Gliders from San Diego: the story of the Bowlus Sailplanes Company

The aircraft manufacturers Convair (originally Consolidated, later Consolidated Vultee) and Ryan come to the average aviation historian's mind when it comes to discussing and recording the history of aircraft development in San Diego in the 20th century, no surprise because the Rosie the Riveter mascot originated at the main Convair plant in San Diego and the aircraft used by Charles Lindbergh for his history-making solo transatlantic flight in 1927 was built by Ryan. During a recent visit to the San Diego Air and Space Museum, I happened to learn that San Diego also boasted a glider manufacturer, the Bowlus Sailplanes Company, after learning that one of the aircraft on display there, the Bowlus SP-1 Paperwing (represented at the museum by a replica), was manufactured in San Diego. Since Bowlus Sailplanes deserves the honor of being the first glider manufacturer from California yet is seldom discussed in most published accounts of the San Diego aircraft industry, I am dedicating this post to the history of Bowlus Sailplanes and its aircraft products.

William Hawley Bowlus (1896-1967), founder of the Bowlus Sailplanes Company

The founder of the Bowlus Sailplanes Company, William Hawley Bowlus, was born on May 8, 1896, in the Ohio Township in Bureau County, Illinois. As a teenager, he began his foray into aviation by building homemade gliders, flying them from the hillsides of San Fernando Valley. In 1917, Bowlus joined the US Army Air Service and learned to fly powered aircraft along with T. Claude Ryan (the founder of the Ryan Aeronautical Corporation) after enrolling in the American School of Aviation in Venice, California. When Ryan went to Oregon State College to study engineering after the end of World War I, Bowlus himself quit the USAAS, eventually re-associating with Ryan but also B.F. Mahoney at the new Ryan Aeronautical Company in 1924. As a member of the Ryan company in the 1920s, he was instrumental in design and construction of the Ryan M-1 and M-2 mailplanes for Ryan Airlines, while helping with construction of the NYP (Spirit of St. Louis) used by Charles Lindbergh to fly across the Atlantic Ocean solo in 1927. 

Left: The Bowlus SP-1 sailplane being towed for launch, January 1930.
Right: A replica of the Bowlus SP-1 on display at the San Diego Air and Space Museum.

Buoyed by the success of the Spirit of St. Louis, in 1928 Bowlus undertook design of his sixteenth glider, the SP-1, which had a shoulder-mounted wing and an open cockpit. Construction of the SP-1 was completed in January 1929, and when the aircraft flew for the first time that month, it became the first indigenous American sailplane to fly. The SP-1 had a wingspan of 44 feet (13 meters), an aspect ratio of 11:1, and a wing area of 179 square feet (16.6 m²), and it had an empty weight of 180 lb (81 kg), a gross weight of 305 lb (138 kg), a cruise speed of 22 miles per hour (35 km/h), and a glide ratio of 20:1. Although the SP-1 was largely made from wood and doped fabric, the ring webs of the wings, elevator, and rudder had to be fabricated from craft paper to make the SP-1 as light as possible, hence the aircraft's nickname "Paperwing". William Bowlus piloted the SP-1 in several regional glider meets in southern California, including two at Pacific Beach and one at Redondo Beach, and on October 5, 1929, the SP-1 set a new soaring endurance record when it flew over the cliffs at Point Loma, for 14 minutes and ten seconds. Fourteen days later, on October 19, it became the first American sailplane to attain an endurance of more than one hour when it flew for 1 hour and 21 minutes. Bowlus established the Bowlus Glider School in San Diego to train glider pilots to fly the SP-1, and in 1930, the Bowlus Sailplanes Company  was established. Although just one SP-1 was built, it served as a technology demonstrator for a series of Bowlus glider designs built in the 1930s, including the SP-D, Model A, and S-1000, which differed from the SP-1 in completely utilizing wood and fabric in their construction. The SP-D, Model A, and S-1000 gliders had a wingspan of 60 feet (18.3 meters) and were used by Charles Lindbergh himself and his wife Anne Morrow when obtaining glider licenses in 1930. Of interesting note is the fact that the design philosophy of the SP-1, SP-D, Model A, and S-1000 influenced that of some gliders, particularly the Silver King designed by Harland Ross and the Nighthawk sailplane used by William A. Cocke to set an air endurance record of 21 hours 34 minutes in 1931. The original SP-1 no longer exists, but a replica of this sailplane was built from scratch in the late 1980s and is now on display at the San Diego Air and Space Museum. The S-1000 derived from the SP-1 is displayed at the Wings of History Museum in San Martin, California, and the Nighthawk sailplane was originally placed on display at the Santa Monica Museum of Flying before being moved to the Los Angeles County Museum of Natural History.

A Bowlus BA-100 Baby Albatross in flight, late 1930s.

Elated by the success of its initial glider designs, the Bowlus company built the first American high-performance sailplane, the 1-S-2100 Senior Albatross, which was based on the Super Sailplane with a shoulder-mounted gull wing that was designed by William Bowlus and German glider engineer Martin Schempp and built and flown in Glendale by the Curtiss-Wright Technical Institute in 1932. The wings of the Bowlus 1-S-2100 spanned 61 feet 9 inches (18.82 meters) and had a wing area of 204.75 square feet (19 m²) and aspect ratio of 18.72:1, and the 1-S-2100 itself had an empty weight of 340 lb (154 kg) and a gross weight of 520 lb (236 kg). The Senior Albatross was first flown in 1933, with six 1-S-2100 Senior Albatross sailplanes built, and during the 1930s the Senior Albatross set a number of records for altitude. In the meantime, the Bowlus Sailplanes Company started development of a cheap strut-braced glider design, the Baby Albatross, which had a shoulder-mounted wing like that of the SP-1 and an open cockpit. The wings and horizontal stabilizers of the Baby Albatross were made from wood and covered with fabric, while the tail boom was of all-metal construction and the open cockpit was made of plywood. The baseline version, the single-seat BA-100, first flew in 1937 and a total of 156 Baby Albatross kits were manufactured, with certification occurring in 1938. A two-seat variant of the Baby Albatross, the BA-102, had a slightly longer rear fuselage with two small portal-type windows and with accommodations for a passengers, and three aircraft were built, the first being completed and first flown in 1938. The aerodynamic liability of the Baby Albatross lay in its poor pitch handling characteristics,  the rotation axis of the horizontal tail being located at 35% chord, the horizontal tail rotation hinge having high friction, and the relatively soft pitch axis cable control system storing elastic energy reacting the friction in the tail hinge. With input from aeronautical engineer Irv Culver, the Baby Albatross designed was modified to have the hinge axis moved forward and the pitch control fitted with a downspring. The BS-100 Super Albatross was a mid-wing single-seat glider that combined the fuselage pod and tail boom of the Baby Albatross with the outer wing panels of the Senior Albatross, and like the BA-100, it was of mixed construction, the wings and horizontal stabilizers being made of wood and covered with fabric, and the tail boom being made from metal. The Super Albatros first flew in 1938 but only two examples were manufactured, the first with a mobile horizontal stabilizer and second aircraft with a fixed horizontal stabilizer and flaps.

Left: The XCG-7 prototype (serial number 41-29621) being towed in flight, October 1942.
Right: The sole XCG-8 prototype (serial number 41-29622) at Rogers Dry Lake in the Mojave Desert, 1943. 

Months before the Japanese attack on Pearl Harbor, on April 29, 1941, Bowlus Sailplanes submitted designs for 8- and 15-seat transport gliders in response to a requirement issued in March by the US Army Air Corps (renamed US Army Air Force on June 20) for large gliders capable for carrying troops and war material to the battlefield in anticipation of the moment when the US would enter World War II to help push back against Axis aggression in Europe. The eight-seat design, designated XCG-7, was 53  feet 4 inches (16.26 meters) long with a wingspan of 65 feet (19.81 meters), a wing area of 700 square feet (65 m²), an empty weight of 2,870 lb (1,301 kg), and a gross weight of 4,800 lb (2,177 kg), and could cruise at 120 miles per hour (190 km/h) when towed by a transport plane. The 15-seat design, the XCG-8, was a scaled-up XCG-7 measuring 61 feet (18.6 meters) long with a wingspan of 85 feet 8 inches (26.04 meters), a wing area of 996 square feet (92.5 m²), an empty weight of 3,895 lb (1,767 kg), a gross weight of 6.800 lb (3,084 kg), and a speed of 120 miles per hour (190 km/h) when towed. Both designs featured a podded cabin with a boom aft fuselage and a cruciform tail empennage, and they were primarily made from spruce and birch, while the cantilever wing surfaces had plywood ahead of the spar and fabric behind it, and the fuselage and stabilizers were wrapped in plywood, whereas the movable surfaces used fabric. In late July 1941, one XCG-7 prototype (serial number 41-29621) and one XCG-8 prototype (serial number 41-29622) were ordered along with static test airframes for both designs and a wind tunnel model of the XCG-7. Due to its existing factory being too small for both the XCG-7 and XCG-8 to be manufactured, Bowlus Sailplanes outsourced construction of these gliders to Douglas, which completed the XCG-7 and XCG-8 prototypes at its facility in El Segundo in early 1942. The static test XCG-7 airframe was delivered to Wright Field on February 11, 1942, for loading tests, but it suffered structural failures and repairs to the airframe meant that static tests did not resume until June 16, yet the static test article failed at 40 percent of simulated loadings. Meanwhile, the sole XCG-7 prototype began flight tests on July 15-16, 1942, displaying good handling characteristics and staying aloft in a thermal, and after completing flight tests at Muroc Army Air Base (now Edwards Air Force Base) in early 1943, it was delivered to Wright Field. The XCG-8 static test article was completed in December 1942, and like the XCG-7 static test article failed loading tests as low as 35 percent of the design limit load. The XCG-8 prototype began test flights at El Segundo on March 29-April 1, 1943, and it was subsequently tested at Muroc, after which it was delivered to Wright Field and eventually Clinton County Army Air Field in Wilmington, Ohio. The USAAF decided not to place the XCG-7 or XCG-8 into production due to its commitments to the Waco CG-4, terminating both programs in August 1943. The XCG-7 was eventually tested to destruction on August 25, and the XCG-8 was destroyed in a windstorm at CCAAF on July 17, 1944.

The first and only completed Bowlus XTG-12 training glider (serial number 42-96830) during testing at Twenty-Nine Palms in the late summer of 1942. This aircraft also carried the civil registration NX28386 (visible on the vertical stabilizer).

As full-scale development of the XCG-7 and XCG-8 began, Bowlus Sailplanes envisaged a two-seat trainer derivative of the BA-100 Baby Albatross with a larger cockpit to accommodate men wearing parachutes, known internally as the BM-5. A mockup of the BM-5 was completed in about November 1941, and on April 28, 1942, a contract was awarded for three BM-5 prototypes (serial numbers 42-96830/96832) plus a static test airframe, and the designation XTG-12 was assigned to the BM-5. The first XTG-12 prototype (which also bore the civil registration NX28386) was completed in late spring and began flight tests in San Bernardino County in the summer of 1942, before being delivered to the US Army Air Force later that year. (One Bowlus-DuPont Utility M1PU3 glider previously owned by Orvil Leigh Smith [civil registration NR15314] was impressed into USAAF service with serial number 42-57200 in July 1942 and designated TG-12A, but the Utility glider was unrelated to the XTG-12 and the Bowlus-DuPont company that manufactured it was based in Delaware, not southern California.) Even though the first XTG-12 prototype probably exhibited satisfactory handling characteristics during flight testing, the XTG-12 program was dogged by government demands for design changes given that the BM-5 was based a prewar glider and did not constitute a new design, and after months of effort by Bowlus, the XTG-12 program was terminated on August 5, 1943, with only the first XTG-12 built and the other two cancelled without being completed. The end of the XTG-12 program eventually prompted the Bowlus Sailplanes Company to go out of business in early 1944, by which time William Hawley Bowlus was involved in development of the General Airborne Transport XCG-16 lifting body transport glider and would later join forces with sailplane pilot Ted Nelson to design the Bumblebee, Dragonfly, and Hummingbird motor gliders.

References:

Byard, J., 2015. On the Wings of an Albatross: Hawley Bowlus and his BA-100 Baby Albatross. Scotts Valley, CA: CreateSpace Independent Publishing Platform.

Fogel, G., 2000. Wind and Wings: The History of Soaring in San Diego. San Diego, CA: Rock Reef Publishing House.

Norton, W. J., 2012. American Military Gliders of World War II: Development, Training, Experimentation, and Tactics of All Aircraft Types. Atglen, PA: Schiffer Publishing.