Lycoming XR-7755, 1947

15 Jan 1947. The AMC wrote Lycoming regarding Contract No. W 33-038 ac-564 stating that: 1) The AMC was revising its program related to this contract and found it necessary to stop the procurement of an additional engine and on the compounded XR-7755 engine version. 2) AMC was not in the position to extend the basic contract beyond what was then obligated. Contract modifications were being considered that would insure a 50-hr flight approval test IAW AAF Specification XR-28398-A was completed even at the expense of sacrificing other contract items. AMC wanted to eliminate, or hold in abeyance, items pertaining to future development so that remaining funds would go toward this test with a minimum of accompanying development. This might have required modified ratings, if necessary, since the test was to be accomplished with engines and parts then available. More information is available in the Contracts and Administrative Section. [RG 342 RD 2311 XR-7755 Contract W-33-038AC-564 Proposed Procurement & Mods]

18 Feb 1947. During a telcon from Lycoming, Ryder and Pinto (the new Army Air Forces Resident Inspector) advised Blackwood that a propeller nut wrench was needed. The reworked supercharger had arrived along with an injection pump installation drawing. Lycoming intended to install the supercharger and fuel injection pump on engine #101, which was headed back to the test stand. [Penciled notes by J.G. Blackwood. RG 342 RD2311 XR-7755, 1943-1948: 503-602 Conf and Tel Notes.]

26 Feb 1947. Carpenter from Lycoming advised Blackwood that Lycoming had put the work reduction into effect and had stopped building the fourth parts set to the extent possible (i.e., no new jobs were started, but those in process were completed). Engine #101 was on the dynamometer, which was having vibration trouble; the engine was rear mounted, but its front end had to be stabilized. The carburetor was erratic up to 1,600 rpm. The dynamometer bearing had heated up, which was being investigated. The run was about four hours short of completion. Engine #102 was being built up with the new link pin retainer and was expected to be ready to run in a couple of weeks; if problems arose with the #102 run, then new parts would be installed. Reduction gear parts were still 3-4 weeks away. The 3-cylinder test engine was back in its test stand. The new link pin retainer and link pins plated with silver-lead-indium were in. [Penciled notes by J.G. Blackwood. RG 342 RD2311 XR-7755, 1943-1948: 503-602 Conf and Tel Notes.]

Engine #101 Run-in Log
Power (bhp)	4,500 to 5,100	4,000 to 4,500	3,000 to 4,000	2,000 to 3,000	1,000 to 2,000	0 to 1,000
Time (hr:min)	1:15	0:47	1:52	3:00	4:27	4:46

4 Mar 1947. During a telcon from Lycoming, Ryder and Pinto reported that #101 had been run in to 2,570 rpm and 5,000 hp. Test engineers were fixing oil leaks, and when the run-in was complete a 50-hr test would begin on 5 or 8 Mar 1947. It appeared Lycoming would just get by with a 100°F induction air inlet temperature and no ram pressure requirements, a marginal situation. The hydraulic pump Blackwood had sent had a 16-tooth spline instead of the 12-tooth spline required by the drive; Blackwood advised the test engineers to proceed without the pump. After engine #101 had completed a 15.5 hr run-in, Lycoming provided a chart of time at power. The 50-hr test would begin Monday, 10 Mar 1947. [Penciled notes by J.G. Blackwood. RG 342 RD2311 XR-7755, 1943-1948: 503-602 Conf and Tel Notes.]

4 Apr 1947. During a telcon from Lycoming, Carpenter apprised Blackwood that the dynamometer on engine #102 was down with front bearing trouble and had been for over a week. This had happened during run-in up to 1,900 rpm. The 3-cylinder engine's main drive shaft to auxiliary section driving fuel injector and oil pump twisted off with a torsional failure due to a bad 1 1/2 order vibration at 2,200 rpm. This did not apply to the 36-cylinder engines. The 3-cylinder was reassembled, run in for two hours and failed again with a broken link rod and badly damaged piston due to a piston pin circlip coming out; it had run 22.5 hrs at maximum cruise power. Engine #101 knuckle pins arrived and assembly would start next week. [Penciled notes by J.G. Blackwood. RG 342 RD2311 XR-7755, 1943-1948: 503-602 Conf and Tel Notes.]

9 Apr 1947. Carpenter reported that the 4,000 hp dynamometer bearing pad casing had been off for about two weeks. He expected #101 to be in operation in about a week with the 0.56 reduction gear and torquemeter. The 3-cylinder engine crankshaft and crankcase was serviceable and would be rebuilt next week. [Penciled notes by J.G. Blackwood. RG 342 RD2311 XR-7755, 1943-1948: 503-602 Conf and Tel Notes.]

12 May 1947. Lycoming's C.H. Wiegman submitted preliminary XR-7755-1 dynamometer calibration data, which demonstrated a minimum carbureted bsfc of 0.38 lb/hp/hr with the minimum bsfc points limited by detonation. Lycoming surmised that better mixture distribution and lower-cylinder charge temperatures would be obtained with cylinder head fuel injection. One friction reading at 1,600 rpm and 22 inHgA manifold pressure yielded a friction horsepower of 305. This all pointed to a lower multi-cylinder fuel consumption than was anticipated from single-cylinder data.

[J.G. Blackwood Notes. RG 342 RD2311 XR-7755, 1943-1948: 503-602 Engineering Data.]

Engine #101 was coming off the propeller stand for inspection after 50-hr endurance test. Pinto was helping try to figure out a way to mount a Curtiss controllable propeller on the 0.56 reduction gear, which had a No. 70 shaft and a No. 80 nose. The problem was how to mount the electric propeller brush holder housing onto the nose bolt flange. Pinto had ruled out the existence of an experimental adapter and was hoping to rework a No. 80 nose casting to work. [Penciled notes by J.G. Blackwood. RG 342 RD2311 XR-7755, 1943-1948: 503-602 Conf and Tel Notes.]

Preliminary Mixture Control Data
rpm	1,000	1,000	1,300	1,300	1,600	1,600	1,600	1,600
bhp	890	1,000	910	1,090	1,410	1,550	1,810	1,970
bsfc (lb/hp/hr)	0.390	0.380	0.420	0.405	0.405	0.395	0.385	0.380
bmep (psi)	91	102	72	86	90	99	116	126
damp (inHgA)	22	24	18	20	22	24	26	28

2 Jun 1947. Experimental Department Report, Liquid-Cooled Section for 16 May – 1 Jun 1947.

Multi-Cylinder Engine Tests
1. XR-7755 #101, Project T-223 Sup. Item 4, Running Time 43:36 hrs. The scheduled 50-hr endurance test at cruise conditions was completed. Inspection of the reduction gear showed these parts to be in good condition. The engine was to be removed from the stand for 100% visual and magnaflux inspections.
2. XR-7755 #102, Project T235 sup. Item 12-11, Running Time 0:00 hrs
  1. Preliminary Induction System Temperature Survey: report was being written.
  2. Preliminary Calibration: report was being written.
  3. Temperature Survey and Calibration: The reassembly of this engine was about 50% complete. Testing was to begin during the week of 9 Jun 1947.
1-Cylinder Test Engines
1. SC-215-3, Project T-235, Sup. Item 2, Account 194, Running Time 19:54 hrs. This test was about 80% complete. Runs were first made to determine the cylinder vibration characteristics with the detonation pickup adapter located on the cam cover and the intake port compared to the standard location in the fuel injector boss. Knock limit runs of 3 – 4 points were then made with the pickup located on the intake port, cam cover and standard location. Results showed that the cam cover pickup location was comparable to the standard location at high cruise and takeoff conditions but it differed at low-cruise operating conditions by about 10 – 20 imep. The new Sperry knock meter was calibrated for single-cylinder engines with the pickup located in the injector boss.
3-Cylinder Test Engine
1. 3C-645 No. 7, Project T-230, Sup. Item 1 Account 204, Running Time 0:18 hrs. Simulated 50-hr Preliminary Flight Test Rating According to Specification No. XR-28398-A. The engine was completely assembled and installed on the test stand. Run-in of the new engine parts was underway in conjunction with study of the crankshaft and rod mechanism movement.
Special Problems Laboratory
1. Fuel Injection Lines for the Multi-Cylinder Engine. Injection line support clamps were received and work fabricating the finished injection lines had started. Lycoming expected the Bendix fuel injection nozzles and American Bosch fuel control unit would arrive during the first week of June.
2. Oil Scavenge Pump, Project T-193, testing had been discontinued; a report was to be written.
3. Multi-Cylinder Valve Gear, Project T-190, results were being typed.
4. Torquemeter and Pump Test initial torquemeter report was being typed; report on the second unit was ready for editing.
5. Supercharger Laboratory
  1. Performance and Distribution Tests of the X-7 Supercharger Housing using the F-8053-Y Baffle, Project T-233, Contract Item 8, report was being edited.

[J.G. Blackwood Notes. RG 342 RD2311 XR-7755, 1943-1948: 503-602 Engineering Data.]

Engine Time at Power, 16 May 1947 to 1 Jun 1947
Test Engines Time at Power
imep at rpm	264 at 2,800	241 at 2,500	155 at 2,200	143 at 1,600	90 at 1,300	Misc	Period Time	Total Time
Eng No. SC-215-3 Time	0:00	2:54	3:14	1:45	0:00	12:01	19:54	250:06
imep at rpm	231 at 2,600	205 at 2,300	155 at 2,200	143 at 1,600	80 at 1,300	Misc	Period Total	Total Time
Eng No. 3C-645 Time	0:00	0:00	0:00	0:00	0:00	0:18	0:18	118:01

XR-7755 Time at Power
Rating, Power Range (hp)	Takeoff, ≥ 5,000	Normal, 5,000 – 4,000	High Cruise, 4000 – 3,000	Medium Cruise, 3,000 – 2,000	Low Cruise, 2,000 – 1,000	Misc < 1,000	Period Time	Total Time
XR-7755-101 Time	0:00	0:00	0:00	31:28	6:50	5:08	43:26	118:00
XR-7755-102 Time	0:00	0:00	0:00	0:00	0:00	0:00	0:00	22:30
XR-7755 Total Time								140:30

Lycoming XR-7755 Performance Data

X-7 Fuel Consumption	XR-7755-102 Performance	XR-7755-1 Minimum Fuel Consumption

2 Jul 1947. In a Lycoming telcon, Carpenter related that the 0.56 reduction gear had been mounted on the dynamometer and run-in up to 1,600 rpm. It had then uncoupled due to pinions being stripped from their carrier. An oil hole lubricating the pinions had become misaligned during assembly; this problem was only applicable to the 0.56 reduction gear. It would be rebuilt as soon as possible. The 3-cylinder engine had been rebuilt with old connecting rods but no added weights. This was equivalent to new rods in the 36-cylinder. Lycoming planned to run it 50 hrs at full power, 2,600 rpm and 5,000 equivalent hp. [Penciled notes by J.G. Blackwood. RG 342 RD2311 XR-7755, 1943-1948: 503-602 Conf and Tel Notes.]

26 Aug 1947. Carpenter reported the engine #102 would be ready to test with new rods in about a week. The 3-cylinder engine would be running at week's end with full-floating pins. In fatigue tests past 10 million cycles, over 1 in² silver came off the unloaded side; Lycoming was making up bronze bushings. The 36-cylinder engines had logged between 130 and 135 hours. [Penciled notes by J.G. Blackwood. RG 342 RD2311 XR-7755, 1943-1948: 503-602 Conf and Tel Notes.]

Engine #102 Knock Limit Data
Speed	bsfc	Power
1,800 rpm	0.40 lb/hp/hr	2,300 hp
2,000 rpm	0.41 lb/hp/hr	2,700 hp
2,200 rpm	0.415 lb/hp/hr	4,000+ hp

1 Oct 1947. In a Lycoming telcon, Don McKay reported the engine #101 was being assembled for endurance running and would be complete in about two weeks. Engine #102 was on the dynamometer undergoing runs to establish its knock limit. A scavenge out tube leak had caused a fire with damage apparently only to the ignition system. [Penciled notes by J.G. Blackwood. RG 342 RD2311 XR-7755, 1943-1948: 503-602 Conf and Tel Notes.]

13 Oct 1947. Carpenter telephoned to report that the one bank of master rod link pin bearings had started to crack. Although not stated, these were apparently in #101, which had recently been rebuilt. This engine had only been run to 4,000 hp at 2,300 rpm. New rods with floating pins were prescribed. The 3-cylinder link pins had accumulated about 20 hrs, 11 of which were at takeoff power. Its pins were satisfactory. On an unspecified engine, about 6 hrs into a 50-hr test, a coolant jacket cracked at a coolant output fitting. A new bank design included a gusset to reinforce this area on all banks. The test would be resumed next day. In a later report, the coolant pump had cracked with 9 hrs left to go. [Penciled notes by J.G. Blackwood. RG 342 RD2311 XR-7755, 1943-1948: 503-602 Conf and Tel Notes.]

The other engine (presumably #102) was on the dynamometer and would be run early next week. Its run-in would be up to 5,000 hp, along with other calibration activities. [Penciled notes by J.G. Blackwood. RG 342 RD2311 XR-7755, 1943-1948: 503-602 Conf and Tel Notes.]

17 Dec 1947. Carpenter reported that link pins were satisfactory and that a secondary balancer quill shaft had broken, but running continued. This presumably referred to engine #102. [Penciled notes by J.G. Blackwood. RG 342 RD2311 XR-7755, 1943-1948: 503-602 Conf and Tel Notes.]

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