Sensenich, arguably the best-known manufacturer of wooden propellers, has been around for almost 100 years. It has a fascinating history, but what does the future hold for this remarkable company?
To gain greater insight, we spoke to Sensenich’s Steve Boser, vice president, engineering. Boser has been with Sensenich from 1993, when he joined the company as a junior design engineer. At the time, rather ironically, he was a glider pilot, although he has since moved on to flying propeller-driven aircraft.
The company was incorporated in 1932, but it began in rural Pennsylvania during the 1920s, when two brothers, Harry and Martin Sensenich, who loved to tinker, procured an old World War I-era engine. According to Boser, they “proceeded to fit it to a wagon, a sled, and different contraptions they could find on their dairy farm. Their wagon worked well. It was called a ‘Wind Wagon’, but eventually they were banned from taking it into town.” The brothers then fitted the engine to a snow sled. One winter, while operating on ice, the brothers’ unique air-driven vehicle crashed, breaking its expensive propeller. At the time, it was rare for someone to be knowledgeable about propellers. Boser explained, “They were pretty good with their hands, so they thought, ‘hey, let’s make our own propeller!’”
The brothers successfully crafted a propeller for their sled. Soon, local pilots took notice and reasoned, “If you can make a propeller for that thing, you can make propellers for our aircraft.” Boser continued, “They started carving aircraft propellers, and by the beginning of World War II, they were the largest manufacturer of wooden propellers in the world. We still have that title today.” During the Second World War, which lasted from 1939 to 1945, Sensenich had more than 400 employees crafting propellers 24 hours a day to support the war effort. These propellers were primarily for liaison aircraft and trainers, as well as experimental projects.
Soon after the war, Sensenich produced a tremendous number of propellers for private light aircraft. Later, in the late 1940s, the company diversified and began making metal fixed-pitch propellers, while also servicing and maintaining other companies’ propellers, in addition to manufacturing a variety of wooden products. During the 1950s, Sensenich also began designing and manufacturing target drone propellers, as well as airboat propellers. Airboats, which have grown in popularity in places such as Florida, are essentially flat-bottom boats pushed by propellers, which are similar in appearance to those found on aircraft. Today, Sensenich produces more airboat propellers than aircraft propellers.
By the late 1980s, the company had been operating separate divisions for propellers and for wood products. The Sensenich family was forced to sell one of its divisions, either propeller manufacturing or its wood product division, which made table tops and bench seats. A Philadelphian family purchased the propeller company and continues to own Sensenich Propellers to this day. In 1994, the company’s three divisions, namely wood propellers, metal propellers and its service division, were separated. The service division had a management buyout, while the wooden propeller division was moved to Florida, the primary market for airboat propellers. The metal propeller division remained in Pennsylvania. In the late 1990s, Sensenich turned its focus to composite propellers for aircraft and airboats, while also ramping up production of unmanned aircraft propellers.
Today, Sensenich has about twenty employees in Pennsylvania, where metal propellers are produced, and about fifty employees in Florida, where the company focusses on wooden and composite propellers.
In terms of aircraft. Sensenich propellers are primarily used by experimental aircraft, trainers and vintage aircraft. Most of the company’s wooden propellers are used by vintage or antique aircraft. Sensenich produces about 4,000 wooden propellers per year, although, due to demand, its carbon fibre propeller production numbers increase significantly every year. How has covid-19 restrictions affected Sensenich? According to Boser, “Last year was probably the busiest year of the past ten years. This year is off to an even better start.” He continued, “When people are at home, they have more time on their hands. They need propellers because they are either working on kit airplanes or they are out flying.”
Sensenich currently produces about 150 to 200 composite propellers per month. Is that where the future lies? “Most of the development is on the carbon fibre product line,” explained Boser. “Wood is economical for developing a propeller in a short timeframe. It requires minimal tooling to make a wooden propeller. The engineering requirements for wooden propellers are much less than metal or carbon props, so new wood props can be made in a couple weeks. A metal prop requires vibration testing for good service life. That is an incredibly involved project and it’s a fairly mature product line. Carbon fibre offers advantages in strength, weight and configuration, with engineering demands between wood propellers and metal propellers.”
What about unmanned aircraft? “We do see a lot of potential with UAVs (Unmanned Aerial Vehicles) in the future, but our sales are fairly steady.” Sensenich develops propellers specifically for mid-size, or tactical-size, UAVs. “We are doing product development across the board with all our products,” said Boser. “We have just received an stc (Supplemental Type Certificate) from the FAA for installation of one of our composite two-bladed propellers on STOL (Short Take-Off and Landing) aircraft. We plan on doing a further STC for lower horsepower SuperCubs. Then we will be looking very closely at the market before we decide on follow-on STCs. The light sport market is very active too. We recently released a number of new prop designs for the light sport and experimental market.” Intriguingly, Boser also mentioned, “We have some pretty exciting things coming up. I don’t want to give out too much about that, but it’s a very new area for us.”
“The recently released STOL propeller for bush planes is very exciting for us,” Boser added. “We are preparing to apply for a Canadian STC.”
Of course, the development of the eVTOL (Electric Vertical Take-Off and Landing) industry is quite exciting. “We have been remarkably busy prototyping for that market, and we have become one of the top fabricators for prototypes and test articles for the eVTOL market.” He added that, “we deal with mature but innovative programmes. There is a whole range of projects out there, so we focus on the ones where we can have the most impact and provide the most value.
Propellers have been used on aircraft for almost 115 years and have evolved to become more efficient and reliable, but do we really understand the tremendous forces and corrosion to which propellers are exposed? How frequently should an aircraft propeller be overhauled? Is the process absolutely necessary? What happens during an overhaul? To find answers to these questions, we paid a visit to Aero Propeller of Calgary.
Located near Calgary International Airport in Alberta, Aero Propeller of Calgary was founded in 1979. Two of its owners, Gord Thompson and Nash Javer, have been with the company since it first opened its doors nearly forty years ago. In 2008, they were joined by Kevin Samuel, an experienced aircraft maintenance engineer and structural technician. Combined, they have more than a century of experience in propeller maintenance. Most of the propellers that enter their workshop belong to general aviation and light commercial aircraft, but the team occasionally works on more interesting examples, such as that of a Hawker Hurricane and Douglas DC-6. When it comes to propeller maintenance, these men have seen it all and were happy to talk about overhauls in the context of aviation safety.
When determining the when a propeller, or related components, need to be overhauled, flight time or calendar dates are not the only factors one should consider. It is important to take operating conditions and the environment into consideration.
That said, what does an overhaul entail? The first step is to mount the propeller and visually inspect it. The paint is removed and blades are examined to see if they had been damaged in any way, and to measure dimensions to determine whether they can be overhauled. Once the propeller has been taken apart, the basic components are cleaned and degreased. The next step is to repair the damage and ensure that the components are within the manufacturer’s dimensional limits. All major components are then sent to a certified workshop for non-destructive inspection. Next, components are polished and dipped in a solution for corrosion protection, before being painted and receiving a durable polyurethane coating. Finally, the propeller is reassembled and set according to the manufacturer’s overhaul manual.
Internal corrosion is extremely dangerous and can only be detected when all the components have been taken a part and cleaned in a workshop. The importance of propeller inspections and overhauls cannot be overstated. When experiencing an engine failure, for the most part, the aircraft can glide and complete a safe forced landing. If, on the other hand, a propeller blade separates, the remainder of the flight can be considerably more eventful, if not catastrophic.
For further information on propeller maintenance, or advice regarding purchasing or owning a propeller, please contact Aero Propeller of Calgary at 403-291-9400.
Information on how frequently propellers need to be overhauled can be found on Transport Canada’s website, www.tc.gc.ca, in the Canadian Aviation Regulations (CARs) section.