The Pratt & Whitney R-2060
by Kimble D. McCutcheon
Published 2 Jul 2025

Pratt & Whitney Aircraft R-2060 (Author)

After U.S. Army aviation had suffered through WWI, for which it was grossly under-prepared, the U.S. Government began funding basic engine research in 1920, hoping to catch up with the rest of the world. This ushered in an engine development golden age for the U.S. that lasted until about 1925. The U.S. Navy won the Schneider Trophy seaplane races in 1923 with Curtiss CR-3, and the U.S. Army Air Service won in 1925 in a Curtiss RC3-2. Both aircraft were powered by a Curtiss D-12 engine, which was so good that some speculated it formed the basis for many Rolls-Royce "R" features; the "R" powered the Supermarine S.6 in 1929 and the Supermarine S.6B in 1931, permanently winning the Trophy for the United Kingdom. In the meantime, R&D funding had waned and the newly-named U.S. Army Air Corps' (USAAC) engine program was decidedly behind. The USAAC, which had been heavily involved in engine design during the early 1920s now had to rely on contract personnel to fill the gap. George Mead and Andy Willgoos , who had been together since Wright-Martin days, were two USAAC favorites. Still, the USAAC couldn't seem to stay away from designing its own engines. The P&WA R-2060 was a 1,000 hp engine initially conceived by the USAAC and built by P&WA. This article comes largely from Chapter 2 of the author's book American Sleeve-Valve Aircraft Engines.

Background

Rentschler	Mead

Frederick Brant Rentschler (8 Nov 1887 – 25 Apr 1956), the Princeton-educated son of an Ohio machine manufacturer, turned his back on the family foundry business to become an Army engine inspector at the Wright-Martin Company during World War I. Wright-Martin built Hispano-Suiza V-8 aircraft engines under license. When the war ended, Wright-Martin was reorganized in Paterson, New Jersey with Rentschler as President of the new Wright Aeronautical Corporation (WAC). Among the people Rentschler retained were George Jackson Mead (27 Dec 1891 – 20 Jan 1949), a MIT-trained engineer, and Andrew Van Dean (Andy) Willgoos (31 Oct 1888 – 1 Mar 1949), an engine designer. Mead and Willgoos had worked together at the Crane-Simplex Company, an automobile manufacturer that merged with Wright-Martin. WAC continued to build Hispano-Suiza engines, while the Mead/Willgoos team improved the Hisso and branched out into new water-cooled designs, working closely with Army, Navy and other engine companies on a variety of government-funded engine development projects. Mead and Willgoos were primarily responsible for developing the air-cooled Lawrance J-1 into the Wright J-4B, the first air-cooled aircraft engine with reasonable reliability, and ultimately, the wildly successful J-5 Whirlwind.

Rentschler thought air-cooled engines were the future but was unable to convince the Wright Board of Directors, composed largely of investment bankers with little knowledge of aviation, to fund research necessary for continued improvement of air-cooled engines.¹ Such philosophical differences led Rentschler to resign from Wright on 1 Sep 1924.²

Ryder, Willgoos

By 23 July 1925,³ Rentschler had struck a deal with the Pratt & Whitney Tool Company of Hartford, Connecticut to fund the development of a high-powered, air-cooled engine for the Navy. Mead and Willgoos immediately left Wright and began designing the first Wasp engine alongside engine consultant Earle A. Ryder, a graduate of Cornell University and formerly of Aeromarine Plane and Motor Company. Pratt & Whitney Aircraft (P&WA) was incorporated on 23 Jul 1925, with Rentschler as President, Mead as Vice President of Engineering, and Willgoos as Chief of Design. Other key personnel, also from WAC, were Shop Superintendent John J. Borrup, Factory Manager Don Brown, and Production Engineer Charles Marks.

The first R-1340 Wasp was completed on 24 Dec 1925 and first ran on 28 Dec 1925. Impressively, P&WA built its last R-1340 in 1960. Although P&WA was created to build air-cooled engines, Mead and Willgoos were two of the world's best water-cooled engine designers and were often consulted by the U.S. military on engine matters.

U.S. Army Air Corps Engines

During the early part of November 1929, the U.S. Army Air Corps Materiel Command Engineering Division (hereinafter MatCmd) Power Plant Branch Chief 1st Lt Edwin R. Page and Experimental Engineering Section Chief Maj C. W. Howard collaborated on a report, published 8 Nov 1929, that helped establish USAAC engine doctrine for the next 15 years. Maj Howard reported that European engines were performing considerably better than ones built in the U.S. While American engines were mechanically equivalent (if not better) than any others in the world, the remarkable performance of Schneider Cup Race engines, such as the Rolls-Royce R, was due largely to improvements in fuel and the designs made possible by the use of such fuels. MatCmd had also been taking steps to improve available fuels. On 22 Jul 1929, a conference was held with representative fuel producers in order for MatCmd to obtain advice on adopting better grades of gasoline and oil. The Air Corps had endeavored to bring its fuel to a standard knock rating equivalent to Fighting Grade California Gasoline with 3.5 ml (0.12 fluid ounces) of tetraethyl lead (TEL) per gallon. It was foreseen that the new fuel might cause corrosion due to its TEL and bromide and that engine materials might have to be substituted or redesigned to accommodate leaded fuels. MatCmd hoped that it might issue a fuel specification in the first half of fiscal 1930, but that was delayed because the Ethyl Corporation failed to deliver its knock-rating test engines on time. Once the knock rating standards were in place, MatCmd proposed to continually raise the standards, thereby ensuring the best quality of gasoline.

Oils were also expected to improve so that de-waxed paraffin-base oils with very flat viscosity versus temperature curves would become standard. Howard pointed out that high-grade fuel allowed engines to run at high mean effective pressures without detonation, noting that the British were running air-cooled cylinders at 200 psi bmep and water-cooled cylinders at 225 psi bmep, whereas American cylinders were operating in the 130 – 150 psi range. He expected new fuels would allow a 20% – 50% power boost, and he (very optimistically) predicted that two years of work would be required to reach these goals. Howard noted that the high-powered British engines were not practical service engines, as both Napier and Rolls-Royce engines only operated for about two to three hours and only with the most careful handling. Howard believed that before embarking on the new development of larger-displacement engines, a practical military engine should be developed, and that the Curtiss V-1570 Conqueror could be made to produce 600 – 700 hp.

MatCmd had been working with Curtiss to this end with promising results. MatCmd proposed to build a service engine capable of several reduction gear combinations for use in pursuit, attack, observation and bombing aircraft. This engine would be designed to develop 1,000 hp at 2,700 rpm, but it would eventually be capable of 3,300 rpm and 1,600 hp. Weight was expected to be about 1,000 lb. It would be Prestone cooled (Prestone was the original Union Carbide trade name for ethylene glycol), use roller bearings, improved cylinders, improved reduction gearing and improved valve gear. It would include a built-in supercharger and would be capable of accepting an additional supercharger to achieve performance at altitude.

This was MatCmd's dream, which it hoped to accomplish with two years of intensive work. In actuality, it would be ten years (1939) before the dream would be realized, when an Allison V-1710 became the world's first engine with a take-off rating of 1,000 hp to successfully pass a type test.

Naturally, as maker of the V-1570, Curtiss was the only American engine company that was both interested and capable at that time, and it was with Curtiss that MatCmd initially teamed. On 29 Jan 1930, MatCmd sent its specification, along with a request for comments, to Curtiss, Allison, Lycoming, and Pratt & Whitney. MatCmd wanted the manufacturers to undertake development of an actual experimental engine but did not want to underwrite the effort. It offered help with studies, analysis and testing.⁴ Lycoming had insufficient resources for such a development and turned down the "opportunity.⁵" Allison questioned whether the proposed engine could have integral banks, citing improved stiffness and external appearance. MatCmd admitted these advantages but insisted that maintenance issues, along with the broad thermal range of glycol cooling and short development cycle, dictated a separate-cylinder design. Upon learning this, Allison decided it was not interested.⁶ It is noteworthy that MatCmd persisted with this separate-cylinder doctrine for most of the liquid-cooled engines it funded from 1930 until the end of WWII. None of these engines were successful, but the Allison V-1710, which retained integral cylinder banks, was.

Curtiss merged with Wright Aeronautical in 1929, a move that changed its way of doing business. In a 20 Jun 1930 letter, Curtiss-Wright (C-W) informed MatCmd that it was unable to undertake the development at its own expense.⁷ A more complete 1,000 hp engine specification was leaked in the 17 Sep 1930 issue of The Aeroplane. Three types of engines were needed: a 600 hp 6-cylinder inline, a 1,000 hp 12-cylinder vee, and a 1,500 hp 18-cylinder broad arrow. All of these were to have interchangeable parts to the maximum extent possible. The V-12 was optimistically expected to weigh 1,000 lb; to produce 1,000 hp at 2,700 rpm and 1,150 hp at 3,300 rpm; to have either a 2:1 or 5:3 reduction gear, a two-stage supercharger, a 6:1 compression ratio, a 175 – 195 psi bmep, a 0.5 hp/in³ specific displacement, roller main bearings, fork-and-blade connecting rods, and be liquid-cooled (ethylene glycol and water with a boiling point of 340 – 360°F). The coolant outlet temperature was to be 300°F, indicating adherence to the high-temperature cooling philosophy that MatCmd would espouse for several years. High-temp cooling theoretically allowed for smaller coolant radiators. Unfortunately, the smaller coolant radiator area was offset by a commensurate increase in oil radiator size, for no net drag reduction. The high-temperature, high-pressure Prestone was also hard to keep contained within the cooling system. The engine was to have two inlet and two salt-cooled exhaust valves per cylinder. MatCmd recommended austenitic nickel chrome steel for valve seats, prohibited nitrided valve surfaces, and admonished that the fuel, with 6 ml (0.2 fluid ounces) of TEL per gallon, was not to corrode valve seats or guides. MatCmd was embarrassed this information had been published, as the entire matter had a Confidential security classification.⁸ Since C-W is mentioned in the article, one wonders whether C-W was the leak.

C-W was closing the former Curtiss Buffalo, New York engine works and transferring its production to Paterson, New Jersey. Curtiss Chief Engineer Arthur Nutt was to be in charge of the united works. On 23 Apr 1931, C-W President Guy Vaughan sent MatCmd pricing on its proposed 1,000 hp engine development program. C-W wanted $173,000 to proceed with engineering and test, a sum that did not include an engine for the Air Corps, which of course, was extra. The C-W proposal suggested parallel development of both liquid and air-cooled cylinders, either of which could be used on the final engine. C-W estimated this effort would take a whopping 109 months to complete.⁹ MatCmd responded on 28 Apr 1931 reminding C-W of the recent bad experience with the air-cooled Curtiss H-1640 Hex engine and wondering why it should put any more money into air-cooled development. Also at issue was some engineering work C-W had done on high temperature cooling, for which MatCmd had apparently paid but not received the design and engineering data.¹⁰

Pratt & Whitney's George Mead indicated in a 5 Mar 1930 letter that P&WA had been working on a 1,000 hp engine for some time and had recently become convinced that such an engine was possible. It is likely that MatCmd and P&WA had been informally collaborating on the preliminary design for some time because engineering drawings from each organization depict designs with too much in common to be coincidence. Mead pointed out the need to agree upon detailed specifications but said P&WA was proceeding with development at its own expense.¹¹

P&WA's version of the specification primarily addressed non-technical issues such as drawings, packaging and marking, delivery, etc. The technical specifications were surprisingly scant, committing P&WA to deliver a liquid-cooled 1,000 hp engine weighing less than 1,800 lb, with a gear-driven centrifugal supercharger and material selection that would mitigate the corrosive effects of TEL. The engine was to provide for an Eclipse Series 11 or Series Y starter, a Type MF generator, two Type E-4 gun synchronizers, two tachometer drives, a Type C or Romec fuel pump, and cover plates for all the unpopulated accessory pads. Specific fuel consumption was not to exceed 0.52 lb/hp/hr, and oil consumption was not to exceed 0.035 lb/hp/hr. The engine was to deliver its rated output with a coolant outlet temperature of 290 – 300°F.¹²

On 12 Dec 1930, Materiel Division Chief Brig Gen Howard G. Pratt wrote P&WA expressing satisfaction with the general trend of development that had been reported by Capt Page after his visit.¹³ After several months of wrangling, P&WA and MatCmd finally agreed on a contract price of $290,000 to cover development and delivery of two R-2060 engines.¹⁴

On 19 Oct 1931, Andy Willgoos sent MatCmd a progress report on its 1,000 hp engine. He stated that the preliminary design was nearly complete and most of the important details had been released to manufacturing. Main crankcase patterns were complete, and a sample casting had been obtained for layout. The rear section pattern was almost ready for sample casting. Several experimental cylinders had been built and tested to destruction. The first was a four-valve design whose exhaust valves ran excessively hot, leading to preignition. A second design was of copper-brazed construction and used two internally cooled valves. The cylinder barrel was a steel forging with a malleable iron valve box and steel cooling jacket that was hydrogen-copper brazed in place. The forged aluminum piston was undergoing endurance testing. This combination had completed 49 hrs of single-cylinder endurance testing, and several sets of parts were on hand or in production. The crankshaft forging dies were complete, experimental shafts had been forged, and the first crankshaft was being manufactured. Master and link rod forging dies were in process, and all parts were expected to be ready for machining by 30 Nov 1931.

Ignition units were being made by both Delco and Scintilla, each designed specifically for the P&WA application. The five distributors, one at the rear of each cam box, would be equipped with automatic advance, achieving proper starting and running timing without the need to interconnect the distributors. Provisions for a MF type generator were in the vee between Banks 1 and 5. The engine rear section accommodated a starter, custom Bendix-Stromberg four-barrel carburetor, two gun synchronizers, a fuel pump, and oil pumps. The 3:2 ratio reduction gear was similar to the planetary unit designed for R-1860 Hornet but with increased capacity and reduced manufacturing cost. A front exhaust collector ring was contemplated, but a final decision was being deferred.¹⁵

The engine Willgoos was describing was the P&WA R-2060 Yellow Jacket, a 20-cylinder liquid-cooled engine with 5 banks of 4 in-line cylinders each. The crankcase was of the barrel type, open at the back to allow insertion of the crankshaft with main bearing diaphragms attached. Necessary fasteners and connecting rods were then added through cylinder pads, and the crankcase closed out by installing the rear section. The five banks were numbered, with No. 1 being at the center bottom, and proceeded clockwise when viewed from the anti-propeller end of the engine. The cylinders were designated A through D, with the A cylinders being closest to the propeller. The bore was 5.188" and the stroke was 4.875" for a displacement of 2,061.1 in³. Compression ratio was 6.18:1. The coolant was either water or a water/ethylene glycol mixture, and the blower ratio 9.4:1.

Pratt & Whitney Aircraft R-2060 Yellow Jacket Factory Photographs (NARA)

Note the induction tubes, which look almost like house plumbing (NARA)

Pratt & Whitney Aircraft R-2060 Yellow Jacket Museum Photographs

The R-2060 as it appeared in the Pratt & Whitney Aircraft Museum, 2006. The coolant pump has been removed, as has the ignition system, save one distributor. (Author)

Pratt & Whitney Aircraft R-2060 Yellow Jacket Drawings (NARA)

Cross Sections	Longitudinal Cross Section	Crankshaft

Pistons, Connecting Rods	Propeller Reduction Gear	Installation Drawing
Apologies for the poor image quality.

Pratt & Whitney Aircraft R-2060 Yellow Jacket Details

Diagrams	Stromberg NA-F7 Four-Barrel Carburetor (Author)	Scintilla W-4A Four-Cylinder Distributor (Author)

On 28 Nov 1931, Maj Howard wrote P&WA complaining that although the agreement between MatCmd and P&WA required monthly financial statements, none had been received.¹⁶ P&WA responded on 9 Dec with a financial statement covering the period of 1 Mar 1931 through 30 Oct 1931. On 19 Mar 1932, MatCmd requested another financial report covering 1 Nov 1931 through 29 Feb 1932. P&WA sent this on 24 Mar 1932.

On 2 Feb 1932, Andy Willgoos sent a letter reporting that a large amount of single-cylinder test work had been done. All detailed R-2060 drawings had been released for manufacture. There were 304 new or special parts, 235 of which had been completed. The crankshaft was about 95% complete, the crankcase was being machined, and the cylinder barrels were machined and ready for assembly. Revised cylinder jackets were finished, as were the cylinder head castings; cylinder assembly was being delayed until single-cylinder work was complete. Since the last report, the cylinder had been redesigned to increase the cylinder head coolant capacity. The exhaust valve guide boss had been lengthened, as had the exhaust valve; a slightly heavier wall thickness was also used. Spark plug location had been changed, and a provision for lubricating the exhaust valve guide added. Piston clearance was 0.028", and the piston incorporated three compression rings and one oil scraper ring. Six oil holes under the scraper drained excess oil to the piston interior. Standard service B.G. spark plugs only lasted about 25 hrs, leading P&WA to use Champion plugs until cylinder development work was complete.

The single-cylinder test engine had accumulated 50 hrs of endurance running, together with a complete calibration using different coolant temperatures and also comparing Prestone with water. Single-cylinder testing at 2,500 rpm produced 52.5 hp with a manifold pressure of 34 inHgA and a specific fuel consumption of 0.55 lb/hp/hr. This testing, however, had been problematic. The cylinder had suffered from exhaust valve stretch, exhaust guide cracking, detonation, ring sticking, high specific fuel consumption, cam lobe wear, and valve stem end wear. Various remedies were being tried, and P&WA expected to continue single-cylinder work until a satisfactory cylinder was produced.¹⁷ In his acknowledgement of the progress report, Maj Howard wrote that the report contained the type of information that MatCmd had anticipated but requested that future reports be issued every two weeks, that drawings be made available to MatCmd as soon as they were complete, and that studies, analyses and design studies should be forwarded. MatCmd also wanted the report to be more formal and in a standardized report format rather than in letter form.¹⁸ P&WA responded immediately, pointing out that the issue of report frequency had been decided back on 17 Sep 1931: reports were to be issued every month, and P&WA "… would dislike very much to render reports more often than monthly as provided in the agreement, at least until such time as the engine is actually undergoing test and more frequent reports might be to our mutual advantage." P&WA did agree to change the report format to a more formal one and to forward major assembly drawings once they were approved.¹⁹ P&WA submitted the second R-2060 progress report, Short Memorandum Report (SMR) No. 1 dated 15 Mar 1932, on 28 Mar 1932. The cover letter references unspecified drawings that were still in process. The actual report is missing from the file.²⁰ The Short Memorandum Report was P&WA's most cursory report format, followed by the more detailed Memorandum Report and Design Report formats. On 7 Apr 1932, P&WA submitted an assembly drawing, a crankshaft detail drawing, and a stress analysis report. Again, we have a cover letter but no drawings or reports.²¹ MatCmd wrote P&WA on 21 May 1932 chiding them for being late with the April report and for not delivering a promised report showing stresses, loadings, etc. for individual parts. MatCmd requested that this information be forwarded as soon as possible.²² P&WA responded the following week with SMR No. 2, dated 15 May 1932, covering progress since 15 Mar 1932. Also included were cylinder assembly, intake and exhaust valve drawings. Data on loadings and stresses was still not available.²³

On 2 Jun 1932, Maj Howard reported that the Navy had ordered three P&WA air-cooled 14-cylinder R-1830 radial engines capable of a 1,000 hp takeoff rating. Although the R-1830 had flown, it was still under development because of inadequate cooling and other difficulties.²⁴

Willgoos wrote MatCmd on 3 Jun 1932 advising that P&WA had not produced a crankshaft stress analysis and inviting MatCmd to do one if it so desired; he sent along a detailed crankshaft blueprint and calculated loads.²⁵ MatCmd declined undertaking the stress analysis.²⁶ When dynamometer running of the R-2060 appeared imminent, P&WA wrote MatCmd asking to take advantage of its liquid-cooled engine experience. P&WA expected to water-cool the coolant radiator and needed to know the volume of water required, the size of the water lines, the size of the radiator, and the most desirable radiator type.²⁷ Willgoos released SMR No. 3 on 1 Jul 1932. This covered work done between 15 May and 1 Jul. P&WA had assigned Project No. 108 to the work. Willgoos reported that the revised cylinder design had run 100 hrs without any trouble or a forced stop of any kind. The running, on 89 octane fuel with Champion 3A spark plugs, was at a bmep of 166 psi and a sfc of 0.55 lb/hp/hr, which corresponded to about 1,100 hp for the multicylinder engine. Next, the same cylinder ran a 50-hr endurance test at the same bmep, but with 87 octane fuel, a sfc of 0.50 lb/hp/hr, and B.G. shielded spark plugs. The plug wiring harness insulation close to the plugs burned away almost immediately and the plug itself soon failed. They were replaced, and running continued uneventfully. The final-design cylinder had accumulated 158 hrs, 50 with shielded service spark plugs. Another 50-hr test at 178 psi bmep was underway. The multi-cylinder engine had been assembled, and Willgoos included preliminary photographs. Dry weight of the engine was 1,299.66 lb without ignition, carburetor, or any accessories. He cautioned that the radio-shielded ignition harness had not yet been installed.

P&WA had prepared the test stand and equipment to the extent possible in preparation for testing, but it anticipated some delay since this engine was so different from its standard models.²⁸ When the R-2060 reached the dynamometer stand on 9 Jul 1932, it was equipped with a Stromberg NA-F7, PN 5463170 weighing 22 lb, a Romec fuel pump weighing 3.28 lb, five Delco 4-cylinder battery distributors with automatic spark advance weighing 8 lb each, and a type E-4 50-A generator weighing 35.1 lb. Total accessory weight was 100.16 lb, bringing the engine total to 1,400.04 lb. B.G. 4B1 spark plugs were initially used, and the initial ignition harness was not shielded. When the cooling system was filled with water, a leak appeared near the 1D cylinder coolant inlet manifold; the manifold had been deformed by an over-torqued hose clamp. When the test crew began motoring the engine over, it was found that the Banks 3 and 4 coolant jackets were air bound; coolant jacket plugs were removed, and coolant circulation established. After 15 minutes, oil began pouring from the nose breather. About 2.5 gal of oil was drained from the lower cam housing. Once the oil warmed to operating temperature, discharge from the breather ceased. Over the next 4 hrs motoring speed was increased to 850 rpm. The Bank 5 cylinder barrels ran hot, indicating poor coolant circulation; the bleed line to the Bank 5 barrels was opened without any improvement. The exhaust manifolds and a new set of B.G. 4B1 spark plugs were installed, and the engine started for the first time. It ran smoothly for 2 hrs as its speed was gradually increased to 1,220 rpm, where there was a slight vibration. Oil leaks were noted at both water pump packings and around the 1A cylinder flange.

The engine was removed from the test stand and torn down for inspection. The Bank 5 rear cam oil pump body had sheared its dowel pin and had turned in its housing, and the cover was frozen to the shaft, probably due to insufficient clearance. Some pistons were scuffed, the order of severity (high to low) being 5C, 5D, 4C, 5B, 5A and 3C. The 5C oil scraper ring was badly worn, and cylinder 5C and 5D showed relatively heavy wear. All Bank 5 cylinders appeared very dry of oil. Bank 1 and 2 tower shaft bearings were running dry, and the tower shaft gear teeth appeared to be wearing unevenly. Three large outer crankshaft bearing races had turned in their crankcase liners, slightly scoring the liners. When the engine was reassembled, the cam oil pump shaft-to-body diameter was increased by 0.004", the keyway made 0.031" deeper, and the pump blade edges rounded. The scuffed pistons were dressed, and the 5C oil ring replaced. Tower shaft bushing clearance was increased to 0.0025", and the oil drain holes enlarged. Leaks in the No. 1 coolant inlet manifold were soldered, and bosses for pencil thermocouples brazed to all coolant outlet manifolds. Petcocks were installed in the coolant outlet manifolds as well. Steel ferrules were soldered  inside all manifold hose fittings to prevent them from collapsing. Two rear discharge ring outlets were moved to the top of the ring, and Banks 1, 2 and 5 bleed lines were connected to the discharge ring. Manifold pressure connections were installed near Bank 4 intake ports and in all crankcase intake castings. Water pump packing springs were replaced with ones having squared ends. Finally, a 0.75" hole was drilled near the front main and center main web tops.

The R-2060 was returned to the dynamometer stand on 12 Aug 1932. The intent was to run it for 11 hrs at 90% power. Each time it was started it soon loaded up with oil, which was drained, and the process was repeated numerous times as engineers tried to determine the scavenging difficulty. The test stand scavenge pump (auxiliary pump), which moved scavenge oil from the engine to the oil tank, was sucking air when the engine was running, but when it was shut down immediately pumped gallons of oil back to the tank. Engineers tried connecting the auxiliary pump to different locations with some improvement but found no solution; oil consumption was unacceptably high 20 – 25 lb/hr. The engine was shut down for the day after 5.5 hrs.

Nothing had improved when the engine was started for the next day's running. Oil was blowing from the nose breather, but a set of readings was taken, each at a higher rpm. Manifold pressure in Banks 1 and 2 was 0.5 inHgA lower than in the other banks, and coolant outlet temperatures varied by 17°F, possibly due to the high oil consumption. At 2,200 rpm the engine suddenly lost 50 rpm; nearly all plugs were fouled. The plugs were cleaned and 2.5 gal oil drained from the "dry" sump. A second oil radiator was installed to control the oil temperature.

On 17 Aug 1932 when running was resumed at 2,200 rpm, oil consumption was 41 lb/hr; the oil temperature could not be controlled, and the spark plugs all fouled. After 2 hrs, the engine was shut down and removed from the dynamometer. When the cylinder banks were removed for inspection, it was found that the Bank 5 rear cam oil pump was again frozen to the shaft and that the supports for both Bank 5 cam pump bodies were cracked.

The engine was reassembled with still more clearance in the cam pumps, and the crankcase drainage was modified by installing baffles and extra case drains in the nose and rear sections. When running resumed on 3 Oct 1932, the scavenging problems remained. Numerous different scavenge plumbing arrangements were tried, but none produced any real improvement.

The engine was returned to the experimental shop with orders to remove Banks 2 and 5 for inspection. When a disintegrated 5C piston was discovered, all banks were removed. Inspectors found cylinder 5C damaged by its disintegrated piston, the water pump packing spring broken, pistons 5B and 5D scored, the second land of all pistons in contact with cylinder walls, and 5A exhaust valve had lost its sodium. The defective parts, along with all other Bank 5 cylinders and pistons, were replaced. The second land of all pistons was turned down to the same dimensions as the top land. Thermocouples were installed on the thrust side of the cylinder flanges.

Willgoos released SMR No. 5 on 1 Oct 1932 covering R-2060 work from 30 Aug through 1 Oct; SMR No. 4 is missing. Apparently, there had been trouble with scavenging and over oiling, which had been partially corrected. While running at rated power and investigating the over oiling problem, a piston scuffed and burned in cylinder 5B. Engine cylinder numbering had been changed so that the banks were now numbered in the direction of rotation with Bank 1 at the bottom; cylinders were counted starting at the engine propeller end. The engine was torn down, inspected and everything was found to be in good condition with the exception of Bank 5, which had other piston distress in addition to cylinder B. With the engine over-oiling, it was hard to blame a lubrication problem. Exhaust stack observations indicated excellent mixture distribution.

P&WA speculated that a coolant circulation deficiency may have been responsible, and was rebuilding the engine with additional Bank 5 coolant temperature thermocouples and short exhaust stacks so that individual cylinder mixture quality could be determined. A redesigned higher-output single cylinder was also being constructed.²⁹

On 19 Oct 1932, MatCmd civilian employee Ford L. Prescott published an overview of the 20-cylinder engine project and summarized its advantages and disadvantages. He noted that the limiting diameter of pistons had probably been reached (perhaps referring to the P&WA R-1860 Hornet with its 6.250" bore) and the only way to increase engine output was to increase the number of cylinders, rpm, or bmep. The 20-cylinder engine offered many desirable features, incorporating the good points of both radial and inline configuration. Fuel injection could allow the use of cylinder arrangements that would be difficult to serve with carburetors and manifolds.

Crankpin inertia loads were decreased by gas loads when five or more cylinders were arranged around the crankpin, and second-order vibration of a 4-cylinder inline arrangement was significantly mitigated with five radial 4-cylinder banks. A MatCmd trade study examining various cylinder sizes, rpms, and bmeps led to the conclusion that an unsupercharged engine displacing 2,060 in³ would produce 1,000 hp at 130 psi bmep and 3,000 rpm using cylinder bores of 5.250" and strokes of 4.750". With supercharging, it was hoped that the engine would produce 1,500 hp at 3,300 rpm.

On 5 Nov 1932, the engine was returned to the dynamometer and run for 6.5 hrs at speeds ranging from 1,100 to 1,700 rpm. It ran another 2.6 hrs on 7 Nov. On 11 Nov, Bank 5 was removed for inspection, which revealed three scratched pistons. The oil baffle above Bank 5 was removed, oil squirt holes lubricating the blower drive pinion and gear were plugged, the Bank 5 coolant inlet manifold was enlarged, fittings for draining water from Bank 5 cylinders were installed, and more thermocouples were added to Bank 5 for monitoring coolant temperatures.

Project Report No. 6, dated 15 Nov 1932, covered work from 1 Oct to 3 Nov. The rebuilt R-2060, with a completely new Bank 5 to which a number of thermocouples had been added, had been run in and up to rated power. Bank 5 temperatures were about the same as other banks, and although the coolant flow was approximately 20% less than the other banks, P&WA engineers did not think this had been responsible for the earlier damage. When the report was published, Bank 5 was being removed for inspection, and a special water manifold was being constructed that would reverse the coolant flow through the one bank.³¹

Progress Report No 7, which Willgoos published on 10 Jan 1933, covered testing during Dec 1932. The revised coolant flow scheme had apparently solved the earlier piston scuffing problems. P&WA was unhappy with the still-high oil consumption of 0.040 lb/hp/hr.

During recent testing, the engine had produced 1,116 hp at 2,500 rpm. Cylinder flange temperatures had all operated below 250°F, but problems with leaking coolant manifolds and coolant jacket cracks had appeared. The engine was being torn down to examine these parts. Total engine time on 30 Dec 1932 was 45.94 hrs.³²

At a 9 Jan 1933 conference at MatCmd, George Mead informed Maj Howard that personnel availability and priority of other work prevented P&WA from continuing to develop the R-2060. Maj Howard followed up with a 16 Jan letter to P&WA stating that it was not in the best interest of the U.S. Government to continue R-2060 development and instructing P&WA to submit a cost analysis. This released P&WA from its obligation to deliver a completed R-2060.

MatCmd's review of P&WA's single-cylinder testing had shown the output was less than that being obtained from other single-cylinder engines operating at the same compression ratio, coolant outlet temperature, speed, and manifold pressure. The R-2060 had produced 1,116 hp at 2,500 rpm, equivalent to a bmep of 171.7 psi. The engine now weighed 1,350 lb, a specific weight of 0.83 hp/lb. By contrast, the Allison V-1710-1 at that time weighed 1,160 lb and was expected to produce 1,000 hp at 2,800 rpm, a specific weight of 0.86 hp/lb. MatCmd thought the developed Allison would be sufficient to determine the merits of a 1,000 hp engine in military aircraft.³³ On 21 Apr 1933, MatCmd wrote P&WA complaining that the data promised during their January meetings had not been received. P&WA sent cost data on 24 Apr, but instead of the requested data, said that George Mead would come to Dayton at MatCmd's convenience.

Project 108 (R-2060) Status as of 31 Mar 1933
Labor, Engineering = $16,300.27
Labor, Experimental Machine Shop = $22,178.94
Labor, Experimental Test = $911.81
Labor, Total = $39,391.02
Material, Experimental Machine Shop = $26,701.45
Material, Experimental Test = $1,299.41
Material, Total = $28,000.86
Overhead (175.7% actual) = $69,227.45
Patterns = $10,027.29
Dies = $4,445.65
Tools = $588.81
Total Project Cost = $151,681.08³⁴

Mead encouraged consideration of an air-cooled alternative, pointing out that unless MatCmd was contemplating surface cooling, the installed air-cooled alternative would produce less drag. Mead thought that fitting air-cooled cylinders to the existing crankcase was a logical first step and noted that P&WA was then ready to proceed with such a development.

Mead followed up this official response with another letter to Maj Howard that same day, expanding on points made in the first letter. He reiterated his preference for air-cooled engines, noting again the disadvantages of surface cooling, which he thought to be the only viable approach to the heat dissipation requirements. Mead observed that engines with high bmeps were very rough running and that the high pressure was extremely destructive to engine components. Mead thought the best solution involved a large number of small cylinders running at high speed, and that this was best achieved with air cooling. On the subject of valve gear, Mead conceded that inline engines had an advantage over traditional air-cooled radials, but that this advantage also accrued in 15 and 20 cylinder radial combinations.

Mead suggested that the multi-bank radial engine type be thoroughly investigated, as it was a good compromise for either wing or fuselage mounting and was mechanically compact.

MatCmd responded to Mead's letters on 28 Jun 1933, requesting more specific information of proposals 2 and 3. P&WA provided this on 11 Jul 1933, but MatCmd decided not to sponsor development.³⁵

Maj Howard wrote P&WA on 1 Sep 1933, pointing out that MatCmd had ordered work stopped on Jan 14 and P&WA had acknowledged on 19 Jan. MatCmd was not obligated for any costs beyond 19 Jan 1933.³⁶ The R-2060 correspondence file ends at this point. We do not know exactly how much P&WA spent developing the R-2060, nor do we know how much MatCmd ultimately paid.

References

1 Fernandez, Ronald. Excess Profits (Reading: Addison-Wesley, 1983) 27.
2 Schlaifer, Robert. Development of Aircraft Engines (Boston: Harvard, 1950) 185.
3 Lippincott, Harvey. “The Navy Gets an Engine”, American Aviation Historical Society Journal (Winter, 1961) 258.
4 USAAC Engines 1000 hp, 4-7. Engines - 1000 Horse Power, 1929 ~ 1936. USNARA RG342 RD3285.
5 USAAC Engines 1000 hp, 21.
6 USAAC Engines 1000 hp, 12, 17.
7 USAAC Engines 1000 hp, 24.
8 USAAC Engines 1000 hp, 27-30.
9 USAAC Engines 1000 hp, 33-35.
10 USAAC Engines 1000 hp, 36. Engines - 1000 Horse Power, 1929 ~ 1936. USNARA RG342 RD3285.
11 USAAC Engines 1000 hp, 18.
12 USAAC XR-2060 Corr, 1-4. Pratt & Whitney R-2060. USNARA RG342 RD3233.
13 USAAC XR-2060 Corr, 5.
14 USAAC XR-2060 Corr, 10-17.
15 USAAC Engines 1000 hp, 41-43.
16 USAAC XR-2060 Corr, 23.
17 USAAC XR-2060 Corr, 31-33.
18 USAAC XR-2060 Corr, 34.
19 USAAC XR-2060 Corr, 35.
20 USAAC XR-2060 Corr, 40.
21 USAAC XR-2060 Corr, 43.
22 USAAC XR-2060 Corr, 45.
23 USAAC XR-2060 Corr, 46.
24 USAAC XR-2060 Corr, 47-48.
25 USAAC XR-2060 Corr, 49.
26 USAAC XR-2060 Corr, 62.
27 USAAC XR-2060 Corr, 58-59.
28 USAAC XR-2060 Corr, 61-62.
29 USAAC XR-2060 Corr, 67.
30 19 Oct 1932 Memorandum Report E-57-29. Preliminary Design Study of a 20-Cylinder 1,000 H.P. Engine. USAAC Engines 1000 hp, 67-69.
31 USAAC XR-2060 Corr, 77.
32 USAAC XR-2060 Corr, 78.
33 USAAC XR-2060 Corr, 80, 83.
34 USAAC XR-2060 Corr, 84-86.
35 USAAC XR-2060 Corr, 87-93.
36 USAAC XR-2060 Corr, 95-96.

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