Configuration Features

Igor Sikorsky and his development team considered the VS-300 to be a flying test bed to experiment with helicopter technologies, including rotor systems, flight controls and lightweight materials. Throughout its development, the VS-300 was improved continuously and had four major configurations, as described in more detail in The Design Evolution of the VS-300 Helicopter.

Flight Controls

The picture below shows the VS-300 on the day of the first flight.  Visible in this picture is the single tail rotor pedal and the collective control wheel, similar to the trim controls on the flying boats, on the right side of the helicopter.  The cables from the top of the main rotor to the blades prevented the blades from drooping too much when the blades were not turning.

Collective control for a helicopter controls its vertical movement by changing the pitch angle of the main rotor blades.  In the VS-300, the engine throttle was mechanically connected to the collective control so that the engine’s speed adjusted accordingly as the collective pitch was increased or decreased.  Igor Sikorsky and the VS-300 team’s solution for collective control was successful and remained essentially the same for all four VS-300 configurations.

Cyclic control for a helicopter, which controls the aircrafts forward, backward and side-to-side movement, was an unsolved engineering problem in 1939.  Juan de la Cierva, an early Spanish pioneer of vertical flight  who in 1923 developed a successful autogyro design, had attempted to use full azimuthal cyclic control on his autogyro but abandoned it after an unexplained accident. Igor Sikorsky also tried to use it in the first VS-300 configuration, however the team’s design resulted in only very limited control and was determined to be the cause of the accident in December 1939 that destroyed the first VS-300 configuration, the Sikorsky design team abandoned cyclic control in their next VS-300 design, which is known as the second VS-300 configuration. Partial cyclic control was returned to the VS-300 during the Summer of 1941, when lateral side-to-side control was returned to the main rotor in the third VS-300 configuration. Full azimuthal cyclic control, which allowed the VS-300’s main rotor to control aircraft movement in all directions, was finally introduced in the fourth and final VS-300 configuration, after the team finally solved all cyclic control issues.

Flights of the fourth VS-300 configuration, designated VS-300A, began on December 8, 1941 and pilot Charles Lester Morris immediately encountered a strong shaking back and forth of the entire aircraft.  This issue was resolved on December 31, 1941 when Igor directed the crew to reinstall dampers, previously used to control blade flapping, in a horizontal position to dampen lead and lag blade movement.  This was the “Silver Bullet” and resulted in a smooth flying machine.  As a historical note, the XR-4 helicopter with full azimuthal flight controls made its First Flight on January 14, 1942, two weeks after control problems were solved on the VS-300A.

Engine

Power was supplied by a 75 hp (at 3200 rpm) Lycoming O-145-C3 air-cooled four cylinder horizontally opposed engine.  The engine was installed with the propeller shaft pointed aft and connected to the main gear box by a series of six V-belts. Tension on the belts was provided by engaging an idler pulley.  In July, 1940 the engine was replaced with a 90 hp (at 2,500 rpm) Franklin 4AC-199-E air cooled four cylinder horizontally opposed engine to provide additional power. In April, 1941 an upgraded 4AC-199 engine with 90 hp at 2680 rpm and 100 hp at 3050 rpm was installed.

Cooling Fan

The engine was cooled by a “squirrel cage“, V-belt driven, cooling fan in a sheet metal enclosure mounted above the engine which forced cooling air down across the cylinder cooling fins.

Starter and Battery

In order to save weight the battery was removed from the VS-300 after the first flight.  Then the starter was also removed. A handle was installed on the starter and it was held in place to start the engine and then removed.  Later the engine was started by a rotary shaft attached to the lower pulley on the engine.  After engine start, the rotor was spun-up by hand and then the idler pulley was engaged to tension the 6 drive belts. A bungee cord maintained tension on the idler pulley.

Landing Gear

The original landing gear consisted of 2 main landing gear with diagonal struts and swiveling front and rear wheels.  This was soon replaced by vertical oleo struts with swiveling wheels on the main landing gear and a nose wheel.  As development progressed diagonal main landing gear was reinstalled and eventually the nose and tail wheel were removed with only a tail skid remaining on the final version.

Fuselage

The original forward fuselage structure framework was constructed almost entirely of 4130 chrome-molybdenum steel thin wall tubing with the aft fuselage an aluminum box structure.  In the second configuration the aft structure.was changed to steel thin wall tubing for strength and easy modification.

Drivetrain

A Dural Pulley was attached to the propeller shaft on the Franklin 90 hp engine which was connected to a larger  Dural Pulley by 6 V-belts (Gates Vulcco Ropes) for the first rpm reduction of 1.76:1. Shafting from the upper pulley went forward to the main gearbox which contained spiral bevel gears from the rear end (differential) of a Mack truck.  This was the second rpm reduction of 5.9:1 to obtain the correct main rotor rpm.  A rear shaft ran aft and powered the anti-torque tail rotor and the horizontal rotors on earlier versions by V-belt drive.  The upper pulley also contained a free-wheeling unit to allow autorotation in the event of engine failure (No autorotations were attempted with the VS-300).

The Gates Vulco Ropes identified in the illustration were a Gates proprietary design V-belt with concave sides.  When the belt was under tension the torque flattened the belt for full contact with the pulley.

Main Rotor Blades

The main rotor blade had a spruce wooden spar extending from root to tip.  The leading edge consisted of lamination of spruce, balsa, and mahogany.  A high speed (since rotor tip speeds are over 254 mph (374 ft./sec) symmetrical NACA 0012 airfoil was used.  This airfoil had a stable center of pressure and the feathering axis and chordwise center of gravity were collocated making it ideal for a rotating wing.

Tail Rotor Blades

The tail rotor blades were all wood. The spar was made of maple, with poplar ribs and birch veneer pockets

VS-300 Flight Simulator

In 1938 Michael Buivid and Bob Labensky designed and fabricated the first helicopter simulator.  The configuration of the simulator changed daily and proved to be a valuable tool in predicting pilot’s ergonomic requirements and reactions to tilting fore and aft and laterally, and rotation for directional control.

Rotor Blade Test Unit

The rotor blade test rig was built to measure the lift and torque required to drive various blade designs.

Cargo Carriers

The VS-300 utilized a wicker basket to carry various items to demonstrate the controllability of the helicopter.

On the VS-300A a converted metal bicycle basket replaced the wicker basket.   

Amphibious Floats

The VS-300 was originally equipped with 2 Hot Dog floats, a tail float, and a basketball for a nose bumper.

Further along in the program the VS-300A was equipped with longer Hot Dog floats which eliminated the need for the tail float and nose bumper.

General Arrangement Drawing

VS-300A (Fourth Configuration) Performance and General Characteristics