The Development of the Huey
More Lift Per Aircraft
The Marine Corps was faced with one inescapable fact. The total number of aircraft it could possess was strictly limited. The ceiling had been imposed by the Department of Defense and Congress. Since each aircraft required manpower, ships, bases, and operating money, control of the total number of aircraft was in effect control of expenditures in other areas. The limitation had been used as a vital tool of management of the military forces. Any attempt to increase the number resulted in a lengthy and often unsuccessful effort. Conversely, a decrease had been imposed often to reduce funds.
Within the ceiling, however, the Marine Corps had some latitude in deciding what types of aircraft would make up the total. Though it was not easy to do, the mix could be varied. The result was that as additional helicopters were necessary a corresponding number of fixed-wing aircraft often had to be deleted from the inventory-a move that was not universally popular with jet pilots. The same limit was a stumbling block to the introduction of large numbers of very small helicopters into the Marine Corps.
From 1952 to 1963 the total aircraft in the Marine Corps had remained slightly more than 1,050, but in that period the makeup of the force had undergone a significant shift. Even more changes were planned. From a ratio of one helicopter to every five fixed-wing aircraft in 1952, the planned expansion of the helicopter program would result in an almost one-to-one ratio in 1967.
Even this increase in helicopters could not meet the almost insatiable demand for more vertical lift capability. Fortunately, there was another way to meet the requirements: improve the load-carrying capability of each helicopter.
As installed in helicopters, much of the power of a conventional piston engine was expended just lifting itself. The figure varied somewhat between different models, but most reciprocating engines weighed approximately three pounds for each horsepower they could produce. Typically, the engine in the UH-34 weighed over 3,500 pounds but could develop continuously only 1,275 horsepower. Higher amounts, up to the maximum of 1,525, were restricted to short periods of time. As the size of a piston engine was increased, the weight to horsepower ratio remained about con. stant but complexity and reliability became such problems that there was an effective limit to the amount of power. If the Marine Corps was to increase the payload capability of new helicopters, a different source of power would have to be found.
Small turbine engines, fortunately, were becoming available which had much different weight to horsepower ratios. The General Electric-built T-64-G-6 jet turbine could produce 2,270 horsepower continuously, was able to exceed 2,800 for short periods, yet weighed only 728 pounds. Every improvement of the weight-to-power ratio was synonymous with additional lifting capability; hence, conversion from piston to jet engines for helicopters was extremely attractive to the Marines. Like so many other aspects of the development of helicopters, however, the introduction of turbine engines was not as simple a problem as it at first seemed to be.
The basic jet engine contains three main parts. Behind the intake is a large fan used to squeeze the air into a dense mass suitable for efficient operation. The compressed air is fed into burning chambers where it is mixed with fuel and ignited. 'The result is a massive expansion of hot air which is then directed out the tail pipe. Before leaving the engine the air passes through a turbine which captures some of its force and transmits it back to turn the compressor. The power of the engine is largely determined by the amount of air the compressor can deliver to the burning chambers and the amount of fuel available for combustion. The turbine simply drives the compressor.
In a conventional jet aircraft this is all that is necessary for operation. The hot expanding gasses ejected from the tail pipe provide almost all of the thrust.
The pure jet engine was not suitable for all aircraft. To take advantage of the light weight and large amounts of power which could be generated, in some designs a fourth element was added. An increase in the size and efficiency of the turbine allowed almost all of the power from the compressor and burning chambers to be captured and used to drive not only the compressor but also a gear box mounted on the extreme front of the engine. By converting the high rpm of the jet engine to a slower more powerful force, the gear box now could be used to turn a propeller. The result was a "turbo-prop" engine.
A few designs were given further modification. Instead of a propeller the gearbox turned the rotor on a helicopter. When the American Helicopter Society held its 17th annual national forum in Washington, DC in May 1961, the members beard the latest developments in helicopter propulsion described:
At first glance, the . . . turbine appears to be the answer to all helicopter pilots' nightmares, namely, the ability to maintain automatic main rotor rpm; and certainly in most regimes of flight [in small lightly-loaded helicopters] this may be true.'
But for most other helicopters all jet engines then available contained a serious flaw. The problem stemmed from two sources. Jet engines operate efficiently only when turning near their maximum allowable speed. The slightest decrease results in a large loss of power. In addition, most of the engines had the turbine and compressor solidly attached to the shaft, which connected them. A gearbox, if installed, was also fixed to the same shaft. In pure jets, turbo-prop aircraft, and even in small lightly loaded helicopters this was not a particular disadvantage; but in a large heavily laden transport helicopter, it could be disastrous.
As previously discussed, the rotor blades of a helicopter achieve lift by the square of the velocity of the air passing around them. To insure that sufficient lift was always available, most helicopters flew with their rotors turning as fast as aerodynamically practicable. Any change in direction of the aircraft was effected by changing the pitch-not the speed-of the blades. Occasionally a pilot inadvertently would allow the rotors to slow up (lose turns) and the aircraft would falter. If not immediately corrected, any further loss of rotor speed would cause the aircraft to enter an uncontrolled descent. The quick response of a piston engine over a wide range of power settings had salvaged many such situations.
In a turbine-driven helicopter with the rotor directly connected to the engine through the gearbox, any such loss of turns also slowed the engine. Now the pilot faced a condition in which he needed maximum power to accelerate the rotor, but the engine could produce only a fraction of its full capacity. The more the pilot needed, the less was available. It could become a vicious circle.
The answer was to design a jet engine in which the turbine was not connected to the shaft. This would allow the compressor and burning chambers to operate at maximum efficiency independent of the rotor system. If more power was required rapidly, it would be available. The result was the "free turbine" or "gas-powered turbine" engine.
Two such engines were becoming available at the beginning of the 1960s. The Lycoming-built T-53 developed approximately 900 horsepower while the larger General Electric T-58 was rated up to 1,250 for short periods of time.
Even with free turbines, the problems of installing jets in helicopters were not completely solved. One of the most serious was foreign object damage (FOD) to the engine. As the compressor sucked in large amounts of air for the burning chambers, it did not discriminate about what else it picked up. Fixed-wing jet pilots long had become accustomed to the sight of motorized sweeper trucks scouring the runways and parking aprons to insure that no debris was lying about to be swallowed by engines which could be seriously damaged by a small stone or piece of metal. For helicopters landing in rocky fields, mountaintops and small clearings in a forest, FOD was going to be a problem. David Richardson, Chief Systems Engineer of the Vertol Division, Boeing Airplane Company, presented his views at the same Helicopter Society forum in 1961:
Foreign object damage with the helicopter turbine engine is becoming an increasingly significant item. The cost in terms of replacement parts . . . is large. As this paper was being written an engine . . . was removed from a Vertol test helicopter for foreign object damage after less than 60 hours of operation. This was the result of a large foreign object.'
He went on to describe a different type of FOD:
There is another type . . . of foreign particle damage. [These] may be ice, salt water, sand, etc. They do not result in as rapid engine deterioration as caused by large objects, but they may be more costly in that more [of the engine may be damaged.
He also noted that recently Bureau of Weapons (BuWeps) had begun including specifications for air filters in new helicopter jet engine designs. Richardson concluded that Vertol was working on a filter but needed more information about the effect of sand and grit from the manufacturers of the engines.
Other difficulties challenged the designers. While in a fixed-wing aircraft, the engine was always in a position to receive ample quantities of air, the effect of a helicopter flying sideways or backwards had to be considered.
Long a problem almost exclusively in helicopters, the effect of air not entering directly from the front of the engine was the cause of the cancellation of the first trans-Atlantic flight of the giant Boeing jumbo jet-the 747. While waiting for takeoff on 21 January 1970, the wind was blowing from the side. The designers had not taken this into consideration for so large an engine. It overheated and the plane had to return to the terminal-precisely the problem facing helicopters 10 years earlier.
No matter where the engines were placed on the aircraft, the down wash from the rotor would affect the air surging into the inlet. The results required careful testing. The vibration resulting from the articulated rotor heads was a new factor to any jet. "An engine which has thousands of hours of test time may not withstand the helicopter vibration unless it was designed and tested ... to the stresses it will be subject to", one report said."
The introduction of turbine engines in helicopters was not just a matter of putting a jet on an existing aircraft. It required a major engineering and design effort and lengthy testing. Enough progress had been made, however, that by 1962 the Marine Corps was about to have jet-powered helicopters.
The proposed replacement for both the HOK and the OE in the VMO squadrons . . . has really been a yo-yo project, alternately being in and out of approved plans, programs and budgets. Again, however, I am happy to state that it is "in."
Colonel Keith B. McCutcheon
Director of Aviation
18 January 1962
A replacement for the OH-43s had become enmeshed in a difference of opinion as to just what was the mission of the aircraft. One view held that there should be a new aircraft fully configured for observation purposes to replace the O-1s in the VMO squadrons, and a distinctly different type of aircraft for assault support. This position was centered at the Marine Corps Schools at Quantico commanded by Lieutenant General Edward W. Snedeker. A veteran of almost every major campaign in the Pacific from Guadalcanal to Okinawa in World War 11 and of the Chosin Reservoir in Korea, General Snedeker had been awarded both the Navy Cross and the Silver Star for heroism.
General Shoup, however, insisted that a single type of aircraft, an assault-support helicopter (ASH), could replace both the OH-43s and the 0-1s. Attempts to procure either---or both-of the new aircraft were consistently frustrated by performance deficiencies of models proposed by manufacturers or by funding difficulties. By 1960 the continued deterioration of the OH-43s added urgency to finding a suitable new helicopter. General Shoup restated his policy in August that year in a letter to General Snedeker:
The number one procurement priority in the light observation area is assigned to ASH … No new evaluations … will be commenced until the ASH is programmed and funded.
General Snedeker still held out for two. The ASH could replace the OH-43, but a short takeoff and landing (STOL) attack reconnaissance aircraft to replace and expand the present mission of the O-1s was also needed. General Shoup was not to be swayed and in February 1961 wrote that until "the Assault Support Helicopter is on track, no other light observation type aircraft will be considered".'
Difficulties in procuring the replacement aircraft were not confined to the Marine Corps. In September the Deputy Chief of Naval Operations (Air), Vice Admiral Robert B. Pirie, summed up the frustrations of the previous months in a letter to Rear Admiral Paul D. Stroop, Chief of the Bureau of Naval Weapons. Admiral Pirie pointed out that in March he had suggested that "a limited competition be conducted [by BuWeps] to select an aircraft to fulfill the Marine Corps ASH mission." In the same letter he had assured Admiral Stroop that:
. . . once a satisfactory selection and model evaluation has been made, that every effort would be expended to effect necessary reprogramming of funds within the FY 62 budget to permit the accelerated purchase of the operational vehicles.
BuWeps had indeed conducted an evaluation. "Representatives of the Bureau of Naval Weapons presented the results of the preliminary study of those helicopters under consideration for selection of the assault support helicopter." Admiral Pirie complained that:
. . . no recommendations were made as to the aircraft best suited to the mission or the most appropriate course of action to be followed in conjunction with an orderly procurement program. Each model reviewed failed to qualify under the recognized guidelines because of one or more deficiencies such as size, cost, capability or lack of qualifications." "It became apparent," he wrote, "that compromises must be made in regard to funding considerations and aircraft selection."
The crux of the matter was that in August Admiral Stroop had requested CNO to provide 5.1 million dollars for procurement before BuWeps even would request manufacturers to propose the modifications to their helicopters which would make them compatible with the stated requirements of the Marine Corps. Admiral Pirie pointed out that the "CNO cannot receive Congressional Committee approval of funding support for the AS[[ requirement without selection (first) of a specific model."
To solve the "chicken before the egg" dilemma, he suggested that:
In the selection of a suitable helicopter, the element of time is of paramount importance. It may well be in the best interests of the service to accept the burden of increased size and cost of an operationally qualified model rather than gamble on a reduced capability or a possible lengthy and costly development program. In such cases, additional potential of such a vehicle in the role of a trainer or light utility vehicle might well be considered."
Admiral Pirie reassured Admiral Stroop that funding could be arranged only if BuWeps would go ahead and select a type of helicopter. The OH-43s rapidly were approaching the end of their usefulness and the "imperativeness of positive action leading to a solution of this increasingly critical subject cannot be overemphasized."
The admiral had made his point. On 16 October, BuWeps solicited bids from 10 different manufacturers for an assault support helicopter for the Marine Corps. Seven responded.
The seven were Bell, Hiller, Kaman, Lockheed, Piasecki, Republic and Sikorsky. The three not responding were Cessna, Gyrodyne and Doman.
The original development characteristic (specifications) published on 29 July 1960, had called for an ASH with a total weight of 3,500 pounds, a payload of 800 pounds or three troops, and a cruising airspeed of 85 knots. There was also a long standing requirement "for the provisioning of all helicopters with the necessary attachments for carrying, either internally or externally, of the maximum numbers of canvas litters practicable, such installations not to jeopardize the primary mission of the helicopter."
The aircraft envisioned was similar to a requirement established by the U.S. Army. If both services could procure a single type, costs could be lowered. Even after BuWeps had published the desired specifications, conversations continued with the Army on their need for a light observation helicopter (LOH). Hiller, Bell, and Hughes all had submitted designs but there were too many differences between what the Marine Corps wanted (including carrying litters) and what the Army desired. The Marine Corps indicated "no immediate interest in the proposals to the Army for a LOH."
Evaluation of the seven proposed designs for the ASH continued into the spring of 1962. On 1 March the selection was approved by the Secretary of the Navy and the next day a public announcement was released that the winner was a slight modification of the Bell Helicopter Company's UH-IB. The U.S. Army had procured several hundred of these helicopters and they were already in action in Vietnam. The designation of the Marine Corps version would he UH-1E … soon shortened to "Huey."
Bell had experimented with tandem-rotor helicopters providing additional speed up to the maximum of 120 knots. Due to its small size and rotor design, stabilization of the UH-1E did not require elaborate electronic systems, though several were tested. Sufficient stability could be achieved by mechanical devices. One characteristic of the airplane not universally appreciated at the time was its extremely low silhouette. It was only 12 feet high and the cabin was even lower.
The adoption of the UH-1E did not still all the doubts previously expressed by some Marines. Of particular concern was that the visibility from the aircraft appeared much less than from the OH-43. Colonel Marion E. Carl, who had become the Director of Aviation in February 1962, decided to prove how well a commander could observe from the UH-1E. Colonel Carl, one-time holder of the world's speed record, commander of the first tactical jet squadron in the Marine Corps, World War 11 ace, and recipient of two Navy Crosses, arrived at the NATC at Patuxent River on a Saturday morning.
One of the aircraft utilized by BuWeps to evaluate the UH-1s had been retained by the center for further testing. This helicopter, a UH-1B, was on loan from the U.S. Army. A few days prior to the arrival of Colonel Carl, a truck had backed into the short wing attached to the tail pylon. The stabilizer was damaged beyond repair and there was insufficient time to order a replacement. Across the Potomac River at Fort Belvoir, the Army had a number of UH-1As A stabilizer was produced and hastily bolted onto the helicopter at Patuxent River.
There was one small problem. The improvements made between the UH-1A and UH-IB included a change in the stabilizers, and the one from Fort Belvoir was only half the size of the one left on the aircraft. Colonel Carl did not seem to be dismayed when he arrived and discovered that the aircraft was decidedly lopsided. He got in the helicopter, along with a test pilot attached to NATC, Marine Captain David A. Spurlock, and took off heading for Washington. The weather was poor with low clouds and intermittent rain. By following highways they soon arrived at the helicopter pad in front of the Pentagon.
There they were met by a delegation of Marine officers, including the Deputy Chief of Staff for Research and Development, Brigadier General Bruno A. Hochmuth. Colonel Carl got out and invited General Hochmuth to get in. He then turned to Captain Spurlock and said, "Show the general how good the visibility is at 3,000 feet. By now the weather had become worse. After a short flight at tree top level to avoid the clouds, a small opening was found and the General and his pilot found themselves evaluating the visibility. The opening, unfortunately, had disappeared. While they were at 3,000 feet, they could see nothing but solid clouds. Later and under better circumstances, the visibility from the UH-1E was found to be excellent and the program was continued.
A total of 72 operational aircraft were required to bring the VMO squadrons up to full strength, replacing both the O-Is and the OH-43s on a one-to-one basis with UH-1Es. The first step was the procurement of four additional aircraft to test fully the modifications from a UH-1B. By October $1.5 million had been provided for the program."
The differences between the Army and Marine Corps versions appeared slight but each was vital if the UH-1E was going to fulfill its role in amphibious warfare. The most important was the installation of rotor brakes. This device was unnecessary when operating from wide open fields and few military or civilian helicopters had them. 'Me major exceptions were the Maine Corps and the Navy. With plenty of room and time, a pilot could shut off the engine of his aircraft after landing and let the rotor slowly wind down to a stop. On the crowded flight decks of amphibious ships this was impossible. The helicopter had to be landed and the rotor rapidly stopped so that the machine could be moved to a parking area to make way for the next one about to come aboard.
During the May 1965 Dominican Republic crisis, a company of ITS. Army UH-1s was rushed to the scene on board the USS Guadalcanal. The lack of rotor brakes required crews to physically catch the blades to bring them to a halt. There were numerous minor injuries from unsuccessful attempts and the loading was considerably delayed.
Even when flight operations were not being conducted a rotor brake was essential for shipboard operations. As the ship steamed through the water, the wind over the deck often would be sufficient to cause the rotor blades to spin unless locked securely. The Bell solution was a simple brake disk on the main transmission, which could be hydraulically activated.
The UH-1E also had to be equipped with radios and communications compatible with both the air and the ground forces. This in turn required that the electrical system of the aircraft be converted from the standard Army direct current to the Navy and Marine Corps alternating current.
The only other significant difference was that much of the UH-1E was constructed of aluminum. Most helicopter designers previously had relied on magnesium to fabricate parts of a helicopter, since the lightness of the metal improved the payload capability of the aircraft and more than compensated for magnesium's inflammability (illumination flares usually are made of magnesium due to the ease of ignition, rapid burning with bright light, and the ability of the metal to burn even under water) and tendency to corrode when exposed to salt air or water. If this corrosion was not halted, the metal soon disintegrated into a pile of white dust. On board ship mechanics constantly had to paint and clean every portion of a helicopter made of magnesium.
By constructing the helicopter of aluminum, much of the problem with corrosion was eliminated. The difference in construction, indistinguishable from previous UH-1s, represented a major improvement in helicopter design. The use of heavier aluminum was possible only as a result of the increased weight/horsepower ratio of the turbine aircraft.
Events moved rapidly once the program was approved and funded. In October even before the four test aircraft had been delivered, funds for the first 30 production models were approved. By the end of January 1963, the aircraft was ready for its first inspection. The configuration engineering inspection (CEI) was a final check to insure that the helicopter was designed as specified. On hand was Colonel George L. Hollowell, the UH-1E program manager for BuWeps. The aircraft passed the test without difficulty.
The aircraft was then turned back to the manufacturer for avionics and structural testing. Bell completed all the required work on 30 July. The next month the helicopters were delivered to NATC Patuxent River for final trials by the Board of Inspection and Survey (BIS). The evaluation concluded on 10 and 11 December as the UH-1E completed carrier qualifications on board the USS Guadalcanal (LPH 2).
Ceremonies at the Bell plant in Fort Worth on 21 February 1964 marked the delivery of the first UH-1E to a Marine tactical squadron. Accepting the helicopter was Colonel Kenneth L. Reusser, commanding officer of MAG-26 and winner of Navy Crosses both in World War II and Korea. Also on hand was the commanding officer of VMO-1, Lieutenant Colonel Joseph A. "Jumpin' Joe" Nelson. The first UH-1E arrived at New River four days later. The schedule called for two additional aircraft to be delivered in March and three each month thereafter. By now the order had grown to over 100 helicopters and almost 15 million dollars." General McCutcheon's yo-yo had finally stopped and a replacement for the aging OH-43s and O-1s was on the way.
"Helicopters. Here we could characterize our needs as almost a bottomless pit … Our lift capability has doubled … but the hunger is still not satisfied. And the valor and skill of the pilots has outrun the book. The stars on their air medals are matched only by the stars in their crowns."
Lt. Gen. Victor H. Krulak
Commanding General, FMFPacific
11 July 1967