Curtiss-Wright R-4090 Development

The Curtiss-Wright Cyclone 22 (R-4090)
and its Role in the Development of Propeller Standards
by Kimble D. McCutcheon
Published 1 Jan 2013; Revised 10 Jul 2024

Little information exists on the Cyclone 22, primarily because WAC literally threw it all away as the company exited the aircraft engine business. Nearly all the information that remains was pilfered from dumpsters by dedicated employees determined to save the WAC history , or is part of the correspondence between WAC and the U.S. Army Air Corps/Forces. That correspondence is now largely a part of the National Archives Record Group 342 RD Number 2442. Unless otherwise noted, the Memorandum Report references that appear in this article came from that source. The information here is organized chronologically and comes almost entirely from primary sources. Although it is incomplete, it is the author's hope that it will provide a basis for further research.

By the middle of 1940, Pratt & Whitney Aircraft (hereinafter P&WA) had begun configuration and cooling airflow studies on a 3,000 hp radial engine concept that would eventually become the R-4360. In the fall of that same year, P&WA notified the Air Corps that it would abandon the liquid-cooled sleeve-valve engines that had been under development since 1937. These included the 1,800 ~ 2,000 hp H-2600 (also known as the X-1800), upon which the Air Corps had counted upon to power several new aircraft designs. This set in motion a flurry of activity as the Air Corps tried to both identify alternative propulsion to keep its aircraft projects moving forward, and at the same time promote development of engines in the 2,000 ~ 3,000 hp category. One of the things Air Corps did was to contact several engine manufacturers, hoping one might pick up where P&WA left off, or provide substitute engines.

On 20 Mar 1941, Chief Engineer Raymond W. Young and Mr. Bergman of the WAC met with Power Plant Laboratory Chief Col Edwin R. Page, Maj Carlson and Opie Chenoweth of the Materiel Command Engineering Division (hereinafter MatCmd) regarding larger engines. Col Page outlined Air Corps needs for high-speed, high-output pursuit engines where fuel consumption was a secondary consideration, and reliable, economic bombardment engines of reasonable diameter. Young said WAC would want to work on air-cooled engines as they already had the liquid-cooled R-2160 Tornado.

Young suggested that WAC would start with a 3,000 hp design with the expectation of reaching at least 3,500 hp. This 55" diameter engine would consist of 18 cylinders with 7" bores, forged heads, two-stage supercharging, provision for two-speed coaxial propellers and a cooling fan. It would have rear exhausts for jet thrust, with front exhausts available for pusher installations. It would probably use 9-cylinder fuel injectors. Col Page encouraged WAC to produce drawings at the earliest opportunity, and to propose a development plan. Young said the WAC sales department would be in touch to present a plan. MatCmd wanted a single-cylinder design with multi-cylinder options. Young stated that ignition developments should aim at 50,000 ft operation.

WAC's turbosupercharger was also discussed. The experimental unit had accumulated 60 hours with its original wheel and thin-edge buckets, which now had two cracks. Young wondered whether WAC should continue active development; Col Page was emphatic that it should. WAC was also working on a turbosupercharger with variable nozzle box, controllable diffusers and special buckets intended for 1,800 – 2,400 hp engines, which Col page also thought important. Col page suggested that WAC should send a turbocharger for evaluation as soon as practical. [28 Mar 1941 Memorandum Report EXP-M-57-503-321]

Nearly four months later, on 22 Jul 1941, WAC engineer Arthur Nutt, in a visit to MatCmd was cagey about revealing 3,000-hp-engine details, seemed embarrassed at being unable to provide the details, implied that an agreement with the U.S. Navy prevented him from discussing the matter, and insinuated that the Navy was withholding information; "he wished that the Army and Navy would get together on this project so that he would be free to discuss all details." MatCmd inferred that WAC had already given the Navy a proposal, since WAC thought the Army was interested in the liquid-cooled WAC R-2160 Tornado that was supposed to eventually be capable of 3,000 hp and erroneously wondered why Army would also be interested in a 3,000 hp air-cooled engine. This misunderstanding may have originated with the agreement Army had with Navy regarding production engines where the Navy Bureau of Aeronautics (BuAer) contracted with P&WA and the Army with WAC. [23 Jul 1941 Inter-Office Memorandum (hereinafter IOM) from Brig Gen George C Kenney, Assistant Chief, Materiel Division.]

MatCmd spoke with BuAer personnel and learned that Nutt had proposed the development of a 22-cylinder air-cooled 3,000-hp-class engine on a strictly confidential basis, a classification requested by Nutt himself. (Note: WAC, which was behind and behind on the R-2160 Tornado project, may have been reluctant to share news of new development projects with the Air Corps, worried that the Air Corps would be suspicious that more recent projects might compete for Tornado resources.) However, BuAer had received no formal development proposal. BuAer was willing to share all available information concerning the proposed development. [5 Aug 1941 IOM from Lt. Colonel B.E. Meyers, Material Division.]

Apparently, the MatCmd Power Plant Laboratory telegraphed WAC requesting quotations for one to ten 3,000 hp air-cooled engines. Without knowing that the Air Corps was talking to the Navy, Nutt perpetuated his subterfuge with a telephone call to his old Power Plant Laboratory pal, Opie Chenoweth, on 11 Aug 1941. Nutt claimed to be curious about a telegram received from the Air Corps requesting a quotation on quantities of one to ten 3,000 hp air-cooled engines. Nutt claimed to have unsuccessfully tried to contact Col Carroll, and reiterated the WAC explanation that the Tornado project made the 3,000 hp air-cooled engine uninteresting to the Air Corps, and if the Air Corps wanted a 3,000 hp air-cooled engine it should contact the Navy. Chenoweth stated that any development larger than the WAC R-3350 should first be presented to the Air Corps. Nutt then stated that a proposal had been given to the Navy, and that Nutt had suggested to Cmdr Botta of the Engine Design Section that a single contract covering both Army and Navy needs be negotiated. Cmdr Botta was amenable to any plan that could be worked out. Nutt planned to answer the telegram with a request that the Army and Navy consolidate their development efforts. [14 Aug 1941 Memorandum Report EXP-57-503-420]

On 4 Sep 1941, WAC's Raymond Young and Mr. Holland met with the MatCmd Aircraft Projects Chief Maj L.C. Craigie and exhibited preliminary X-924 drawings and an installation drawing. Young said he was on his way to the West Coast to discuss the 3,000 hp engine with Boeing, Douglas, Consolidated and Lockheed. WAC had attempted to expedite the engine's development by using as many proven parts as possible. Its first attempt was an 18-cylinder engine with a 7" bore; this was abandoned because of high bearing loads. The current engine design employed 22 cylinders with the same bore as the R-2600 and R-3350. With a 6.125" bore, 6.312" stroke, 4,091.59 in³ displacement and 6.85:1 compression ratio using PN 100/130 fuel, it was takeoff rated 3,000 hp at 2,800 rpm, military-rated 2,520 hp at 2,700 rpm and 11,000 ft, and 2,900 hp at 2,700 rpm and 20,000 ft. It was normal rated 2,400 hp at 2,600 rpm and sea level, 2,400 hp at 2,600 rpm and 6,700 ft, and 2,190 hp at 2,600 rpm and 24,200 ft. Its two-speed supercharger used a 14" impeller, 5:1 and 7:1 supercharger drive ratios. It employed an R-3350 nose section with a 0.333:1 gear ratio driving a Society of Automotive Engineers (SAE) No. 60 propeller shaft. The rear section was from an R-3350-C. The X-924 was 91" long, 58" in diameter and weighed 3,230 lb. With two-speed dual-rotation propeller (the XR-4090-3) it weighed 3,260 lb. Young expected the first engine to run in about 15 months (January 1943) and said that the most serious development obstacle was the lack of WAC experimental shop machine tools. (Note: This excuse is a recurring WAC theme. Too stingy to build its own well-equipped experimental machine shop, WAC depended on outside vendors for prototype parts. This would be a major impediment to WAC's experimental engine development and especially to its WWII response to design changes.) Still, Young optimistically projected the second experimental engine would be available in April 1943, followed by additional engines in June, July and every two months thereafter. Flight engines, complete with dual-rotation two-speed propeller reduction gearing, cooling fans and torque meters, would be available between March and June 1944. [5 Sep 1941 Memorandum Report EXP-M-50-588]

WAC was considering two reduction gear configurations, one a strengthened R-3350 nose case with a 0.35:1 ratio and a torquemeter but no cooling fan provisions, and the second a universal gear set that would give reduction ratios ranging from 0.25:1 to 0.50:1 with torquemeter and probably a fan drive.

Young stated that WAC planned to build 20 engines—5 for the Army with 5 complete spare part sets, and 5 for the Navy with 5 complete spare part sets. WAC lacked the capacity to build more, but did not elaborate on a plan for how more might be built. MatCmd representatives suggested that WAC submit a proposal for 1 – 5 two-speed supercharger versions with 0.35:1 reduction gear ratio by 11 Sep 1941. Young thought that could be accomplished, yet when the 11 Sep date arrived and no proposal had been received, Lt Col A.E. Jones telegraphed WAC inquiring when the proposal would be sent. Later that day, WAC telegraphed MatCmd that the proposal had been air-mailed special delivery on 10 Sep 1941. [8 Sep 1941 Memorandum Report EXP-M-57-503-438, Conference 9/4/41 with Representatives of WAC Aeronautical Corp.]

On 8 Sep 1941, the Power Plant Laboratory Chief, Lt Col E.R. Page, recommended to the Experimental Engineering Section Chief that WAC's 3,000 hp engine project be classified Confidential. As a result, Col Carroll approved his recommendation on 10 Sep and assigned Classified Project Number MX-153, titled "WAC 3000 H.P. Air-Cooled Engine." [8 Sep 1941 IOM]

On 9 Sep 1941, the Engineering Division Propeller Laboratory hosted a conference attended by R.M. Bear of BuAer; G.W. Brady, J. Thomson and C.W. Chillson of the Curtiss Propeller Division; Allan Chietan, Gustaf Camelli, A.V. Sheak, K.M. Lane and T.Bergmann of WAC; E.W. Morris, Charles MacNeil and W.L. Greene of Aeroproducts Propeller; Thomas Barish of Marlin-Rockwell; G.T. Lampton and John W. Cehrli of Aviation Manufacturing Corporation; Ted Bosler and C.J. McDowall of Allison; Allen C. Staley and D.M. Borden of Chrysler; Thomas B. Rhines, Murray C Beebe, E. Martin and W.F. Chappel of Hamilton Standard Propellers; James. .F Kinnucan of Continental Motors; Andrew Willgoos, WAC A. Parkins, C.T. McKinnie, G.S Beardsley and V.J. Moncrieff of P&WA; Maj H.H. Couch, Maj S.R. Brentnall and H.A. Nicol of the Materiel Division. The group decided that:

The shafts to be developed would be confined to the SAE No. 40-60 for engines up to 2,000 hp, SAE No. 50-70 for 3,000 hp engines, and SAE No. 70 for single-shaft 3,000 hp engines.
Engine manufacturers would be responsible for developing and furnishing the oil seals between coaxially rotating propeller shafts to prevent engine oil from working forward into the propellers or the propeller lubrication from working back into the engine. This seal could be located at any convenient point along the shafts, but could permit no leakage.
The Materiel Division would assume responsibility for developing the 40-60 and 50-70 shafts, not including the inner bearing and oil seal, and the No. 70 single-rotation shaft.
The No. 40-60 shaft, complete with engine nose, was shown on Air Corps drawing X42H4482, a redesign of X41H3035.
The No. 50-70 shaft, complete with engine nose, was shown on Air Corps drawing X42H4483, a redesign of X41H3010.
The front cone dimensions for both Nos. 40-60 and 50-70 shafts were tabulated on Air Corps drawing X42B4484; rear cone dimensions on drawing X42B4485.

The engine noses for these dual-rotation configurations provided a propeller control mounting surface complete with the necessary pilot and mounting stud holes, which were located outside the area dedicated in the past for thrust bearing mounting studs or cap screws. The propeller control manufacturer was required to provide a clearance envelope that left space for the bearing mounting studs or cap screw heads.

Drawing X41H4041 (Shaft – Proposed Standard No. 70 Propeller), complete with attaching parts, Drawing No. X37D5560 (Nut – Propeller Hub Retaining #70), Drawing No. S37B5557 (Cone – Propeller Hub Front, Tentative Standard No. 70), Drawing No. S37B5558 (Cone – Propeller Hub Rear, Tentative Standard No. 70) and Drawing No. S37B5556 (Ring – Propeller Hub Snap, Tentative Standard No. 70) were released for incorporation in Specification AN-9506 (Ends; Aircraft-Engine, Nose-and-Propeller Shaft). The No. 70 engine nose incorporated the same advantages as those mentioned in the No. 50-70 shaft discussion.

The group concluded that:

Inner shaft deflection at the point where the inner bearing race was located could be no more than 0.5°. If the deflection was larger, a self-aligning inner bearing was necessary and this was considerably larger and would occupy valuable space. It was also very difficult to seal grease in a self-aligning bearing. Deflection exceeding 0.5° would also present serious control problems in coordinating the pitch-change mechanism between the front and rear propellers.
An auxiliary plain bearing with sufficient clearance to prevent contact during normal operation was to be used to limit shaft deflection caused by high gyroscopic action, such as might occur during spin recovery from spins with the engine running at maximum rpm. This bearing was to be a material that would operate for short periods not exceeding 12 seconds (i.e., during a spin) without lubrication. Oilite bearings or bearings of light lead content were suggested. Such construction would also help keep the coaxial shafts centered during propeller removal or installation.
The most severe inner shaft deflection was predicted to occur during spin recovery at maximum engine rpm. For single-engine pursuit aircraft, this was 3 radians per second; for twin-engine pursuit and light bombers, 2.5 radians per second.
Manufacturers were to construct the first experimental engines and propellers in accordance with Drawings X41H3035 (No. 40-60) and X42B4483 (No. 50-70); these did not include requirements for auxiliary plain bearings.
Auxiliary bearings would be loaded to maximum deflection for about 12 seconds during each spin. The maximum allowable stress under the front propeller rear cone at maximum engine rpm was not to exceed 90,000 lb/in². Maximum allowable fluctuating shaft stress for continuous (normal) operation was not to exceed 40,000 lb/in².

The group recommended that engines and propellers be built and tested before any further drawing changes were considered. [6 Dec 1941 Memorandum Report EXP-M-52-593-35-3. Propeller Shafts, Single and Dual, for use in Engines of from 1,500 to 3,000 hp]

On 15 Sep 1941, MatCmd's Col Page and Opie Chenoweth hosted a meeting that included MatCmd's Propeller Laboratory Maj Couch, Messrs. Mills and Dickey, BuAer Cmdr Botta and Lt Cmdr Mechling, and WAC representatives Arthur Nutt, Allan Chilton and M. Holland. MatCmd and BuAer agreed that dual-rotation propellers were needed by both services, and the Army needed two-speed drives for its bomber aircraft. A target takeoff rating of 3,200 hp was set for turbosupercharged aircraft reaching 40,000 ft and aircraft with engine-driven two-stage superchargers reaching 35,000 ft. However, it was noted that geared superchargers could not maintain the full 3,200 hp to 35,000 ft, and that the output at that altitude would be reduced by as much as 500 hp. Lt Cmdr Mechling agreed work with Propeller Laboratory personnel to produce a separate report.

Cmdr Botta produced a letter from P&WA stating that single-stage single-rotation engines with either single or two-speed reduction gears could be delivered for $75,000 each, and that engines with two-stage superchargers would cost $95,000 each. If 24 engines were purchased, delivery could be completed by June 1943 according to a schedule making one available in September and October 1942, two in November and December 1942, three in January 1943, and three per month thereafter. P&WA estimated that no two-stage engines would be available until late summer 1943. P&W was unwilling to quote cost and delivery for two-speed or dual-rotation reduction gearing.

The Navy wanted 13 engines: 2 for test, 9 with single-rotation propeller reduction and two-stage superchargers, one with dual-rotation two-speed propeller drive and two-speed supercharger, and one with dual-rotation two-speed propeller drive and two-stage superchargers.

The Army tentatively wanted 15 engines, all with two-speed superchargers, but was unsure about propeller drives. Hence, the Army expected to order the engines and then issue change orders when the propeller drive issue was clarified. The Army wanted its engines equipped with 100 hp power takeoffs at the accessory section's aft bottom to drive large cabin superchargers.

Arthur Nutt was then called into the meeting to discuss WAC's 10 Sep 1941 proposal. Nutt stated that either the 0.35:1 R-3350 reduction gear or the 0.333:1 Tornado reduction gear could be supplied, both with torque meters and SAE No. 60 propeller shafts. The engine could be either tractor or pusher, and a cooling fan would be provided with the first engine. Nutt was also informed of the 100 hp cabin supercharger power takeoff requirement. [18 Sep 1941 Memorandum Report EXP-M-503-447. Conference between Representatives of the Bureau of Aeronautics, WAC Aero. Corp., and the Division on the X-Wasp and WAC 3,000 hp Engines.]

On 21 Oct 1941, WAC representatives K.A. Brown, Allan Chilton, Arthur Nutt and R.W. Young met with Curtiss-Wrigh Corporation Propeller Division George Brady and L.H. Enos, along with Maj Howard H. Couch and Messrs. Dickey, Mills and Nichol of the MatCmd. Following conferences with BuAer and Hamilton Standard Propellers, Air Corps representatives stated that agreement had been reached regarding propeller and reduction gear requirements for various service airplanes. These data were submitted to the Curtiss-Wright Propeller Division and WAC for consideration relative to the X-924 engine project.

Bombers (3,000 hp at 40,000 ft) Basic propeller speed = 825 ± 25 rpm for Vmax, 800 ± 25 rpm at approximately 50% power for minimum fuel consumption cruise. This requirement involved a dual-rotation 2-speed propeller with eight 16 to 18 foot diameter blades and a SAE No. 70-90 propeller shaft.
Navy Boat for Operation at 20,000 ft. Basic propeller speed = 825 ± 25 rpm for Vmax, 800 ± 25 rpm at approximately 50% power for minimum fuel consumption cruise. This requirement involved a single-rotation 2-speed propeller with four 16 to 18 foot diameter blades and a SAE No. 70 propeller shaft.
Army and Navy Pursuit. Basic propeller was a compromise at 1,025 ± 25 rpm for Vmax and climb. This requirement involved a single-speed dual-rotation propeller with SAE No. 60-80 propeller shaft sizes. During the discussion it emerged that P&WA and Hamilton Standard preferred a 1,000 ± 25 rpm, the Air Corps preferred 1,050 ± 25 rpm, and Curtiss-WAC Propeller preferred 1,000 ± 25 rpm. Thus a compromise of 1,025 ± 25 rpm with six or eight blades and 13 – 14 foot diameter was chosen.

A discussion of propeller shaft sizes resulted in WAC promising to investigate the layout for a SAE No. 60-80 shaft that would meet Air Corps deflection limits. Stresses would be calculated on the basis of a 3-radian/sec spin of 9 sec duration. If the results were favorable, WAC would present the layouts to MatCmd for further discussion. If the results were unfavorable, WAC would proceed with SAE No. 70-90 layouts. WAC also agreed to report the effects on delivery for the shaft size modifications. WAC agreed to locate the inner shaft centerline 3" forward on the SAE No. 60-80 shaft to accommodate wider propeller blades.

WAC representatives stated that the X-924 would omit all engine oil lines for hydraulic propeller operation since this was the responsibility of the hydraulic propeller manufacturer. WAC also agreed to investigate incorporating an outboard bearing between the propeller disks as an engine design problem. The Army and Navy agreed to standardize the propeller characteristics and include this as requirements for airframe proposals. [22 Oct 1941 Letter]

BuAer Cmdr Rico Botta and Lt Cmdr W.B. Mechling and MatCmd Maj H.H. Couch, Maj E.J. Hale, D.A. Dickey, R.H. Mills, and H.A. Nicol all traveled to Hartford, Connecticut on 17 Oct 1941, and then to Paterson, New Jersey on 21 Oct 1941. This travel was to meet with P&WA and Hamilton Standard Propellers on the 17th, and with WAC and Curtiss Propeller Division on the 21st, to discuss propeller speed and shaft sizes. The 17 Oct 1941 meeting was attended by Erle Martin, George Rosen and S.P. Craig from Hamilton Standard, L.S. Hobbs from P&WA, and F.W. Caldwell from United Aircraft Corp. The 21 Oct 1941 meeting was attended by Raymond W. Young, Arthur Nutt, K.A. Browne and Roland Chilton from WAC, and by George W. Brady, L.H. Enos and C.W. Chillsion from Curtiss Propeller.

The meeting addressed the proper propeller rotation speeds for 3,000 hp engines supercharged to 40,000 ft as applied to long range bombers, and to pursuit airplanes with 3,000 hp engines supercharged to 20,000 ft, as well as navy patrol boats and fighter aircraft. The participants recommended dual-rotation, two-speed propellers for long range bombers. For 3,000 hp engines operating at military power, the reduction gear should drive the propeller at 800 ± 25 rpm; at 50% rated power with the engine operating at the proper speed for minimum specific fuel consumption, the reduction gear should drive the propeller at 800 ± 25 rpm. For 3,000 hp, 20,000 ft engines in patrol boats, the participants recommended two-speed single-rotation propellers and reduction gearing that drove the propellers at 850 ± 25 rpm for military power, and at 800 ± 25 rpm at 50% rated power with the engine operating at the proper speed for minimum specific fuel consumption. For 3,000 hp engines operating at military power in pursuit and fighter aircraft the participants recommended single-speed dual-rotation propellers running at 1,050 ± 25 rpm. The relative priority assignment for these was 1) Pursuit Fighter; 2) Patrol Boat; 3) Long-Range Bomber. However all participants wanted concurrent development of all three options.

These discussions addressed the same aircraft types as the propeller speed discussion. Hamilton Standard and P&WA wanted SAE No. 70-90 shaft sizes for the two-speed dual-rotation reduction gear on 3,000 hp engines for long-range bombers. They also wanted SAE No. 70 propeller shafts for the two-speed single-rotation reduction gears used in patrol boats. They thought a 4-blade, 18 foot diameter propeller would be adequate. A compromise single-speed dual-rotation reduction gear with SAE No. 60-80 propeller shaft was deemed suitable for both Army Pursuits and Navy Fighters.

The WAC/Curtiss Propeller team thought the SAE No. 60-80 propeller shaft adequate for pursuit for fighter applications, but the SAE No. 70-90 shaft was too heavy for long-range bombers or patrol aircraft; they wanted to study the matter further. Erle Martin informed the BuAer/Matcmd representatives that the SAE had appointed a subcommittee consisting of propeller and engine manufacturing interests to establish shaft standards and thought that standard should be the basis for such decisions. MatCmd agreed with Martin's proposal, but reserved the right to coordinate the standard development and require the changes it deemed advisable when combinations were furnished on Army or Navy engines. The entire inside of the shaft was to be made available for lubricating the bearing and any related seals should be the problem of the engine designer, not the propeller designer. It was also decided that the SAE subcommittee was to consider and study the insertion of plain bearings between the dual-rotation shafts and the associated lubrication requirements. Finally, the subcommittee was to prepare a revised SAE No. 50-70 drawing in which the spacer bearing length was increased from 2.375" to 4.375", which would result in a commensurate length increase for the No. 50 inner shaft.

All parties concluded that SAE No. 60-80 shafts would be satisfactory for pursuit and fighter aircraft and that the SAE subcommittee would proceed with that standard. The SAE No. 70-90 shaft standard was to be delayed until the SAE propeller study results were available.

[27 Oct 1941 Memorandum Report EXP-M-52-592-35. Propeller Speed for 3,000 hp Engines], [31 Oct 1941 Memorandum Report EXP-M-52-592-35-2. Propeller Shafts, Single and Dual, for the Single-Speed and Two-Speed Gears for 3,000 hp Engines]

On 26 Nov 1941, WAC representatives R.W. Young, H. Holland and R.E. Johnson met with MatCmd representatives Maj O.R. Carlson, Opie Chenoweth, E.A. Wolfe, R.E. Hoffman and W.W. Woodard at WAC Field. WAC reported on a number of projects it had under way:

A turbosupercharger of its own design that was expected to be ready for delivery by mid-December. Young requested that MatCmd test the unit as soon as possible so that production might be expedited. MatCmd agreed to perform a 100 hour endurance test, but also insisted on a turbine wheel overspeed test to be performed by WAC. Young stated that the overspeed test would be delayed until at least February 1942 as WAC had no facilities for such tests.
Automatic Boost Control. Young inquired as to Air Corps requirements for an automatic boost control. Chenoweth explained that MatCmd thought it essential that all engines be equipped with automatic boost controls equivalent to those on the Rolls-Royce Merlin engines, and that MatCmd hoped these would evolve into single-lever engine power controls. Young requested that MatCmd organize a conference between control and engine manufacturers.
Fuel Injection Schemes. WAC was concentrating on fuel injection system development for both the R-3350 and the X-924 project. The R-3350 system would consist of two pumps, each with 9 pistons; the X-924 injector would have one pump with 22 pistons. WAC did not currently have facilities to test either.
Project X-924. During Arthur Nutt's last visit to WAC Field, he had agreed to submit a new X-924 proposal that would facilitate the Army to procure these engines for both the Army and Navy. MatCmd understood that this proposal was to include an engine with a two-speed supercharger to be used in conjunction with a turbosupercharger, and also a two-speed, two-stage engine. No such proposal(s) had yet arrived. Young stated that WAC was having trouble procuring the large crankcase casting and had resorted to welding fabrication. He was also distressed that there was still controversy regarding propeller size, rpm, reduction gear ratios, and propeller shaft size that was stressed to endure spins of two radians per second.
R-2600 and R-3350 Cold Starting Tests. Young requested that when MatCmd performed these tests that several different priming schemes be evaluated:
1. A standard R-2600-9 engine with a Stromberg PT-13E2 carburetor and standard Army priming system;
2. The same engine with a three-point priming system;
3. The same engine with a Holley 1685H carburetor and three-point priming system;
4. A forth test for which WAC would submit parts (which were at that time unavailable) for full oil circulation to the rocker boxes. Young wanted to check valve timing at various sub-zero temperatures.
Rough-Running R-2600-9 Engines in North American B-25. These engines had apparently been modified with "bottom-filled superchargers" and were running rough between 12,000 and 18,000 ft; WAC was continuing efforts to eliminate this roughness when it received a B-25 assigned to it for experimental work in Caldwell, New Jersey that same week. (Note: the author has never encountered the term "bottom-filled supercharger." Could this refer to an updraft carburetor mounted below the engine centerline?)
R-2600-11 Distribution Characteristics. The Power Plant Laboratory was conducting tests to determine mixture distribution characteristics; WAC could offer no suggestions that might have helped this endeavor. Apparently, R-2600-11 engines installed in Douglas A-20A aircraft were overheating. The A-20B model was improved, but still not acceptable. MatCmd insisted that WAC pursue R-2600 distribution tests.
R-3350 with 2,300 hp Takeoff Rating. WAC was working toward uprating the R-3350 in two steps:
1. Provide 26 revised engines for experimental aircraft as an intermediate action. Only the Army XP-62 (Project MX-88) was affected by this, but affected Navy projects included ones by Boeing, Martin and Douglas. The contemplated first-step changes included:
  - Install C-14B cylinders with cast aluminum heads and rear exhausts in the front cylinder row.
  - Rework C-14B cylinder baffles. (Note: WAC claimed to be pursuing these rear-exhaust cylinders for the front cylinder row, but when B-29 engines actually entered production the front-row cylinders exhausted forward into a large collector right that proved to be a maintenance headache and fire hazard.)
  - Use present type short crankcase main section.
  - Use high-tension ignition systems with supercharged magnetos and distributors on the present engine nose section.
  - Use present supercharger front housing having 18 intake outlets and provision for 9-point dynamic suspension.
  - Use present deep C-18BB oil sump with the pump sandwiched between the crankcase and sump.
  - Use present C-18BB nose pump and sump.
  - Install special two-speed supercharger control
2. The second-step changes would affect Curtiss P-62 and Boeing B-29 airplanes. It was to entail:
  - Install C-14B rear-exhaust cylinders and Siamesed intake pipes to front and rear adjacent cylinders. WAC anticipated these cylinder heads would be forged, but the machine tools necessary to machine the fins might not be available.
  - Install redesigned cylinder baffles and air deflectors with the cowl seal moved forward of the rear cylinder row centerline.
  - Increase crankcase main section length by two inches.
  - Change the ignition system to a Scintilla low-tension type with the generators on the rear cover and low-tension distributors on the nose section.
  - Incorporate a new crankcase front section with the ignition distributors located radially.
  - Revise the supercharger front housing to employ 9 intake pipe outlets and provide for a 6-point dynamic suspension.
  - Provide a new oil sump with integral oil pump and electric pre-oiling pump.
  - Provide a new nose pump and sump.
  - Provide a new two-speed supercharger control for use with the new oil pump.

[6 Dec 1941 Memorandum Report EXP-M-57-503-498. Conference on Development of Experimental WAC Engines. P152660]

(Note: The foregoing meeting report gives the reader a sense of the WAC engine development and production milieu as of late 1941. WAC had way too much on its plate and was doing a poor job of completing projects to Air Corps' satisfaction. At least two other significant concurrent things were not discussed at the meeting:

R-2160 Tornado development was going poorly. Three 14-cylinder T-14 modules would comprise the full-up T-42. One module had completed a 150-hour endurance test on 14 Jun 1940, but the test was anything but official. Numerous rebuilds and part changes were required to get through the test, yet no penalty runs were assessed. Additionally, the T-14 was not making 1/3 the power WAC had promised for the T-42. Despite the T-14 difficulties, WAC had pressed on with building and trying to test the first T-42. This met with disaster when it was installed on the test stand with the throttle connected backwards. When it started, at essentially wide-open throttle, its speed went far over redline and the engine destroyed itself in a second. A T-42 ran successfully for Maj F.O. Carroll on 4 Nov 1940, but much work remained. At the end of 1941, the engine was still unreliable, overweight, underpowered and suffered from poor mixture distribution. The advent of WWII would change WAC's priorities, leading to eventual abandonment of the project.
R-2600 engines had quality problems and were failing in the field. After the XR-2600-1 passed its type test, the Air Corps ordered 467 R-2600-3 engines for $4,857,582.70 on Contract W-535-AC-12061 on 27 Dec 1938. The R-2600-3, although similar to the R-2600-1, had higher takeoff and normal ratings, a two-speed supercharger, a different reduction gear ratio and a different propeller shaft. When the first R-2600-3 came to Wright Field for calibration prior to a type test, its carburetor was too small. WAC personnel at Wright Field putzed around until 6 Jul 1939 but could never get the engine to produce the promised power at altitude. After a trip back to Paterson, the engine returned to Wright Field for another try at the type test, but failed after 19 hours with damaged piston rings, supercharger drive clutch discs, supercharger impeller and diffuser. WAC wanted to make some changes to the engine, but Wright Field refused WAC's request to replace some magnesium parts with aluminum. (WAC was waiting on the required magnesium to become available.) WAC and the Air Corps proceeded with a model test series on several different R-2600 models. These tests were plagued with cylinder barrel corrosion, cylinder hold-down stud breakage, broken and stuck piston rings, excessive oil consumption, excessive oil leakage, gear breakage. Despite all of the development trouble, various R-2600s were being produced and installed in aircraft, which were subsequently being grounded with the same problems that had been evident all along. In April 1941, the new WAC plant in Lockland, Ohio started producing R-2600s. That plant became targets of the FBI and the United States Senate Special Committee Investigating the National Defense Program (aka, Truman Committee) in early April 1943. They were looking into allegations of sabotage, management incompetence, lack of supervision, poor training, falsifying inspections, bribing Government inspectors, and reusing failed parts in new engines. The FBI was unable to prove that sabotage had occurred, and the well-connected WAC managed to get the investigation quashed.

While no one at WAC went to jail over the Lockland debacle, what was clear is that Lockland was an example of how the entire Curtiss-Wright organization did business.)

On 1 Dec 1941, Acting BuAer Chief Capt D.C. Ramsey wrote the Air Corps Chief requesting that WAC X-924 procurement for the Navy be administered by the Air Corps. The Navy wanted services and material as necessary to furnish one engine in accordance with WAC Specification No. N-792 and conduct acceptance tests. The Air Corps was also to conduct a 50-hour development test and furnish five copies of the report covering that test. Further, the Navy wanted an option to purchase two additional engines in accordance with WAC Specification No. 791 and equipped with two-stage superchargers, within 180 days of final acceptance. A similar joint agreement was in place for the Navy to administer Air Corps procurement of the P&WA X-Wasp (R-4360). [1 Dec 1941 Letter][3 Dec 1941 Confidential Technical Instruction CTI-405. RD2442] The Air Corps Contract Section Chief asked the Experimental Engineering Section Chief to request a formal quotation from WAC, which would then lead to Authority for Purchase. As it turned out, the Power Plant Laboratory already had a new WAC Specification No. N-792 that contained information on power and fuel consumption. [11 Dec 1941 Memorandum]

On 29 Dec 1941, Arthur Nutt of WAC met with Mr. Colwell of Thomson Products, and Col Page, Maj Smith, Messers Sadler and Chenoweth at MatCmd. Mr. Nutt was told of plans to purchase five engines for the Air Corps and one for the Navy. Nutt explained that engines that were part of the first contract would not be fitted with fuel injection and would have R-3350-style rear sections. A discussion ensued about the need for a high-powered drive for cabin superchargering. The 60 hp drive WAC had proposed was inadequate as about 130 hp was required under certain circumstances. Maj Smith and Mr. Sadler explained that a drive torque of about 850 lb/in and speeds of 7,500 to 8,250 rpm at normal engine speed would be required. They suggested that since WAC would have to make gearbox changes anyway that they should consider a 200 – 250 hp power takeoff.

Thompson products was interested in building turbosuperchargers or parts thereof, but needed a MatCmd decision on whether WAC or General Electric turbosuperchargers were to be used. The Power Plant Laboratory planned to altitude-test the WAC turbocharger as soon as it arrived. Once the tests were complete, MatCmd would make a decision.

MatCmd informed Arthur Nutt of a need for 600 – 700 hp engines for pursuit twins and wondered whether a single 14-cylinder module from the Tornado engine might be appropriate; Nutt was asked to study this and submit a weight estimate of a 14-cylinder engine suitable for flight.

A discussion about forged cylinder heads for various WAC engines led Nutt to estimate that they would be available for R-1820 engines within 18 months but that they would not be available for R-3350s before 1944. (Note: As it turned out, neither estimate was true.)

(Note: Clearly, WAC was having trouble on several fronts, even before the Japanese bombed Pearl Harbor and before WAC would have to compete with all other manufacturers for materials, machine tools, management talent, engineering talent and workers. It lacked a decent experimental machine shop and had failed to cultivate a vendor network that could help when the workload was high.)

Around 8 Dec 1941, Lt. Col. Carroll began thinking about aircraft that would be suitable for flight testing the XR-4090. Although there is no record that the XR-4090 was ever flight tested, it is noteworthy that P&WA chose this same aircraft type for flight testing its XR-4360. [8 Dec 1941 Inter-Office Memorandum to Chief, Power Plant Laboratory from Chief, Experimental Engineering Section.] On 1 Jan 1942, Power Plant Laboratory Chief Col E.R. Page wrote the Experimental Engineering Section Chief, notifying him that WAC wanted a Vultee A-31 Vengeance for flight test work. The North American B-25 WAC had been promised had not been made available. WAC wanted the airplane for testing R-2600-B, R-3350 and MX-153 engines. [1 Jan 1942 IOM]

On 1 Jan 1942 Power Plant Laboratory Chief Col. Page wrote Experimental Engineering Chief Lt. Col F.O. Carroll complaining that the numerous project titles (C-22, WAC X-924, WAC 3000 and WAC XR-4090) for Project MX-153 had become confusing, and that some related material was classified while other was not. Col. Page requested that since the engine had been designated XR-4090 and Project MX-153 was already established, that all related material be classified "Confidential" and that the Project MX-153 title be changed to "WAC XR-4090 Engine". This took effect on 3 Jan 1942. [1 Jan 1942 IOM. Confidential Status of the WAC 3000 H.P. Air Cooled Engine, Project MX-153]

On 26 Feb 1942, BuAer Cmdr Sheldon B. Spangler wrote the Materiel Division Assistant Chief with comments on the Navy review of WAC Specification No. N-792:

BuAer had insufficient data to judge whether cone galling on SAE No. 60 propeller shafts on a 3,000 hp engine. However, if WAC would guarantee satisfactory shaft and propeller mounting of 4-blade 18-foot propellers weighing 1,200 lb, BuAer wanted that shaft size to remain in the specification. However, a change to SAE No. 70 was recommended if such guarantee was not given.
BuAer was satisfied with any reduction gear ratio acceptable to the Air Corps.
BuAer recommended that the last sentence of paragraph E-24f be reworded to read, "The oil pressure pump shall function properly when its inlet pressure is not more than 5 inHgA below atmospheric pressure when using 1100 oil at 70°C." This was consistent with P&WA X-Wasp specifications.
BuAer was satisfied if the engine were equipped with one Type I-A and one Type II-A drive in accordance with the first paragraph under "3y". However, BuAer recommended that the speed range be changed to 7,500 – 8,600 rpm and that appropriate gear ratios be selected for the first production engines.

Regarding the Air Corps suggestion that the generator and power takeoff drives be grouped under one heading, BuAer wished to retain separate headings. If Air Corps disagreed, BuAer suggested that this question be left to a conference to be held for the revision of Specification AN-9500a (aircraft engines) in the near future. [26 Feb 1942 Letter, BuAer to Air Corps Materiel Division Assistant Chief]

On 28 Mar 1942, Col Page sent an IOM to Propeller Laboratory Chief Lt Col H.H. Couch requesting comments on Navy's position concerning No. 60 versus No. 70 propeller shaft sizes as explained in Navy's 26 Feb 1942 letter paragraph 1. Col Couch stated that the Propeller Laboratory considered the No. 70 shaft size necessary for engines rated at 3,000 hp, such as the WAC R-4090 and P&WA X-4360, but the above-mentioned decision requires that the X-4360 use the No. 60 shaft size. The Propeller Laboratory initiated development of suitable propellers for 3,000 hp class engines in order to maintain interchangeability and intended to require that all engines of this class use the same shaft sizes or the No. 60 extended shaft as depicted on Drawing No. X42G12442. The extra shaft length was needed because of the extremely large propeller blade width and shank sizes to be used on engines of that power and altitude rating. Some propeller manufacturers also needed additional length at the shaft inner end to provide space for control mechanisms. The Propeller Laboratory concurred with BuAer's opinion that shaft sizes should remain the responsibility of engine manufacturers. However, the longer and/or larger shaft sizes would be necessary to function satisfactorily on high-power high-altitude engines.

BuAer was notified of the Propeller Laboratory recommendation the WAC Specification N-792 be amended to provide a No. 70 shaft instead of the original No. 60. Materiel Command wanted to make the No. 70 shaft standard for the 3,000 hp engine class. [28 Mar 1942 IOM. Propeller Shaft Size for WAC R-4090 Engines.]

On 23 Apr 1942, Col F.O. Carroll telegraphed the Materiel Command Engineering Section about WAC commitment to the XR-4090. WAC had decided at that time to develop only a single-speed supercharged engine without two-speed reduction gearing and coaxial propeller shaft. The XR-4090 was to be built to WAC Specification N-790, not N-792, and WAC would not agree to the option calling for two additional engines designated double-row cyclone No. 792C22AA1 and constructed in accordance with WAC specification N-791. Procurement of engines to WAC specification N-792 would require purchase at a later date on a separate contract. The bid invitation had called for one engine, WAC Model No. 792C22AA1 (XR-4090-1); two engines, 792C22AA1 (one designated XR-4090-1, and one designated XR-4090-2 and assigned to BuAer); and three engines, 792C22AA1, equipped with coaxial propellers and two-speed reduction gear (XR-4090-3). Since only single-speed supercharger engines were to be developed, the bid invitation was revised to one 790C22AA1 (XR-4090-1), three 790C22AA1 (two designated XR-4090-1 and one designated XR-4090-2 to be assigned to BuAer). Col Carroll requested that BuAer be advised of these changes and forward comments regarding the proposed bid invitation. [23 Apr 1942 Telegram, Experimental Engineering Section to Engineering Section]

On 28 Apr 1943, Erle Martin, Hamilton Standard Propellers Engineering Manager, wrote the Experimental Engineering Section Chief to report progress on dual-rotation propeller shaft standards being developed by the SAE subcommittee on dual-rotation propeller shafts. Hamilton Standard had been assigned this task at the 17 Oct 1941 meeting. The SAE Nos. 40-60 and 50-70 proposals were substantially in agreement with principal dimensions in the Army Standard with the exception of the increased axial spacing, which was incorporated in the No. 50-70 standard per the agreement reached on 17 October. The No 60-80 shaft was identical to the Army 60-80 standard, and provided two distinct axial propeller spacings. The No. 60-80 standard incorporated a 16" spacing between the propeller rotation planes, and the No. 60L-80 incorporated a 21" spacing. The shaft proposals had been unanimously approved by the SAE subcommittee, and was then being circulated to Propeller Subdivision members; upon their approval, it would be turned over to the Aircraft Engine Division for coordination with engine manufacturers and then to the SAE Standards Committee. SAE Subcommittees P-5 and P-6 had prepared drawings of proposed standards for single and dual rotation propeller hubs and cones; these were in the process of subcommittee member approval. Similarly, drawings of a revised No. 60 and 70 single rotation propeller shafts were being standardized. Revised drawings were to be sent to the Materiel Center. [28 Apr 1943 Letter, Hamilton Standard Propellers to Experimental Engineering Section Chief]

On 16 Jun 1942, Lucas at WAC telegraphed the Materiel Center requesting permission to furnish the Eisemann Magneto Company, of Brooklyn, New York with MX-153 information and data necessary to assist in the design of the ignition system. Col A.E. Jones telegraphed this permission on 18 June. [16 Jun 1942 telegram, WAC to Materiel Center][18 Jun 1942 telegram, Materiel Center to WAC]

An Air Corps summary of experimental engines under development dated 29 Jul 1942 shows four XR-4090 engines under contract W-535-AC-30116, Authority for Purchase 224908. The first of these (a XR-4090-1 for Air Corps) was slated for delivery on 1 Aug 1942. The Navy XR-4090-2 was to be delivered on 15 Oct 1942; the two remaining XR-4090-1 Air Corps engines were to be delivered on 15 Nov 1943 and 1 Jan 1944. A total of $757,000 was allocated for this purchase, of which the Navy paid $141,500 for its XR-4090-2. [Experimental Aircraft Engines, D1-a, 1941-1946. NMUSAF Archives]

(Note: The following is extremely telling of the WAC milieu in late 1943 and for the remainder of WWII.) On 13 Aug 1942, MatCmd Lt W.W. Woodard met with WAC representatives Raymond W. Young, H.C. Hill, E.L Gostin, Allan Chilton and E.C. Sulzman at the Materiel Center. The R-3350-13 engine, which was undergoing a 150-hour model test, had been examined and showed improvements since the last engine teardown at 65 hours. At the last assembly, the main bearings were fitted more tightly with the main bearing clearance being set to 0.001" to 0.003" versus the previous 0.004" to 0.007" clearance. In addition to tightening the main bearing clearance, the rear propeller shaft bearing clearance was tightened and the bearing material changed to silver-lead instead of the previous copper-lead bearing material. These changes were intended to prevent the propeller shaft from assuming the conic whirl that had been experienced in previous engine runs. Changes were also made to the reduction gear assembly to include a spline near the stationary reduction gear hub that would allow the stationary gear to float in a plane perpendicular to the propeller shaft, relieving stress on the reduction gear pinions. In addition, the pinion carrier ring was also redesigned to provide a bearing on both sides of the pinion gears that mate with the stationary reduction gear. The previous design had featured overhung pinion gear and a straddle bearing at the pinion gear shaft rear across the gear that mated with the driving gear shaft. It was believed that this change would greatly improve the 0.350:1 reduction gear.

The model test engine nose section casting cracked through the bolt location near the front sump. This was the second nose failure that occurred during the model test. The nose section casting had been redesigned, and the change would be made available on all Chrysler-built R-3350s. Because of engine requirements for airplanes then under construction, it was necessary to accept some R-3350 engines with old-style nose sections. Some rework of the present nose sections might aid in preventing additional nose section casting failures. However, the design was such that constructive changes were difficult. (Note. R-3350 reduction gears would give trouble until 1944, when it was discovered that the pinion carriers were machined so that the pinions were not concentric to the sun and ring gears.)

During the final hours of testing, the torquemeter gave erroneous readings, the continuation of a trend that had been present throughout the entire model test. It was thought that this difficulty resulted from insufficient torquemeter oil pressure and a two-gear oil pump was planned for the next engine rebuild.

Despite the afore-mentioned problems, the model test engine power section was in exceptionally good condition; the valves had seated properly, and only two or three piston rings were scuffed.

The model test engine was initially built with one loose-fitting and one tight-fitting master rod bearing. Both were silver-lead types. The loose-fitting bearing exhibited a more uniform bearing surface that the tight-fitting bearing. In machining the master rod bearings the edges were tapered between 0.0002" and 0.0004" to relieve the high loading that normally occurred at both sides of the bearing edges. It may have been that the tightly-fitted master rod bearing had not been sufficiently relieved to eliminate the high loading at the bearing edges, whereas the loose-fitting master rod bearing clearances were sufficient to relieve the loading condition.

All rear-section gear case parts were in good condition with the exception of the supercharger drive gears; one tooth was broken from the large drive gear and the pinion teeth were badly pitted. To prevent this condition from reoccurring, WAC was developing a spring-loaded supercharger drive that was to operate in a manner similar to the spring-loaded accessory drives in the R-1820 and R-2600 engines. The spring loaded gear was only located in the supercharger drive train and would not affect other rear-case gears. The front supercharger housing was cracked at the attaching bolt locations and was being redesigned with heavier bosses. (Note. With the advantage of hingsight, we now know that these supercharger section cracks were indicative of secondary crankshaft vibration, which, again, was finally fixed in 1944.)

In view of the model test failures, it was necessary to re-run the test to account for the valve failures at 35 hours, nose section at 56 hours, reduction gear at 65 hours, and supercharger front housing at 150 hours. MatCmd thought it imperative that the R-3350-13 accumulate as much time as possible prior to Boeing XB-29 and Consolidated XB-32 flight tests. Because of this expediency, the engine was being rebuilt for the 150-hour penalty test without all of the latest parts. While WAC planned to rework the nose section and correct problems with the torquemeter, it was doubtful that the supercharger gear train could be rebuilt with spring drives.

Despite the subtle hints, MatCmd thought the engine to be "free from design and material defects and expected it would be completely satisfactory for Army Air Forces acceptance and use." (Note. If they had only know what was to come!)

Young and Hill showed layouts for a proposed axial-flow cooling fan mounted ahead of the cylinders on the nose section. This fan featured adjustable vanes in front of the fan blades to permit proper cooling. The cooling fan was intended for use between 30,000 and 40,000 feet with fully open vanes and the vanes would close at lower altitudes to reduce cooling fan power requirements.

Allan Chilton and R.W. Young showed a similar fan layout for the XR-4090. This scheme featured an elaborate set of bevel gears for guide vane actuation where the R-3350 cooling fan used wires and pulleys.

E.L. Gostin discussed R-3350-13 delivery requirements, stating that the WAC delivery schedule far exceeded the airframers' needs.

The engine delivery schedule was obtained by Goetin from memoranda by the WAC West Coast representative T.F. Bergmann. Because engines to be delivered would require modification, Goetin was informed that the engine production schedule could be revised to conform with airframers' requirements, plus those engines required as spares for the XB-29 and XB-32 airplanes.

The need for a higher torque rating for R-2600-15 generator drives was discussed with Young and Sulzman, who were briefed on the Martin XB-33A electrical requirements. Sulzman agreed to examine the R-2600-15 design to determine what changes could be made to provide power takeoffs that met the requirements.

Because of the increasing number of oil seal failures in all WAC accessory drives, WAC was requested to obtain a more positive seal for all accessory drives, particularly for generators and starters. Young said WAC was testing seals made of Morganite (a carbon-based seal material trade name), but that few had shown better characteristics than the seals in common usage.

Young stated that a recent R-1820-G200 piston failure during a piston ring test was unrelated to the piston ring, but rather appeared to have originated at the pin retainer. [28 Aug 1942 Memorandum Report EXP=M-57-503-700. Conference at WAC Aeronautical Corporation on R-3350-13 Engine and Other Experimental Developments of the WAC Aeronautical Corporation.]

On 2 Sep 1942, WAC wrote Experimental Engineering Chief Col F.O. Carroll regarding the 31 Oct 1941 Memorandum Report EXP-M-52-592-35-2 on 3,000 hp two-speed propeller shaft sizes. WAC regretted taking nearly 10 months to reply on the subject of controlling propellers driven by two-speed reduction gears. WAC blamed the delay on the "complexity of the problem and necessity for awaiting the completion of the final coordinated design for two-speed reduction gears to be used on the WAC C-22, 3000-hp engines." The latest design was then being fabricated but the problem of propeller governors and their locations could not be determined until the gear shifting mechanism characteristics had been thoroughly determined by test. WAC was therefore "unable to fully comply" but would do so at the earliest possible date when more information was available. WAC requested that a decision about two-speed reduction gear control be delayed. [2 Sep 1942 Letter, WAC to Col F.O. Caroll]

On 28 Sep 1942, Col Carroll telegraphed WAC requesting a R-4090 mockup for display purposes. WAC replied the next day saying that there was only one partial mockup, which was currently being used for test equipment fitting and not suitable for display purposes; hence WAC was unwilling to comply. [28 Sep 1942 telegram, MatCmd to WAC][29 Sep 1942 telegram, WAC to MatCmd]

Destination	Engines
	2nd Airplane	3rd Airplane	4th Airplane
R-3350-13, -21	26 Aug 1942	12 Oct 1942	1 Jan 1943
Boeing	2 Sep 1942	12 Oct 1942	1 Jan 1943
3 at Seattle	9 Sep 1942	12 Oct 1942	1 Jan 1943
1 at Wichita	14 Sep 1942	12 Oct 1942	1 Jan 1943
R-3350-13, -21	1 Sep 1942	1 Nov 1942	1 Jan 1943
Consolidated	15 Sep 1942	1 Nov 1942	1 Jan 1943
3 at San Diego	15 Sep 1942	1 Nov 1942	1 Jan 1943
1 at Ft. Wort	15 Sep 1942	1 Nov 1942	1 Jan 1943
R-3350-35	1 Sep 1942	15 Jan 1943	15 Jan 1943
Lockheed	1 Sep 1942	15 Jan 1943	15 Jan 1943
All at Burbank	1 Sep 1942	15 Jan 1943	15 Jan 1943
	1 Sep 1942	15 Jan 1943	15 Jan 1943
Notes: 1) Spare engines not included. 2) Miscellaneous "X" projects not scheduled. 3) 2,500 hp not included.

As can be seen from the above timelines, the Cyclone 22 was behind schedule at the end of 1942. There is no reason to imagine the picture ever improved. Wright, whose management and engineering teams were always shallow, was overwhelmed with the events of WWII. Where prudent advice for any project was to "under promise and over deliver," WAC's policy was just the opposite. Between R-3350 development problems and the difficulties involved with ramping up production to meet war demands, a number of experimental projects languished; the Cyclone 22 was among them. I have found no indication that any aircraft manufacturer ever seriously considered the Cyclone 22 to power a design. At least one XR-4090 was delivered, appearing in a U.S. Air Force Museum engine inventory compiled by Robert Casari in 1958; that engine is no longer there, nor is it among the National Air and Space Museum collection, where a number of other engines from that inventory now reside. Like the Chrysler XI-2220-11 at the Walter P. Chrysler Museum and WAC XR-2160-3 at the New Jersey Hall of Fame and Museum, it was probably scrapped during one of the U.S. Air Force Museum's 1960-era house cleanings. Sadly, unlike the XI-2220 and XR-2160, the XR-4090 does not appear to have been rescued from the scrap yard by a Walter Soplata.

I am hopeful that additional primary information on the Cyclone 22 will be discovered. The Arthur Nutt paper collection at the National Air and Space Museum Archives is a candidate, as is the collection of Curtiss-Wright material at the New Jersey Aviation Hall of Fame and Museum.

The following references are from the U.S. National Archives at College Park, Maryland.
RD2442 = Record Group 342, RD Number 2442. The RD (Research and Development) numbering is peculiar to this record group.
P152660, et al. = Record Group 342, Finding Aid UD, Entry 1002-A, Box 5, Power Plant Laboratory Microfilmed Memorandum Reports Reel 15, Frame 2660.
Case History of the R-2600 Engine Project (Record Group 18 Entry 22 Box 45).
ase History of the R-2600 Engine Project Lockland Investigation (Record Group 18 Entry 22 Box 45).

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