Stinson SR-10F Reliant airplane
On long-term loan from the National Air and Space Museum, the Stinson SR-10F Reliant on view at the National Postal Museum was part of a series of powerful cabin airplanes outfitted as well-appointed executive and business aircraft or as sturdy utility craft and airliners. It was used in a series of airmail pick-up experiments by All American Aviation (AAA).
The airplane is made mostly of welded chromium molybdenum steel tubing structures covered with fabric. The wing has riveted square aluminum tubing ribs that are attached to the spars with riveted gussets. The tail assembly was built of welded steel tubing and includes an adjustable horizontal stabilizer. It is powered by a nine-cylinder Pratt and Whitney Wasp Junior radial 450 hp engine and capable of operating at speeds of 150 miles per hour. The airplanes were fitted with a long take up boom with a hook and a winch that caught and reeled in mail containers.
AAA used aircraft like this in a series of airmail pick-up experiments in a selection of Pennsylvania and West Virginia communities. The airplanes collected and delivered mail and express packages at communities without landing. On the ground, the postmaster loaded the town's mail into a container which was then placed on top of a contraption resembling a goal post. The airplane's crew consisted of the pilot and a flight officer who worked the pick-up mechanism, making the mail exchange. As the pilot guided the airplane down, the flight officer lowered a grappling hook to snag the container while mail destined for the community was then dropped from the plane onto the airfield.
This unusual system began on May 12, 1939, and was modeled the Railway Mail Service's mail-on-the-fly service. The experimental service never turned a profit, and the company discontinued it in 1949.