Continental XO-1430 Development
Part 6: 1 Jul 1935 to 31 Dec 1935
by Kimble D. McCutcheon
Published 28 Aug 2025; Revised 29 Aug 2025

Prescott Indicator Patent

10 Jul 1935. PPL civilian engineer Ford L. Prescott released Memorandum Report E-57-285-16 reporting a 26-28 Jun 1935 meeting involving Continental's President William R. Angell, Long and Tilley and MatCmd's Prescott. The single-cylinder engine had been operated up to rated power and speed, and indicator cards taken for cross check against cards taken with the Farnborough indicator. Difficulty in obtaining good cards with the Prescott indicator was traced to using too large a sealing oil reservoir on the system's pressure side. This gave a large clearance volume to be filled with gas and made the indicator action slow. Another point was that the oil volume extracted by the indicator piston when under pressure was discharged into the atmospheric oil chamber, quickly robbing the indicator of sealing oil. This was avoided by changing over to atmospheric or boost pressure when the cylinder pressure was equal to or less than the boost pressure. In this way the oil level in the high-pressure seal system could be maintained or increased.

Continental asked about the dynamometer engine mount plate, Dwg No. 500355, release status and was told this was delayed pending further design changes. Continental said no further changes would be made and requested the drawing be released; this was done.

Prescott pointed out that the supercharger shaft seal air vent opened upward and would under some conditions provide a 3" oil column. When the throttle was closed, this oil would be drawn into the supercharger. Since the vent's purpose was to relieve either air or oil within the seal, Prescott suggested that the vent be moved to one side and inclined downward.

Crankshaft single- and two-mode vibration was discussed. In single-mode vibration the frequency was approximately 74 Hz giving a 1.5 order period at 2,990 rpm and a 2.5 order period at 1,795 rpm on the assumption that the gear deflections reduced the natural frequency 50% over a direct-drive engine. If the gear deflections reduced the frequency 30%, which was a more reasonable assumption, the 1.5 order period would be at approximately 3,600 rpm with a 2.5 order period at 2,160 rpm. Analysis indicated that the 2.5 order excitation was much stronger than the 2.5 order excitation for a horizontally-opposed engine (the XO-1430 was a 180° vee, not a horizontally-opposed boxer). If this was the case, a 2.5 order period at 2,160 rpm would do no harm and the 1.5 order period at 3,600 rpm would be of low amplitude at 10% overspeed (3,300 rpm). The two-mode vibration was being investigated. Rough calculations showed the frequency to be approximately 375 Hz, which would give possible vibration periods at the following speeds:

It was not known which of these periods was potentially serious, since the vector diagrams of exciting torques would require revision because of the different shaft elastic curve characters. Further investigation was ongoing to decide if dampening would be required to limit two-mode vibration to safe limits. All agreed that this should be settled expeditiously because of possible impact on the crankshaft, crankcase or accessory housing.

Facilities for 12-cylinder engine testing were discussed. Continental would require a water brake with a 10-week to 3-month lead time, and would have to move and install an existing 300 hp dynamometer and its controls. A room was available for this work where the engine could be secured from unauthorized observation, but a month would be required to build the test room. The water brake was the most serious delay, and if started immediately, it would be 1 Oct 1935 before full-power 12-cylinder testing could begin. Since the engine had been promised for 19 Aug 1935 and testing could begin before 1 Sep 1935. Prescott suggested that Long and Tilley visit MatCmd and go over the contract testing details in order that procurement authority could be initiated. Prescott further suggested the Bachle come to discuss water brake and laboratory requirements with MatCmd personnel charged with such work. The group felt that the dynamometer room could be under way by 15 Jul 1935, if possible.

Prescott looked over 12-cylinder engine parts in all stages of fabrication. Continental reported difficulty in obtaining castings with uniform wall thickness despite patterns being made at by the foundry to insure close cooperation between pattern shop and foundry. In some cases, three trials were necessary to secure satisfactory castings. Prescott reported that Continental seemed to be doing its best to put quality materials and workmanship into the XO-1430, in some cases discarding parts with defective machining when the defect would have caused no trouble. The workmanship so far was what one expected in a highly-developed aircraft engine.

The herringbone reduction gears were inspected and found to have defects serious enough to warrant returning them to the vendor. There were several marks on the tooth faces and tips, and since no method was on hand to determine the material quality, the participants did not wish to jeopardize the project by using the gears. Hence, the gears were rejected, new ones ordered and plans made to magnaflux the blanks before the teeth were cut. MatCmd offered use of its facilities for this purpose.

Angell was under the impression that all drawings furnished to MatCmd were open to examination by other contractors and were being copied, and that MatCmd personnel had divulged O-1430 engine details to others. The only basis for this suspicion that could be traced was the loan of "Hyper No. 1" cylinder to the Lycoming Manufacturing Company. Prescott pointed out that this was not a breach of confidence since that cylinder was entirely a MatCmd design and used a cylinder head made by Allison. Further, that cylinder was unrelated to the "Hyper No. 2" cylinder upon which the O-1430 was based. Angell was assured that Continental intellectual property, contractual details and work product were safe with MatCmd. As a result of this frank discussion, Prescott felt that a better basis for understanding and mutual confidence was established at this conference.[USNARA RG342 P031255.]

Total cost for conducting the 50-hr development test was $30,535.00, which was based on the completion of each step outlined in 90 days, or a 1-year period for completion of the entire development test.

MatCmd stated it was unlikely that any equipment cost could be charged to the Government since said equipment would be Continental property at project conclusion and would be comparable to any other fixed investment that Continental might incur for machinery or buildings in the course of contract completion. A Steel Products Engineering Company water brake would be available to Continental on loan from the Government for the test duration.

MatCmd suggested that Continental may have over-estimated the run-in and calibration severity; this matter was to be taken up in detail with the Engineering Section Chief. MatCmd further suggested that all important steel parts be forwarded to the PPL for magnafluxing as part of regular inspection, in order to provide additional security against parts failure during test. However, MatCmd would not be responsible if such parts failed in test since the magnaflux testing was only valuable as additional security against failure due to material defects.

Continental requested that the Government issue a deviation covering the Farrell-Birmingham herringbone gears, whose outside diameters were slightly undersize and marked at some points with pits that initially appeared to be forging defects. The Farrell-Birmingham representative opined that the pits were formed when the gear blanks were in the heat-treating furnace and were not a structural weakness; he further stated that the Farrell-Birmingham Company would guarantee satisfactory gear performance and would replace them if they failed. MatCmd concurred if Continental relieved MatCmd of all responsibility for gear failure during the preliminary running and 50-hr development test.

Long asked about the status of the additional single-cylinder testing for which Authority for Purchase (AFP) had been initiated. This matter had been temporarily delayed for slight AFP revision. Long requested a copy of the test requirements included in the AFP. He stated that fabrication of parts from the 12-cylinder drawings was nearly complete and that the single-cylinder engine was being overhauled and prepared for more testing, and that Continental did not wish to delay the test program until the contract was formally released.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 69 – 71.]

W-535-AC-6322 Item 2 – Crankcase. The main crankcase had been studded, bolted together and the main bearing bosses bored. The reduction gear housings were in work. The crankcase was expected to be done by 31 July.
W-535-AC-6322 Item 3 – Crankshaft. The quill drive adapter was rejected because the spline dimensions were incorrect; completion of the new quill drive adapter and crankshaft dynamic balancing were expected by 31 July.
W-535-AC-6834 Item 1 – Reduction Gears. The gears that had been shipped to Wright Field for magnafluxing tested OK. Since Continental was responsible for the actual gears and gear design, another reduction gear set was ordered to ascertain the tests would check the actual design and not discrepancies from the design.
W-535-AC-6834 Item 2 – Rear Accessory Housing Assembly. The supercharger impeller shaft was rejected due to faulty hardening and was being remade. The replacement was expected by 31 July, when it was to be shipped to General Electric (GE) for balancing with the impeller. All parts were expected by 15 August.
W-535-AC-6834 Item 3 – Camshaft Housing Assembly. All parts for this item except rocker arms and mount plates were expected by 15 August. The rocker arms were still delayed pending single-cylinder tests. Engine mount plates for test purposes had been released for manufacture and then delayed pending approval of MatCmd to substitute these for parts originally designed for the type test and/or flight test.
W-535-AC-6834 Item 4 – Connecting Rod Assemblies. Forgings had been received but machine work was delayed pending single-cylinder tests.
W-535-AC-6834 Item 5 – Cylinder Assemblies. The head castings were promised for 20 July. Other parts were practically complete, and the item was expected to be done during August.
W-535-AC-6834 Item 6 – Piston Assemblies, etc. to Complete Engine. Piston work was delayed pending single-cylinder tests. Radio shielding and ignition assembly awaited engine assembly.

Engineering: Routine drawing changes continued. A chart showing stud assembly data for various engine parts had been made to aid assembly. The crankshaft counterweights had been slightly modified to put the crankshaft in dynamic and static balance. The bearing load polar diagrams were being revised accordingly. The single-cylinder crankshaft drawing showing material removed to achieve balance had been completed.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 79 – 82.]

31 Jul 1935 Progress Report. The single-cylinder test engine with a forked connecting rod and new cylinder assembly with valve gear identical to the 12-cylinder engine was started on 31 Jul 1935 and run-in for 5 hrs. Connecting rods, piston pins, rocker arms and shafts had been received from Wright Field, which reported that magnafluxing disclosed no defects. One of the two cylinder assemblies on order was lost in manufacture due to faulty furnace regulation. This cylinder was overheated enough to cause the valve seat inserts to loosen and drop out of the head. The replacement cylinder head was to be assembled to the barrel on 1 Aug 1935 and the complete cylinder assembly was to be available during the week of 5 Aug 1935.

W-535-AC-6322 Item 2 – Crankcase. This item's completion date was now estimated to be 12 August.
W-535-AC-6322 Item 3 – Crankshaft. A new quill shaft adapter had been shipped to Wright Field for magnafluxing. Tools for undercutting the crankshaft crankpin and main journals had been delayed. The crankshaft was promised for 15 August.
W-535-AC-6834 Item 1 – Reduction Gears. Forgings for the new gearset had been received at Farrell-Birmingham, which expected to complete finished units on 25 September.
W-535-AC-6834 Item 2 – Rear Accessory Housing Assembly. The supercharger impeller shaft was promised for 9 August. The accessory housing was promised for 14 August. The GE supercharger was promised for 21 August. A considerable number of other parts were being inspected, except for the six bevel gears being cut by Bilgram Gear Company. A few other parts were to be finished by 20 August. This item was expected to be complete by 20 August.
W-535-AC-6834 Item 3 – Camshaft Housing Assembly. All parts except the rocker arms and mount plates were expected to be complete by 15 August. The rocker arms were delayed pending single-cylinder tests, and the engine mount plates were delayed waiting on MatCmd deviation approval for substitute parts originally designed for type and flight tests.
W-535-AC-6834 Item 4 – Connecting Rod Assemblies. Forgings had been received, but machining was delayed pending single-cylinder tests.
W-535-AC-6834 Item 5 – Cylinder Assemblies. Eleven of the sixteen head castings received were to be released to the shop; the remainder was rejected due to thin casting sections. Other parts for this item were nearly finished. If the other heads could be received shortly, this Item should be completed by 1 September.
W-535-AC-6834 Item 6 – Piston Assemblies, etc. to Complete Engine. Piston finishing was delayed until single-cylinder tests were completed. Radio shielding and ignition assembly awaited engine assembly.

Engineering: Routine drawing changes continued. A deviation to balance the first crankshaft and approve changes for future crankshafts had been requested from MatCmd. The bearing load polar diagrams were being reviewed to compensate for this crankshaft counterweight change. Plans for testing the 12-cylinder engine were coming together.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 84 – 87.]

6 Aug 1935. Prescott issued Memorandum Report E-57-285-18 covering a 19 Jul 1935 meeting between Long and Tilley of Continental, and Maj Powers, Chenoweth and Prescott of MatCmd. Development test details were discussed, along with a 22 Jul 1935 letter requesting a quotation for the test. The letter contained full information on the test and presumably resolved any misunderstanding about what the tests involved. Tilley requested a copy of MatCmd's report on checking the filling of internally-cooled valves by the electrical conductivity method. Tilley mentioned that an RCA Cathode Ray Oscillograph had been fitted with a suitable pickup to record torsional vibration in inaccessible shafts; information on this was to be requested. Tilley asked if Continental's questionnaire on test apparatus had been answered; MatCmd's reply was being prepared and would be sent when all drawings, etc., were received. Tilley requested an opinion on methods of positive rocker box lubrication on radial engines. MatCmd opined that either the steady, scavenged type or metered unscavenged type was satisfactory, but a manually-operated device was not considered acceptable for military use since no means existed to insure lubrication at proper intervals.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 88 – 89.]

Bachle was also given drawings of the Steel Products Engineering Company water brake, MatCmd's thermoid coupling design, and the new oil cooler type.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 90.]

15 Aug 1935 Progress Report. Single-cylinder run-in was interrupted after 9 hrs by a cylinder head crack in the barrel-end thread. This was probably caused during assembly when the cylinder was cooled by Prestone and dry ice while the jacket was slipped into place. The second cylinder was disassembled and rebuilt with a new head; it was to be ready for test on 16 August. Another cylinder was lost in manufacture due to clamping on the head casting flat side, which had cracked the cast jacket. Another cylinder was in work to replace the second cylinder.

Continental estimated that this construction was 75% complete; several items were delayed pending successful single-cylinder tests.

W-535-AC-6322 Item 2 – Crankcase. The crankcase and reduction gear housing were being inspected and were to be available for the Air Corps Inspector on 4 September.
W-535-AC-6322 Item 3 – Crankshaft. The new quill shaft adapter, after successful magnaflux at MatCmd, had been shipped to the Ohio Crankshaft Company for matching the bolt holes. Crankshaft delivery was promised for 31 August.
W-535-AC-6834 Item 1 – Reduction Gears. The four new gears were to go to Wright Field for magnaflux inspection on 24 August. Finishing would require about 4 weeks thereafter.
W-535-AC-6834 Item 2 – Rear Accessory Housing Assembly. The supercharger impeller shaft was incorrectly machined; a new one was being made, and was expected during the week of 19 August. The GE supercharger was to be shipped 5 days after receipt of the shaft, which GE required for balancing the impeller assembly. This Item was scheduled for completion in September.
W-535-AC-6834 Item 3 – Camshaft Housing Assembly. All parts except rocker arms and mount plates were expected to be complete during the week of 19 August. The rocker arms were waiting on single-cylinder tests and the mount plates were awaiting a deviation to substitute parts originally designed for type and flight tests.
W-535-AC-6834 Item 4 – Connecting Rod Assemblies. Forgings were on hand but machining was delayed until single-cylinder tests were complete.
W-535-AC-6834 Item 5 – Cylinder Assemblies. All head castings had been received. These assemblies were expected to be complete during September or early October.
W-535-AC-6834 Item 6 – Piston Assemblies, etc. to Complete Engine. Piston finishing was delayed pending single-cylinder test completion. Radio shielding and ignition assembly awaited engine assembly.

Engineering: Routine drawing changes continued. A preliminary 12-cylinder testing layout had been made. Revised reduction gear and propeller thrust bearing loads were very close to the original calculations.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 91 – 94.]

31 Aug 1935 Progress Report. The new cylinder was run-in, inspected and measured. The Prestone pump had seized at the oil sealing baffle cups, damaging the pump drive gears and idler gear support. The old pump was installed to permit continued testing. During run-in the small valve springs showed signs of tossing (valve float) at 3,350 rpm. At run-in completion the inner spring was broken. Metallurgical examination showed a wire defect. Total time on the spring was about 19 hrs including run-in time. A 5-hrs run under contract conditions was achieved on 28 August. This test used a forked rod, which was in satisfactory condition upon completion. The engine was reassembled for more testing. Another cylinder had been assembled and was complete except for bore grinding, coolant port facing and stud insertion.

W-535-AC-6322 Item 2 – Crankcase. All parts were complete and accepted by the Air Corps Inspector.
W-535-AC-6322 Item 3 – Crankshaft. Magnafluxing was witnessed and accepted by the Air Corps Inspector. Delivery was promised for the week of 7 September.
W-535-AC-6834 Item 1 – Reduction Gears. Reduction gear blanks were magnafluxed at Wright Field and the blanks returned to Farrel-Birmingham Company, Buffalo, New York. The propeller shaft had been sent to Wright Field for magnafluxing and had not been returned. Reduction gear completion was expected during the week of 30 September.
W-535-AC-6834 Item 2 – Rear Accessory Housing Assembly. The supercharger impeller shaft was in work and was to be ready for gear tooth grinding on 11 September. The carburetor had been received. Seven other part numbers were still in work including the accessory housing. Completion was expected during September.
W-535-AC-6834 Item 3 – Camshaft Housing Assembly. Rocker arm finishing was still delayed pending single-cylinder test completion. Engine mount plates were being released in view of the Government's decision to obtain another set of mount plates for testing. The other 10 part numbers were in work.
W-535-AC-6834 Item 4 – Connecting Rod Assemblies. Machining was delayed pending single-cylinder tests.
W-535-AC-6834 Item 5 – Cylinder Assemblies. Heads were in work. Barrels and jackets were complete but not assembled. Other parts were finished.
W-535-AC-6834 Item 6 – Piston Assemblies, etc. to Complete Engine. Piston finishing was delayed by  single-cylinder tests. Radio shielding and ignition assembly awaited engine assembly.

Engineering: Routine drawing updates continued. A new single-cylinder coolant pump layout was completed and partially detailed. This pump incorporated Sweitzer Cummins packing-less seal for the Prestone and a spring-loaded packing for the oil seal. Test equipment layouts for the 12-cylinder test cell continued.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 96 – 98.]

15 Sep 1935 Progress Report. After 12 hrs running under contract conditions, the single-cylinder test engine forked connecting rod failed, breaking up the piston skirt, cylinder skirt and cracking the piston pin. The rod appeared to have split down the column center. A separate failure report was being prepared. The crankcase was completely inspected and cleaned. An attempt was made to fit the used long-jacket cylinder to the base, but this would have required modification to the cylinder adapter to drop the cylinder by 0.250", locating it identically to the other test cylinders. A new-type cylinder and new blade rod were assembled to the test engine and run-in started. Continental planned more frequent inspections, hoping to obtain more information on the rod failure. Another forked rod with additional metal at the failure point was promised for 20 September. A re-check of valve clatter speed with the 137 lb small-diameter valve springs showed clatter speed to be at 3,250 rpm.

W-535-AC-6322 Items 2 and 3 – Crankcase and Crankshaft. Complete and accepted.
W-535-AC-6834 Item 1 – Reduction Gears. In work at Farrel-Birmingham Company, promised for week of 14 October. The propeller shaft was in the Wright Field Inspection Branch, which has magnafluxed it and was checking the spline dimensions.
W-535-AC-6834 Item 2 – Rear Accessory Housing Assembly. The supercharger impeller shaft was at GE for impeller balancing. Five part numbers were in work, the supercharger was promised for 27 September, and this Item was to be complete in September.
W-535-AC-6834 Item 3 – Camshaft Housing Assembly. Rocker arm finishing was delayed by single-cylinder tests.
W-535-AC-6834 Item 4 – Connecting Rod Assemblies. Machining was delayed until single-cylinder tests were complete.
W-535-AC-6834 Item 5 – Cylinder Assemblies. Heads were in work; barrels and jackets were complete, as were the other parts.
W-535-AC-6834 Item 6 – Piston Assemblies, etc. to Complete Engine. Piston finishing was delayed until single-cylinder tests were complete. Radio shielding and ignition assembly awaited engine assembly. Coolant pipe assemblies were being reordered as the initial sets were unsatisfactory.

Engineering: Routine drawing updates continued. A chart showing fits and clearances for all important engine parts had been started. The new single-cylinder coolant pump had been, detailed, checked and released for manufacture. It incorporated a Sweitzer Cummins packing-less seal for the Prestone and a spring-loaded packing for the oil seal. The connecting rod piston pin end had been revised and released for manufacture of one forked rod. Layouts for 12-cylinder test equipment continued.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 100 – 102.]

25 Sep 1935. Prescott released Memorandum Report E-57-285-21 confirming a 13 Sep 1935 conference at MatCmd involving Long and Tilley from Continental, and Chenoweth and Prescott of MatCmd. The single-cylinder test engine was discussed, and Continental stated that the piston had pulled in two through the pin bosses; the rod had apparently split under the pin and pushed up into the ribbed piston crown. The connecting rod small end was to be modified to increase its strength under the eye. This change increased the engine weight by 0.25 lb, but considerably improved the piston strength under the wrist pin. A new rod, piston and cylinder were being prepared.

Long raised the question of responsibility for the failure and asked whether the Government was to replace parts that failed, as had been agreed for the 12-cylinder testing. MatCmd replied that Continental was entirely responsible for single-cylinder part failures. Long inquired as to the contract status on two 50-hr single-cylinder tests, and the 50-hr development test on the 12-cylinder engine. The single-cylinder contract had been sent to Washington, DC on 19 August and the Contracting Office advised it would be satisfactory for Long to check up on this during his next Washington visit. The 50-hr development test contract was being prepared and awaiting a decision from the Judge Advocate before completion.

Long asked what steps would be required to secure water brake and Toledo dynamometer scale shipment. This equipment could be loaned against the current contract, independently of completion of the proposed 50-hr development contract; MatCmd suggested that a formal request be made for the equipment.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 103 – 104.]

30 Sep 1935 Progress Report. The single-cylinder blade rod was run 10 hrs under contract conditions; after each 5-hr period the rod was magnafluxed and found OK. It was also examined with a 50 power magnifying glass. The rods were re-polished to eliminate certain marks, none of which showed as cracks under magnaflux. This run was being continued. The new forked rod with additional metal at the failure point was complete.

W-535-AC-6322 Items 2 and 3 – Crankcase and Crankshaft. Status unchanged.
W-535-AC-6834 Item 1 – Reduction Gears. The propeller shaft was found OK by the Wright Field Inspection Branch. All other parts were complete except the reduction gears, which were promised for the week of 14 October.
W-535-AC-6834 Item 2 – Rear Accessory Housing Assembly. All parts accepted by the Air Corps Inspector.
W-535-AC-6834 Item 3 – Camshaft Housing Assembly. Status unchanged.
W-535-AC-6834 Item 4 – Connecting Rod Assemblies. Status unchanged.
W-535-AC-6834 Item 5 – Cylinder Assemblies. Status unchanged.
W-535-AC-6834 Item 6 – Piston Assemblies, etc. to Complete Engine. Piston, radio shielding and ignition assembly status unchanged; subassembly of completed items had begun.

Engineering: Routine drawing updates continued. Work on the fits and clearances chart was about half done. Calculations and layouts had been made for the airplane type mounting plate and new details were being made which would be submitted to MatCmd for approval. Equipment layouts for the 12-cylinder test cell continued. The water brake and Toledo scale were received and position layouts for them started. Excavations had been made and a bed plate put in place preparatory to pouring the concrete sub-base.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 106 – 108.]

16 Oct 1935. Prescott penned Memorandum Report E-57-285-22 about a 14 Oct 1935 meeting with Ray Long at MatCmd. Long stated that inquiries had been received on two 50-hr single-cylinder tests and on the 50-hr 12-cylinder development test. Neither inquiry called for a performance bond, yet a letter said a bond would be required for both. The Contracting Office agreed that it should have been stated that the bond would be required. Several bonding companies refused to consider the matter because of its experimental nature. Prescott instructed him to write a letter setting forth these considerations and requesting that the bond requirement be waived.

Three payments for the 50-hr development test of 10%, 10% and 80% meant that Continental would be called on for large initial capital outlay and would then have to wait for completion and acceptance of the entire test for the final 80%. The Contracting Office suggested this partial-payment distribution be revised to 25% at the conclusion of run-in, 10% after calibration and 65% after the 50-hr test. Long was satisfied with this arrangement.

Long requested that a copy of the single-cylinder order be forwarded to the Air Corps Inspector on part-time duty at Continental so that single-cylinder equipment inspection and acceptance could be expedited. Inspection Branch was contacted and Long advised that it had been done. [USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 109 – 110.]

15 Oct 1935 Progress Report. After 18:52 hrs endurance running on the blade rod, the single-cylinder barrel cracked circumferentially above the first stiffening flange from the shrink band at the jacket bottom. Another cylinder was placed on the test engine and testing resumed for another 21:35 hrs until the barrel also similarly cracked. Total blade rod endurance time under contract conditions was 40:27 hrs. The shielded HT300A1 spark plugs gave trouble after 3 – 8 hrs operation under contract conditions, compared with 16 – 18 hrs on the original unshielded spark plugs. A replacement cylinder was expected to be assembled to the test engine by 19 October.

Setup for 12-Cylinder Test: Mounting plates were promised for 22 October. The concrete sub-base and steel facings were in place and the floor was complete. The electric dynamometer, together with its conduit, wiring and resistance grids, had been set up. Some time was spent studying a method to obtain torsional vibration characteristics of the crankshaft/reduction gear system. A candidate method involved using the cathode ray oscillograph with a magnetic actuator.

Engineering: Routine drawing updates continued. Details for the airplane-type mounting plate were completed and were to be submitted to the Air Corps for approval by 19 October. A stress analysis was included with the above drawings. The mathematical investigation of two-mode crankshaft vibration had been continued in an effort to determine the value of the stresses and their influence on crankshaft failure. A report was in preparation. Layouts for test equipment in the 12-cylinder test cell continued.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 112 – 115.]

26 Oct 1934. Prescott published Memorandum Report E-57-285-23 confirming a 17 to 19 Oct 1935 conference at MatCmd between Continental's Tilley and MatCmd's Prescott on XO-1430-1 single-cylinder test. Tilley brought detailed drawings of the proposed mount plate for MatCmd comments. This was discussed with Aircraft Branch personnel and was left with them for study and suggestion as to mount pad dimension standardization between the Continental O-1430-1 and Lycoming XO-1230-1 engine. Tilley stated that the new-design multi-cylinder connecting rods had run about 40 hrs under contract conditions and that the valve gear had about 70 hrs under contract conditions without failure. Tilley stated that a peculiar cylinder barrel breakage had been encountered. Two cylinder sleeves had cracked circumferentially above the second stiffening flange. These barrels broke at about 10 hrs testing time. Analysis of this breakage was incomplete, but Tilley believed that the forging structure was at fault. Only a small quantity had been purchased from the steel company, which doubtless used whatever equipment was available and probably did not leave enough stock for roughing, so as to produce a sound forging. No such crack was observed in the cylinder in which the piston and rod broke during the pervious attempt to complete a 50-hr test on the 12-cylinder rod and valve gear. On the basis of these failures, the cylinder barrel forgings, which had been procured for the 12-cylinder engine, were rejected and new forgings ordered.

Tilley stated that a peculiar condition had arisen in connection with ring wear in the present testing program. When rings previously procured for single-cylinder testing were used, no excessive ring wear was observed, but when rings were drawn from stock, which had been procured for the 12-cyllinder engine, the wear was very rapid, indicating some fault in the rings that had been procured for the 12-cylinder engine. If further investigation bore this conclusion out, those rings were to be rejected and new rings procured for the 12-cylinder engine.

Tilley stated that the new reduction gears, which had been fabricated by Farrell-Birmingham Company, Inc., because of the first gear set rejection by the Air Corps Inspector, were now on hand and appeared to be perfect.

Tilley stated that 12-cylinder subassemblies were being built up, but that the complete engine could not be assembled because of cylinder, piston, and connecting rod fabrication pending single-cylinder test completion.

Prescott/MatCmd Torsiometer Patents

Connection of the MatCmd torsiometer to the XO-1430-1 engine was discussed. It was feasible to use the standard torsiometer at the engine front by passing a hollow shaft through the propeller shaft back to the crankshaft front, or the quill shaft rear using special propeller nut to support the torsiometer. All O-1430 accessory drives used resilient members so that crankshaft torsional vibration would not be observable at the starter or generator mount and the crankshaft rear end was not accessible for torsiometer attachment.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 116 – 118.]

31 Oct 1935 Progress Report. The blade rod 50-hr test was complete. Inspection of the rod and bearing revealed no trouble. The cylinder barrel and connecting rod were magnafluxed and no defects found. A report of this test was being prepared and would be submitted separately. The test engine was rebuilt with the forked rod and the same cylinder used. After 0.5 hr under contract conditions the test engine crankshaft broke at the crankpin magneto end. The new crankshaft forging was promised for 5 November.

Continental and Bethlehem Steel Company metallurgical examination of the broken cylinder barrels previously reported revealed that while the production barrel steel was slightly more open-structure than the hand-forged carbon barrels previously used, the steel in the failed barrels represented the best obtainable. As the operating conditions with the short rod were slightly more severe than the previous tests, layouts were made for a stiffer and heavier barrel.

Contract W-535-AC-7917 – Setup for 12-cylinder Test: Angles were riveted to the mount plates and the assemblies finished-machined. Completion was promised by 13 November. Plans for supercharger test using engine assembly test stand were started. An orifice tube for measuring air flow to the supercharger was started. The coupling for connecting the engine to the dynamometer was complete except for splines, the cutting of which was in process.

Engineering: Routine drawing updates continued. Airplane mounting plate details were submitted to the Air Corps for moment and approval in the Conference on 17 Oct 1935. As additional study was necessary by MatCmd, further action was deferred. Revised blade connecting rod drawings and valve rocker adjusting screw assembly were made and sent to the Air Corps for approval. Tabulation of accumulated and desired XO-1430-1 parts fits continued.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 120 – 123.]

20 Nov 1935. Prescott published Memorandum Report E-57-285-25 documenting a 16 Nov 1935 conference with Continental's Kinnucan and Morehouse. Kinnucan brought up the question of drawing and manufacturing limits on bevel gears, with the idea of eliminating shims for adjusting backlash. He showed that variations in backlash of 0.020" or more were possible with the manufacturing limits specified on the engine parts involved. All agreed that this tolerance was too large and it was proposed that the bevel gear thrust bosses be left long enough so that a light cut during assembly could give the correct bevel gear backlash. In this case only two limit dimensions were involved; one for the case and one for the gears. Backlash could be kept within reasonable limits. As to the desired backlash, it was stated that MatCmd preferred a minimum of about 0.002", desired 0.007", and set a 0.012" maximum in order to eliminate extreme variations in engine timing, as well as gear impact loading during operation.

Kinnucan asked about the ethylene glycol brand used by MatCmd, stating that the Eveready ethylene glycol Continental had been using deteriorated in service. MatCmd used plain ethylene glycol without an inhibitor since the aircraft engine operating conditions caused rapid inhibitor deterioration.

Kinnucan stated that the stud drawings to which MatCmd had objected had been redrawn so that the threads were correctly represented and notes updated, but that MatCmd's Van Dykes would not be replaced until contract completion, after all changes had been made and when a complete new Van Dyke set was to be delivered.

Kinnucan stated that the failed cylinder barrel composition did not differ much from previous successful barrels. However, in previous tests a 9.25" connecting rod was used, while a 7.75" rod was used in current tests, thus considerably increasing the side thrust on the cylinder barrel. In view of this, the cylinder barrel wall thickness had been increased by 0.020", making them 0.100" thick. Two additional reinforcing ribs had also been added. While this would result in a slight weight increase, Kinnucan thought it essential to address the failures. The second 50-hr test was to resume with a new crankshaft, the latest forked connecting rod design, and stronger cylinder barrels.

Kinnucan requested the latest SAE No. 50 propeller shaft data. He also asked about MatCmd's attitude regarding the propeller shaft that had been magnafluxed and dimensionally inspected at MatCmd. The spline spacing had been found slightly in error. MatCmd stated that the slight dimensional discrepancies did not prevent the standard hub and No. 50 spline gage fitted the shaft properly, so MatCmd's and the Air Corps Inspector's previous acceptance would stand.

Kinnucan discussed the O-1430-1 installation drawing and advised that a new, completely up-to-date drawing would soon be available. This new drawing was to correct previously-identified discrepancies and would be to scale. He asked whether the carburetor should be shown in place. MatCmd opined that since the first engine would be tested as a carbureted engine, the drawing should show that equipment. The question of installing the fuel injector and fuel lines on the wood O-1430-1 model was discussed. The engine had been laid out around an early Marvel Chandler fuel injector with provision for readily adapting any future fuel injector type. The final manifold and fuel injection lines design was not yet complete, so it seemed prudent to make the model in a way that allowed either a carburetor or fuel injector to be fitted for mock-up.

A suitable drive for the MatCmd torsiometer was discussed and it was decided that the most promising attachment method was via a special starter gear train that would be geared directly to the crankshaft forward end. This would involve fabricating four special gears, but no modification to the basic engine. The torsiometer would connect directly to the crankshaft rear end, permitting torsional characteristic investigation while running the 50-hr development test.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 124 – 126.]

15 Nov 1935 Progress Report. A request to purchase a test engine crankshaft, along with a drawing of the proposed replacement crankshaft was sent to MatCmd. Wyman-Gordon supplied a hammer forging, shop work was started and shaft completion was expected on 20 November. A new cylinder was assembled using a barrel with slightly thicker walls and closer stiffening rib spacing. Single-cylinder tests were expected to resume on 21 November.

W-535-AC-6322 Items 2 and 3 – Crankcase and Crankshaft, and W-535-AC-6834 Items 1 and 2 – Reduction Gears and Rear Accessory Housing Assembly. Complete and accepted.
W-535-AC-6834 Item 3 – Camshaft Housing Assembly. Rocker arms and associated parts were in work. A 16 Nov 1935 conference between MatCmd Power Plant Section, Airplane Section and Continental addressed the mounting plate; Continental was to submit new layouts and details to MatCmd for approval.
W-535-AC-6834 Item 4 – Connecting Rod Assemblies. Forked rod release was delayed pending single-cylinder testing.
W-535-AC-6834 Item 5 – Cylinder Assemblies. Cylinder barrel release was delayed pending single-cylinder tests.
W-535-AC-6834 Item 6 – Piston Assemblies, etc. to Complete Engine. Piston release was delayed pending single-cylinder testing. Radio shielding completion awaited engine assembly. The complete engine, minus cylinders, rods and valve gear was assembled. Cover plates were made for the cylinder openings and the engine was ready for supercharger testing.

Engineering: Routine drawing updates continued. Additional airplane-type mount plate studies were discussed during a 16 Nov 1935 Wright Field conference. A revised carburetor elbow drawing had been produced and was ready for release. Work on the fits and clearance charts continued. The single-cylinder test engine balance was checked, and new balance weight drawings were made and released.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 128 – 130.]

30 Nov 1935 Progress Report. A cost summary for the single-cylinder test engine replacement crankshaft, along with revised drawings, was prepared for MatCmd. The crankshaft had been completed and the test engine assembled with a new cylinder, forked connecting rod and big-end bearing, and the rig run-in. Endurance running under contract conditions was begun, with stops for inspection at 5, 15 and 30 hrs. Connecting rod magnaflux inspection revealed no flaws and the other parts were in good condition. Total time for this cylinder and forked rod was 30 hrs.

W-535-AC-6322 Items 2 and 3 – Crankcase and Crankshaft, and W-535-AC-6834 Items 1 and 2 – Reduction Gears and Rear Accessory Housing Assembly. Complete and accepted.

W-535-AC-6834 Item 3 – Camshaft Housing Assembly. Rocker arms and associated parts were in work. New mounting plate layouts were submitted to MatCmd and awaited approval.
W-535-AC-6834 Item 4 – Connecting Rod Assemblies. The blade rod was in work; forked rod release was delayed pending single-cylinder testing.
W-535-AC-6834 Item 5 – Cylinder Assemblies. Cylinder barrel release was delayed pending single-cylinder test completion.
W-535-AC-6834 Item 6 – Piston Assemblies, etc. to Complete Engine. Piston release was waiting on single-cylinder testing; radio shielding completion awaited engine assembly. The complete engine, minus cylinders, rods and valve gear was assembled and ready for supercharger testing.

12-Cylinder Engine Test: Miscellaneous small parts for the mount plates had been made and some Prestone system pipe fittings received. Layouts for electric dynamometer and water brake connection by torsion members had been completed and parts released for manufacture. Design of fuel weighing scale to incorporate an electric switch for simultaneous stop clock operation, revolution counter and light had been started.

W-535-AC-7917 – Mounting Plates, PN 500555: Complete and accepted by the Air Corps Inspector.

W-535-AC-8196 – XO-1430-1 Engine Mock-Up: Construction of all parts had begun except the fuel charger, which was pending information from MatCmd. Details for metal facings for accessory supports were made and released for Manufacture.

Engineering: Routine drawing updates continued. Revised airplane-type mounting plate layouts were made in accordance with the 16 Nov 1935 Wright Field conference and were mailed to Wright Field for approval. Complete details were to be finished by 7 December. Layout and details of the new single-cylinder crankshaft, including flywheel cones and other associated parts, had been made.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 132 – 134.]

15 Dec 1935 Progress Report. Single-cylinder testing under Contract No. W-535-AC-7917 completed the forked connecting rod test, and a report was prepared and delivered to MatCmd. The test engine and cylinder were run-in with piston rings from the batch procured for the 12-cylinder engine. These rings had square-cut gaps instead of the previous angled gaps. Inspection after run-in showed the rings had slight wear. The rings were then run to 3,000 rpm and 13 inHgG boost when the run was stopped because the exhaust valve developed a leak allowing the sodium to escape. The test engine was not damaged by the sodium. This valve had been operated for 87 hrs of which 63 were under contract conditions.

W-535-AC-6322 Items 2 and 3 – Crankcase and Crankshaft, and W-535-AC-6834 Items 1 and 2 – Reduction Gears and Rear Accessory Housing Assembly. Complete and accepted.
W-535-AC-6834 Item 3 – Camshaft Housing Assembly. Rocker arms were in inspection and associated parts in work. Material was on order for the mounting plates.
W-535-AC-6834 Item 4 – Connecting Rod Assemblies. When the forgings were rough-machined it was discovered that the hardness was above specification. These rods were erroneously re-heat-treated. After magnaflux inspection they were full of cracks and rejected. New rods were placed in work and enough additional forgings ordered to make a complete set.
W-535-AC-6834 Item 5 – Cylinder Assemblies. Cylinder barrel forgings were promised for 18 Dec 1935. Other parts were finished to the point of assembly.
W-535-AC-6834 Item 6 – Piston Assemblies, etc. to Complete Engine. Pistons were in work. Radio shielding completion awaited engine assembly. The engine, minus the cylinders, rods and valve gear, was assembled.

12-Cylinder Engine Test – Contract W-535-AC-8131: The engine was set up on the dynamometer for supercharger tests. Run-in was started. The cast iron 12-cylinder engine base had been finished-machined as well as the supporting screws and spring mounting parts. Two test mounting plates, PO 36-1088 under Contract No. W-535-AC-7917, PN 500555, had been completed and accepted by the Air Corps Inspector.

Contract W-535-AC-8196, XO-1430-1, PO 36-2160, Engine Mock-Up: All parts had been completed and were partially assembled. A wooden fuel injector mock-up, Air Corps type S-2 had been started.

Engineering: Routine drawing updates continued. Revised airplane-type mounting plates had been made incorporating changes per Air Corps letter of 7 Dec 1935. Details had been made for the plate and brackets. Drawing checks for all mount drawings was to be completed by 21 December.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 136 – 139.]

30 Dec 1935. Prescott issued Memorandum Report E-57-285-26 documenting a 13 Dec 1935 MatCmd conference including Ray Long of Continental, and Chenoweth and Prescott of MatCmd. Long asked about the contract status for testing the 12-cylinder engine. Investigation showed that this had again been returned to Washington for revision, but was once more ready for Continental's signature. Long carried the papers with him to Detroit for signature and immediate return to MatCmd for transmittal to Washington. Long pointed out the urgency of completing this contract as quickly as possible, since the supercharger was required to be tested within two weeks to be inside GE's 90-day guarantee. MatCmd assured Long in a conference with Capt Snodgrass that such testing would not cause legal difficulties subsequent to Continental's signature, but prior to final Washington approval.

Long inquired about the status of the single-cylinder test engine and the cylinder, piston, valve gear, connecting rod, and crankshaft Continental wished to conduct piston ring or indicator tests. Long was told that the parts called for in connection with contracts covering single-cylinder tests should be submitted to the Air Corps Inspector for payment, after which the equipment would be loaned to Continental for further testing, upon formal request from Continental.

The question of the MatCmd torsiometer to the XO-1430-1 engine was discussed. Long stated that Continental's cost estimate for conducting this test was $500.00. He was told that no funds were obligated to cover this test, but that it was in Continental's and Air Corps interest to conduct torsiometer tests before the 50-hr development test.

Long asked about the procurement authority to cover the single-cylinder test engine crankshaft, replacing the one that had failed after 700 hrs testing time. MatCmd advised him that this was in process and would reach Continental in the near future.

[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 136 – 139.]

31 Dec 1935 Progress Report. No single-cylinder running had occurred during the last two weeks of December because no answer had been received regarding test engine use. Wilcox-Rich was exchanging two-piece exhaust valves for a one-piece type that were promised to be free from the leakage previously reported. Replacement valves for the complete engine were to be available on 15 Jan 1936.

The Scintilla Company had appointed Walter Lees as local representative for H.T. Spark Plugs to insure closer contact coordination on spark plugs. As unsatisfactory spark plugs had been returned to H.T., there was to be some delay in forwarding spark plug samples requested in the Wright Field letter of 26 Dec 1935. B.G. had sent spark plugs that could not be used because of lack of space. A Bosch radio-shielded spark plug had been received and awaited test.

A metallurgical report of piston rings that were satisfactory in test, and the rings procured from the 12-cylinder engine batch was being prepared.

W-535-AC-6322 Items 2 and 3 – Crankcase and Crankshaft, and W-535-AC-6834 Items 1 and 2 – Reduction Gears and Rear Accessory Housing Assembly were complete and accepted.
W-535-AC-6834 Item 3 – Camshaft Housing Assembly. Rocker arms were in inspection and associated parts in work. Mount plate completion was promised for 10 Feb 1936.
W-535-AC-6834 Item 4 – Connecting Rod Assemblies. Replacement forgings had been received and the new rods were in work.
W-535-AC-6834 Item 5 – Cylinder Assemblies. Cylinder barrel forgings had been received and were in work. Other parts were complete to the point of assembly. Exhaust valves were being replaced with valves with integral heads.
W-535-AC-6834 Item 6 – Piston Assemblies, etc. to Complete Engine. Pistons were in work. Radio shielding completion awaited engine assembly.

12-Cylinder Engine Test: The engine was run for 2 hrs up to 750 rpm propeller speed. Inspection after the test showed bevel gears that drove the oil pump were being non-uniformly worn. These parts were being re-inspected dimensionally. A bushing in the rear reduction gear case, which was the accessory drive idler gear shaft bearing, had turned in the casting, and was being replaced. The 12-cylinder cast-iron base had been cleaned, painted and assembled. Mounting plates, from PO 36-1088 were complete and being held for use in the complete XO-1430-1 engine test.

W-535-AC-8196 – XO-1430-1 Engine Mock-Up: The wooden engine model had been completed, accepted by the Air Corps Inspector, and shipped to Wright Field on 31 Dec 1935. Bill of Lading number was WQ 1319363.

Engineering: Routine drawing updates continued. Assembly and detail airplane-type mount drawings required under W-535-AC-6834 were completed and a blue print file had been forwarded to Wright Field for comment.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 143 – 145]

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