Now that we have several flight hours on the museum’s Stearman C3B, its time to start taking care of the squawks that have turned up on the airplane. One of those was the propeller. On take-off, the Wright J-5 engine wasn’t turning up to the proper RPM, only about 1,500 instead of the expected 1,800. Also, in cruise flight, the airspeed was a bit higher than expected, about 105 MPH instead of 95. Those symptoms point to the wrong propeller.
The prop that was on the Stearman was put on after it’s only previous flight in 1997 and had never been flown. In fact, it had never even been ground run. Our “first flight” back in August was its first time in the air and that’s where the problems turned up. With too course of pitch, there is a bigger load on the engine, sort of like when you’re starting off on a bicycle in high gear. It’s tough pedaling! Its also difficult to slow down on approach to landing. This isn’t always a big deal, but the Wright J-5 is notorious for cracking pistons in this situation and new pistons are virtually non-existant. On the advice of several J-5 experts, the search was on for a new prop.
Luckily, we have another J-5 in the museum on our 1927 Travel Air 4000. Since this aircraft is still technically under restoration and will not fly until next summer at the earliest, we pulled that brand new prop to try it out on the Stearman. Everything was much better on the test flight, with take-off RPM at 1,700 and cruise speed of 95 MPH.
The new prop had a varnished natural color hub though, and the Stearman’s was painted along with the spinner or “beanie cap” on the nose. Leaving the beanie cap off ruined the lines of the airplane, so we decided to paint the new one to match. Jim Weeden fabricated a small wooden adapter and painted the hub today. It all looks great and we will fly it again next week after the prop is hung again.