I think most helicopter people would agree that today’s MD 500 series helicopters are at or near the top of almost every pilot’s aircraft bucket list.
From a practical standpoint, the size, speed, agility, performance, simplicity, reliability and relatively inexpensive operating costs of the 500 make it uniquely suited to any number of missions. This is confirmed by the fact that it continues to be highly sought after by many utility, parapublic and specialized military operators worldwide.
I suspect, however, that many who dream of flying the MD 500 want to do so simply because of its sleek styling and reputation as an exhilarating helicopter to fly. After having flown these machines myself for nearly 20 years, I can confirm that the MD 500 is definitely all that — and a bag of chips!
So, I was particularly excited when I discovered, in February of this year, that the 500 had reached an impressive milestone: the 50th anniversary of the first flight of the line’s original incarnation, the Hughes OH-6.
In the half-century since that day in 1963, the Hughes/MD 500 has evolved, undergoing many cosmetic and performance upgrades. Now, the current manufacturer, MD Helicopters Inc., is busy putting the finishing touches on the latest, much-improved incarnation of this legacy performer, the MD 540F.
How the Legacy Began
The forerunner of the 500 can be traced back to the mid-1950s, when the Hughes Tool Co.’s aircraft division (based in Culver City, Calif.) decided there was a market for a low-cost, lightweight helicopter, and created the Model 269. Although it first flew in 1956, and the United States Army evaluated pre-production models in 1957-58, Hughes did not put the three-bladed, piston-powered helicopter into production until 1960, as the Model 269A.
By 1964, Hughes had already produced over 300 269As, but things were about to get even better: the U.S. Army selected the 269 (designated the TH-55 Osage) as its new primary training helicopter. This eventually led to about 800 TH-55s being produced. Versions of the 269 (later known as the 300) are still produced today, as part of the Sikorsky S-300 line.
The success of the 269 fueled the enthusiasm of billionaire aviation pioneer Howard Hughes, leading him to explore other opportunities in the light helicopter market. His next helicopter project would compete for another lucrative military contract, for the U.S. Army’s light observation helicopter (LOH).
The Army’s LOH request-for-proposal stipulated that the helicopter be turbine-powered, and be a “small, lightweight, inexpensive, reliable and easily maintainable vehicle.” It also needed to fulfill a multi-mission combat role that included visual reconnaissance, target acquisition, and command and control.
To meet these demands, Hughes engineers focused on performance, sturdy simplicity and crashworthiness. The resulting prototype, the Model 369 [later the 500/OH-6], had an innovative egg-shaped main cabin with a distinctive V-tail. The interior allowed seating for up to five individuals and was contained within a central pyramid/A-frame structure with two bulkheads, a keel beam and an integrated edge-to-edge roll bar to protect passengers. The surrounding structure was designed to be “crushable” to absorb crash forces and ensure the passenger area retained its shape. Adding to the crashworthiness, this fuselage sat atop durable shock-absorbing landing gear.
“The design of the 500 is based on a simple premise: crashworthiness,” said Donald Porter, who worked for Hughes for about a decade and today is considered an authority on the history of the company and its rotary-wing products. “As an OH-6A tech rep in Vietnam, I investigated many accidents where the pilots walked away unscathed. I doubt this would be the same outcome with most other helicopters.”
To meet the rigors of flying combat missions, the 369 had a fully articulated four-bladed main rotor mounted atop a static mast. The blades were interconnected through innovative, laminated, stainless-steel strap packs. The design also employed a one-piece tail-rotor driveshaft that eliminated maintenance-intensive hanger bearings.
The 369 employed simple, non-boosted mechanical flight controls. It was powered by a single Allison T63-A-5A (civil model 250-C18) turboshaft engine producing 317 shaft horsepower (s.h.p), but de-rated to 252 s.h.p.
On Feb. 27, 1963, the first prototype logged its maiden flight. Soon after, the first of five prototypes, designated as YOH-6As, along with the Bell YOH-4A and Hiller YOH-5A prototypes, were delivered to the Army for evaluation.
In the end, Hughes emerged on top, and in 1965 received the first of two orders that would eventually total over 1,400 units. Designated the OH-6A Cayuse, the model would become known as the “Loach,” for the LOH abbreviation, and the “Flying Egg,” because of its shape.
Getting a Fast Start
In April 1965, even before the LOH contract announcement, Hughes revealed the development of two commercial variants of the OH-6A: one targeted at executives; the other earmarked for the utility market. Both were to be powered by the Allison 250-C18A. It would take four years, however, before a civil variant became available.
While both the military and civil machines were outwardly similar, the civil variant had front cabin modifications that provided additional seating. Most notably, the pilot-in-command position was moved to the left seat. This provided front cabin configuration options for either two passengers and a pilot, or a center console with a pilot and single passenger.
The OH-6A entered service in the Vietnam War in the fall of 1966. Before that, however, it established 23 world records in a variety of performance-related categories, including a non-stop, unrefueled flight that lasted just over 15 hours and covered more than 2,200 miles — a mark that still stands today.
In describing its flight characteristics, Hughes chief test pilot Bob Ferry, a retired U.S. Air Force lieutenant-colonel, was quoted in the 1960s as saying, “The OH-6 handles very much like an agile fighter plane. It climbs and rolls into banks much like a P-51 [Mustang]. Bank angles of 60 degrees are normal flight practice.”
Because of its versatility in the military arena, many other variants were introduced, each with specialized upgrades and capabilities to better meet the increasing popularity of the helicopter and the demands of domestic and foreign military operators.
That booming military business, combined with production glitches, was largely responsible for the aforementioned delay in bringing a civil variant to market. Because, while the civil model made its first flight and earned U.S. Federal Aviation Administration (FAA) certification in 1966, Hughes didn’t start delivering the Model 500 until July 1969.
Once in production, it became sought-after on a global level: manufacturing licenses were granted to Italian and Japanese firms in 1969 to begin building their own versions, primarily for military and civil defense missions. By 1970, military and civil variants were flying in 16 foreign countries.
Innovation was equally swift: the Hughes 500C with its more-powerful Allison 250-C20 engine was introduced in 1970. The company then quickly introduced the 500MC, with a larger main rotor and upgraded transmission, as a military variant for foreign customers.
Picking Up Steam
About the same time, Hughes began work on a military project to reduce the noise signature of the OH-6. The project, originally codenamed “Mainstreet,” produced a variant known as “The Quiet One,” which saw the installation of a new five-bladed main rotor with reshaped blade tips, and a four-bladed, scissor-type tail rotor (later used on the Hughes AH-64 Apache). These additions, along with transmission, gearbox and engine modifications, allowed the main rotor to be operated at a significantly lower r.p.m. The development team also utilized an engine exhaust muffler, lead-vinyl pads around the mounting interface of the transmission, and a baffle and noise-deadening material on the air intake. Combined, the upgrades resulted in noise reductions of up to 20 decibels.
While the military chose to discontinue the program, two machines, dubbed 500Ps (penetrators), were produced, one of which was utilized by the CIA’s covert
airline, Air America (see p.108, Vertical, Aug-Sept 2010), in 1972 for a single, secret, two-day phone-line-tapping mission in North Vietnam.
A version with the more-powerful Allison 250-C20 engine became the OH-6C prototype, which attained a top speed of 200 miles an hour in testing.
In 1975, Hughes integrated much of The Quiet One’s program technology onto a structurally reinforced 500C airframe to develop the Model 500D. The 500D offered a gross weight of 3,000 pounds (1,360 kilograms) and was powered by the 420-s.h.p. Allison 250-C20B engine. It incorporated the five-bladed main rotor, along with a redesigned T-tail and options that included high-ground-clearance landing gear and a four-bladed tail rotor.
An enhanced, armed military variant, the 500MD Defender, earned a great deal of interest from foreign governments due to its ability to fulfill a wide variety of military roles.
In the mid-1970s, Hughes engineers also began work on a potentially revolutionary anti-torque system known today as NOTAR (no tail rotor). It wasn’t until December 1981, however, after the now-named Hughes Helicopters Inc. had received a government research contract, that the first NOTAR prototype, a modified OH-6A, made its first flight.
That flight coincided with a stabilizing and resurgence of the company, which had fallen into financial difficulty after Howard Hughes’ death, and had stayed that way until Jack Real, a former personal advisor to Howard Hughes, took the helm.
Adhering to Howard Hughes’ belief in regular ongoing innovation, the company, under Real, pushed forward with new ideas and models.
In 1982, the 500E was introduced. It didn’t have many technical innovations, but it did have several new client-pleasing features, including a sleek, tapered nose that gave the helicopter a more streamlined look. The interior had a standard T-shaped instrument panel (which had been optional on the 500D) that provided added room for avionics and radios. Front and rear passenger comfort, meanwhile, was enhanced through improved overall seating and increased legroom; plus, there was also improved headroom and visibility for rear cabin passengers.
Military operators maintained a strong dependence on the 500 line, continuing to adopt several sub-variants of the armed 500E (500MG Defender) for specialized missions such as anti-tank, anti-submarine and reconnaissance.
Also in 1982 came the 530F, an enhanced 500E variant engineered for hot and high conditions. It featured the 650-s.h.p. Allison 250-C30 engine driving a main rotor 12 inches larger than its predecessor. The tail rotor was also enlarged, by two inches, to provide increased thrust and directional control at high altitudes.
The tail rotor gearbox, meanwhile, was mounted to an extension added to the tail boom, shifting it aft eight inches. Less obvious were tweaks to the horizontal stabilizer to address the altered flight dynamics.
Although the improvements provided only a small increase in payload, key benefits were realized in other areas. During performance testing, for instance, the 530F set two impressive time-to-climb world records that still stand today (breaking, ironically, the OH-6A’s 1966 records). The first was to 3,000 meters (9,842 feet), and took three minutes and 15 seconds; the second was to 6,000 meters, and took just over six-and-a-half minutes.
Good Times and Bad
With increasing production, Hughes soon needed more expansive facilities. It settled on Mesa, Ariz., which offered the company attractive incentives to relocate. In 1982, ground was broken on a new 549,000-square-foot facility that would house consolidated assembly lines, and a flight test and delivery center.
Shortly thereafter, in 1984, Real’s turnaround of the company was complete when aerospace giant McDonnell Douglas purchased Hughes Helicopters Inc. for $470 million US and renamed it McDonnell Douglas Helicopter Systems (MDHS).
MDHS’s first two new models — the MD 520N and MD 530N — were announced in the late 1980s. They were based on the 500E and 530F, respectively, but would be the first models to utilize the NOTAR system.
After successful first flights (Dec. 29, 1989, for the 530N; May 1, 1990, for the 520N), MDHS decided to only pursue certification for the 520N, which was attained on Sept. 12, 1991. The first aircraft was delivered on Oct. 31, 1991.
The MD 520N, with its large composite tail boom, was powered by the Allison C250-C20B and -C20R variants, and certified to 3,350 pounds maximum gross weight. It was the first helicopter in the Hughes/MDHS line to have a yaw stability augmentation system (YSAS) to reduce pilot workload.
The next advancement for MDHS occurred in 1995 with the MD 600N, a “stretched” 520N that the company hoped would appeal to executive transport and air medical operators.
The design of the 600N called for a 21-inch extension of the rear cabin and a redesigned tail boom. The larger cabin increased seating capacity to eight people, while redesigned rear cabin doors provided for much-improved passenger loading capabilities.
The MD 600N’s main rotor was enhanced to a fully articulated six-blade design and the landing gear was “beefed up” to accommodate the larger airframe. Like the MD 520N, the 600N saw the addition of YSAS, but was powered by the Rolls-Royce (formerly Allison) M250-C47 engine and had a maximum gross weight of 4,100 pounds.
The MD 600N got its certification on May 15, 1997, with deliveries beginning in June. But, this would be the last piece of good news for a long time.
In the summer of 1997, McDonnell Douglas merged with Boeing to form The Boeing Co. This powerful, new conglomerate had little interest in the MDHS light helicopter lines and chose to sell them off, keeping only the AH-64 Apache attack helicopter and the rights to the NOTAR system/technology.
Citing a potential monopoly, the U.S. Federal Trade Commission blocked Boeing’s sale of the Hughes/MDHS light helicopter lines to Bell Helicopter. As a result, a new deal was finalized in February 1999 to sell the lines to RDM Holding Inc. (headed by the now-notorious Joep van den Nieuwenhuyzen).
The new RDM-owned company became MD Helicopter Holdings (MDHH). As part of the agreement with Boeing, MDHH retained a license to use the NOTAR system on its existing lines: the MD 520N and 600N, plus the 900/902 Explorer twin-engine models.
Unfortunately, the sale to RDM proved to be what many feared — the kiss of death. Spare parts availability and customer service declined to unacceptable levels, and aircraft deliveries slipped to near zero. The company was bleeding financially. Many frustrated operators began to consider abandoning the line entirely.
Coming Back From the Brink
It was 2005 when a private equity firm, Patriarch Partners LLC, stepped in and purchased the struggling company. New chief executive officer Lynn Tilton announced not only a much-needed infusion of capital and management personnel, but spoke of an optimistic and ambitious future for the company, which was rebranded MD Helicopters Inc. (MDHI).
As part of that future, MDHI focused on the potential of its single-engine lines. And, great emphasis was placed on modernizing its models, while addressing the needs of its customers.
As MDHI VP of engineering, Chris Nehls, told Vertical, “We had a lot of customers, both commercial and military, that told us they needed additional gross weight and useful load capability in the 530F. So, we looked at a lot of different ways to enhance performance and increase gross weight.”
The realization of that customer input will be seen in the upcoming MD 540F, which will borrow the six-bladed main rotor and high-stance/high-capacity landing gear of the 600N. The rotor blades, though, will be a new composite design developed with Van Horn Aviation of Tempe, Ariz.
“The six-bladed rotor head is straight off the MD 600, yet it is more agile on the 540,” said MDHI production test pilot Nick Page. “The 540 has a faster roll rate than the standard MD 530F, and the need to use the cyclic trim is much less — trim inputs throughout the flight regime were almost nil.”
Nehls said the tail rotor is expected to be a modified two-blade design using a simplified hub that eliminates the tension-torsion straps. MDHI engineers believe this will allow the use of a larger blade chord, thus increasing tail rotor lift while retaining two-bladed simplicity.
Initially, the MD 540F will include a partial glass panel, utilizing the Garmin G500H integrated flight display in combination with traditional engine instrumentation. Providing a glimpse into the future, however, Nehls said, “We are working with a company to develop a cockpit display system with [an] integrated engine instrument display that will replace all engine instruments and [the] rotor tach for all the single-engine aircraft.” Nehls said this might enable the return of an optional narrow “slimline” panel that was popular with utility operators.
The design engine for the 540F will be the Rolls-Royce M250-C47E/3 turboshaft with dual-channel, full-authority digital engine control. (MDHI is considering using a de-rated version of this same engine on new 530Fs and 600Ns.) Flight-testing to gross weights of 3,800 pounds has produced exciting results, but the company anticipates FAA certification of the 540F will be around 4,100 pounds.
“The 540 is coming down the line and it’s a big step for us,” said Carl Schopfer, MDHI’s president. “It’s the first new model to be introduced in the 500 series since the split from Boeing in 1999. So, it’s really exciting! I think it provides a good next step as far as capabilities go. When you increase lifting capability from 3,100 pounds [in the MD 530F] to over 4,000 pounds, that’s a big step.”
MDHI continues to innovate and modernize the existing 500 series helicopters, as well. Engineering is in progress to develop a glass cockpit, similar to that proposed for the MD 540F, for all its single-engine models. It is believed this solution will also be available as a simplified retrofit for aircraft already in the fleet.
Nehls said engineering is also being conducted to develop and certify a common airframe for the 500E and 530F. Presently, there are minor structural differences between the airframes of the two models.
One program that has made great strides recently is another project being developed with Van Horn: a new composite main rotor blade for the 500E and 530F. It is expected this new blade will provide a significant bump in useful load — as much as 250 pounds.
Positive Affirmations
Of course, what may be most impressive is what pilots and operators say about the 500.
One particular supporter is Chin Tu, president and chief flight instructor of Civic Helicopters in Carlsbad, Calif. In the early 1970s, after serving a tour of duty in Vietnam, Tu became a production test pilot for Hughes. Decades later, he is still enamored with the 500: “I love lots of different helicopters, but if you strap on a 500 — and notice I said ‘strap on’ — it’s like a robotic extension of your body. You can think about doing something with your body and it’s like the 500 knows exactly how to execute it. . . . When I fly a 500, my heartbeat goes up. I come alive! It’s like, wow, this is what a helicopter should be like. I don’t feel that with any other helicopter.”
Prism Helicopters of Pitt Meadows, B.C., meanwhile, has largely built its business around the 500D. With currently more than a dozen 500Ds (about half of what it once had), Prism is perhaps the largest 500 operator in North America.
The company started in 1985, with president Dave Zall long lining red cedar shake block using a single 500D. Today, due to the decline in logging work, Prism has shifted mainly to oil, gas and mining support missions, with some topping and pruning of tall timber. Even with this change, Prism’s fleet of 500s continues to serve the company well.
“The 500 is so well-suited for long lining on small drill jobs,” remarked Prism’s operations manager, Jeremy Zall. “The machine’s efficient and easy to long line from. Also, its size and great visibility makes it ideal for confined areas and working into small or undeveloped areas. For tree topping, we can’t beat the 500 for quick maneuverability when the tree tops are moving around from the rotor wash.”
Of course, that nimbleness was originally developed for operations of a very different kind. “The OH-6A’s performance and amazing agility was realized during service in Vietnam,” recalled Porter (the former OH-6A tech rep, now Hughes/MD historian). “Operating for long stretches under high DA [density altitude] conditions, exceeding redlines and design loads, with enemy rounds often hitting even major dynamic components, the helicopters made it back home more often than not. This is the heritage the Model 500 is built on.”
Looking back at the engineering of the 500, Nehls remarked: “I have a great appreciation for what they were able to accomplish with a slide rule and a pencil and paper. They designed a helicopter that was basically used as a target, and needed to be agile in order to get people out of harm’s way after they drew fire. So, you end up with a very fast, very agile aircraft. . . . That was the whole idea behind the Loach.”
It’s interesting to note that, in spite of producing over 1,400 units, the OH-6A was never profitable for Hughes. High manufacturing costs and miscalculated business gambles early on would haunt the company to the end. There is no discounting, however, the OH-6 and Model 500’s distinguished place in rotary-wing history and their influential role in the development and advances that have created today’s exciting single-engine MDHI helicopters.