Continental XO-1430 Development
Part 13: 1 Jul 1939 to 31 Dec 1939
by Kimble D. McCutcheon
Published 5 Nov 2025; Revised 7 Nov 2025

11 Jul 1939. CMC Design Engineer James W. Kinnucan and salesman Arthur W. Wild met MatCmd civilian engineer Ford L. Prescott at Wright Field. Kinnucan requested information on the permissible XO-1430-3 vibration limits. This direct-drive engine was to be coupled to a right-angle reduction gear via an extension shaft, and the reduction gear was coupled to the propeller via another extension shaft. The combination had been studied in great detail so as to prevent destructive torsional vibration. Since the system behaved as three torsional systems, many vibration modes had to be accounted for. Kinnucan said some type of damper would be required on each extension shaft, along with the crankshaft damper in the engine. MatCmd stated that a Specification No. 95-28184 provision gave special consideration to unusual designs such as extension shafts with or without remote gearboxes; therefore torsional limits could not be specified without detailed vibration analysis. This matter was to be studied around 14 Jul 1939 with CMC engineers and University of Michigan vibration expert Professor Jesse Ormondroyd.

The new crankshaft had been magnafluxed using new magnaflux equipment purchased by CMC. Due to the high flux density possible with this equipment indications were discovered that were not cracks yet the Air Corps Inspector at CMC wanted to have the crankshaft magnafluxed by MatCmd, so it would be forwarded to MatCmd in the near future.

Kinnucan said that the remaining five forked connecting rods should be reconditioned since some galling had occurred in points between the connecting rod shanks and bolt bosses. It would be necessary to regrind these rods by an amount not exceeding 0.010" and provide connecting rod bearings to fit the oversize rods. Magnaflux inspection had not indicated any signs of imminent failure and the regrinding process should make them equivalent to new rods. These rods had been equipped with several rod bearing sets during engine development and in some cases it was necessary to grind of the bolt boss ends to provide proper bearing crush. In such cases the holes in the connecting rod big ends were no longer round and would be completely restored by regrinding them oversize.

Kinnucan presented drawings depicting two forged piston designs; one featured a waffled head underside and the other had ribs running in one direction across the piston head. The ALCOA representative had said the waffled construction was undesirable since it provided more places for fatigue to start, and mentioned  a case in which repeated failures were experienced until the cross-ribs were removed, after which no more failures occurred. It was agreed that the plain ribbed type would be more desirable. The piston incorporated a new feature in which the lower piston pin boss portion was not attached to the piston skirt; ALCOA said this eliminated piston skirt distortion; Prescott objected that this construction weakened the piston pin boss underside, causing the inertia force to be carried by a strap that was completely separated from the piston skirt. These piston pin boss straps were to be appropriately strengthened and the design pushed as rapidly as possible using both the twin-cylinder and XO-1430 engines.

In studying the new accessory bearing diaphragm it was discovered that a material savings accrued by fabricating it as a separate piece attached at the crankcase front. This design did not clamp the diaphragm between the crankcase and reduction gear housing, thus eliminating an oil joint. A very simple oiling system had been worked out that was better than the previous design. The group studied layouts for a proposed engine mount fabricated almost entirely fro high-strength steel tubing. This design was lighter and stronger than the previously-proposed aluminum mount plate design that was to have been clamped in the joint between the reduction gear housing and crankcase. Kinnucan said that further design work was to be done and this would be discussed more fully at a later date. [USNARA RG342 RD1676 503-106 O-1430 390621-400828 Vol. 4. 15 Jul 1939 Memorandum Report E-57-285-108, Conference with Representatives of Continental Motors Corporation on XO-1430-3 Engine. 7 – 9.]

14 Jul 1939. Kinnucan and Prescott studied a revised forged piston drawing omitting the previously-proposed strap-type piston pin boss. It was unnecessary to add pin boss material for weight control (weight control was the process of making piston weights equal for engine balancing). Instead, metal could be removed from the piston skirt inner diameter at the skirt base or the piston skirt base could be shortened. As to the material used, Mr. Kennedy of the Materials Branch stated that both modified Y-alloy and Low-X had essentially the same properties in forged condition. Both were in service use and both seemed to be performing equally well.

The front accessory diaphragm layout revealed three large dowels intended to maintain front accessory bushing alignment. Beside each dowel hole was a suitable puller hole tapped into the diaphragm. Prescott thought this diaphragm design very carefully worked out and predicted it would be more satisfactory than the previous arrangement. The revised oiling system in this diaphragm was considerably simpler than the previously-used scheme, which was clamped between the crankcase and reduction gear housing.

The right-angle reduction gearbox now incorporated Lanchester-type friction dampers. Kinnucan stated that University of Michigan Professor Ormandroyd thought this damper, in conjunction with the present quill shaft in the engine, would satisfactorily maintain low torsional amplitude in the entire engine and reduction gear system. An oil pump pad on the right-angle gearbox could be used to obtain torsional data at the gearbox. In addition, the torsiometer could be attached to the starter mount and also to the special torsiometer pad on the new-design accessory housing; these should furnish torsional vibration data at all vital points in the system. Kinnucan stated that according to Specification 95-28184 that a two extension shafts with the right-angle gearbox constituted a "special system" in which the vibration amplitudes would be based upon satisfactory stress ranges in the various elastic system parts. Once torsional vibration data were collected and stress calculations performed, it could readily be determined if torsional vibration was within satisfactory limits.

Kinnucan expected the twin-cylinder test engine to be operational about 25 Aug 1939; CMC was expediting parts fabrication. In order to expedite higher engine output, CMC offered to loan MatCmd a cylinder assembly with masked bushings and spark plugs like those found satisfactory during the XO-1430-1 50-hr development test. CMC also offered a finished piston with the revised piston ring setup. These parts were being forwarded to MatCmd.

A new crankcase incorporating all desired changes was being fabricated as rapidly as possible. However, this crankcase would not incorporate the newest engine mount scheme. The cross-mounting type with aluminum alloy cross members clamped between the crankcase front and rear and the corresponding accessory housings had been found too heavy and resulted in a new design with fabricated steel members. More details were to follow on 17 July for MatCmd consideration. The crankcase then in fabrication, along with all new crankcases, would provide for the new mount scheme.  [USNARA RG342 RD1676 503-106 O-1430 390621-400828 Vol. 4. 18 Jul 1939 Memorandum Report E-57-285-109, XO-1430-3 Engine. 10 – 12.]

25 Jul 1939. Wild met Prescott at Wright Field and noted that CMC had previously requested information on the maximum sustained climb angle in order to determine how to properly scavenge the XO-1430-3 cam housings. The MatCmd Aircraft Branch had said it was about 30°, but that 40° would be better. Wild thought a scavenge pump for the cam housing rear ends would be necessary to ensure they were not flooded with oil during steep climbs. Dives would only last a few seconds, which meant the forward cam housings would not require separate scavenging. CMC planned a revised XO-1430-3 installation drawing to further these discussions.

Wild stated that the wooden model delivery was held up pending final decision on the mount type to be used; once that was settled the model would be available in a short time. Wild had brought drawings covering the proposed steel tubing engine mount structure that reflected Kinnucan's recent MatCmd visit. These were discussed and Prescott offered minor suggestions on members required to transmit engine thrust to the engine mount. These drawings also showed newly-designed detachable crankcase lifting eyes that would facilitate engine handling.

Prescott asked about the time required to secure forged pistons for MatCmd's single-cylinder test engine; Wild was to reply after his return to Detroit and furnish a quotation for six pistons. Wild, after his return to Detroit, was to also estimate when the XO-1430-1 would resume testing. Wild had brought with him the valve gear that had been formerly used on MatCmd's single-cylinder test engine when it was at CMC; this was loaned to MatCmd in connection with the high-output single-cylinder test then being conducted. The data obtained thus far on the XO-1430 single-cylinder engine was discussed. MatCmd planned to install an oil jet for piston cooling. Wild left with a copy of the data with hopes of furnishing MatCmd with a 1,800 hp 12-cylinder engine. Piston rings CMC had loaned to MatCmd had insufficient side clearance; Wild was to obtain information on the proper side clearance and forward this to MatCmd. [USNARA RG342 RD1676 503-106 O-1430 390621-400828 Vol. 4. 29 Jul 1939 Memorandum Report E-57-225-110, XO-1430-3 Engine. 51 – 53.]

3 Aug 1939. Wild met Prescott at Wright Field and confirmed that the piston CMC had lent MatCmd for single-cylinder performance studies did not have the proper ring side clearance. These values should have been 0.008" for the top ring and 0.003" for the oil ring. MatCmd planned to grind the rings to achieve the proper clearance. CMC had promised the twin-cylinder test engine would be in operation by 25 Aug 1939, but the labor required to build the engine had been underestimated and it would be impossible to complete the engine before 1 Sep 1939.

The XO-1430-1 rebuild was progressing and expected to be complete on 4 Sep 1939; at that time testing under Contract W-535-AC-12741 would continue. The XO-1430-1 wood model constructed to mock-up XO-1430-1, -3 and -5 models would be complete by 4 Sep 1939, at which time it would be delivered to MatCmd. Numerous layout drawings covering the right-angle drive, extension shafts, XO-1430-3 engine, and the new tubular engine mount structure were ready for MatCmd approval. Wild requested the presence of an Air Corps representative early in the week of 6 Aug 1939. Regarding the release of the XO-1430-3 project, Wild stated that the required copies of CMC Specification No. 1002, XO-1430-3 installation drawing, and extension shaft assembly layouts including the right-angle gearbox would be transmitted to MatCmd for official release. [USNARA RG342 RD1676 503-106 O-1430 390621-400828 Vol. 4. 12 Aug 1939 Memorandum Report E-57-285-111, Conference with Representative of Continental Motors Corporation, Detroit, Michigan, on XO-1430-3 Engine. 65 - 66]

7 – 8 Aug 1939. Prescott traveled to CMC to review several XO-1430-3 design elements in preparation for formal MatCmd approval. The 19-lb Lanchester-type vibration damper to be used in the right-angle gearbox would reduce torsional vibration to about ±0.6°. The damper mass for a ±1.0° amplitude was about 12 lb. CMC planned to increase the damper radius to secure the maximum effect from its mass. This damper design employed three steel plates, four moulded friction-material plates, and was loaded to about 50 psi. CMC was trying to reduce the unit loading to ensure long friction-surface life. The springs were designed to provide for 0.063" wear and still maintain the damper in optimal operating condition; this wear level was considered adequate for the damper's life. However, if it were necessary to compensate for wear, 0.063" thick steel plates could be added. Damper lubrication and cooling required a continuous oil flow, which was accomplished by an oil slinger on the second bevel gear that threw oil continuously into the hollow shaft on which the damper was mounted. This oil flowed into the damper through holes with standpipes. CMC was to furnish MatCmd a complete layout covering the right-angle drive and damper for release in connection with Contract W-535-AC-12994.

Kinnucan stated that the present cylinder cooling jacket was too expensive and proposed a new design in which the jacket body was machined from seamless tubing. Forged coolant entrance and exit bosses would be welded to the jacket. CMC had studied several cambox scavenge pump designs. The most practical was a simple centrifugal pump operating below the oil level in the cambox; this would function correctly regardless of engine rotation direction. The rigid metal cambox scavenge lines were also to be changed to rubber hoses, which would be less expansive and not prone to fatigue cracking.

Professor Ormondroyd visited Detroit and spent the evening of 7 August discussing XO-1430-3 torsional vibration. He said that the analysis was nearly done and that a report would be available on 15 Aug 1939. Four vibration modes were expected with this system and both the present quill-shaft damper and the newly-designed Lanchester extension-shaft dampers would be required to adequately damp the entire engine-gearbox-propeller system. Ormondroyd brought with him a report covering his complete XO-1430-1 analysis based on torsional vibration records taken with the MIT torsiometer. Studying this data had established the engine damping in order to predict the XO-1430-3 maximum amplitudes. This analysis showed that the forth vibration mode gave a 385 Hz natural frequency with a mode just aft of the No. 4 Main bearing. In this vibration form both the quill shaft damper and Lanchester damper would be very effective. He emphasized that this vibration form was dangerous because a relatively small amplitude was capable of causing crankshaft fatigue failure.

The right-angle gearbox would ideally be mounted in the airplane using three rubber bushings; two of these would be as far apart as possible on the gearbox outboard side. The third would preferably be mounted on a light steel tubing torque arm attached to the gearbox and placed directly opposite the gear-type universal joint on the engine nose. In this way minimum universal joint deflection would be obtained and the very large low-speed propeller torque would be carried over a considerable distance by the torque arm, thereby reducing the force necessary to take this torque.

Kinnucan Shafting Patents

US2300293A	US2306960A

The extension shaft and coupling designs were reviewed. Prescott stated that it was preferable that the extension shaft be made in one piece with the ends upset and flanged rather than attached to the steel tubing by means of welding or riveting. While this construction was slightly more expensive, it would be lighter. The gear-type coupling was made so that by merely sliding the external coupling member away from the extension shaft, the shaft could be lifted out without moving either the gearbox or the engine. The entire extension shaft and coupling layout was to be incorporated in the right-angle drive drawing and submitted to MatCmd for official release. Kinnucan stated that the XO-1430-3 drawings would be sent to MatCmd as soon as they were completed.

CMC was building a new test laboratory at Muskegon, Michigan that would consolidate the industrial and aircraft engine manufacturing at Muskegon and also provide a location that permitted engine operation without interference from Detroit city officials. CMC had found that even operating a small A-50 engine at night produced complaints from residents. CMC believed it essential to move the plant out of Detroit in order to permit unhampered test stand operation for high-powered engine development. [USNARA RG342 P031014. 12 Aug 1939 Memorandum Report E-57-285-112, XO-1430-3 Engines - Contract W-535-AC-12994.]

18 Aug 1939. Prescott visited CMC to meet with Professor Ormondroyd, who had data on the XO-1430-3 torsional vibration amplitude and stresses. In the second vibration mode two periods had excessive stress but very low frequency, making it difficult to design a vibration damper. However, he thought the present damper designs could be modified sufficiently to address this vibration mode. In the forth vibration mode a node existed just aft of the No. 4 main bearing, and this amplitude was also too great to permit engine operation in the 7-1/2 order period without damping. He proposed that the front and rear crankshaft counterweights be redesigned to incorporate pendulum dampers to address this vibration period. It was feasible to construct these dampers without adding any weight by modifying the existing counterweights to accommodate the pendulum damper. Ormondroyd intended to investigate the XO-1430-1 torsional records in order to predict the vibration severity in this engine.

The cambox scavenge pump design was reviewed and it was found that the intake connection could be made using a short tube held at both ends with a gland and synthetic rubber ring. The pump design appeared to be satisfactory and Prescott thought it would work extremely well with the engine design and in any attitude due to aircraft maneuvering. Also reviewed were the front accessory diaphragm layouts; this diaphragm was to be attached to the crankcase front. The design eliminated a joint between the reduction gear rear housing and crankcase and also gave a slight weight reduction.

Right-angle gearbox layouts were almost ready for release with only minor details yet to be worked out. During CMC's planned move to Muskegon the engineering force would move last and CMC expected the XO-1430-3 design and drafting work would be complete before the move. The twin-cylinder test engine parts were being manufactured in the Detroit plant and would be ready for fabrication within a few days; engine operation would be delayed past the promised 25 Aug 1939 date. [USNARA RG342 RD1676 503-106 O-1430 390621-400828 Vol. 4. 23 Aug 1939 Memorandum Report E-57-285-113, XO-1430-3 Engine. 57 – 58.]

26 Sep 1939. Kinnucan and Wild met with Prescott at Wright Field where Kinnucan inquired if a 3" or 4" airflow orifice would be available for testing the XO-1430-3 and the O-1430 type twin-cylinder engine. MatCmd agreed to investigate and report on this request. These orifices were not available at MatCmd and it was suggested that CMC obtain castings from MatCmd patterns and machine them. A search was made for the patterns, but it appeared that these were in the Thompson Grinder Company plant in Springfield, Ohio, who was to be contacted regarding the castings.

Kinnucan inquired whether it would be permissible to omit hydraulic propeller control on the XO-1430-3. He stated that it was extremely difficult to conduct oil at 600 psi through the hollow shafts to the propeller from the propeller governor in the reduction gear housing. This matter was discussed with Aircraft Laboratory personnel who believed it satisfactory to omit hydraulic control provisions in view of the weight savings made possible by the use of electric controllable propellers. Provisions for electric controllable propellers would be required, but not for the hydraulic control.

Prescott advised Kinnucan that MatCmd personnel were having extreme difficulty securing spark plugs that would stand the high output required during MatCmd single-cylinder tests. Kinnucan stated that the CMC twin-cylinder engine would be in operation in approximately 10 days, at which time testing would proceed at the CMC plant in an effort to improve the spark plug situation in conjunction with Wright Field tests. [USNARA RG342 RD1676 503-106 O-1430 390621-400828 Vol. 4. 2 Oct 1939 Memorandum Report 57-503-14, Conference with Representatives of Continental Motors Corporation on the XO-1430-3 and Twin-Cylinder Tests. 69 – 70.]

2 Oct 1939. Tests were conducted to determine the suitability of the O-1430 type cylinder for high output using non-detonating fuels. Power Plant Fuel No. 628 was found superior to Power Plant Fuel No. 625. It also appeared that Power Plant Fuel No. 566 was superior to No. 625. It also appeared that the O-1430 type cylinder was capable of operation at outputs considerably in excess if the rated output when using non-detonating fuels.

Curve No. 1	Curve No. 2	Curve No. 3

The carburetor air supply system was arranged so that the air could be heated before going to the carburetor by steam coils within the surge tank. This allowed the air temperature to be raised to approximately 215°F. The air supply was taken from the Ingersoll Rand air compressor in the PPL basement. Early in the test the engine output was low in relation to the carburetor air pressure; this was because a carburetor with a 1-13/16" venturi had been used. A carburetor with a 2-1/16" venturi was installed and the engine output returned to normal. This fact should be taken in to account with the Power Plant Fuel No. 566 test, which was run with the 1-13/16" venturi. Consequently the Curve No. 2 carburetor air pressure for a given output was in excess of the proper value for comparison with Curve No. 3.

Test engineers attempted to hold the air temperature to two values corresponding to each carburetor air pressure. One value was based on 85°F air supplied to a supercharger having an adiabatic efficiency of 75%. The air temperature was calculated on this basis to correspond to the use of a geared supercharger with no air cooling. The second temperature set was obtained by calculations for 85°F but assuming one-half of the temperature rise absorbed by an intercooler. The temperatures obtained were shown on Curve No. 1 corresponding to the carburetor air temperature. Curve No. 2 was based on these air temperatures. Power Plant Fuel No. 566 was used with a 30° spark advance, the mixture control set for maximum power, the coolant-out temperature was 250°F and the rpm 3,000. A complete curve up to the compressor capacity limit was obtained along air temperature Curve B from Curve No. 1. The corresponding record for air temperature "A" from Curve No. 1 was carried as high as the air temperature heating coil would permit. In order to check the power lost due to heating the intake air the heating coil was used as a cooling coil by circulating water through it and a point was obtained at maximum air compressor output and 77°F. It was found on this basis that approximately 22 psi imep was lost in raising the air temperature from 77°F to 201°F. Curve No. 2 plots imep versus absolute carburetor air pressure and includes a partial specific fuel consumption record.

Curve No. 3 was run with the carburetor air temperature ranging from 80°F to 90°F. The imep versus carburetor air pressure for 100 octane fuel was included as a check on the results obtained with Power Plant Fuels 625 and 628. Power Plant Fuel 625 appeared to reach a limit at approximately 375 psi imep. This was obtained with a 70 inHgA carburetor air pressure. Power Plant Fuel No. 628 was found capable of operation up to the air compressor capacity limit, which was approximately 76 inHgA. The fuel limit was not reached during these tests. The specific fuel consumptions corresponding to the foregoing tests were included in Curve No. 3. These indicate Power Plant Fuels 566 and 628 were superior in the matter of maximum power fuel consumption. The highest output attempted during these tests was about 404 psi imep at 76 inHgA carburetor air pressure.

Fuels 566 and 628 limits were not reached because the engine crankshaft failed while testing Power Plant Fuel No. 625; the engine output at the time was considerably below what the engine had previously produced. The crankshaft break appeared to be a typical fatigue failure at the crank cheek between the main crank and forward balancing mechanism crank. The crankcase was damaged beyond repair. While the tests were incomplete they were useful until a new test engine could be obtained.

Power Plant Fuel No. 625 was in use when the failure occurred. About 12 hrs after the failure the engine was disassembled and the cylinder bore was found entirely coated with a very heavy rust deposit. This was attributed to the Power Plant Fuel No. 625 alcohol content, which probably absorbed the atmospheric moisture that attacked the cylinder. This would be a serious defect in a fuel for high-output engines since the rust formed would act as an abrasive that would attack the piston rings. In this respect fuels 566 and 628 were superior. As soon as a new test engine was available MatCmd expected to continue the tests and reach the high-output limit for the O-1430 type cylinder. [USNARA RG342 RD1676 503-106 O-1430 390621-400828 Vol. 4. 12 Oct 1939 Memorandum Report 57-5030-18, High Output Test on Single Cylinder O-1430 Type Engine. 71 – 76.]

11 Oct 1939. Kinnucan met Prescott at Wright Field and reported that the strike at the Bohn Bearing Plant had been settled and that bearings required for the XO-1430-1 and XO-1430-3 would be delivered in a few days. The twin-cylinder test engine was expected to be in operation around 14 October and the XO-1430-3-1 could be again operational about 23 October. CMC requested that a MatCmd representative visit Detroit around 20 October to review the remaining XO-1430-3 layouts and drawings in preparation for final release.

Kinnucan had, at MatCmd's request, presented two proposals for engines in the 1,800 hp to 2,400 hp range. The limited time for preparation had not permitted a thorough analysis of problems expected in connection with these designs. (Could these be the first mention of the IV-1430?)

Kinnucan and Prescott examined MatCmd's single-cylinder test engine cylinder. The forged piston, after having delivered 408 psi imep, was in good condition. The damaged cylinder was MatCmd's property, which meant that the cylinder loaned by CMC had not been damaged. [USNARA RG342 RD1676 503-106 O-1430 390621-400828 Vol. 4. 14 Oct 1939 Memorandum Report 57-503-20, Conference with Representative of Continental Motors Corporation, on the XO-1430-3 Engine. 77 – 78]

23 Oct 1939. Kinnucan met Prescott at Wright Field and reviewed the new XO-1430-3 rear accessory housing and gear case. A method of simplifying the gear train driving the oil and coolant pumps was discussed, but it was insufficiently advantageous to warrant the change in rotation direction that would be required by the oil pump; the coolant pump could not be reversed because the pump outlet had insufficient clearance in the reverse location. Kinnucan stated that the gears comprising the propeller drive train had mocked-up and that sufficient clearance existed for its assembly. It was decided that the present layout was preferable even though it required one extra gear.

The right-angle drive gearing and housing were reviewed. The bearing layout recommended by the bearing manufacturers was satisfactory; the Lanchester damper's introduction had caused the bearings to be moved further apart, resulting in a radial load reduction at the large bearings, making it possible to use smaller bearings, which reduced weight by about 6 lb. The proposed scheme for mounting the right-angle drive gearcase in the airplane consisted of three points with the Lord mounts spaced well apart in the high-speed drive shaft direction by means of a long arm; this did not require rubber bushings of excessive size. The bushings that took the torque reaction could be closer together because the torque was much lower than their limit. Kinnucan showed a proposed reversible oil pump layout for use on the right-angle drive gear housing. This pump was arranged so that the pump body could be removed and turned over in assembly, providing opposite rotation for the right-angle gearbox on either side of the airplane.

Kinnucan brought with him a revised XO-1430 layout with the propeller shaft center line lowered 10", which placed it at the center of a circle enclosing the engine. This layout was transmitted to the Aircraft Laboratory, where design studies had been under way and it was found advantageous to make the offset 9" instead of 10" and reduce the nose length by 4". This change was considered entirely feasible in view of the fact that the provision for hydromatic propeller operation was not required. Kinnucan stated that a revised layout incorporating these changes would be forwarded to MatCmd. [USNARA RG342 RD1676 503-106 O-1430 390621-400828 Vol. 4. 26 Oct 1939 Memorandum Report EXP-M-57-503-26, Conference with Representative of Continental Motors Corporation, on the XO-1430-3 Engine. 79 – 80]

24 Nov 1939. Prescott visited CMC where Kinnucan asked how the $492.66 credit reported in the 28 Feb 1939 Progress Report was to be handled as this did not appear in the invitation to bid  on replacement parts covering the final XO-1430-1 operating period; Prescott stated the matter was being handled through an Amendment to be executed upon receipt of the returned invitation after execution by CMC. Kinnucan stated that the last invitation was being held until this matter had been settled and requested further information on how to proceed. Investigation showed that the invitation should be executed and returned to MatCmd after which the Amendment would be prepared covering the credit.

Air Corps Inspector Robert P. Triggs requested information about accountability for the replacement parts on hand at CMC but not installed on engines covered by contracts. It had been necessary to make up to four accountability transfers between the Government and CMC when these parts were installed on engines under test. Both CMC and Triggs wanted to eliminate the interchange of paperwork that accounted for these parts. This matter was taken up with Inspection Branch personnel who reported that a decision would be obtained and transmitted directly to the Air Corps Representative located at CMC.

The twin-cylinder engine fabricated in connection with Contract W-535-AC-12741 had been run in and was ready to conduct the tests called for under the subject contract. These tests were to begin about 27 Nov 1939. Tear-down inspection of this engine was being conducted at the time of Prescott's visit. The XO-1430-1 engine, upon which further tests were to be conducted in connection with Contract W-535-AC-12741, was being fabricated; the last item required for its final assembly was 12 forged pistons being fabricated at the Muskegon plant. Breakage of a special cutter used to mill the piston inside, as well as a piston defect that had been discovered, caused six pistons to be lost. However 12 new pistons were to be available on 8 December, at which time XO-1430-1 assembly and testing resumption were expected. The extra crankcase was being machined to have as a spare in case additional trouble emerged. This crankcase, together with other spare parts then on hand at CMC, were expected to enable test completion without excessive delay.

The wood XO-1430 type engine model was complete except parts such as the reduction gear housing, on which final decision had not been made, especially in reference to the mounting method. Right-angle gear drive drawings were reviewed and Kinnucan said that an effort would be made to incorporate a bearing for the large bevel gear that would not be loaded as heavily as the bearing shown in the present layout. In this connection, it was brought out that the bearing now specified was a special bearing of limited availability whereas a standard bearing, weighting slightly more, could be obtained from several sources. MatCmd was keen on eliminating the single-source bearing.

The revised XO-1430-1 and XO-1430-3 rear section was reviewed and a further gear train simplification evolved along with a coolant pump assembly having a much-improved bearing installation and a more positive seal against oil and coolant leakage. In view of the excellent service experienced by steel parts running directly in magnesium or aluminum bearings, the rear-section bushings were to be omitted, resulting in cost and weight reductions. It was pointed out that the only engine bearing that had not given trouble were these steel-on-magnesium or –aluminum ones, which was surprising since all available bearing metals had been tried, including copper-lead and steel-backed.

Layouts of the redesigned cylinder heads with relocated spark plugs were reviewed. Prescott objected that the first proposal decreased the coolant to the spark plug bosses. Kinnucan stated that additional layouts would be made to determine the best spark plug position so that accessibility and cooling were both addressed and shielded plugs could be used.

Kinnucan said that moving the CMC Engineering Department into temporary quarters in a building near the Test Laboratory had caused some disruption and interruption in the engine program. The Experimental Engineering Department had been settled and that work was then going forward at an acceptable rate. No machine shop facilities were available at the CMC plant but this did not interfere with the rapid prosecution of projects on hand since several excellent job shops were available that could do work more rapidly than the CMC tool room. New parts produced at Muskegon could be transported by truck in five hours; this did not present serious test delays. A new XO-1430-3 test stand was being temporarily erected in Detroit and a test would be conducted at that location rather than at Muskegon. [USNARA RG342 RD1676 503-106 O-1430 390621-400828 Vol. 4. 26 Nov 1939 Memorandum Report EXP-M-57-503-36, Contracts W-535-AC-8131 and W-535-AC-12593 - XO-1430-1 and XO-1430-3 Engines. 81 - 83]

7 Dec 1939. Triggs reported that the twin-cylinder test engine had been run-in for 20:10 hrs of which about 10 hrs were under its own power. When first run with pressure-boosted carburetor air the engine produced no more power than under no-boost conditions. It was retimed after which the power increased with increases in carburetor air boost. With a carburetor air temperature of 175°F and 8 inHgG, the engine developed 147 hp at 3,000 rpm, but it also appeared to be detonating; the gasoline may not have been the specified grade. The carburetor air temperature was dropped to 86°F and the boost increased in 1 inHgG increments to 14 inHgG where the engine developed 182 hp at 3,000 rpm. At this point both exhaust pipes on the test stand failed and had to be repaired. At this point the air flow, coolant flow, fuel weighing, and various pressure and temperature instruments had not been set up. No official runs had been made. [USNARA RG342 RD1676 503-106 O-1430 390621-400828 Vol. 4. 84.]

15 Dec 1939. Triggs reported that the twin-cylinder test engine had been run-in for 29:55 hrs. The tachometer had been registering about 25% too high due to having the wrong gear on the dynamometer shaft. Therefore the power reported on 7 December was too high by about 25%. The gear had been replaced and a flowmeter had been placed in the oil-in line; an oil scale had not yet been installed. The air preheaters were insulated and the carburetor air-in temperature had been raised to 205°F. Runs were made at 4, 8 and 12 inHgG to examine the mixture distribution between the two cylinders by monitoring cylinder temperature rise; they were found to be unequal. Power increased with boost and specific fuel consumption seemed to decrease with boost. Still, no official runs had been made. The O-1430-1 was being assembled and was expected to run on Saturday, 16 Dec 1939. [USNARA RG342 RD1676 503-106 O-1430 390621-400828 Vol. 4. 85.]

15 Dec 1939 Progress Report. No O-1430-1 running had been done during this period. However, the engine had been partially assembled and a new-part run-in was expected within the next few days. Time run under the performance Contract W-535-AC-12594 was 42:12 hrs total, 6:58 hrs motoring, 35:15 hrs under power and 2:12 hrs above 160 bmep. Accumulated engine time was 696:02 hrs total, 182:50 hrs motoring, 513:12 hrs under power and 107:34 hrs endurance under Contract W-535-AC-8131.

Twin-Cylinder Engine Performance Test Contract W-535-AC-12741. The engine was assembled and initially run-in during November. After the first run-in period, numerous engine parts and test equipment changes were made. The dynamometer coupling clearance was increased to prevent universal joint binding and the engine was realigned with the dynamometer. The primary and secondary balance weights were incorrectly installed due to errors in marking the gears. Several other minor changes were made to facilitate engine operation. After 4:30 hrs running under its own power (13:50 hrs total) the rear main roller bearing failed due to insufficient roller end play in the races after thermal expansion. The proper bearings had been ordered, but due to an error by the bearing manufacturer, the wrong bearings were shipped and installed in the engine. The failure caused no serious damage and the bearings were replaced.

After a run-in period up to 3,000 rpm and 14 inHgG, the dynamometer and fuel flow meters were calibrated prior to testing power versus mixture ratio; curves at 3,075 rpm and 200°F carburetor air inlet temperature were run at 4, 8, and 12 inHgG. Power versus spark advance was determined at 3,075 rpm and 8 inHgG. As these were preliminary runs to determine engine operation, no official data was submitted. Twin-cylinder engine time to date was 31:55 hrs total, 13:10 hrs motoring, 18:45 hrs under power and 0.04 hrs above 160 bmep.

Converting Wood Model – Contract W-535-AC-12298 – PO 39-3952. The model was about 50% complete and was expected to be finished by 1 Jan 1940, at which time it was to be shipped to Bolling Field for the Air Corps Demonstration.

XO-1430-3 Right-Angle Drive Engine – Contract W-535-AC-12594. Progress on checking the new accessory housing, drive, oil and coolant pump drawings, was 60% complete; major parts were expected to be released within two weeks. The right-angle drive unit was about 80% detailed; checking was being concentrated on the long-lead-time items. A new camshaft housing, Dwg #504043, had been released for use in connection with the new tubular mount. This housing differed from the original by the addition of ribs and relocation of the doweling to eliminate the cracking experienced on previous cam boxes. This housing could also be used with the plate mounting by removing 0.25" from the cylinder contact face. No additional spares were used during this period, but a cost recapitulation was attached. [USNARA RG342 RD1676 503-106 O-1430 390621-400828 Vol. 4. 95 – 99.]

22 Dec 1939. Triggs reported that the O-1430-1 had been run for 9:55 hrs. The first run was for 4:45 hrs of which the first hour was motoring after which the engine was fired and run on the 600 hp propeller load curve up to 3,000 rpm. The front case was then disassembled for inspection, which was satisfactory. The engine was then reassembled and run at 3,000 rpm from 0 to 14 inHgG for 5:10 hrs of which at least 25 minutes were at 1,000 hp. It was then again disassembled for inspection. The twin-cylinder test engine had run 35:30 hrs. A fuel-air ratio indicator measuring exhaust gas temperature was installed to facilitate correcting the mixture distribution between the two cylinders. No official runs had been made. [USNARA RG342 RD1676 503-106 O-1430 390621-400828 Vol. 4. 86.]

20 Dec 1939. Kinnucan showed Prescott a layout depicting the revised spark plug position intended to increase spark plug accessibility and to enable using all plug types. In this layout the spark plug in the crankshaft plane was retained at 45° but the angle relative to the horizontal plane was 15°. Spark plugs from adjacent cylinders were parallel and about 1.5" apart, providing sufficient clearance under the cam boxes to permit ready removal and replacement. This new spark plug placement would probably require a special spark plug wrench in order to remove both plugs from the same engine side. The new position did not interfere with spark plug boss cooling and appeared to be satisfactory from the ignition, clearance and accessibility standpoints.

Kinnucan had a layout showing a revised gear train for driving the XO-1430-3 oil and coolant pumps. The simplified gear train provided a hub on the accessory drive gear bracket that formed a bearing support for a combination spur/bevel gear. By this means two bevel gears and a troublesome stationary shaft were eliminated. The pumps were driven via a single cross-shaft passing through the accessory case.

Kinnucan said that an attempt would be made during XO-1430-1 testing on Contract W-535-AC-12741 to determine the effect of exhaust back pressure on engine performance. This information would be valuable in connection with proposed high-performance engines then under consideration. The information would also be of value in determining turbosupercharger-based altitude performance. He asked what was the maximum exhaust back pressure expected in service; MatCmd personnel said that exhaust back pressure as high as 17 inHgG has been used experimentally in Wright Field laboratories and that further consideration included the possibility of pressures as high as 25 psi. Kinnucan said that CMC's exhaust system was incapable of furnishing such back pressure as all exhausts were carried to a central exhaust tunnel; he thought 8 inHgG might be possible with present equipment. The cracked cam boxes experienced during XO-1430-1 testing had been explained and measures to eliminate this trouble was now available. The XO-1430-3 wood model was nearing completion and was to be shipped around 2 Jan 1940 for use in an exhibit prepared for Congressional Members and others interested in Air Corps equipment status. [USNARA RG342 RD1676 503-106 O-1430 390621-400828 Vol. 4. 12 Dec 1939 Memorandum Report EXP-M-57-506-45, XO-1430-3 engine. 87 – 88.]

Curve No. 17

31 Dec 1939 Progress Report. On 18 Dec 1939, the reassembled XO-1430-1 engine, with forged pistons, redesigned crankcase, and redesigned front accessory drive housing, was run-in for 4:45 hrs on a 600 hp propeller load curve to 3,000 rpm. After an inspection of various accessory drive gears at the engine front, which were all in perfect condition, the engine was reassembled for further operation. A satisfactory run-in commenced to 3,000 rpm and 1,000 hp except for a spark plug that blew out of its insert; it was believed that the copper gasket at the plug end burned out due to improper plug seating, which had allowed it to become loose. No damage resulted to the insert or cylinder head and a new spark plug was installed.

The stepped studs that had been installed in the right cam housing after re-tapping their holes stopped the cam housing oil leak. Complete engine inspection showed the No. 3R piston pin and piston pin hole scored; this was thought caused by insufficient oil being thrown onto this piston. The pin and piston were touched up and running continued with the same parts.

A short run was made at 3,000 rpm and 800 hp to check the exhaust pressure setup in the exhaust tunnel, and after minor adjustments, curves of power versus exhaust back pressure at 800 hp and 1,000 hp at 3,000 rpm were run. Curve Sheet No. 17 shows these test results. The 800 hp curve was run in order to obtain data in a cruising condition.

The engine front end was again inspected and all parts were in perfect condition. Apparently the new diaphragm design, in conjunction with the lead-bronze bearings and ensuring proper gear location was working very satisfactorily. Engine run time to date was as follows:

Engine time was 712:39 hrs total, 185:35 hrs motoring, 527:04 hrs under power, 120:41 hrs above 160 bmep and 107:34 hrs endurance time under Contract W-535-AC-8141.

Twin-Cylinder Test Engine – Contract W-535-AC-12741. The test setup had presented significant difficulty and several changes were necessary to achieve proper operation. Coolant flow to the left and right cylinders was determined using orifices that were calibrated using city water to obtain 20 gpm flow for a 20 inH₂0 pressure drop; the orifice diameter was 0.812". The blow-by orifice was calibrated to give an airflow of 130 ft³/hr using a 28 inH₂0 pressure drop across the 0.140" diameter orifice. A mixture ration curve at 3,000 rpm, 4 inHgG manifold pressure and 210°F carburetor air temperature was run. The setup as originally configured did not provide equal fuel distribution to both cylinders and a tube with its top edge cut at an angle was set in the manifold pointing toward the left cylinder. By regulating this tube's angle it was hoped to obtain equal mixture distribution. A friction power curve from 1,500 rpm to 3,000 rpm at 0, 10, and 20 inHgG was run.

An engine inspection revealed that all parts were in good condition except for the right cam and rocker arm roller were badly scored. A new roller was installed and the cam and rocker arm were stoned and polished. It was thought this damage was caused by a plugged camshaft oil hole. A pipe plug on the right cylinder head was leaking coolant and a new plug was installed. Twin-cylinder engine time to date was 44.35 hrs total, 18:20 hrs motoring and 26:15 hrs firing.

Converting Wood Model – Contract W-535-AC-12298 – PO 39-3952. The XO-1430-3 wood model was complete and ready for shipment to Bolling Field for the Air Corps Demonstration. After the Demonstration it was to be returned to Detroit and inspected by an Air Corps Inspector.

XO-1430-3 Right-Angle Drive Engine – Contract W-535-AC-12594. New tubular mountings for both the XO-1430-1 and XO-1430-3 engines had been designed and were being detailed. The accessory housing and drive, including the new oil and coolant pumps, were 80% checked and the major parts were being released. The right-angle drive unit was completely detailed and its drawings were being checked.

Engineering. Layouts had been made changing the XO-1430-1 cylinder head angular spark plug location to facilitate accessibility. Detail drawings were in process and would be released as soon as available. It was expected to have these new cylinder heads incorporated into cylinder assembles by 28 Feb 1940. Details for 8.5:1 and 7.5:1 compression-ratio pistons for the twin-cylinder engine had been made and released. Spare parts, together with Government liability, were attached [USNARA RG342 RD1676 503-106 O-1430 390621-400828 Vol. 4. 99 – 110.]

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