Continental XO-1430 Development
Part 12: 1 Jan 1939 to 30 Jun 1939
by Kimble D. McCutcheon
Published 1 Nov 2025

Right-Angle Drive Patent US 2,342,672

6 Jan 1939. CMC engineer James W. Kinnucan and salesman Arthur W. Wild met with Power Plant Laboratory (PPL) civilian engineers Opie Chenoweth and Ford L. Prescott at Wright Field. Wild produced a letter giving prices for one to five XO-1430-3 engines in response to a 5 Jan 1939 telephone conversation. These were in addition to the type test XO-1430-3 for which procurement authority had been initiated. The letter was not made a matter of record because the accessory drive arrangement would not be finalized until 10 Jan 1939. Wild was asked to return on that date to meet with Douglas Aircraft Company and MatCmd personnel, and to be prepared to furnish quotations and delivery dates on 1 to 5 XO-1430-3 engines with optional accessory arrangements as a basis for the final decision in this matter. Chenoweth stated that the PPL was disturbed by the delivery dates because the airplane in which the first two XO-1430-3 engines would be used was required to be in the air by January 1940. On this basis the XO-1430-3 engine would necessarily have to be at least through a 50-hr endurance test and the engines delivered by 30 Sep 1939. He asked CMC to submit a revised plan for XO-1430-1 and XO-1430-3 testing, which was to include the tentative schedule for XO-1430-1 development testing, a plan for testing the XO-1430-3 on procurement and a plan for delivering the first to of any XO-1430-3 engines to be purchased after the current procurement.

Kinnucan and Wild stated that the XO-1430-3 military rating was 1,150 hp for the present procurement, but that development work over the next two years was expected to raise the military rating to 1,250 hp. MatCmd observed that it was essential to immediately construct a twin-cylinder test engine and initiate development that would raise the normal and emergency rating of these engines. Kinnucan stated that the tentative plans were to fabricate a steel crankcase that would accept as many standard XO-1430-1 parts as possible. Kinnucan stated that the scheme to deliver clean oil via the accessory drive shaft fitted with a central standpipe had not yet been implemented, but would be incorporated into an engine under test in the near future; the plan to install an auxiliary oil gallery had been temporarily abandoned until the accessory drive shaft oil cleaner scheme was explored.

It was suggested that the torquemeter pistons themselves could serve as control valves, making torquemeter operation automatic and bi-directional. Kinnucan said that the torquemeter cylinder heads could be quickly removed and plates installed with rubber discs to render the torquemeter inoperative in case it malfunctioned.

Kinnucan asked if it were permissible to secure takeoff and emergency ratings by means of the turbosupercharger rather than by making the supercharger gear ratio high enough to obtain this rating without the turbosupercharger. MatCmd said this was the preferable method to obtain high engine ratings and that available turbosuperchargers could provide a 5-minute military rting at 20,000 – 25,000 ft without difficulty. [USNARA RG342 P031063. 11 Jan 1939 Memorandum Report E-57-285-94, Conference with Representatives of Continental Motors Corp., on the XO-1430-1 and -3 Engines.]

11 Jan 1939. Chenoweth confirmed a conference at Wright Field between CMC's Kinnucan and Wild, and MatCmd's Engineering Section Chief Maj J.P. Richter, PPL representative Capt Charles A. Bassett and Chenoweth. Capt Bassett explained the general plan for expeditiously obtaining engines for an attack bomber proposed by the Chief of the Air Corps that was to fly within one year. This had been discussed with CMC on 6 January; CMC followed up with three letters explaining its plans. The first involved an additional sum of $10,000.00 for an accessory gearbox to be mounted on the XO-1430-3 right-angle drive; this was based on a request by Douglas Aircraft. Maj Richter explained that an engine with such an accessory drive was undesirable and that the basic XO-1430-3 should be considered.

PPL representatives suggested that the first XO-1430-1 be retained at CMC for continued running after the 50-hr development test without the right-angle drive or shafts simply as a means of accelerating the basic engine development, obtaining higher outputs, and exploring the structural limitations. PPL also suggested that the first engine be subjected to approximately 50 hrs endurance running since it would probably be necessary to deliver the engine for aircraft installation prior to type test completion. CMC suggested that immediately after 50-hr development test completion the parts unaffected by the right-angle drive be released for fabrication, but that the right-angle drive and shafts not be released until the 50-hr XO-1430-3 endurance test was complete.

Maj Richter emphasized the necessity of obtaining a right-angle drive mockup for Douglas Aircraft as soon as possible; in one of its letters CMC had submitted a quotation for modernizing this mockup within 60 days after receipt of the XO-1430-1 at Wright Field. Although only three XO-1430-3 engines (one for the 50-hr endurance test and two for Douglas) had initially been considered, Maj Richter changed the number to five to provide Douglas an immediate mockup tht would later serve as a spare and also a spare type-test engine. He further directed that a 50-hr minimum would be required on the XO-1430-3 prior to aircraft installation and that CMC should quote on 20-hr increments of additional testing if time permitted. CMC submitted the following Authority for Purchase No. 149840 schedule:

This schedule involved 40 hrs minimum running, but that was extended to 50 hrs and instead of shipping the engine to Wright Field on 10 May 1939, it was to be retained by CMC. It was further decided that the 15 May 1939 date was not to be considered since the XO-1430-1 was to continue running without the right-angle drive. Wild stated that the 15 Aug 1939 date would still hold for the 50-hr test since the running would be accomplished at CMC and the additional 10 hrs could be run during the same period than if the engine were shipped to Wright Field for 40 hrs running. [USNARA RG342 P031060. 18 Jan 1939 Memorandum Report E-57-285-95, Conference with Representatives of Continental Motors Corporation on Problems in Connection with the O-1430 Engine Development.]

27 – 28 Jan 1939. Prescott traveled to CMC and met with Kinnucan to review XO-1430-3 engine details. Kinnucan produced drawings showing a new rear accessory housing with a modified accessory arrangement. The coolant pump was moved from the engine bottom to the accessory gearbox side, thus reducing the engine's height. Another height improvement was to redesign the intake manifold using a flat elliptical duct section instead of the present round one. These two changes reduced the engine's height from 33" to 22". Kinnucan pointed out that it was necessary to omit the fuel injector drive to achieve this height reduction. Prescott had no objection to these measures since the use of a non-icing pressure carburetor was planned; he advised CMC to get MatCmd approval before any parts based on fuel injector drive omission were fabricated.

Layouts for the proposed right-angle drive gear housing included a one-piece housing with bevel gear bearing housings fitting into openings in the gear housing large enough to permit assembling the gears through the openings. Further examination revealed that this construction would yield a very weak housing, especially in the smallest section between the two openings. Prescott suggested making layouts with the housing split on a horizontal center line to provide for assembly without the large openings. CMC stated that the new rear accessory gearbox would delay fabrication of the five engines according to the schedule defined by Authority for Purchase No. 149840.

On 29 January, University of Michigan Professor of Engineering Mechanics Jesse Ormondroyd, a vibration and instrumentation expert, came to CMC to discuss XO-1430-3 torsional vibration. Ormondroyd was briefed on several points that had been unclear to him and was to proceed with a complete XO-1430-3 torsional vibration analysis. He pointed out that the right-angle gear drive polar moment of inertial was of considerable magnitude and being placed within the elastic drive system from the engine to the propeller would introduce the possibility of a two-node vibration. He stated that all possible vibration modes would be considered in his analysis and that he would report to CMC on 1 Feb 1939.

Prescott examined the proposed XO-1430-3 test setup, but advised Kinnucan to contact those in charge or MatCmd engine testing before test setup final details were completed. CMC personnel stated that test stand noise was a problem and that every precaution was being taken to ensure noise would be minimized. The test house section surrounding the propeller was to be circular thereby eliminating impulses due to blade passage near the floor, ceiling or walls. Although the present requirement was for a 12.5-foot propeller, provision was being made for 17-foot propellers.

Kinnucan and Prescott discussed right-angle gearbox mounting on both the test stand and airplane. If the engine was mounted using rubber vibration isolation, it appeared unnecessary to also rubber-mount the gearbox. In fact such mounting might be quite undesirable in view of the severe operating conditions imposed on the gear-type universal joints at the gearbox driving and driven shafts; introduction of rubber mounts at this point would vitally affect the drive's torsional characteristics because of the two drives being at right angles. Ormondroyd's analysis would consider this. Kinnucan said that the reduction gears had not yet been returned from Gleason Gear Works and that completion of the tests under way at Gleason was delayed by failure of the test apparatus. However, the gears would be returned to CMC and XO-1430-1 testing would resume on 2 Feb 1939. [USNARA RG342 P031057. 2 Feb 1939 Memorandum Report E-57-285-96, XO-1430-3 Engine.]

Reduction Gear Patent US 2,253,977

9 Feb 1939. H.N. Kitchen of Farrel-Birmingham Company, Buffalo, New York met with Prescott at Wright Field and asked about the objection to the original XO-1430-1 herringbone reduction gears. Investigation had shown that these gears failed because of misalignment under operating conditions caused by the plain bearing clearances. A spur-gear set made to replace the herringbone gears immediately showed tooth loading on one side of the gears. Since it was impossible to redesign the old reduction gear to incorporate rolling-element bearings with no clearance, a different reduction gear type similar to those used in large radial engines was chosen. [USNARA RG342 P10447. 13 Feb 1939 Memorandum Report E-57-4047-1, Conference with Representative of Farrell-Birmingham Company on XO-1430-1 Reduction Gears.]

10 Feb 1939. Kinnucan, Tilley and Wild met with Prescott at Wright Field and reported that XO-1430-1 operation with the new reduction gear was much improved over the herringbone and spur gears. Endwise vibration that had previously been objectionable was absent. The reduction gear parts were in excellent condition after run-in. Oil flow through the engine was reduced by about 10 lb/min. Extremely satisfactory bevel pinion lubrication was achieved by a lubricant stream to the closing gear and pinion teeth. Some difficulty had been encountered because of the gear housing filling with oil; the oil drain holes from the reduction gear housing to the crankcase sump had been closed to accurately measure oil flow through the reduction gear, but this did not affect normal engine operation and was to be addressed by temporarily increasing the reduction gear housing scavenge pump volume for flow measurement. Kinnucan stated that a 5-hr run-in period up to approximately half power was followed by 3 hrs up to rated power with examination after the 5-hr period. This running included 0.5 hr at 3,000 rpm and 900 hp, 0.5 hr at 3,000 rpm and 1,007 hp. The boost was 14.0 inHgG, which was the lowest yet required to make rated power. The previous boost had been 14.8 inHgG. No explanation other than the increased reduction gear efficiency explained the boost reduction.

Kinnucan said that a new propeller shaft had been made with a portion immediately behind the reduction gear spider splines was erroneously ground undersize by about 0.031" and wondered if this would be acceptable if a steel sleeve were shrunk over this shaft portion and ground to the standard size so that the shaft was interchangeable with other shafts. Prescott opined that the section in question was considerably stronger than the adjacent section from which the splines were cut. He suggested sending a letter and marked-up blueprint requesting a deviation to MatCmd.

Kinnucan had drawings for the proposed twin-cylinder test engine in which the cam housing front and rear were identical to the XO-1430-1 cam housing so that the accessories used on the cam housing rear could also be mounted on the twin-cylinder engine. This was acceptable to Prescott. The Eaton Manufacturing Company had proposed a number of valve and valve seat material changes, which were claimed to be improvements over those then in use. Prescott observed that completing the XO-1430-1 50-hr development test was a vital step in developing the XO-1430-3 engine and that no changes that might cause delay should be incorporated at this time. The new valve materials were acceptable for the twin-cylinder engine.

During this visit Mr. Collbohn of Douglas Aircraft was also at Wright Field and came to offer suggestions on XO-1430-3 accessory placement. MatCmd countered that nothing should be done to the XO-1430-3 that might jeopardize modified 50-hr type test completion. The Engineering Section's opinion on placing a number of accessories on the right-angle gear box had not changed. A proposed arrangement of engine, coolant radiator, oil cooler, gas and oil tanks showed that the wing would be filled with equipment. It also showed the turbo compressor mounted in the fuselage and the carburetor removed from the engine rear to a point about three feet to one side. Prescott pointed out that this distance was excessive and that the mixture after the carburetor should not travel more than 12" before entering the supercharger. Douglas Aircraft wanted the coolant flow to be changed so that both coolant-in and coolant-out connections were at the engine propeller end. Prescott objected that it was necessary to place the coolant-in connection opposite the coolant-out connection for each cylinder bank in order to ensure uniform coolant flow through all six cylinders. Consequently, it would be necessary to conduct one coolant line to the engine rear. The coolant pump location on the rear accessory gearbox side was probably as convenient as any.

Kinnucan stated that the new reduction gear arrangement incorporating a bearing diaphragm sandwiched between the crankcase front flange and reduction gear housing flange appeared to be a vast improvement over the previous design, making drive gear shaft bearing alignment easier. Two or three alternative methods for reducing bearing loads or increasing bearing life were being studied and parts were being made to substitute for the present parts if difficulty was encountered during the XO-1430-1 50-hr test.

Professor J. Ormondroyd was still working on XO-1430-3 vibration characteristics and expected to be finished around 13 Feb 1939. Since XO-1430-1 operation with the new reduction gear was much improved, CMC anticipated that the engine's development test should proceed with very little delay. [USNARA RG342 P031054. 14 Feb 1939 Memorandum Report E-57-285-97, Conference with Representatives of Continental Motors Corporation on XO-1430-1 and -3 Engines.]

1 – 2 Mar 1939. Kinnucan and Wild met Prescott at Wright Field and reported that after completing 15.5 hrs test time on the XO-1430-1 with its new reduction gears the engine was torn down and examined. All parts were in excellent condition except for a small 0.312" long crack in the forward crank cheek adjacent to the No. 4 main bearing. The crack was located approximately 20° away from the vertical centerline on the outward crank cheek portion and extended from the lightening hole radially outward, apparently starting at a sharp corner. The crankshaft was carefully magnafluxed with MatCmd's equipment and several very small magnaflux indications were observed. Also observed in a forward main bearing journal was a helical indication that did not appear to be a crack because the magnaflux liquid did not squeeze out of the crack when the current was on. The indication was stoned in an effort to discover whether it was a deep defect and a portion of the indication disappeared. It was concluded that the indication was a small inclusion that had been present from the time the forging was made. This indication's location was not in a location where failure due to torsional fatigue would have been expected and did not start or end in the fillet. The small crack in the crank cheek was also carefully analyzed from the standpoint of torsional fatigue; since it was in an area where the stress was extremely low it was probable that the indication had been present for a long time but was unobserved. It was decided that none of these defects appeared to indicate shaft failure and the shaft would again be installed and run for 5 hrs after which the crankshaft would be reexamined and the crack's length and appearance compared to the earlier indications. Prescott suggested a new crankshaft be immediately fabricated from a forging that was on hand; this new shaft was to be available in about four weeks. It was further decided that when the present crankshaft was reassembled in an engine a torsiometer would be fitted and the crankshaft torsional characteristics with the new reduction gear investigated before further engine running.

Kinnucan stated that CMC would expedite machining of the spare crankshaft and also the torsional vibration study. The additional 5 hrs running was expected about 8 or 9 March. He promised to telephone MatCmd with results immediately upon completion of the study. He said that engine operation was the best it had ever been and that 1,000 hp was now obtained with 13.6 inHgG boost; fuel consumption at rated power was 0.524 lb/hp/hr and the engine seemed to operate without distress under rated power conditions at 0.500 lb/hp/hr.

Professor Ormondroyd had released a preliminary torsional vibration study report that analyzed three vibration modes; however, it was noted that the vibration mode with a node near the center main bearing had not yet been considered. He further stated that this vibration be studied in connection with other possible vibration modes. The discussion established the basic advantage in a flat engine in that the one order vibration was completely cancelled out for all vibration modes. This meant that the entire range from 1/2-order to 1-1/2 order period was completely free of torsional excitation.

Kinnucan showed twin-cylinder test engine drawings in which it was proposed to balance the engine using rotating weights within the crankcase. CMC planned to build this engine in connection with the proposed additional five-engine procurement.

The group discussed XO-1430-1 installation problems with Maj Green of the Aircraft Branch. It appeared the hopes of installing flat engines in the wings of high-performance aircraft could not be fulfilled. For two 1,000-hp engines the aircraft gross weight should not exceed 18,000 lb and probably 16,000 lb as studies progressed. For four 1,000 hp engines the gross weight should be 35,000 – 40,000 lb. It would be necessary to mount these engines in a wing with a chord of at least 12 feet. He suggested studying an installation where the engine was separated from the reduction gear by a short extension shaft with the engine mounted behind the front spar and the reduction gear in front. [USNARA RG342 P031051. 6 Mar 1939 Memorandum Report E-57-285-98, Conference with Representatives of Continental Motors on XO-1430-1 Engine Development Test.]

8 – 9 Mar 1939. Tilley and Wild visited Prescott at Wright Field and reported that XO-1430-1 torsiometer tests were under way in preparation for an additional 5-hr running period after which the engine would be torn down and the small crankshaft crack discovered during the last tear-down inspected. Results of these tests reached MatCmd on 9 March; no large-amplitude vibration had been observed at any speed and the maximum amplitude at propeller load through 3,000 rpm and 1,000 hp was approximately ±0.75°, whereas the permissible amplitude was ±1.0°. No evidence of 2-node vibration was observed, suggesting the friction damper across the quill shaft was working. MatCmd stated that Procurement Authority had been initiated covering replacement parts up to 15 February and also covering the right-angle drive for one complete engine with options covering up to four additional engines, all the XO-1430-3 type. These prices were based on quotations from a 9 Jan 1939 CMC letter.

Wild stated that the XO-1430-1 would be inspected immediately upon completion of the next 5-hr period, reassembled if parts were satisfactory, and started on the remaining 30 hrs endurance running, which was hoped to be complete by 18 Mar 1939. He said that MatCmd would be contacted as soon as the crankshaft condition was ascertained. [USNARA RG342 P031049. 10 Mar 1939 Memorandum Report E-57-285-99, Conference with Representatives of Continental Motors Corporation on XO-1430-1 and -3 Engines.]

10 Mar 1939. In a Wright Field meeting, Wild advised Prescott that CMC had run 2.5 hrs of the 5-hr period on 9 March. However, magneto difficulties stopped the testing early. New magneto parts were on hand and CMC expected testing would resume on 10 March, with completion of the 5-hr period, tear-down, crankshaft inspection and preparation for completing 50 hrs development testing. Crankshaft examination and photography was to be accomplished on 11 March and that the engine would be operational on Monday morning, 13 March.

CMC had decided it feasible to rebuild the XO-1430-1 mockup with a detachable nose section and right-angle drive reduction gear end so that it could be assembled with XO-1430-3 parts to build XO-1430-1, XO-1430-3 or XO-1430-5 mockups. The XO-1430-5 was a XO-1430-1 with an extension shaft and thrust bearing support. This would make the mockup available for any of the three forms in which the engine was expected to be used.

Prescott said that the final engine mount form should be settled since it was impractical to mount the engine in an airplane with the rail-type engine mount then being used for development. The right-angle gearbox mounting scheme should consider a torque arm in order to absorb the large gearbox torque around the propeller shaft axis. Wild stated that this would be studied and work started on a wood model in order to complete this task as soon as possible. [USNARA RG342 P031047. 13 Mar 1939 Memorandum Report E-57-285-100, Conference on March 10, 1939 with Mr. Wild of Continental Motors Corporation Regarding XO-1430-1.]

13 – 14 Mar 1939. Prescott visited CMC and learned that after the last 5-hr run a cylinder had been removed and the crankshaft examined; the 0.312" crack previously reported had opened up considerably although outright crankshaft failure had not occurred. The engine was torn down for complete examination, which revealed that the crack had progressed in the spiral direction around the crankpin and stopped at the oil hole. The crack appeared to be a typical torsional fatigue failure and would have normally been attributed to the oil hole weakening the crankpin except for the good fortune of detecting the crack's beginning before the 5-hr run. The crankshaft section from the crank cheek end to the oil hole was cut out for examination and photographs were made of the crack itself and the fractured piece that had been removed. The photographs clearly showed the crack's progress. A photograph of the broken piece showed that the fatigue started at a sharp corner in the counterbore in the crankpin lightening hole end. This counterbore was made with a sharp-pointed tool whereas it should have been made with a tool with a definite corner radius on the cutter. Calculations made on the sharp corner showed that the stress concentration caused by the missing fillet was up to 2.8 times the stress that would otherwise been present. The examination indicated that the missing fillet and lack of rounded corners on the sharp crank cheek and lightening hole edges could fully explain the crankshaft failure.

The crankshaft drawing showed a radius but it was not dimensioned. Future crankshafts were to call for a 0.125" fillet radius in the counterbore. The drawing also called for breaking all sharp corners 0.016" to 0.031"; this had not been done, making the sharp corners a contributing factor. As an added precaution it was proposed that the chamfer at the crankpin and main bearing ends would be decreased by 0.125" to provide additional strength at the lightening hole ends. While this would slightly increase the crankshaft weight, it was believed worthwhile in view of the failure that had occurred.

CMC was to prepare a new crankshaft drawing covering all the above changes, with copies to MatCmd for future release; in the meantime a new crankshaft was in work at CMC in which the suggested changes would be incorporated. Two previously used crankshafts that were candidates for further use were examined; crankshaft No. 1 was not in a condition for continued testing and crankshaft No. 2 had been reconditioned after its No. 1 connecting rod bearing had failed and was in condition for further use. Approximately three weeks would elapse before the new crankshaft was ready and in the meantime the No. 2 crankshaft could be fitted with a special undersize No. 1 crankpin bearing and running resumed in about a week.

It was decided to install this shaft that already had 19:09 hrs endurance time to its credit and further investigate the torsional vibration characteristics, especially with regard to the 2-node vibration responsible for stressing the shaft at its failure point immediately forward on No. 4 main journal. An old rear section would be fitted with an extension shaft from the crankshaft rear through the accessory housing rear in order to obtain torsional vibration data directly at the crankshaft rear; previous torsional vibration records had been taken at the crankshaft front since both single-node and 2-node vibration was present at the front with a possible amplitude reduction of 10% - 20%. Even allowing for a 50% amplitude increase at the shaft rear, the previous records indicated that both single-node and 2-node vibration were well within Air Corps specifications. This suggested that the failure was not due to excessive torsional vibration, but the presence of concentrated stress due to a missing fillet at the failure point. A possible contributing factor was that this No. 3 crankshaft had been through one very severe wreck due to the herringbone reduction gear failure, and other minor wrecks during its service life. The three crankshafts used in official development testing were as follows:

Crankshaft No. 1 had no counterbores at the lightening hole ends; consequently it was not weakened by any sharp corners.
Crankshaft No. 2 was found to have very good fillets although not as large as could be desired.
Crankshaft No. 3 had square corners at the crank cheek counterbore ends, which failed in test.

From the above data it was concluded the Crankshaft No. 2 after rounding the sharp corners and polishing the counterbore fillets should be in good condition for development test continuation. As a matter of safety, it was decided that a small damper would be designed especially to eliminate 2-node vibration.

Right-Angle Gearbox, Oil Pump Patents US2278110A and US2305012A

CMC was tasked with preparing drawings for an engine mount suitable for airplane installation. CMC pointed out that the new rear accessory section design must be finalized in order to proceed with the XO-1430-1 mockup. The new gearbox incorporated a coolant pump drive on the left side with a vacuum pump drive immediately above it. The hydraulic pump drive was on the right side above a redesigned oil pump and Cuno oil filter. This gearbox followed the same general lines as the one in use, but the accessories were moved to new locations to reduce engine height; this gearbox was substantially the same as shown in the most recent installation drawing No. L-161-HP-6 recently furnished to MatCmd. The final layout form was to be submitted to MatCmd for release in connection with the XO-1430-3 for which Procurement Authority had been initiated. The first new gearbox was to incorporate provisions for measuring torsional vibration at the crankshaft rear end through a bevel gear pair. The fuel injector drive provision had been omitted in order to minimize engine height. The latest pressure carburetor would be used to overcome possible carburetor icing, making fuel injection unnecessary for wing installations. The lack of a commercial fuel injection system was also a factor in omitting the injector drive.

CMC proposed a new oil pressure regulator that provided a simple relief so that cold oil pressure was not appreciably higher than hot oil pressure. This regulator used a differential piston that eliminated the effect of Cuno filter pressure drop and held oil pressure at a predetermined value. CMC was tasked to provide MatCmd with torsiometer records taken at the crankshaft rear as soon as available. Revised engine mount and rear accessory section drawings were also to be provided to MatCmd as soon as available. [USNARA RG342 P031042. 18 Mar 1939 Memorandum Report E-57-285-101, XO-1430-1 Engine.]

30 Mar 1939. Wild met Prescott at Wright Field to report that about 4 hrs into an XO-1430-1 10-hr run, the dynamometer load had dropped slightly and then recovered. The engine was immediately shut down and examined to find the ball bearing on the high-speed supercharger shaft had hailed causing damage to the supercharger impeller and drive shaft. These parts were being replaced from stock and testing was to resume for the remaining 6 hrs on 3 April. CMC planned to then examine the engine and if in good condition, run the final 10-hr period to complete the 50-hr development test. Wild wanted to again check the torsional vibration characteristics before running the next 10-hr period using the MIT torsiometer on 3 or 4 April. [USNARA RG342 P031041. 3 Apr 1939 Memorandum Report E-57-285-102, Conference of March 30, 1939, with Mr. Wild of Continental Motors Corporation Regarding 50-Hour Development Test of XO-1430-1 Engine.]

14 – 15 Apr 1939. Kinnucan, Tilley and Wild met with Chenoweth and Prescott at Wright Field to present an endurance time tabulation for all major XO-1430-1 parts that had completed 50 hrs or more endurance running as called for under Contract W-535-AC-8131. The most serious weakness the engine exhibited during this endurance test was the cracking of two crankcase main bearing diaphragms at approximately 62 hrs endurance time. The crankcase had been examined and was in satisfactory condition at 55 hrs; according to the Contract terms the part successfully passed the required test. It was obvious that design changes were necessary before a type test engine was procured. Since the failure did not restart the 50-hr development test, the weakness indication before starting any type test was believed fortunate since design changes could be made before a type test was attempted. The Contract required CMC was to prepare a report covering the 50-hr development test, and to bring an updated Van Dyke file with all the latest design changes to MatCmd.

Drawings for the new rear section, which reduced overall engine height to about 24", were reviewed. Chenoweth and Prescott found the new rear section to be in good order except for a few minor changes to be incorporated in the final design. CMC proposed to complete the final design during the week of 16 April and furnish drawings to MatCmd for release in connection with the XO-1430-3 engine. Kinnucan stated that a very small crack was discovered in the rear accessory housing after having operated for hundreds of hours. This crack did not increase in size; however, in redesign this area was to be strengthened. Two new cracks had also appeared in the cam boxes after extended operation, but had not increased in size; these were attributed to cylinder base hold-down stud failure. These studs used standard coarse threads in the aluminum and fine threads for the hold-down nut; MatCmd observed that these studs might be improved by necking the studs between the different threads to better distribute stresses over the reduced section instead of concentrating stress at the thread roots as at present. It also appeared that the cylinder base flanges had been weakened by scallops between the stud holes to form lugs. The contact areas between the cylinder lugs and crankcase indicated these lugs deflected during operation, subjecting the studs to bending fatigue; this matter was to be considered in the final cylinder flange design and next crankcase.

Torsional vibration records taken at the crankshaft rear revealed a 7-1/2 order two-node vibration that appeared at approximately 2,900 rpm; the vibration amplitude was very low, well under the Specification 28184 limits. A 1-1/2 order single-node vibration was also well within limits. These data indicated the torsional damper was entirely satisfactory for this engine model. However, it was obvious that a different torsional damper would be required for use with a long extension shaft with or without a right-angle drive. MatCmd tasked CMC to begin looking into a damper that would be satisfactory with the proposed XO-1430-3 using an extension shaft and right-angle gearbox. [USNARA RG342 P031039. 19 Apr 1939 Memorandum Report E-57-285-103, Conference between Messrs. Wild, Tilley, and Kinnucan of Continental Motors Corporation. Chenoweth and Prescott of this Division on April 14 and 15, 1939, on the XO-1430-1 Engine Development Test.]

21 – 22 Apr 1939. Prescott visited CMC and examined drawings of the new accessory housing. This design featured a scheme to eliminate torsiometer drive backlash using a torsion spring that applied a load to two driving bevel gears, both meshing with a single driven bevel gear. During assembly, sufficient pressure was applied by the torsion spring to prevent the gear tooth faces from separating during engine operation. This facilitated using the MatCmd-type torsiometer on the crankshaft rear.

Prescott also reviewed the new engine mount, which incorporated transverse mounting plates clamped between the crankcase front and rear accessory housings; this mount was being designed in cooperation with the Douglas Aircraft Company, which aimed to modify an existing airplane to accept the XO-1430-1 and make possible flying the engine at an early date. [USNARA RG342 P10094. 1 May 1939 Memorandum Report E-57-4151-1, XO-1430-3 Engines.]

2 – 3 May 1939. Kinnucan and Wild attended a conference with Prescott at Wright Field where Kinnucan complained of difficulty locking the supercharger impeller nut. The steel pin used was apparently easily damaged during installation and one pin had come out and caused considerable damage to the supercharger. Prescott suggested a locking device similar to that being used in the new reduction gear be substituted for the pin; Kinnucan agreed to study this.

Kinnucan stated that no solution had been found for long cylinder cam box stud breakage. These were made from stainless steel because of its higher coefficient of thermal expansion; he was searching for a steel type with better strength and fatigue resistance.

Kinnucan asked if MatCmd had found a way to install thermocouples on spark plugs with bottom-seating gaskets. MatCmd had no experience with these but suggested installing the thermocouples directly in the spark plug bushings; Kinnucan was to study this.

Kinnucan stated that the torsiometer records clearly showed the 7-1/2 torsional vibration with a node just forward of the center main bearing. The amplitude of this vibration was extremely low, but, the feared that there would also be a 6-order vibration at approximately 3,600 rpm. In the discussion that followed it was stated that 6-order vibration would be accounted for in the complete 12-cylinder engine. It was believed that a possible of a 6-order 2-mode vibration would be of minor importance. Kinnucan stated that a study would be made of the excitation present in the engine to cause a 6-order period; it was feared that the change from dynamometer to torque stand might lower the crankshaft natural frequency and bring the 6-order period within the engine operating range.

The forward crankcase bending moment using the transverse engine mount plate was discussed. Prescott suggested that it might be desirable to reinforce the crankcase by adding material in the crankcase wall from the front crankcase tapering back into the main crankcase portion. Kinnucan stated this matter would be studied in connection with the crankcase redesign to provide additional main bearing diaphragm strength.

Several hold-down studs had failed during the 50-hr development test. The stud design did not provide for a necked-down section between the course crankcase threads and fine cylinder base nut threads. Prescott suggested that the necked-down portion be extended approximately 0.125" below the aluminum crankcase surface in order to provide a 0.031" or more reduced diameter, which would give additional flexibility and stretch. Prescott also suggested a fillet size increase in order to stiffen the cylinder hold-down flange. Crankcase examination had showed evidence that the cylinder hold-down flange was deflecting under load and it was considered possible that this deflection was at least partially responsible for the stud failures.

The question of where to add crankcase mount material to compensate for the 0.250" mount plates not needed with the new mounting scheme was discussed. It appeared that this material should be added to the cam box with the idea of preserving as much spark-plug clearance as possible. Kinnucan suggested that spark plug relocation should be studied to accommodate a wider spark plug type selection. The present cam box and cylinder head design permitted only unshielded plugs. Kinnucan pointed out that it was feasible to shield the entire pocket in which the plugs were located so as to make individual spark plug shielding unnecessary. However, it was believed desirable to study the plug relocation by staggering the plugs and changing their angles to provide better spark plug accessibility. [USNARA RG342 P031035. 8 May 1939 Memorandum Report E-57-285-104, XO-1430-1 Engine.]

26 – 27 May 1938. Kinnucan and Wild traveled to Wright Field to meet Prescott where Wild stated that CMC intended to cover Government liability for parts used in the twin-cylinder test increased with the increased XO-1430-1 rating, and also in the run-in test of the XO-1430-3 engine. In the 9 Jan 1939 CMC letter covering the furnishing of one XO-1430-3 engine, no statement was made by CMC covering Government liability for parts that failed during the required run-in test, consequently it was stated that Government liability for parts could not at this time be introduce into this contract. The 25 Apr 1939 letter CMC letter, covering quotation on additional XO-1430-1 tests together with twin-cylinder tests, did not specify Government parts liability. Kinnucan and Wild explained that the Government could not assume responsibility for parts failures in a contractor-owned test engine. However, it was stated that the Authority for Purchase would be modified to include two cylinder assemblies, two piston assemblies and one complete connecting rod assembly. In this case, parts liability, in case of failure, would be assumed by the Government on Government-owned parts while the contractor would assume burden of any contractor-owned test engine failure.

Reports covering the XO-1430-1 50-hr development tests, together with Van Dykes of the entire drawing set covering this engine, were delivered to MatCmd. However, Kinnucan stated that one drawing was still missing — the XO-1430-1 installation drawing. He stated that this drawing would be forwarded to MatCmd within the next few days and that delivery of reports and drawings completed all Contract W-535-AC-8131 requirements. MatCmd would review these drawings and reports before final payment on the Contract would be authorized.

Right-angle gearbox drawings for use in the XO-1430-3 were examined and found in good order and had been worked out so that turning the oil pump 180° performed the scavenge and pressure line reversal so that the gearbox could be use for either right- or left-rotation. Kinnucan stated that one final decision remained — the reversing method for right- and left-rotation drives. The proposed helical bevel gear gave a much greater thrust load to the ball bearings when rotated in one direction than in the other. Therefore, the optional rotation provision necessitated employing bearings large enough for the maximum bearing load. These bearings would be much oversized in the opposite-sized gearbox. It was considered that the necessity for right- to left-rotation was not as vital in the gearbox as in the engine. Consequently, two methods were open; one would furnish the gears cut with an opposite spiral angle so as to transmit a minimum thrust load to the bearings; in this case the gearboxes would be assembled as right- and left-gear boxes and would be more-or-less permanently installed in the airplane with provision for the proper rotation. MatCmd pointed out that this method was open to some objections since it would always be possible to use these gearboxes in the wrong directions in which case the bevel pinion thrust bearings would be overloaded. A smaller thrust bearing was suggested in the position to take the inward thrust. Kinnucan stated this matter would be studied before a final decision was reached. The present bearing layout was definitely on the heavy side.

Wild stated that CMC would be interested in accepting a proposition covering six engines, one of which would be guaranteed on a short-time basis as a very high-output pursuit engine having a short-time 1,800 hp rating; he was requested to prepare an quotation on this basis. [USNARA RG342 P031033. 2 Jun 1939 Memorandum Report E-57-285-105, XO-1430-1 and XO-1430-3 Engines.]

The crankshaft was damaged slightly but could be reconditioned. There was no indication of bearing trouble nor did any parts exhibit overheating. Since the 50-hr development test was concluded, only 13 hrs had been run, and only 30 minutes had been run above 165 bmep. On 14 June, Tilley came bringing broken parts for examination. There was a deep indentation on the side of a piston that could have readily accounted for the piston skirt cracking, after which complete failure happened in only a few revolutions. The pistons were the cast type, having the inner strut and had been used during the entire 700 hrs of miscellaneous testing, including 107 hrs endurance running. Kinnucan promised a full report when more information was available.

Kinnucan brought with him two drawings, one showing a XO-1430 design with vertical cylinders. This engine was not attractive in view of the 44" height. The other drawing showed an inverted V-12 design with a frontal area below 5 ft². This design was obviously most advantageous in a single-engine installation because of the excellent visibility afforded with a concentric bevel reduction gear.

Kinnucan said that XO-1430-3 analysis indicated that two torsional vibration dampers would be necessary; one at the crankshaft rear and the other in the right-angle gearbox. Design work was proceeding on both but a satisfactory design had not yet evolved. Kinnucan inquired about MatCmd's desire for bmep indicator boss improvement on the Hyper No. 1 cylinder being repaired by CMC. A burned cylinder head was examined, which showed extreme burning at thread inner ends. Kinnucan stated that a bushing seating against the cylinder head on its interior end could be installed in the cylinder head, and in which the passage into the combustion chamber was reduced to a small-diameter hole. MatCmd suggested that this hole be made 0.188" diameter instead of the present 0.563" diameter.

Improving the Hyper No. 1 cylinder and coolant jacket corrosion resistance was also discussed; the cylinder sleeves were fabricated with a narrow land at the upper end that would completely mask the extension of the aluminum head so as to prevent electrolytic action between the aluminum and steel cylinder barrel sections. MatCmd stated that if this construction was found satisfactory it would furnish a means to overcome the corrosion difficulty on all composite steel/aluminum assemblies and ald would also prove valuable even if the scheme was unsatisfactory; either way, valuable information would be obtained by incorporating this change in Hyper No. 1 cylinders being repaired. [USNARA RG342 P031030. 21 Jun 1939 Memorandum Report E-57-285-106, XO-1430-1 Engine.] and [RG342 RD1676 503-106 O-1430 390621-400828 Vol. 4. 6.]

15 Jun 1939 Progress Report – 12-Cylinder Engine Performance Tests, Contract W-525-AC-12741. The total oil flow through the engine was believed excessive and tests were run to determine the flow through various engine sections. The accompanying curves showed the results obtained. The following was a detailed descriptions used in the determinations.

Curve #8: Cam Box Oil Flow versus rpm. The main engine oil pressure was measured at two points, one at the rear accessory case adjacent to the fuel pump mounting pad and the other at the reduction gear and torquemeter housing bottom. The cam box oil pressure was measured at the camshaft end. The cam box oil flow was measure by plugging the cambox rear oil drain and allowing the oil to flow through the drain to a pan mounted on a Howe scale. After each reading the oil was pumped out of the pan into the oil supply tank and the total oil flow was measured after the rear drain plugs were removed and the front oil tubes were connected to drain the crankcase. It should be noted that the cam box oil flow decreased with an engine speed increase with the given main oil pressure. This was due to the intermittent camshaft and bearing oil feed.

Curve # 9: Cam Box Oil Flow versus Oil-In Temperature. These tests were run in the same manner as outlined above. The oil flow through the cam box was not particularly affected by the engine oil-in temperature due to the extremely small oil quantities being measured.

Curve # 14: Front Section Oil Flow versus rpm. The curves present results of oil flow versus engine rpm when operating on the 600 rpm and 1,000 hp propeller load curves/ The data for the 1,000 hp curve were incomplete due to poor engine operation at 2,800 rpm, caused by defective spark plugs. The points on the 1,000 hp curve were obtained during the mixture ration tests shown on curve No. 15.

Curve #15: Front Section Oil Flow versus Oil-In Temperature. For this test the #500810 adapter was plugged at the lower oil drain and the front oil pump connected so as to scavenge oil from the front section ahead of the adapter. The leakage from the accessory drive gears mounted on the adapter was taken in with the main power section. The front section oil flow was measured separately and the total oil flow determined with the same setup using the engine oil scavenge pump and front external scavenge pump both discharging into the main oil tank. The engine oil supply to the front and the rear was from one source and the difference in pressures at these points could be explained by the fact the rear oil pressure connection was adjacent was more remote from the inlet connection, while the front connection was adjacent to the oil feed line from the Cuno filter to the front housing. This oil pressure difference did not measure the loss through the engine as an outside line was brought directly to the reduction gear housing; this line was being eliminated in future engines.

Curve #16: Rear Accessory Case Oil Flow versus rpm. Oil flow was measured by allowing the oil from the rear housing to drain into a pan on a scale and after weighting an oil sample was pumped back into the supply tank by an external scavenge pump[. The front external scavenge pump was used to scavenge the remaining engine oil. Based on 3,000 rpm crankshaft speed at 600 propeller-load power with 180°F oil-in temperature and 110 psi main oil pressure, the following oil flow and flow percentage various engine parts summary was produced:

Curve 8	Curve 9	Curve 10	Curve 11	Curve 12	Curve 13	Curve 14	Curve 15	Curve 16

Curve #10: Power versus Spark Advance. This curve was run in order to determine the optimum spark advance setting for a 900 hp power curve to be used in future tests. It was noted that a slight bmep increase was obtained from 29° to 35° spark advance. However, a spark advance increase gave a corresponding maximum pressure increase and it was doubtful whether the slight power increase accompanied by increased loads would be desirable.

Curve #11: Mixture Ratio Curve-900 Actual bhp at 2,925 rpm. This curve shows a 0.520 lb/hp/hr specific fuel consumption at best power and constant speed (2,935 rpm) and airflow (6,600 lb/hr). The "best setting" fuel consumption was 0.500 lb/bhp/hr. These values were not particularly low and further work was to be done in an effort to reduce fuel consumption.

Curve #12: Power versus Manifold Pressure. These data depict a family of part-throttle power curves versus absolute manifold pressure and will be used for future reference. These curves were not extended to the full throttle point for the three speeds shown.

Curve #13: Part Throttle Mixture Ratio Curves Based on 1,000 bhp Propeller Load. The best-power specific fuel consumption points for 2,200, 2,400 and 2,600 rpm were, respectively, 0.515, 0.545 and 0.515 lb/bhp/hr. Data on 2,800 and 3,000 rpm were not completed due to defective spark plug operation.

After the mixture ration curves shown in Curve #13, the engine was inspected and the right distributor was found badly burnt and the distributor finger was cracked. Both were replaced. The left camshaft idler spur gear was also found cracked; this was replaced with a new part. While running the oil flow tests on the rear accessory case operating at 3,000 rpm and 600 hp propeller load a sudden excessive noise developed and the engine was shut down. The No. 3L and 3R pistons and connecting rods had broken and the rods were driven through the crankcase. A complete tear down and inspection of all parts and a detailed report of this failure were to be made in the next Progress Report. Total running time on the engine for the performance test contract was 20:03 hrs; motoring time was 2:26 hrs; under power was 17:35 hrs; time above 165 bmep was 2:07 hrs. Total engine time was 696:02 hrs; motoring time was 182.50 hrs; under power was 513:12 hrs; time above 160 bmep was 117:32 hrs and total endurance time on Contract W-535-AC-8131 was 107:34 hrs.

Wood Model Conversion – Contract W-535-AC-12298, PO 39-3952. The XO-1430-3 model was held up pending release of right-angle drive layouts.

Two Hyper No. 1 Cylinder Assembly Repairs – PO 39-5508. It was decided to change the combustion chamber pressure connection to the cylinder head to eliminate excessive burning that had been noted with the present design. This would cause a slight delay in cylinder delivery.

XO-1430-3 Right-Angle Drive Engine – Contract W-535-AC-12594. Design of suitable dampers continued and it was clear that objectionable harmonics could be addressed. Damper layouts were being made and were to be brought to MatCmd for discussion.

Engineering: Layouts showing necessary and suggested crankcase changes had been made. Twin-cylinder test engine detailing continued and was to be complete by 15 July. Spare parts and Government liability were attached. [USNARA RG342 RD1676 503-106 O-1430 390621-400828 Vol. 4. 13 – 30.]

23 Jun 1939. Kinnucan and Wild met with Prescott at Wright Field; Wild brought with him a letter addressed to the Materiel Division Chief furnishing quotations covering from one to five O-1430-9 engines, which had been previously designated by MatCmd as O-1430-5 engines. They were of the same type as the improved O-1430-1 engine but incorporated a five-foot drive shaft and an outboard thrust bearing support. Kinnucan asked whether it was advisable to add material to the crankshaft crank cheeks in order to provide for increased strength at the point where the 30° chamfer was removed from the crank cheeks; previous forgings had barely sufficient material to enable cleaning up the crankshaft to drawing dimensions. The crankshaft forging dies had been properly made, but the forgings had been removed at too high a temperature. One forging was reheated to the proper temperature and struck with the dies, after which it was in the correct condition for machining. On this basis it was considered unnecessary to modify the dies at this time.

Kinnucan wondered whether the complication of including the torsiometer drive in the first engine to incorporate the new rear section was warranted since MatCmd still had the Sperry-type vibration pickup equipment; MatCmd thought it advisable because a number of torsional vibration studies were planned on various engine models. The time and money consumed to obtain torsiometer records with the torsiometer in CMC's possession were considered excessive to determine if new engine models were torsionally satisfactory.

Regarding the crankcase failure after 62 hrs endurance testing, Kinnucan stated that compression and tension tests on the diaphragm sections cut from that crankcase did not disclose any weakness. However, it was observed that when the sections were cut a very high stress existed in the crankcase casting curved outer portions. This condition was thought caused by the rapid thin outer section cooling followed by the heavier diaphragm section cooling, leaving the outer sections in considerable tensile stress. Several methods to reinforce these diaphragms were discussed; it was finally decided that the simplest was to add 0.063" to the radius around the bearing through-bolts and also add 0.031" to each side of the small panel between the outer diaphragm rib pairs. The weight increase due to this change was considered insignificant. The matter of eliminating these stresses would be discussed with ALCOA.

Kinnucan showed a layout in which the front accessory bearing diaphragm was redesigned to eliminate the rather thick section now clamped between the crankcase flange and reduction gear intermediate section. This diaphragm would be considerably lightened because the sections were much thinner than with the previous herringbone reduction gear design. This diaphragm would be attached to the crankcase front by means of six studs and two dowels. This diaphragm design would also incorporate improved lubricating oil transfer from the engine to the reduction gear.

Revised layouts showing a new mounting plate revealed that the cross-type mount plates were inherently weak when transmitting engine thrust. Kinnucan said that studies would be made of mounting plates clamped between the cam boxes and cylinders incorporating Lord mount bushings at the plate's front and rear. This design was to be submitted to MatCmd for consideration at a later date. [USNARA RG342 P031030. 26 Jun 1939 Memorandum Report E-57-285-107, Conference with Representatives of Continental Motors Corporation on O-1430 Type Engines.]

XO-1430-1 Development Cost Summary

24 Jun 1939. MatCmd published an XO-1430-1 development cost summary. [USNARA RG342 RD1676 503-106 O-1430 390621-400828 Vol. 4. 61 – 63.]

CMC XO-1430-1 Damage after 12 Jun 1939 Failure

Fig. 1.	Fig. 2.	Fig. 3.	Fig. 4.	Fig. 5.	Fig. 6.	Fig. 7.	Fig. 8.	Fig. 9.	Fig. 10.

These cast pistons had been in the engine during the entire development period. It is possible that a slight crack appeared and then suddenly disintegrated. This is a common failure mode for cast pistons. It had previously been decided to bring along a forged piston development and designs were already made. Several had feared that at some time such a failure as here described would occur. There was also severe galling in evidence between the connecting rods and bearing shells and the fatigue evidence in Figure 7 could account for the failure. These connecting rods had been reground on the inside diameter to provide for proper bearing crush. Such a process does not leave a perfectly round hole and was an expedient used to salvage the connecting rods, which had been used with several bearing pairs. All remaining rods were carefully examined and one rod showed concentrated loaded due to bearing shell galling. In order to avoid a recurrence of this failure the forged pistons were released and the inside diameters of all remaining connecting rods were to be ground and fitted with new bearings having sufficient outside diameter increase to provide proper crush; this would give the same fitment as a new bearing in a new rod.

As of 30 Jun 1939 on Contract W-535-AC-12594 the XO-1430-1 had accumulated 20:03 hrs total time, 2:28 hrs motoring, 17:35 hrs under power and 2:07 hrs above 160 bmep. Overall engine time was 696:02 hrs total, 182:50 hrs motoring, 513:12 hrs under power, 117:32 hrs above 160 bmep, and 107:34 hrs endurance time on Contract W-535-AC-8131.

Wood Model Conversion – Contract W-535-AC-12298, PO 39-3952. The XO-1430-3 model was held up pending release of right-angle drive layouts.

Two Hyper No. 1 Cylinder Assembly Repairs – PO 39-5508. It was decided to change the combustion chamber pressure connection to the cylinder head to eliminate excessive burning that had been noted with the present design. This would cause a slight delay in cylinder delivery.

XO-1430-3 Right-Angle Drive Engine – Contract W-535-AC-12594. Damper layouts and calculations continued.

Engineering: Layouts were made for the revised crankcase front end incorporating a separate diaphragm at the crankcase front, and having the flange revised to reduce overall engine height. Twin-cylinder test engine detail drawings were made and several parts released for manufacture; the engine was to be ready for operation by 25 Aug 1939. No spare parts were required during this period and total Government liability was attached. [USNARA RG342 RD1676 503-106 O-1430 390621-400828 Vol. 4. 31 – 45.]

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