Hollywood goes ape over hydraulics

Jessica Lange, as Dwan in MGM's 1976 remake of King Kong, is lifted and held by a giant electrohydraulic hand powerful enough to easily crush her. Some clever engineering was employed to ensure that couldn't happen.

In February 1976, producer Dino De Laurentiis was one month into the shooting schedule for King Kong when the engineering firm bidding to build the giant ape informed him that, using an electromechanical system, would require five months to build a small prototype model, and an additional year to scale it up to its final size. And De Laurentiis had to release the film in December, 1976, less than 11 months in the future!

Glen Robinson, MGM's chief of special effects on loan to De Laurentiis came up with the answer. "We can do it in four months. But you'll have to let me do it my way — with hydraulics."

With an estimated cost of $500,000, De Laurentiis gave the go ahead. Robinson, his special effects foreman Joe Day, layout foreman Jimmy Thomson, and a host of welders and hydraulic mechanics were on their own.

No time for circuit diagrams

Considering the tight time schedule they faced, there was no time for designing the circuits first on paper. Based on anatomical sketches by Italian sculptor-engineer-designer Carlo Rambaldi, King Kong's hydraulic systems were breadboarded directly on the floor of a cleared section of MGM's construction shop.

"If we had relied on engineering drawings, we really would have been in a bind because we had to change the size of Kong three times," Robinson said.

Breadboarding was well on the way for a 35-ft ape when it was discovered that leading lady Jessica Lange, who plays Dwan, could not snuggle safely in the palm of a 6-ft, 2-in. hand. The hand was reworked to a span of 6 ft, 10 in., and in proportioning, King Kong grew first to 48 ft, then shrank to 42 ft.

With no engineering drawings, the practical experience and inventiveness of Robinson and his crew were of prime importance. Because there was no time to order custom cylinders, they used standard cylinders, tested them in assembly, and then improvised if something didn't work right.

For example, there was danger at one point that the cylinders that animate King Kong's hand might over stroke and cause the ape's fingers to crush his leading lady in his palm. To overcome this problem, they incorporated positive stops into each cylinder that shortened the stroke of each finger cylinder and stopped piston travel at a precisely measured point. They could have used conventional external control valves to limit piston travel, but that would have meant adding equipment that might fail— something the leading lady wouldn't like!

The stops were simple, failsafe, and quickly made in the machine shop. They machined a brass cylindrical "plug" to fit the ID of the ¾-in. bore by 2-in. stroke finger cylinders. The plug was drilled with a center hole through which the piston rod passed. Axial holes provided free flow of fluid inside, Figure 1.

Figure 1. Steel or brass plug was turned into stop for piston by drilling a hole through the center where the piston rad would pass. Additional holes allowed free flow of hydraulic fluid. Plug was cut-to-length to shorten the stroke of each cylinder as desired.

Each plug was then cut to the exact length to accommodate various piston strokes. When installed in the cylinder, there was no way the piston could travel beyond the positive stop.

Success of the design was demonstrated during an early set-up scene with stunt woman Sunny Woods substituting for Jessica Lange. As Kong's huge arm lifter her into the air, a ¼-in. wrist cable failed. The hand suddenly drooped limply from the wrist, swinging her abruptly from a vertical to a horizontal position. But the stops held the fingers in position, neither crushing her, nor permitting her to fall.