The importance of propellers and the people who keep them turning.
Propellers come in all shapes and sizes. There is the fixed-pitch wood variety that make great office decorations. There are high-tech six-blade composite designs like those that power the C-130 Hercules. And let’s not forget the first effective aircraft propellers carved out of spruce, designed and engineered by the Wright Brothers. Wilbur and Orville were the first to realize that the propellers were airfoils, too, and they fabricated and shaped the Wright Flyer’s two 8-foot diameter blades after extensive research and experimentation with shapes in their self-built wind tunnels.
The Wrights tested them in their Dayton bicycle shop using a two-horsepower motor. They added a twist along the blade’s length to create a more consistent angle of attack for the blade, ensuring that it pulled a consistent amount of air toward the plane with each rotation. A recent historical summary produced by Hartzell Propellers reported that the Wrights’ design produced a maximum efficiency of about 70 percent. Today’s propellers are around 90 percent efficient.
Like the airplanes that utilize them, propellers have evolved considerably over time. When you consider all the variants produced and all the attention paid to creating more efficient, durable technology, it’s obvious that the Wright Brothers were not just bicycle mechanics. Not only did they design and build a craft capable of sustained flight, they created a platform for an impressive array of interwoven technologies that they meticulously researched, developed, fabricated and modified into an incredible collection of products that spawned multiple industries. It’s no wonder the Wrights spent a significant amount of time after 1909 in court, defending and trying to protect the systems they designed. Needless to say, propellers were among the most important. Their innovative design moved aircraft propulsion from an idea to a reality.
Orville Wright actually inspired Robert Hartzell to start manufacturing hand-carved propellers from his walnut wood factory in 1917. Since then, the sharing of insights, developments and technological innovations has evolved into the rule rather than the exception – and the basis for the regulatory environment in which improvements have flourished.
Rebecca Williams is director of parts and propellers at Yingling Aviation, a full-service maintenance, repair, overhaul (MRO) and fixed base operator at Wichita, Kansas’ Dwight D. Eisenhower National Airport. She says communication and cooperation, even among competitors, are key to continued advancement in propeller design, efficiency and safety.
“In truth, we all work together,” Williams said. “Many of the propeller shops are either recommended, OEM factory-trained and certified, or OEM authorized service providers. The collaboration among propeller service providers worldwide has helped us expand the scope and quality of our overhaul, repair and final assembly of propellers. In some instances, we (propeller shops) are the customer, and in others, we are competitors – but we are really a family.”
Randy Lammon is a 25-year Airframe and Powerplant mechanic who has been at Yingling since 2004. He currently serves as the company’s lead propeller specialist.
“From a technical perspective, we don’t want there to be any accidents,” Lammon stated. “The manufacturers put out required inspection guidelines for well-established reasons. Propellers are technically a shelf-life item. There are certain things we do to protect the integrity and durability of the products, but the hardest part of maintaining propellers may be to get the customers to pay attention to them. A neglected prop can degrade the performance of the aircraft – and pose a real safety problem if left unaddressed.”
Lammon promotes some basic guidelines a shop technician considers foundational:
- Read and follow the owner’s manual
- Keep your propeller logbook up to date
- Maintain and properly grease your propeller (and be careful not to ‘over grease’ it or you could throw off the balance)
- Don’t ignore recommended maintenance intervals or service bulletins
- Midlife inspections and reseals are a good idea
- Refresh paint to protect from corrosion
- Stay up to date on FAA advisory circulars
- Make a visit to your local propeller shop occasionally
Of course, there are a lot of owners that do maintain and care for their
propellers as prescribed by the OEM, and others who get just as excited about new propeller developments as they do about engine or avionics upgrades. They want the latest technology and improvements, including things like better take-off performance, alloy leading edges for erosion protection, more ground clearance, and less cabin noise. Established propeller shops are where they go to make sure the upgrades are done right.
Yingling has been a leader in propeller service for more than 50 years. Like Randy Lammon, Jeff Sawyer, an A&P mechanic, authorized inspector (IA) and licensed pilot, actually began working in Yingling’s Service Department in 2000 and moved into the prop shop full time in 2010. He, too, is a protégé of Leroy “Red” Phillips. Phillips launched the firm’s propeller service in the 1950s and spent a half-century working on them until his death in 2006.
“Red knew just about everything and everyone there was in our business, and he did his best to help us – and them – adapt as the industry and the technology changed,” Sawyer pointed out. “There are still guys like Red out there in the propeller world. They’ve created new techniques and technology to improve our processes in the repair stations – things like a report for service bulletins similar to CAMP – but specific to propellers and automated blade measuring systems using laser sensor technology, MRP tracking software, and, of course, specialized tooling,” he said.
Sawyer shares a pilot’s perspective in advising customers to “always inspect your propeller before flight. Look for surface irregularities, dents, delamination, scratches, corrosion. Know what repairs can be made in the field. When in doubt, let your local prop shop check it out!”
“Don’t forget the same applies to your spinner and hub. Check for surface damage such as cracks, ensure the spinner and attaching parts are “normally” tight, and take a glance at the back of the hub and ensure the hub’s surface is not damaged. Unless it’s absolutely necessary, avoid high static RPM on dirt, gravel or rocky runways. Even glancing around the ground or ramp and removing any debris can go a very long way in protecting your propeller,” he advised.
He also recommended wiping the propeller with a lightly oiled rag after each flight, especially if flying in a corrosive environment. When it comes to the propeller’s finish, he cautioned against a “spray can” overhaul – just putting a quick coat of paint over problems. Know the correct procedures for your paint. It is important to maintain good paint coverage, one for safety and another for longevity. Better yet…call your local propeller shop to ensure it’s done right.
“Some things just don’t occur to operators, I guess, such as avoiding pushing or pulling the aircraft by the propeller blades or spinner,” he added. “I also suggest that, if you are flying a twin over the same consistent flight pattern, it’s a good idea to occasionally rotate your propellers. Finally, I personally would not use reverse except in short-field landings or emergencies. You can control your speed by taxiing in beta without producing thrust and it will reduce potential blade damage.”
Another savvy industry veteran is Bob Finke of International Propeller in Lincoln, Nebraska. He fits the mold of Red Phillips and touts the collaboration and cooperation of the “propeller community,” too. He spent 25 years at Duncan Aviation before he and another former Duncan colleague, Scott Lau, started International Propeller five years ago. Bob is on the board of WAPA and says, “It’s awesome – we communicate with other members virtually every day to find overhauled or used parts, compare techniques and do what we can to keep our clients’ costs down. I have email addresses for virtually every prop shop in the world,” he added.
Finke also has a vast worldwide clientele. International Propellers was named the Exporter of the Year for the Midwest Region three years ago by the Small Business Administration (SBA). “We deal primarily with turbine operators but we have lots of owner-pilot customers, too. My current inventory includes everything from metal single-engine aircraft props to five-bladed composite models for the King Air 350 – and if I don’t have what a customer needs, I have the means to find it quickly,” he said.
At the home of Raisbeck Engineering in Seattle, Washington, Director of Sales Rob Richardson has been helping owners maintain and upgrade their propeller-driven aircraft for decades…and he has seen lots of changes over the years. Raisbeck has been developing performance and aerodynamically designed enhancements for OEM production aircraft since 1982 and received its first STC for propel-lers in 1985.
“Back in the 1980s, we were working on corporate-owned, crew-flown turboprops, both Part 91 and Part 135 operators. Now, a lot of those same airplanes are privately owned and flown. Those operators all want to go fast and have the best performance available. They’re willing to spend the money to upgrade the prop just like they do with the airframe and electronics.”
“We see cooperation between propeller service providers and even MROs because we’re all trying to deliver quality support and enrich our customers’ flight experience. The number of FAA propeller repair stations in the U.S. is probably around 50, so we all know each other,” Richardson commented.
“It used to be that the propellers and cowlings were the last things to be addressed during mandated inspections – right before the airplane went back to the operator. That perfunctory check allowed a lot of them to go back into the air without proper lubrication or with corrosion issues, and that could produce a dangerous situation.”
“We have seen a lot of aircraft with high-time props. The operators think they’re saving money by stretching them to the limit. But, when they finally get around to inspecting them, the blades all need to be replaced. At $7,000 per blade on a pair of four-bladed props, the cost to repair the old props gets pretty close to the expense of buying all-new, zero-time replacements.”
The network of propeller manufacturers, maintainers and prop shop operators really is, in Rebecca Williams’s words, “a large but small group.” They aren’t vast in number, but their role in keeping the flying public safe is significant, even if it’s often overlooked. But that’s okay with them. They actually prefer to be like the products they service: quiet, efficient and indispensable!