Sensenich’s Ground-Adjustable Props

[n2582d]

For those wondering about the prop blade length, it may be helpful to know that there exists regulation in that regard to prevent prop-stikes. Tricycle gear airplanes must be tested with flat nose tires and nose struts and still maintain a 7” ground clearance IIRC as do taildraggers with flat mains and most-nose-down/hard-landing demonstrations.

The Helio Courier prototype was called the Helioplane. It had a 9 foot diameter Aeromatic propeller driven by a C-85. The plane now hangs in the Smithsonian. Here's an interesting vignette related to this CAR 3 propeller clearance requirement and the certification of the Helio: "In spite of the lengthened landing gear, the ideal ground clearance for the prop, at least nine inches, was not achieved. In fact, it was a negative 1.5 inches! The C.A.A. pounced on this, and sent no less than four test pilots to Canton, with the stated intent of making the prop strike the ground. Try as they would, they were not able to do so. With the application of full throttle, the plane would rise up on its twelve-inch-travel oleos, and would be off the ground before they could even think about raising the tail. In fact, the tailwheel was always the last to depart. Likewise, touchdowns always occurred in either the three-point attitude, or tailwheel-first. Finally, the C.A.A. threw in the towel, and accepted the design, as-is."

[c170b53]

That’s amazing stuff Gary thks