Enstrom Helicopter

Enstrom Artisans Build Helicopters with Personality

November 5, 2018 by Scott Spangler

Waggism, playful lightheartedness, is the last thing one would expect to see at a facility dedicated to the deadly serious business of building FAA-certificated aircraft. But then I met Sally, her name printed on an aluminum placard in red Sharpie on the wide end of a fixture used to build tail booms at Enstrom Helicopter in Menominee, Michigan.

Curious, I asked Dan Nelson about it. Was this the work of some unknown wag, an aeronautical version of Kilroy was Here?. Taking a moment, he carefully put down his Cleco pliers and explained that Sally was the name of the piston-powered helicopter just conceived at the factory. “We started naming them some months ago,” said Dan, a sheet metal master who introduces newcomers to the craft and mentors their mastery of it.

“There was a picture on Facebook of a fleet of our helicopters on the ramp for delivery, and someone said we should start naming them.” The piston-powered F-28F and 280FX get girl names, and boy names identify the turbine-powered 480B. “It’s just for fun,” he said with the unapologetic tone of a father talking about his children.

Perhaps naming these gestational helicopters isn’t so waggish. Expectant parents often name the nugget of their baby to give it an identity, to make it more than a bump, to connect on a more intimate, personal level. The only real difference is that the helicopter’s names stay in the womb. Like all parents, the customers who take the newborn Enstrom home have the naming rights.

The riveted monocoque is just one appendage connected to the welded steel-tube pylon that is the Enstrom’s thorax. Working in robust rotating fixtures that look like complex gyms—yellow for pistons an green for turbines—it takes Enstrom’s state-certified welders about three weeks to weld a pylon, said Dennis Martin, Enstrom’s director of sales and marketing.

The welders work with pre-notched tubing, he explained, and the three weeks includes their final fitting, sand blasting, multiple inspections, and a light skim coat of primer that makes imperfections stand out. “We like steel because it’s easier to inspect and repair,” said Martin. “But the main reason is that steel will absorb a great deal of energy.

“If you look at the S-N Curve [a plot of the magnitude of an alternating stress versus the number of cycles to failure for a given material], once it fails, steel continues to absorb energy, which means it is not transferred to the occupants. It doesn’t have a sharp drop off; once aluminum or composites fail, it’s done—it doesn’t absorb any more energy,” said Martin.

Just around the corner, in the composite shop, Tom Retlick is laying up the some seats that combine different layers of foam and glass that work in concert to provide lightweight rigidity, comfort, and a degree of energy absorption. Just celebrating 23 years at Enstrom, he’s surrounded by his work, artistry embodied by the split molds for each model’s cabin and attendant fairings.

The heart of Enstrom’s birthplace is the climate-controlled cube that is the quality department. “It’s such a crazy juxtaposition,” said Roger Hardy after setting a raw casting of the idler pulley for the piston power train in the Conner CNC measuring machine. Just outside those doors there are artisans bucking rivets, welding steel, and laying up and cooking composites “all under one roof with CNC measuring and milling machines.”

“It takes some time to program the machine” to measure dozens of specific points on a part, said Hardy, who starts the effort with the part’s drawing. “But it goes to the exact same point on every part with a consistency that gives a true measure of each part.” He’ll see this part again, after it takes its turn in a CNC mill to become a finished idler pulley.

After making sure my curiosity had satisfied its current queries, he thanked me, and returned to work, as had all of the artisans I’d talked to this day. Each of them was knowledgeable and friendly, and prompted by my questions, they eagerly shared their knowledge in terms neither patronizing nor overtly technical. As a group, their personality was one of proud parenthood. — Scott Spangler, Editor

Cody Parkovich, Enstrom Helicopter Production Test Pilot

July 12, 2018 by Scott Spangler

Just six months on the job as Enstrom Helicopter’s production test pilot, Cody Parkovich traces his position to the night he was bartending in Marinette, Wisconsin, just across the river from Menominee, Michigan. “That night I found out, when I was 23,” that Enstrom was a hometown company. “And I grew up here.”

Just discharged from the U.S. Marine Corps and home from San Diego where he’d served as an F-18 mechanic, “I didn’t know that flying a helicopter was an occupation outside the military,” he said. His original plan was to “go to school and go back into the service, but I got the itch and started flight training in Duluth two weeks later.”

Then he moved around the country to build time and experience in a number of different helicopters, the Robinson R44, Bell 206, the A-Star 350 series, ” and I instructed in a new Guimbal Cabri G2,” he said.

After teaching, Parkovich flew commercial ops in Utah, flying aerial tours in Michigan’s mitten, some ag spraying, and some utility pipeline inspection around Louisville and railroad track surveying with LIDAR, so the Canadian National could measure the grade before they increased the cruising speed of their freight trains.

“This is the life of a professional helicopter pilot,” said Dennis Martin, Enstrom’s director of sales and marketing. “Airplane pilots fly airliners, Helicopter pilots do 25 different things.” In short, they have to be as versatile as the rotary-wing aircraft they fly.

When Parkovich started work at Enstrom two years ago, “I thought I was a halfway decent mechanic from working on fixed wings, and then I found out that helicopters were a whole other ball of worms.” Like most of Enstrom’s workforce of 150, Parkovich works in different areas that cross-complement his primary responsibilities.

“Because I still work on the floor as a mechanic, I know these ships like a doctor knows human anatomy. I’ve been hands-on with the rigging process.” As we talked, he was prepping a turbine-powered 480B, with a Garmin G1000 in the panel, for its final inspection, just across the aisle from the final assembly area. In front of it was the hangar door.

Summarizing the purpose of a production test flight, Parkovich said it takes, on average, 5 hours to demonstrate that the helicopter meets all of its documented performance numbers and that all of its equipment, regardless of how it is equipped for the customer, works as its documentation proclaims.

More specifically, this involves flights at different centers of gravity, making sure it has the same cyclic throws and maneuverability. Accelerating to V_NE — the never exceed speed—he checks for adverse vibration and retreating blade stalls.

He also flies to track and balance blades and helicopters, a process that reduces the whole-ship vibrations to the absolute minimum. All of the helicopter’s rotating pieces can produce vibration, but they start with the main rotor, which can vibrate on both the vertical and lateral planes.

New blades are balanced chord-wise, the added weights written on the tips, and span-wise. Those balances are refined by flying the blade set in a known ship, said Parkovich. Putting them on a new helicopter would introduce too many variables, such as tail rotor vibrations.

This also saves start cycles on the Rolls-Royce turbines, said Martin. “They only get 3,000 cycles before they need hot-section maintenance, and when you’re making blade adjustments, you have to shut down, adjust, and restart. And if it takes 25 or 35 cycles, you don’t want to give that to a customer.”

Production flight test doesn’t involve a lot of test equipment, said Parkovich. His most important instrument? The seat of his pants. In another summary, his job is to “make sure very helicopter feels the same, flies the same way.” — Scott Spangler, Editor

Enstrom Helicopter Blade Maker

June 25, 2018 by Scott Spangler

In the simplest terms, a helicopter’s rotor blade is a wing that generates lift by flying in a circle. But the similarity between a wing and rotor pretty much ends at the airfoil because the forces acting on each of them is vastly different. Imagine flying an aircraft that is constantly trying to shed its wings through the centrifugal force of normal operations. From building airplanes small and full-scale, I know how the skeleton of the wing deals with the forces of flight when fixed in one position. But when it comes to wings that fly in a circle, my understanding is destitute. Enstrom Helicopter Corporation, which for 60 years has been building piston and turbine helicopters in Menominee, Michigan, just up the coast from Green Bay, said they could fix that.

On the wall outside the Leland Burdue Training Center on the second floor of the Enstrom factory at the Menominee-Marinette Twin Country Airport (MNN) are two rotor blades. It’s clear that like the first propellers, the first rotor blades were carved out of wood by artisans of the drawknife and spoke shave. This long, wooden aerodynamic blade probably lifted one of Rudolf “Rudy” Enstrom’s prototype helicopters to a hover sometime in the late 1940s or early 1950s. “We’re really not sure,” said Dennis Martin, director of sales and marketing. “A family member found this in a barn [after Rudy passed on September 25, 2007], but we’re pretty sure it flew” on one of his early prototypes, which employed a two-bladed teetering rotor system.

Tool marks are visible beneath the worn black paint on the yellow-tipped wood blade. Beneath it is a seamless black-and-white striped metal blade. It is one of a trio that creates the fully articulated rotor system on the piston-powered F-28F and 280FX and the Rolls-Royce turbine-powered 480B. The rotor systems are essentially the same for all models, and together the main rotor systems have logged 4 million flight hours without a catastrophic failure.

Building Blades

The wood and metal blades have two things in common. Both are 16-feet long give or take, and artisans make both. Working what looks like an orbital sander loaded with a fine abrasive that seems to be polishing the metal is the leader of Enstrom’s blade shop, Ken Clark. Asked how many blades he’s built, Ken furrowed his brow for a second. “I’ve been here 32 years, more than half my life,” he said. Founded in 1959, Enstrom has been in business for 60 years, “So about half the number ever made.” That would be approximately 3,200 blades, with a birthrate of 12 per week.

“I have a couple of guys who work with me, and we make the tail rotor blades, too,” Clark said. When called for, another couple of workers join the crew. With 150 total employees, most of Enstrom’s technicians are cross-trained in several departments, and the blade shop is one of the more demanding studios. “This is an art,” said Clark. “This is nothing anyone is going to teach you in school. To take a guy fresh, it’ll take about seven years to teach him everything.” His apprentices have been working with Clark for about two years, and like many of the skills Enstrom’s artisans employ, their education is on the job.

Given the forces involved, I expected a more complex design. But Enstrom blades are built around an extruded D spar leading edge. Two sheets of 2024 are bonded to the recesses on the top and bottom of the spar, and at the training edge. “There are no ribs, no honeycomb, they are hollow all the way through,” said Martin, but the blade’s interior is epoxy primed to prevent corrosion. There are some doublers at the blade’s root, where the grip that connects it to the hub is bonded in, added Clark. He’s never counted the steps involved in building a blade. “It doesn’t matter; it’s got to be done either way.” The most challenging part of the process is, however, setting the tip cap rivet. “You’re almost done with the blade, and one wrong hammer—and it’s scrap.”

All of Enstrom’s metal blades have been built in the same fixture, which holds the pieces in place, forms the fully symmetrical airfoil, which includes a 7-degree twist down near the tip, and electrically heats the bonding seams and the entire fixture, with a box that encases it once all the pieces are in place. It takes an hour to warm up, it spends an hour at the perfect adhesive bonding temperature, and it takes an hour to cool. The twist, Martin explained, comes into play during an autorotation, a helicopter’s engine-out glide. Air passing through the center of the rotor disk turns the blades, and the outer portion provides the lift.

The relatively simple design blade wasn’t its only surprise. With so many rotating parts working in critical concert, their lifespan counts the hours of operation. Asked how long a rotor blade lives, Martin smiled: “97,500 hours. Effectively, they are on condition. There’s no calendar life, no hour life. They will last as long as they are maintained. The oldest calendar set that I’m aware of has been flying since 1973. The highest time I’m aware of is 22,000 hours. If you take care of the blades, keep them clean and corrosion free, they’ll last forever.”

Another question Martin often hears, he said, was about composite blades. He keeps his answer in a green, four-drawer file cabinet in the corner of the blade shop, in a drawer labeled “Broken Blades.” Halfway expecting some Harry Potter magic to produce a 16-foot blade, Martin instead pulled a deformed tail rotor blade out of the drawer. “This guy had a bad day,” he said. “But he still had something back there doing work for him. He put the helicopter back on the ground safely.” While the aluminum was bent and cracked, the bonding adhesive was unbroken. A composite blade would shatter and shred itself to an ineffective stump.

Blade Matching

“Everyone thinks you just throw the pieces in the fixture, and it’s magic,” said Clark. “But there’s a lot you have to do to make sure it comes out right.” Quality control begins before the pieces get near the fixture. Enstrom helicopters have mechanical controls, so they are sensitive to blade balance. “If the blades have different weights, they will fly differently, so we weigh every spar and rout the inside of the D to equalize the weight. After we build them, we match them in sets of three,” said Martin.

The birth certificate of every blade is the record of several hundred measurements and a profile of the entire blade. This data is fed to a spreadsheet that creates a chart for every set of blades. Call it a family born of a common fixture. “We keep this information forever,” said Martin, “If a customer needs a new blade or two, we look at that chart [for the family of blades delivered with his helicopter] and send replacements with matching numbers. Usually, they track very well. But if they don’t the customer sends them back and we send another one.”

Rotor blades are not the only components Enstrom builds from scratch. It’s easier to itemize the components it does not build: engines, avionics, and instruments. “We don’t have a foundry to cast parts like the main transmission housing and tail rotor gear boxes,” said Martin, “but we have four CNC vertical machines and three turning centers, so we do the final machining. We also have a CNC router for cutting metal, and CNC press brakes for bending it.” Because it is a critical component, Enstrom has two firms that precision grind the hollow main rotor masts to 5/10,000th of an inch. One is in Traverse City, Michigan, and the other (which made parts for the space shuttle) is in Green Way, Wisconsin. Without doing the math, Martin estimated that 99 percent of the Enstrom is made in America, and most of the handful of foreign vendors is Canadian.

One of them extrudes the rotor blade D spar. “Spar thickness is critical to the blades’ performance, and we can tell when the company’s die starts wearing out because the blades fly differently on the helicopter,” said Martin. “So call them up and say that it’s time to refresh the die.” —Scott Spangler, Editor