Beartrap - A Cana­dian In­ven­tion

RCN News - - News -

THE PI­LOT moves the he­li­copter slowly ahead, keep­ing pace with the ship. He is about 50 feet above a heav­ing, rolling deck. He re­leases a thin wire mes­sen­ger. It brings back a heav­ier wire from the flight deck. The slack is taken up—it tight­ens. Slowly the he­li­copter de­scends on its “um­bil­i­cal cord”. The de­scent quick­ens. As the he­li­copter touches down, steel jaws grip it. What is this? “Beartrap” they call it — the new haul-down sys­tem for land­ing he­li­copters on de­stroyer es­corts. Why is it? Ba­si­cally, to make pos­si­ble the land­ing and se­cur­ing of heavy he­li­copters on de­stroyer -size ships in rough weather.

The project had its be­gin­nings nearly 10 years ago, when the he­li­copter-de­stroyer com­bi­na­tion was se­lected by the Royal Cana­dian Navy as a promis­ing an­ti­dote to the high-per­for­mance nu­clear sub­ma­rine.

To start with, the Navy fit­ted a small, ex­per­i­men­tal flight deck to a frigate, HMCS Buck­ing­ham. Tri­als were suc­cess­fully car­ried out, us­ing a Siko­rsky HO4S-3 he­li­copter. The next move was to put a plat­form on the de­stroyer es­cort HMCS Ottawa. Fur­ther tri­als were con­ducted, us­ing an RCAF Siko­rsky S-58. On the ba­sis of the tri­als, the con­cept of op­er­at­ing he­li­copters from de­stroy­ers was rec­om­mended and re­ceived ap­proval in prin­ci­ple.

Two things were needed. One was a he­li­copter ca­pa­ble of all-weather day and night op­er­a­tion (the HO4S3 was not). The other was a sys­tem for han­dling and se­cur­ing a he­li­copter on a small flight deck in rough seas.

The for­mer was found, in the 9.5 ton Siko­rsky CHSS-2 Sea King. The land­ing-han­dling prob­lem was solved by the Beartrap.

Dur­ing the tri­als, it was found that land­ing was not so much a prob­lem as was the han­dling of the he­li­copter af­ter it had landed. Man­han­dling was nei­ther quick enough nor cer­tain enough to es­tab­lish the mea­sure of con­trol nec­es­sary to en­sure that, in cer­tain cir­cum­stances; the he­li­copter will not take charge, and go over the side.

The Navy went to the draw­ing boards and came up with a scheme that promised to make the con­cept

prac­ti­ca­ble. Con­ceived by the RCN, the haul-down and Beartrap sys­tem was en­gi­neered by Fairey Avi­a­tion, Dart­mouth, N.S. A pro­to­type was de­signed and built by Fairey, un­der RCN su­per­vi­sion, and was in­stalled in HMCS Assini­boine dur­ing her 1962-63 con­ver­sion.

Tri­als with a newly-ac­quired Sea King be­gan late in 1963. By mid-1964 the day­time tri­als were com­pleted and pro­nounced suc­cess­ful. Us­ing the new sys­tem, no man­han­dling was needed to get the he­li­copter on the deck and in or out of the hangar. The he­li­copter was solidly se­cured on land­ing and re­mained so un­til the next take-off.

In con­junc­tion with the he­li­copter car­ry­ing fea­tures and hangar fa­cil­i­ties, roll-damp­ing fins were added to the de­stroy­ers be­ing so built or con­verted. Th­ese fins re­duce the roll of the ship and aid land­ing and take­off op­er­a­tions dur­ing rough weather.

An av­er­age land­ing doesn’t take any more than five min­utes from ap­proach to the snap­ping shut of the Beartrap. The ap­proach is made from the stern of the ship. When in po­si­tion, an op­er­a­tor in the he­li­copter low­ers a wire rope mes­sen­ger. To this mes­sen­ger a man on the flight deck at­taches a heav­ier haul down cable. (A pair of grounded tongs dis­charges any static elec­tric­ity in the mes­sen­ger so that the man won’t get a rude jolt.) The mes­sen­ger and haul down cable then are drawn into the he­li­copter through a probe in the he­li­cop-

ter’s belly. Af­ter the haul-down cable has been locked in po­si­tion in­side the probe, the slack in the cable is taken up. A land­ing con­trol of­fi­cer (LCO) on the flight deck con­trols the haul -down and land­ing from this point on­ward.

The pi­lot keeps his he­li­copter hov­er­ing in the cor­rect po­si­tion over the trap. Like an an­gler reel­ing in a jump­ing trout, the LCO slowly be­gins to reel in the he­li­copter. The LCO reg­u­lates the rate of de­scent of the he­li­copter on the con­trol con­sole. When it is in a po­si­tion just off the deck, he can then in­crease the rate dur­ing a lull in the ship’s mo­tion. He plays the he­li­copter quickly into the Beartrap where steel jaws snap around the probe and hold the “chop­per” se­curely against any mo­tion the ship might of­fer.

This op­er­a­tion can be per­formed with the ship rolling as much as 310 and with pitch­ing mo­tion as much as 8°.

Break­ing the sys­tem into its com­po­nent parts, the largest and most com­plex arc in the de­stroyer es­corts, with the light­est and small­est in the he­li­copter.

The he­li­copter con­tains the main probe, a tube-like struc­ture pro­trud­ing from the un­der­side of the fuse­lage, through which the mes­sen­ger cable is paid in and out. The winch op­er­at­ing the mes­sen­ger sits on top of the probe, and is con­trolled by an op­er­a­tor in the he­li­copter. The probe in­cor­po­rates pins to en­gage the haul -down cable and lock it in po­si­tion. A se­ries of mi­cro-switches then ac­tu­ate the locks, dis­en­gage the mes­sen­ger from the haul-down cable, and stop the winch

De­stroyer equip­ment is di­vided into three sec­tions—winch unit, power unit and Beartrap rapid se­cur­ing de­vice. Mo­tive power for the sys­tem comes from a 60 hp elec­tric mo­tor. This op­er­ates a hy­draulic pump and mo­tor which in turn ac­tu­ate a dou­ble drum winch through re­duc­tion gears. Each drum is op­er­ated in­de­pen­dently and has its own clutch and brak­ing sys­tem. The en­tire hy­draulic sys­tem op­er­ates at 3,000 psi and is rated at 4,000 psi.

The sys­tem main­tains con­stant ten­sion in the haul-down cable. This is of great im­por­tance for, with­out it, the he­li­copter would be dragged down and jerked dras­ti­cally when­ever the ship pitched to any ap­pre­cia­ble de­gree.

Con­stant ten­sion in the cable is main­tained by an in­tri­cate sys­tem of “black boxes”, or mod­ules. Ba­si­cally, they com­pare se­lected ten­sion on the con­trol con­sole with ac­tual cable ten­sion. The dif­fer­ence is mea­sured and fed to a valve which con­trols the pay­ing in or out of cable. The sens­ing de­vices, in com­pany with the five con­trol mod­ules which make up the con­stant ten­sion equip­ment, are so sen­si­tive to change that nar­row lim­its are achieved even in the rough­est of weather con­di­tions.

A shock ab­sorber is built into the sys­tem as well, to ab­sorb snatch loads in cable ten­sion. Th­ese loads oc­cur par­tic­u­larly when the slack in the cable is be­ing taken in be­fore haul -down. The shock ab­sorber is a pis­ton-

cylin­der ar­range­ment with dou­ble sheaves on ei­ther end around which the haul-down cable passes. The cylin­der is charged with air un­der pres­sure.

The Beartrap rapid se­cur­ing de­vice sits in a slot in the flight deck and trav­els fore and aft in re­sponse to a com­mand sig­nal from the LCO’s con­trol con­sole. It se­cures the he­li­copter im­me­di­ately upon land­ing by en­gag­ing the main he­li­copter probe.

The six-foot square Beartrap se­cures the he­li­copter when the LCO pneu­mat­i­cally fires two par­al­lel beams equipped with steel, spring-loaded teeth. The beams pre­vent the probe from mov­ing port or star­board and the teeth pre­vent probe move­ment fore and aft. The end of the probe is swaged so that it can’t jump out of the Beartrap.

The Beartrap has a cen­ter­ing de­vice. Cen­ter­ing is ac­com­plished by travers­ing the Beartrap unit aft. The beams are equipped with a fail-safe de­vice which keeps them to­gether in case of sys­tem fail­ure.

The en­tire Beartrap mech­a­nism trav­els in a slot along the cen­tre-line of the flight deck. It can be tra­versed with its cap­tive he­li­copter the full length of the flight deck, in or out of the hangar. This elim­i­nates the dan­ger­ous man­han­dling prob­lems which could ex­ist with a 9.5-ton air­craft, par­tic­u­larly in rough seas.

While the haul-down cable is op­er­ated from one of the twin drums on the winch unit, the travers­ing sys­tem is con­trolled by the other.

With the land­ing com­plete the LCO cen­ters the he­li­copter, the ro­tor blades and tail py­lon are folded by the pi­lot and the he­li­copter is stowed in the hangar.

Safety and ease of han­dling are the keynotes in this sys­tem. Day land­ing tri­als on the Assini­boine were com­pleted last sum­mer and Ex­per­i­men­tal Squadron 10 (VX 10) pi­lots have be­gun a se­ries of night land­ing tri­als.

Reprinted from Crowsnest Mag­a­zine Vol 17

A Sea King he­li­copter be­gins its ap­proach to the flight deck of the Assini­boine. Flight

deck crew­men wait be­side the Beartrap de­vice.

This is "Beartrap", a rapid se­cur­ing de­vice, which, with the coiled haul down cable, lies ready for the land­ing op­er­a­tion. Flight deck

per­son­nel will grab a mes­sen­ger cable from the he­li­copter.

Amid multi-wired ca­bles, the land­ing con­trol of­fi­cer pre­pares to haul down the teth­ered Sea King. The LCO is con­stantly in ra­dio voice

con­tact with the he­li­copter pi­lot.

Beartrap jaws grip the Sea King’s probe, clamp­ing the 9.5ton “chop­per” firmly on deck. The he­li­copter thus is poised for cen

ter­ing and shift­ing into the hangar.

Land­ing the old-fash­ioned way—man­u­ally! Sea King about to land on air­craft car­rier Bon­aven­ture. The AORs Provider, Pro­tecteur and Pre­server also em­ployed this method.

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