The Stearman Sa-1 and the Model 75 Ag Plane

//The Stearman Sa-1 and the Model 75 Ag Plane

The Stearman Sa-1 and the Model 75 Ag Plane

Although much is known about the life and accomplishments of Lloyd Carlton Stearman, little is known about an agricultural aircraft he designed for production in 1944. Recently, a carton of blueprint drawings have surfaced containing all structural drawings for the Stearman SA-1 agricultural aircraft. The carton was found many years ago in the old operations building on Eagle Field by Tom Louden and recently have found their way to me through Bruce McElhoe. Not much data can be found regarding this aircraft, so this article attempts to bring forward information on the SA-1 Stearman design.

2013-aug the stearman SA-1

fig. 1

In Fig.1, piles of the Stearman SA-1 drawings separated according to the prefix preceding the number – A, B, C, D, E, H and supplier drawings from Cleveland Pneumatic, Pratt and Whitney, Continental Motors, Wagner Electrical, Goodyear Tire and Rubber Company, etc. There are a total of 78 blueprint drawings in the file, plus another 19 drawings from the Stearman Aircraft Company and the Boeing Airplane Company, Wichita, Kansas that are from the model 75 and E75N1. Possibly these were reference drawings so Lloyd would not have to redesign such items as oil tank, wing ribs, fuel tank, brake installation, Lycoming R-680-17 engine installation, etc. To trace Stearman’s SA-1 design it will be necessary to follow his career in the 1940’s beginning with his appointment as manager of the Airplane Division of the Harvey Machine Company. Harvey Aluminum had a plant in Torrance, California adjacent to the Douglas Aircraft plant back in the late 1950’s. While Harvey Aluminum plants had locations worldwide, the business was founded in 1914 by Leo Harvey, the son of a small factory owner in Lithuania. Harvey immigrated to the United States and found employment with the Hot Point Company in Ontario, California. Harvey started his own business in 1914, hiring two men to work in his small shop in downtown Los Angeles. By 1920 the company employed more than 300 people and was named Harvey Machine Company. Harvey took out numerous patients in specialized machinery and equipment and one of his patients included that for a peel-off, pop-top aluminum can. It was this machine business that Lloyd Stearman was employed in 1941. There he designed aircraft engine cowlings for manufacture by the company for the military at a plant in Long Beach, California.

Agricultural aircraft was still one of Stearman’s main focus points and near the close of WW2 he resigned from the Harvey Machine Company and began designing a specialty biplane for use in agricultural pest control. Based on the dates found in the drawing title blocks, Stearman must have been designing the airplane while still at Harvey and before he moved to Dos Palos because the military was still using Eagle Field for primary flight training.

After the war ended a group of individuals headed by C.S McBrien started a crop dusting and spraying company they called AgAir, located at Eagle Field, Dos Palos in California’s central San Joaquin Valley. The partners were Lex Erman, Harry White and an attorney from Visalia named Dick (my source could not remember a last name). Bud McBrien (son of C.S McBrien) recalled that his father received a phone call from a fellow in Wichita who said he had a line on some 102 Boeing PT-13/PT- 17 biplanes, they could be purchased for only $225.00 each – and they were all flyable. C.S collected enough money to purchase them all, along with thirty R-680- 17 Lycoming engines for $50.00 each. Lloyd resigned from Harvey Machine Company and moved to Dos Palos at the closing of the military use of Eagle Field, rented one of the hangars and attached buildings and set up a new business he called Stearman Engineering Company. Eagle Field was located 10 miles south of Dos Palos in California’s central valley. The field had opened June 1942 for the purpose of offering primary flight training to cadets using Ryan PT-22 and later Boeing PT-17 aircraft. It closed December 1944. The city of Dos Palos acquired all the land and buildings and this is where Lloyd Stearman set up his new business. At first he converted aircraft for agricultural use – those aircraft being Travel Air and Fleet biplanes, any aircraft that had two sets of wings. C.S McBrien was his chief mechanic in charge of rebuilding and converting these aircraft. McBrien was the head of the CAA for four western states but disliked his job, according to his son Bud. Thus the move to start a crop dusting and spraying operation at Eagle Field when the Boeing Stearman aircraft became available as surplus equipment after the war ended. On the CAA 337 form below, note that the owner of this Curtiss Wright Travel Air 4000 is Stearman Engineering Company, Box 745, Dos Palos, California.

2013-aug the stearman SA-2

fig. 2

In Fig.2, the bottom of this CAA form 337 showing a date of March 4, 1945 with the signature of C.S Mc- Brien as the supervising mechanic. His A&E number appears to be 10869.

It is unclear exactly where the SA-1 drawings were compiled but perhaps when Lloyd Stearman was still employed by Harvey Machine Company in the Los Angeles area.

This fact is assumed due to the dates on the three-view drawing of the model SA-1, which are 7-31-44 when drawing C-007 was completed by S. R Sohoni. The drawing was checked by Walter C. Clayton and dated 9-13-44 and finally it was approved by Lloyd Stearman and dated 9-15-44.

Tom Louden is an agricultural pilot who has flown for several notable operators in both the Imperial and San Joaquin Valleys. The true story of how these rare Stearman drawings were rescued is fascinating. Tom flew for Ag Air at Eagle Field near Dos Palos, a small San Joaquin Valley town, between the years 1963-1968 and 1979-1982. Tom remembers that Ag Air had a large fleet of Boeing Stearman aircraft modified for agricultural use, in fact they had 30 aircraft licensed and ready to fly and another 30 in the hangar, disassembled for storage, along with many engines including Pratt and Whitney 450 hp R-985’s. He remembers when Ag Air moved from their office facility in the old base operations office into new quarters near the hangar, they moved everything they needed but left a lot of “stuff” laying around the old office. Tom went in and began to sort through that stuff and found a box containing blueprint drawings of Lloyd Stearman’s SA-1 Ag biplane design. Tom states, “I’ve had possession of these drawings for over 50-years and now decided something had to be done with them, so I asked Bruce McElhoe to find a home for them.” It is interesting to note that Ag Air owned at least 60 WW2 surplus Boeing Stearman biplanes and to speculate some, they were no doubt part of the 102 airplanes that were originally purchased by Ag Air. The rest were probably sold at a profit to pay for the initial purchase. Tom recalls when the wood hangar containing the disassembled Stearman biplanes and engines caught fire and burnt to the ground.

Found in the file of SA-1 blueprints was a blue folder detailing Report No. 9 that was a means to convert Travel Air 2000 and 4000 aircraft landing gear shock strut absorbers from bungee cord to rubber disc. On the first page the following is stated, “The Stearman Engineering Company’s present fleet of crop dusters are Travel Air airplanes using rubber tension shock absorbers. The war situation has made it progressively more difficult to obtain fresh shock cord of 5/8” diameter. In order to keep these agricultural airplanes operating, a rubber compression disc shock absorber has been designed to replace the tension rubber shock absorber. Aside from the necessity of doing something to keep these airplanes in service, it is felt that the new shock absorber represents a definite improvement in the airplane for the following reasons:

  1. There is better control of the shock absorber characteristics, as the compression disc characteristics cannot be changed as can the tension rubber by tighter wrapping.
  2. Rubber deteriorates less rapidly in compression then in tension and is less susceptible to complete failure.
  3. There is greater energy dissipation with the discs due to slipping of the rubber on the metal spacer discs, hence fewer tendencies for rebound.
2013-aug the stearman SA-3

fig. 3

In Fig.3, is the Stearman Engineering Company’s Report No. 9 typewritten title on the folder. This is a little slice of aviation history that may have never been seen if the SA-1 drawings were never found. We are indebted to Tom Louden for saving these important historical documents.

Stearman must have left Eagle Field in late 1945 to form Inland Aviation Company in Los Banos. Stearman partnered with Barney Negra, Tom Jergenson and George Willet, who served as chief pilot. Here they were involved in converting surplus stock Stearman biplanes for agricultural operations. These aircraft, originally sold to the government as primary trainers used aluminum for the firewall. The CAA mandated that all aluminum firewalls be replaced with stainless steel or galvanized steel before they could receive a license Dispersal equipment such as hoppers, spreaders, booms, pumps and nozzles had to be specifically fitted to the aircraft and Stearman was the man who had to design such installations, mainly the hoppers and associated airframe modifications.

Back at Ag Air, C. S Mc- Brien had designed the agitator for dusting hoppers, which surely Lloyd had adapted to his modifications in Los Banos. McBrien also adapted an auger to a surplus Army vehicle to make a loading device to dump heavy wet sacks of rice seed into the hoppers for seeding operations. Before this the 80-pound bags had to be hand loaded.

Right is my photo of a Boeing E75N1 aircraft owned by George Baldrick, whose operation was located at the airfield in Hanford, California. This was a stock Stearman converted for the spreading of dust. Still used were the original Lycoming R-680- 17 engine of 225 hp, and a McCauley steel prop. I vividly recall having to hand-prop this ship to get it started because it had no electrical system and therefore no electric starter. The original hand inertia starter was removed because of its weight. I remember it was very difficult to prop start, but I was young at that time. The fuselage was metalized and the wings were lengthened by one full bay, the tips squared with spill plates on tips. Note that the exhaust collector ring has been rotated so the tail pipe is well above the spreader. This aircraft was used to spread sulfur dust that was very flammable. This would be typical of early conversions of the PT- 13/PT-17 surplus aircraft. Many of these aircraft were converted to dust or spray application by their new owners, which is the case of this aircraft. It was later converted to 450 hp by the installation of a Pratt Whitney R-985 engine as removed from a BT-13.

End of Part One – To be Continued

By |2016-11-13T09:33:18+00:00August 11th, 2013|Flying-Wire|Comments Off on The Stearman Sa-1 and the Model 75 Ag Plane

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