Seattle World Cruiser

Our recent trip to Seattle also included a morning visit with Bob Dempster. Bob is a relentless aeronautical researcher who is building a replica of the first planes that flew around the world, the Seattle World Cruiser. One of Bob’s biggest challenges with this project was developing a propeller from scratch to match the engine and flight characteristics of his plane, especially since he was unable to find any plans or drawings of the original prop.

While wandering one day through the archives of the Seattle Museum of Flight, Bob came across a propeller that was tentatively identified as one from a Douglas World Cruiser. The curator allowed him to examine it more closely and, from its design features and markings, Bob was able to verify the propeller’s authenticity. Now he knew there was an original propeller close at hand, but how could he capture data from it?

That’s how Mastercam got involved. Our reseller in Washington, Cimtech was able to use a handheld laser scanner and a high-end data-collection package to accurately capture all of the geometric data from the huge 10’ 4.5” prop in less than a day. The data was exported as an STL file, which can be read natively in Mastercam. Nothing else had to be done to the data in preparation for creating the toolpaths.

Back at the shop the club would be machined from a huge block of birch weighing 300 lbs. and measuring 96 inches in length. The real challenge was cutting the 7-foot club using a VF4 Hass milling machine with only 50 inches of travel.

They used a technique called “Picture fame machining” that is used widely in aerospace for making large monolithic aerospace components tables without enough travel. In this instance the technique involves machining a blank with straight, parallels and a bore. These characteristics allowed them to accurately pick up location of the blank for each stage of the machining process.

The end result of this process was a perfect part held within a frame of birch material by several small tabs that were cut using a Sawsall and finished by hand. The flat parallel frame and bore allowed the part to be accurately located after each move so that machining could be held to within 0.001.”

Bob expects all the pieces of his plane to come together one day and he will put the Seattle World Cruiser through more than 40 hours of in-flight tests in order for it to meet FAA certification requirements. Then, look out world here they come . . .

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