and search and res­cue roles.

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