Jacobs Aircraft Engines
Compiled by Kimble D. McCutcheon
Published 6 Apr 2013; Revised 12 May 2018


Jacobs L-4 (R-755)
Fischer & Jacobs was organized in Philadelphia, Pennsylvania on 1 Jan 1926, and constructed an experimental air-cooled 4-cylinder, 2-stroke radial intended to replace Curtiss OX-5s. Although the engine reportedly weighed less than 250 lb, and produced equivalent power, it was never produced.

Renamed Aircraft Engine Corporation, the company moved to Camden, New Jersey for a short time, and finally settled in Pottstown, Pennsylvania when it acquired a plant from the Light Machine and Foundry Company during its 1931 liquidation. The Pennsylvania Secretary of State Corporation Registry indicates that the Jacobs Aircraft Engine Company was incorporated on 31 Aug 1932.

 

Albert R. Jacobs

Albert R. Jacobs, born in Philadelphia in 1894, developed an early interest in the Wright Brothers work on aircraft. He attended Girard College in Philadelphia, where he graduated with high honors, obtaining an engineering degree. He designed and built race car motors and learned to fly, receiving U.S. flying license No. 4 from Orville Wright. Jacobs' combined engineering skills and flying interest led to the design of his first Jacobs aircraft engine, which formed the basis of the Camden, New Jersey plant.

Early Engines

The first Jacobs engine, the Model LA-1, was a 7-cylinder air-cooled radial with a bore of 4.500" and a stroke of 4.750" that displaced 528.8 in³. Weighing 390 lb, it produced 180 hp at 1,800 rpm. The LA-1 received Approved Type Certificate No. 31 on 7 Feb 1929. Power was increased to 170 hp at 2,125 rpm in mid-1931, and about 60 were manufactured before the Type Certificate expired on 1 Dec 1935.

The LA-2, an enlarged version of the LA-1 with a 4.750" bore, displaced 589.2 in³. It weighed 400 lb and produced 195 hp at 2,075 rpm. This engine was awarded Approved Type Certificate No. 82 on 6 May 1932, which expired on 1 Dec 1935.

 

Jacobs briefly experimented with, but never produced, a Model B-1. This air-cooled 2-cylinder 2-stroke, with a bore of 3.000" and a stroke of 2.500", displaced 35 in³, weighed 60 lb, and produced 20 ~ 25 hp at 2,500 ~ 3,000 rpm.

 

 

The Jacobs Model L-3, which received Approved Type Certificate No. 75 on 12 Aug 1931, produced 51 hp at 2,125 rpm and weighed 189 lb. With a bore of 4.125" and a stroke of 4.750", the 3-cylinder L-3 displaced 190.4 in³. The Jacobs L-3, could be operated in either tractor or pusher configuration. Two flange-mounted Scintilla magnetos provided dual ignition, and a Stromberg NAS-3 carburetor furnished the mixture. Approximately 44 L-3s were built before the Type Certificate expired on 23 Jul 1941.

 

Classic Jacobs Engines — the L-4, L-5 and L-6

The Jacobs Model L-4, which received Approved Type Certificate No. 121 on 27 Feb 1934, incorporated many features of earlier Jacobs engines. The R-755 series military designations were built in profusion during WWII, powering numerous training and light transport aircraft. Displacing 754.8 in³, the original L-4 had a bore of 5.250", a stroke of 5.000", and a compression ratio of 5.375:1. When initially certified and weighed 505 lb, it had a normal rating of 225 hp (245 takeoff hp) at 2,000 rpm on 73 octane gasoline, but its output grew to 350 hp at 2,500 rpm in the R-755E.

Model L-4 cylinder heads, with integral rocker boxes, were heat-treated aluminum alloy castings into which forged steel cylinder barrels were screwed and shrunk. Intake valves were of stainless steel and exhaust valves were of chrome-nickel steel with sodium-filled hollow stems. Aluminum bronze was used for valve seats. Valves were actuated by a cam ring with three intake and three exhaust lobes. It ran at 1/6 crankshaft speed.

The two-piece crankshaft captured a one-piece master rod with six articulated rod. The crankshaft, master rod, and wrist pins were of alloy steel, but the articulated rods were aluminum alloy forgings machined to final dimensions by diamond boring, eliminating the need for bushings.

Forged aluminum alloy pistons had two compression and one oil ring above the wrist pin bore, and an oil ring below the pin. Full-floating wrist pins were positioned by aluminum end plugs.

Six main parts comprised the crankcase. A magnesium front case housed the cam mechanism and supported the propeller thrust bearing. An aluminum alloy diaphragm supported the front crankshaft main bearing. An aluminum alloy barrel type crankcase provided mounting pads for cylinders, a bearing diaphragm for the rear main crankshaft bearing. An aluminum alloy rear section contained a ring-type inlet manifold. An aluminum alloy intermediate rear bearing plate fed lubricating oil to the crankshaft and supported auxiliary drive gears. A magnesium accessory case provided mounting pads for ignition, generator, starter, oil pump, and tachometer.

Dual ignition typically consisted of both a battery/distributor and Scintilla magneto. A Stromberg NA-B7A carburetor was provided.

 

The Model L-5 (Military R-830), an enlarged version of the L-4, was introduced in 1936. Its bore was increased to 5.500", producing a displacement of 831.5 in³. The L-5 produced 285 hp at 2,000 rpm and weighed 515 lb.

The Model L-6 (Military R-915), an enlarged version of the L-5 with a stroke increase to 5.500" and displacement of 914.7 in³, appeared in 1938. It produced 300 hp at 2,100 rpm from 535 lb, and could produce a takeoff rating of 330 hp at 2,200 rpm for 5 minutes.

 

Jacobs L-4 and L-5 Specifications
Designation L-4 L-4M L-4MB L-4MA7 L-5 L-5M L-5MB L-5MA7
Takeoff Rating (hp @ rpm) 225 @ 2,000 225 @ 2,000 225 @ 2,000 225 @ 2,000 285 @ 2,000 285 @ 2,000 285 @ 2,000 285 @ 2,000
Normal Rating (hp @ rpm) 225 @ 2,000 225 @ 2,000 225 @ 2,000 225 @ 2,000 285 @ 2,000 285 @ 2,000 285 @ 2,000 285 @ 2,000
Cruising Rating (hp @ rpm) 175 @ 1,900 176 @ 1,900 177 @ 1,900 178 @ 1,900 210 @ 1,900 211 @ 1,900 212 @ 1,900 213 @ 1,900
Cylinders 7 7 7 7 7 7 7 7
Bore 5.250" 5.250" 5.250" 5.250" 5.500" 5.500" 5.500" 5.500"
Stroke 5.000" 5.000" 5.000" 5.000" 5.000" 5.000" 5.000" 5.000"
Displacement 757.66 in³ 757.66 in³ 757.66 in³ 757.66 in³ 831.54 in³ 831.54 in³ 831.54 in³ 831.54 in³
Compression Ratio 5.375:1 5.375:1 5.375:1 5.375:1 6.0:1 6.0:1 6.0:1 6.0:1
Ignition (Scintilla) 2 Distributors 2 Magnetos 1 Distributor
1 Magneto
2 Magnetos 2 Distributors 2 Magnetos 1 Distributor
1 Magneto
2 Magnetos
Normal Fuel Consumption
(lb/bhp/hr)
0.50 - 0.55 0.50 - 0.55 0.50 - 0.55 0.50 - 0.55 0.53 0.53 0.53 0.53
Cruising Fuel Consumption
(lb/bhp/hr)
0.48 - 0.52 0.48 - 0.52 0.48 - 0.52 0.48 - 0.52 0.35 0.35 0.35 0.35
Length 38.875" 40.375" 40.375" 40.375" 36.969" 36.969" 36.969" 36.969"
Diameter 43.500" 43.500" 43.500" 43.500" 43.500" 43.500" 43.500" 43.500"
Basic Dry Weight 480* ± 3 lb 473 ± 3 lb 494* ± 3 lb 476 ± 3 lb 510* ± 3 lb 504 ± 3 lb 525* ± 3 lb 510 ± 3 lb
Specific Takeoff Power 0.469 hp/lb 0.476 hp/lb 0.456 hp/lb 0.473 hp/lb 0.559 hp/lb 0.566 hp/lb 0.543 hp/lb 0.473 hp/lb
  * Includes generator and control box

 

Specifications Pertinent
to All Jacobs L-4 and L-5 Models
Ignition Timing 30° BTC
Spark Plugs BG 482
Minimum Fuel Grade 73 Octane
Normal Oil Consumption 0.018 lb/bhp/hr
Cruising Oil Consupmtion 0.014 lb/bhp/hr
Carburetor Stromberg NA-R7A
Valve Timing at Hot Clearance
(IN = 0.035"; EX = 0.040")
 Intake Opens 12° BTC
 Intake Closes 55° ATC
 Exhaust Opens 55° BBC
 Exhaust Closes 10° ATC
 Intake Opening Duration 248°
 Exhaust Opening Duration 248°
 Intake Cold Clearance 0.008"
 Exhaust Cold Clearance 0.008"
Crankshaft Spline SAE No. 20

 

- More About the Jacobs L-4 (R-755) in the Members’ Section -

The XR-1530

In early 1943, Jacobs proposed two new 14-cylinder two-row engines based on R-755 components to the US Army Air Corps, and sent draft specifications on 24 Mar 1943. These engines probably were to have had a bore of 5.25" and a stroke of 5.063", for a displacement of 1,534.3 in³. The XR-1530C, which was projected to produce 900 hp, was direct drive, and the geared XR-1530D was to produce 1,140 hp. Jacobs reported the R-1530C design to be complete and 90% of the detail drawings done in an 11 May 1943 letter to the Chief, Power Plant Laboratory.

On 25 May 1943 conferences among representatives of the Production Engineering Section and Power Plant Laboratory met to decide the fate of Jacobs R-1530 engines. The group decided that it improbable that the R-1530C could really be completed within a year, as Jacobs had promised, and that the R-1530D was too powerful for training use but not powerful enough for tactical use. With no current application or perceived future need for either engine, the group recommended that the Army Air Forces not pursue their development. These findings were summarized in Memorandum Report ENG-57-503-592 dated 17 Jun 1943, which was forwarded to Jacobs.

Despite this rather chilly reception, Jacobs Vice President Henry McFadgen and Chief Engineer CE Mines persisted, apparently convincing the Power Plant Laboratory to lend accessories for the testing of an R-1530D. It is not known whether any R-1530s were ever completed or tested.

In addition to making Jacobs-designed engines, the Jacobs firm also produced over 10,000 Pratt & Whitney R-985s and R-1340s under license from 1941 through 1945.

Post War

A nationwide aviation industry slump followed the end of WWII. The Jacobs Aircraft Engine Company was acquired by a Philadelphia investment syndicate. In an effort to save his company, Albert Jacobs bought the firm from the syndicate but was unable sustain its operation. In 1946, he sold Jacobs Aircraft Engine Company to Republic Industries, Inc., a New York manufacturing conglomerate, and Jacobs Aircraft Engine Company continued as a division of Republic Industries, Inc., with Albert Jacobs serving as vice president and general manager until 1950, when the Barium Steel Corporation acquired Republic Industries. Albert Jacobs left Jacobs Aircraft Engine Company in 1950 to become a consulting engineer for the Lycoming Motor company, where he remained until his retirement in 1954. Jacobs died in Sep 1960.

In 1946, Jacobs announced five designs intended for what became the booming post-war general aviation market. The smallest was based on cylinders with a 4.000" x 4.000" bore and stroke, as displacement of 50.27 in³. The rest were based on cylinders with a 4.375" x 4.000" bore and stroke, a displacement of 60.13 in³. All had a compression ratio of 6.5:1. These were horizontally-opposed, direct drive, unsupercharged engines featuring steel cylinder barrels, aluminum alloy cylinder heads with one intake and one exhaust valve, and one-piece counterweighted crankshaft.

The O-200A was an air-cooled four cylinder, similar to the O-240A, that displaced 201.6 in³ and had a takeoff rating of 85 hp @ 2,350 rpm and weighed 190 lb, for a specific output of 0.48 hp/lb.

The O-240A was an air-cooled four cylinder with a magnesium alloy crankcase that displaced 240.52 in³, had a takeoff rating of 100 hp at 2,300 rpm and weighed 200 lb, for a specific output of 0.50 hp/lb.

The http://www.airrepairinc.com/ was a liquid-cooled horizontally-opposed four cylinder based around a two-piece aluminum alloy crankcase; two cylinders were integral with each case half and included steel dry cylinder liners. An aluminum alloy cylinder head was provided for each block. The O-240L had a takeoff rating of 100 hp at 2,300 rpm and weighed 220 lb (dry), for a specific output of 0.42 hp/lb.

The O-360A was a six-cylinder version of the O-240A with a takeoff rating of 165 hp at 2,400 rpm, a weight of 300 lb, and a specific output of 0.55 hp/lb.

The O-360L was a six-cylinder version of the O-240L. Its takeoff rating was 165 lb and it weighed 245 lb (dry) for a specific output of 0.48 hp/lb.

None of Jacobs' horizontally-opposed engines ever received a type certificate and there is not record that any ever flew.

Jacobs introduced a helicopter engine in 1953, the R-755HE. This engine featured an integral reduction gearbox with concentric rotor drive and SU direct fuel injection. Rated at 370 hp and 2,650 rpm for takeoff and 360 hp, 2,500 rpm normal, it weighed 520 lb, for a specific output of 0.71 hp/lb. The R-755HE apparently never received a type certificate.

Jacobs Aircraft Engine Company continued making radial engines into the mid-1950s for Cessna 195s and their military counterparts, and for agricultural aircraft. Cessna stopped production of the 195 in 1955 and ag operators developed a preference for the more powerful Pratt & Whitney R-985 and R-1340.

 

After Jacobs Aircraft Engine Company

Clarence E. Page was an Oklahoma aviation legend who served with the U.S. Army Air Service during WWI, barnstormed part-time between the wars, and operated flight schools that trained over 8,500 aviation cadets during WWII. After the war, Page created a number of corporations that were involved in aircraft sales, maintenance, engine overhauling and engine component overhauling. Page, who was active in the support of agricultural aircraft, acquired most of Jacobs Aircraft Engines' type certificates when Jacobs Aircraft Engine Company ceased production and was dissolved on 22 Jul 1957.

New engines built by Page's company were called Jacobs-Page. Jacobs-Page also developed a new engine, a refined R-755 with a turbosupercharger, known as the R-755S. This engine used an Airesearch TE 06 turbosupercharger with the entire exhaust stream always passing through the turbine; no waste gate was employed. Manifold pressure was limited by a relief valve installed between the compressor and the carburetor. Excess air was vented overboard by this valve so that the manifold pressure did not exceed a maximum value. The turbosupercharger was lubricated by engine pressure oil obtained from a fitting on the rear crankcase. This oil drained by gravity back to the engine sump after passing through all air-oil separator.

On 12 Dec 1972, Page created a new company called Page Industries of Oklahoma, which absorbed all of Page's other companies and became the type certificate holder for Jacobs engines. These type certificates were sold to Jacobs Service Company, an Arizona company, in the late 1970s or early 1980s, and resold to a Mississippi company, Air Repair, Inc., on 2 Jan 2002.

Air Repair embarked on a Jacobs engine improvement and modernization program in early 2003. In addition to enhancing performance by converting 220 hp engines into ones producing 275hp, the program incorporated modern materials, improved oil consumption, and improved oil drainage. Certification of the changes involved a successful 150 hr endurance run with 50 hours at 300 hp, 500°F cylinder head temperature, 300°F cylinder barrel temperature, and 210°F oil temperature.

These modern Jacobs engines continue used in Cessna 195s, Boeing Stearmans, and various Wacos, among others. More information is available from the Air Repair website.

References

Aerosphere 1939
FAA Type Certificate Data Sheets
Aircraft Engines of the World, 1947, 1953, 1955. Paul H. Wilkinson.
National Archives Record Group 342, RD2629, Jacobs R-1530-0 Engine 1943
Pottstown Mercury Newspaper, 21 Sep 1960.
Telephone Conversation between Pete Jones of Air Repair, Inc. and the Author, 8 May 2018.

Acknowledgements

Many thanks to Paul Christainsen, who located and forwarded the R-1530 file from the US National Archives. Thanks also to Michael Smith who provided material from which the specifications were drawn.

Thanks also to Pete Jones of Air Repair, Inc.

Nice images of the Jacobs manufacturing facility, brochures and posters can be see at the Bomber Command Museum of Canada web site.