Solar Aircraft Company, San Diego, California

12 September 1949: Chance Vought (CV) wrote a memo to the Navy Bureau of Aeronautics (BuAer) asking for approval of the overall engine replacement time in the F6U-1 in spite of various difficulties regarding the starter connections, afterburner (AB) clamps and connections, and various other difficulties related to the lack of clearance in the fuselage.

13 September 1949: BuAer refused to authorize CV flight tests of a production F6U-1A with an AB with the revised Solar 551 burner installed on contract NOa(s) 8783. (At that point the early production airframes were undergoing initial airframe and maneuvering testing. In dives a Mach number of 0.775 had been reached in a dive from 31,000 ft before pitch-up prevented a faster speed during Flight 21 on BuNo 122480 on 17 September 1949.)

20 September 1949: Something must have removed BuAer’s objection, as on Flight No. 36 of F6U-1 BuNo 122478, an AB with a modified 551 fuel ring was used. An AB climb was made beginning at 10,000 ft and 300 kt IAS and continuing to 31,000 ft where the AB was shut down due to rough operation and a decreasing Turbine Out Temperature (TOT). The TOT had been properly controlled up to 28,000 ft before it began to decline by at least 20 – 30°C. AB starts were successfully made at 23,400, 20,600, 15,200, 11,400 and 10,000 ft at the relative airspeeds of 300, 320, 244, 261, and 180 kt IAS. Operation was rough until the combat power temperature came up to about 630°C and operation smoothed out. The AB start at 20,600 ft was held in a climb to 26,600 ft then shut down. An attempted restart at 27,000 ft was unsuccessful.

22 September 1949: BuAer authorized 20 ABs to be made available for F6U-1 installation. Solar was instructed to ship six as of that date.

22 September 1949: BuAer notified CV via the Navy Bureau of Aeronautics Representative (BARR) that they were authorized to make 13 AB test flights including test stand operation as agreed on 20 September 1949 in conference under contract NOa(s) 8783.

23 September 1949: The Ryan BARR was asked to provide 12 heavy gauge AB shrouds to CV in Dallas as replacements for the initial shrouds shipped with the Solar ABs under production contract NOa(s) 10023. The original shrouds were repeatedly cracking beyond field repair limits when the ABs were used.

26 September 1949: Flight 38 F6U-1 BuNo 122478. The AB was turned on at 10,000 ft at 300 kt IAS and the aircraft climbed until the AB blew out, this occurring at 36,500 ft. The TOT did not get too low. The AB was smooth throughout the climb. AB restarts were attempted at 5,000 ft intervals while descending with the first successful restart occurring at 25,000 ft at 290 kt IAS. At 20,000 ft, a successful start was made at 220 kt IAS but would not relight at 200 kt IAS.

26 September 1949: CV issued a work order that was to provide for the installation of a tailpipe instead of the Solar AB on the F6U-1 aircraft if necessary. Written notes clarify the original intent was to provide a way to fly the airplanes if AB delivery was late. It was decided to allow the work order to be retained as a provisional option should trouble with the ABs be encountered.

27 September 1949: XF7U-1 BuNo 122472 Flight 128. Pylon installation check. ABs started at 5,000 ft at 305 kt IAS, throttles at Military. Both starts were smooth and gave rapid airframe acceleration with airspeed building up to 415 kt IAS before a climb was initiated. Airspeed declined at 5 kt per 1,000 feet gained. AB operation was very smooth at all times. At 15,000 ft the climb was stopped and a stabilized run was made with the ABs operating for another 5 minutes (7 minutes total) with the air speed stabilized at 447 kt IAS (0.89M). TOTs were low at 580°C left and 590°C right.

28 September 1949: F6U-1 BuNo 122480 Flight 27. After a normal takeoff and climb to 12,000 ft, the AB was started satisfactorily at 12,500 rpm at 255 kt. The climb was continued to 20,000 ft where a speed of 0.765M was reached. Even with full nose-down elevator trim and push force of approximately 200 lb, the airplane was unable to attain a speed higher than 0.765M. A climb was then started to reach 30,000 ft, but the AB blew out at 28,700 ft. In a dive from that altitude a speed of 0.805M was reached using full nose-down trim and 180-200 pounds of push force. At that point the elevator was observed to be in the full down position. A higher speed could not be attained.

28 September 1949: BuAer asked the Westinghouse BARR to inform them of any actions being taken to resolve recurring issues being experienced by CV with the acceleration fuel valve on the R-46 fuel control on the J34-WE-30A engine used in the F6U-1. Engine roughness was being reported over an rpm range of 8,000 – 11,000 rpm with a maximum roughness noted at 10,000 rpm.

28 September 1949: XF7U-1 BuNo 122472 Flight 132. AB operation check above 20,000 ft with the ABs operating. Engine startup was normal on left engine. On the right engine a small explosion was heard in the tailpipe as the engine lit off. Inspection revealed no damage. Aircraft began a left yaw as the gear retracted. Right rudder could not stop the yaw and the throttles were closed. The left wing made contact with the ground and the aircraft hit in a left skid. The nose section broke off just aft of the cockpit and rotated 90°, ending on its left side. The pilot was unhurt. The ABs had not been used.

30 September 1949: F6U-1 BuNo 122479 Flight 32. The AB eyelids were clamped in the closed position for the flight, the purpose of which was investigation of high Mach number handling, speed brake limits, rudder overbalance and aileron rolls. The AB was not used during the flight.

30 September 1949: BuAer responded to CV’s request for a waiver on the F6U-1’s engine replacement time. In view of the limited number of airframes being procured and that the airframe was largely the same as the XF6U-1 except for the addition of the AB in the engine compartment, it was considered that any major redesign at this time to improve the various deviations pointed out by CV were not warranted.

5 October 1949: Solar Contract NOa(s) 8203 Program Progress Report for September 1949:
The original simulation of the altitude data correlation method used the compressor inlet total pressure, turbine discharge total pressure and turbine discharge temperature. Experience and further study indicated that the most practical data for altitude simulation were the total and static pressure at the burner inlet. The curves in Figure 1 were taken from calculated data and would be used for convenient determination of a flight condition on any of the various altitude test stands.

Fig. 1. Burner Inlet Pressure versus Altitude for Various Airspeeds

6 October 1949: F6U-1 BuNo 122478 Flight 39. It proved impossible to successfully weld cracks in the AB burner section before flight and the AB was not used during the flight.

6 October 1949: F6U-1 BuNo 122480 Flight 28. Flight was to obtain oscillograph records at a high Mach number. The AB was started at 12,000 ft, 260kt IAS, 12,500 rpm. A combat power climb was made to 20,000 ft. The flight was terminated due to erratic AB operation (the details were not included in flight report).

7 October 1949: BuAer informed Solar that the request for a delivery date extension by amendment would not be acted upon. The Cost Inspector was authorized to approve for reimbursement invoices for costs incurred in the performance of the contract subsequent to the delivery date in the contract but prior to 15 February 1950. The authorization would allow payment for work then underway under other Navy contracts (NOa(s) 10023, NOa(s) 10051, and NOa(s) 10435), such work having a close relationship to NOa(s) 8203 tasks.

10 October 1949: Four (4) pressure rakes were requested from Westinghouse for use on Contract NOa(s) 8337 under the XF7U-1 AB Program.

12 October 1949: F6U-1 BuNo. 122480 Flight 30. The AB was started at 12,400 ft, 261 kt IAS, 12,500 rpm. After start, the TOT fluctuated between 580 – 595°C accompanied by intermittent slight rough running. The AB was shut down and restarted at 330 kt IAS. The TOT stabilized at 590°C and operation was smooth. An AB climb was made to 21,000 ft. A level run with the AB turned on was made and full nose down trim was required to trim to zero stick force at 0.745 indicated Mach number. Increasing the push force up to 100 lb allowed speed to build to 0.78M with a slight tail buffet being felt in both the stick and rudders. A climb was made to 24,000 and a level run made with the same results. The AB was turned off and a dive starting from 25,000 ft was made. Buffet and airspeed results were the same.

18 October 1949: CV noted that a service bulletin for the F6U-1 had been requested showing a method of installing a tailpipe in lieu of the AB. Thirty parts kits to go with the tailpipe were requested. They asked that one F6U-1 be assigned to CV to allow for installation of a tailpipe and for ground and air testing of the tailpipe installation. After the tests, the airplane would be delivered to the U. S. Navy and flown away with the standard AB installed. The BARR recommended the nineteenth airframe be allocated for the test installation. The service bulletin in question was associated with a memo sent to BuAer by CV on 14 June 1949. This was in response to a BuAer request for a cost quotation for replacing the ABs with a tail pipe in the F6U-1. CV pointed out the change would require an ejector in the tail to ensure proper cooling, the capping off of fuel, air and electrical lines and installation of ballast in the tail to make up the 153 lb weight difference between the AB and the tailpipe. The memo shows the concern of BuAer over the AB readiness for the production F6U-1 airplanes.

F6U-1 performance of the with a tailpipe was estimated to be:

21 October 1949: CV notified BuAer that on 19 September 1949 they had reached agreement on a revised AB altitude test program to consist of 13 flights and supporting ground runs. A revised detailed price estimate was forwarded to replace the rough estimate given for an 8 flight program.

24 October 1949: CV wrote a letter of clarification to BuAer regarding the importance of obtaining from Solar the new 0.031” AB shrouds to replace the 0.025” original shrouds so that the XF7U-1 flight test program could continue. They included the fact that the two cracked original shrouds had only 8.4 hr total time, 1.37 military time and 0.42 hr AB time on the first, 14 AB starts, and 12.60 hr total time, 1.63 hr military time, 0.46 hr AB time, 16 AB starts on the second.

26 October 1949: The BARR was notified to ship the AB fabricated under NOa(s) 8203 (model H085000000) and allocated for used under contract NOa(s) 10435 (F7U-1 modernization) to the Aeronautical Engine Laboratory (AEL) for use on control system tests.

29 October 1949: F6U-1 BuNo. 122478 Flight 43. Afterburner Climb test to 40,000 ft or blow-out altitude. Before flight, replaced the AB, replaced the fuel ring with a modified 551D ring, installed a pressure transmitter in the engine compartment and piped it to an elbow in the CECO-Manning line, removed all emergency systems, replaced the AB ignition leads, replaced the Manning, Maxwell & Moore (MM&M) AB amplifier and control box, and made other airframe and engine checks and updates. The AB was lit at 15,000 ft and an indicated Mach number of 0.63. Operation was very smooth and the TOT regulated well up to 35,000 ft where the temperature dropped off slowly. The thrust output over 30,000 ft was low as evidenced by a very slow rate of climb. At 38,000 ft the AB began to run somewhat roughly and the TOT began to drop rapidly. The AB blew out at 38,500 ft (corrected to 39,140 ft).

1 November 1949: F6U-1 BuNo. 122478 Flight 44. Afterburner Starts and Engine Controls. Successful AB starts were made at 20,000, 25,000, and 30,000 ft. The burner ran slightly rough until the TOTs stabilized. An attempted start was made at 35,000 ft, unsuccessfully but another at 33,000 started with low TOT temperature and ran very rough until it was shut down. Other engine operation checks were made but the last using the emergency governor down to 5,200 rpm resulted in an engine flameout. A restart could not be accomplished and the airplane made a successful dead stick landing.

4 November 1949: BuAer reviewed the engine time report of 1 October 1949 and even though engine WE002025 had 60 hours total time, additional running was authorized prior to overhaul. The reason for the exception was that the engine was being used primarily on the altitude test stand in the role of providing gas for reduced scale burner tests.

Fig. 2. Thrust Performance Tables, A-103B AB Sea Level Static and 551C Burner in H049000000

11 November 1949: Under contract NOa(s) 8783, CV added 13 additional test flights to provide a more thorough investigation of Solar A-103B AB altitude ignition and operating characteristics in the F6U-1.

22 November 1949: CV shipped 12 Solar Model 579 (Non-AB) tailpipes to Mechanicsburg, PA to become reserve stock. Two remaining tailpipes were retained for trial installation of ejector kits to provide for the possible removal of ABs from the F6U-1.

28 November 1949: The CV BARR acknowledged BuAer’s communication that there was no overhaul program in place for damaged or defective ABs. He stated they had seven SAC-472 and two SAC-562 defective units. He requested disposition instructions for the units.

5 December 1949: Solar Contract NOa(s) 8203 Program Progress Report for November 1949:

A “hot-streak” ignition system was fabricated and installed. Ignitions with the system were successful but a false “no burning” signal was sensed by the AB control system, which then automatically shut down the AB in a “cycling” operation. The effect of combustion length was investigated. At high fuel-air ratios, increasing the length of the combustion shell from 7-15/16 inches to 22-7/8 inches more than doubled the thrust ain. Such a length change might improve high altitude performance. Further length increase produced very little thrust gain. This was deemed to indicate the majority of the burning was accomplished in 24 inches from the flame holder. Two new burner types were fabricated and made available for altitude testing. One had a wider than standard gutter and the other had a series of stepped annular “V” flame holding gutters to give high solidity and flame retention with low flow restriction. Further high altitude investigations would continue with these burners and other modifications.

Fig. 3. Effect of Combustion Section Length on Thrust Gain

(Note: Progress reports for contract NOa(s) 8203 for December 1949 and January 1950 were not found.)

24 February 1950: CV Report No. 8186, Model XF7U-1 Airplane Afterburner Flight Tests from 28 June 1949 to 28 September 1949:

This report summarized the results of the AB flight test program in the XF7U-1 BuNo. 122472 during the period. The Solar Model A-100B ABs were upgraded with the low fuel flow Solar Model 551 AB fuel rings and the engines upgraded with Holley flyball governors. AB starting and blow-out characteristics were investigated. Both performance AB climbs, level runs, and takeoffs were accomplished. (3 Tables, 7 Charts) The automatic afterburner fuel control functioned very well during the tests. To further complete the control range required of the MM&M and  CECO valve system, it would be necessary to do wave off tests at sea level and obtain low speed level flight runs at altitude.

Afterburner Starts: The pilot needed to turn on the AB master switch at least 30 seconds before using the AB as the fuel control amplifier needed that amount of time to warm up. The AB ON‑OFF switch was then turned on. This turned on the fuel pump, opened the fuel valve and turned on the ignition. A pressure switch sensed the surge in pressure and acted to open the eyelids, turned off the ignition and set up the blowout protection circuit. The AB could be turned off either with the master switch or the ON-OFF switch.

Afterburner Unit Service Life: The exhaust collectors proved prone to cracking and had to be returned for repairs. The initial units were returned to Solar and were replaced by serial number 9 on the right engine and serial number 8 on the left hand engine.

3 March 1950: Contract NOa(s) 8783 Amendment 11 was issued covering the trial installation of a tail pipe in lieu of the Solar AB (Item 15) and (Item 16) the manufacture/assembly of 29 kits of parts necessary for installation of the tail pipe. The total cost was $18,030.35.

5 March 1950: Solar Contract NOa(s) 8203 Program Progress Report for February 1950:

Burner performance at high altitude testing continued. Extending the spacing length from the fuel manifold to the flameholder in an effort to improve fuel preheating, vaporization and mixing resulted in the flameholder disintegrating from overheating. A fuel distribution of 60% secondary, 40% primary was found to give the optimum thrust for burner configuration with the primary fuel injected close to the gutter and the secondary fuel injected at an upstream location. The ratio of the secondary and primary flows was found to vary depending on the rate of total fuel flow to achieve the highest thrust. Below a 5,000 pound per hour fuel rate the best distribution shifted to 80/20. A burner (NACA model 3615) was fabricated in accordance with NACA recommendations for high altitude performance. Tests indicated a thrust 20% below than obtained with a standard (551C) burner.

Fig. 4. Installation Sketch of an NACA Model 3615 Burner in A-103B AB.

The final summary report on the contract NOa(s) 8203 would be completed at the end of March 1950. This report, called for in Item 5, was Solar Report 134 and it was forwarded to BuAer on 19 September 1950. (The report was not found.)

6 April 1950: CV Contract NOa(s) 8783 Model F6U-1 Flight Test Summary Report for the Week Ending 1 April 1950. This covered three flights. Flight 63 used BuNo. 122478 with the Solar Model “G” AB burner ring. After an attempt to start the AB at 15,000 ft failed, a successful start was made at 14,300 ft and an AB climb was then made from 14,300 to 40,375 ft where the AB blew out. Engine operation was normal during the climb. AB starts were attempted from 28,000 to 40,000 ft without success. Post-flight, broken AB leads were found to be the cause. BuNo. 122478 was scheduled in future flights to complete the Acceptance Trial Part II Power Plant Demonstration.

25 April 1950: The BuAer Supply office noticed that Amendment 11 on Contract NOa(s) 8783 stated that the ABs might be removed from all F6U-1 aircraft and asked for clarification on whether the ABs would be used on future deployment of the Model 1 F6U aircraft. They noted an AB spare parts contract of considerable money value was in process at that time. A response on 3 May 1950 stated “present plans require that the Solar A-103-B afterburner be used in the F6U-1 aircraft.”

28 April 1950: CV asked for disposition instructions for AB Serial No. 115 removed from BuNo 122491 for cracks found after a check flight. Total AB time was 0.5 hr. The AB shroud was also found to be cracked.

5 May 1950: CV wrote to BuAer with a suggested change to the engine fuel system to satisfy BuAer’s request the system be modified to allow full AB boost without the fuel system boost pump in operation. The request had come after a boost pump failure during an F6U-1 AB take off, resulting in considerable loss of thrust. CV suggested that in lieu of adding another cockpit gauge reading boost pump pressure, the fuel lines should be rerouted using new connections. CV provided actual test measurements showing that the fuel pressure in the rerouted lines was adequate to provide full engine and AB thrust without the boost pump being operative. They offered to assist Westinghouse design a modification to accomplish the change.

22 August 1950: BuAer shared information with the BARR at CV regarding the Solar Model A‑103B AB and prior communication. The first had recommended installation of the 551-D type burner rings in all Solar ABs. In test it had demonstrated superior high altitude blowout performance, having shown its blowout altitude to be between 35,500 and 39,000 ft versus the 21,000 to 26,000 ft of the original burner. High altitude starting was not fully confirmed, but appeared to be 28,000 ft for electric starting versus 15,000 ft for the original burner. The second communication had confirmed the AB test flight program had been completed. Finally, Solar had informed the Bureau that in view of the recent 551-D burner failures when installed in the XF7U-1 ABs, it was not sufficiently durable for service use. In view of this, it had been decided that no more time nor money would be expended on the (AB) project. All remaining ABs would be equipped with the original durable 551 burner even though the AB operating and starting altitude limits were low.

24 August 1950: CV published a full report (No. 8392) covering flight tests with the Solar AB removed and replaced with a tailpipe and ejector. CV stated they believed no difficulties would be encountered in the operation of the subject model (F6U-1) with a tailpipe and ejector installed in place of the AB. It also noted that the performance of the airplane with the tailpipe, when corrected to standard conditions and comparable turbine temperatures, was consistent with that obtained with the afterburner installed (But not operating.)

The supporting information had some weaknesses. For instance, different engine data and flight parameters had to be used for the comparison of engine plus AB and engine plus tailpipe/ejector. The variations of the several parameters of the basic gas generator with corrected engine speed and ram pressure ratio were shown to be “quite consistent” with previous data for J34-WE-30A engines and with “engine internal performance trends….”

Another issue was the lack of basic information on the variation of nozzle flow coefficient for the Solar clamshell nozzle. This made it difficult to analyze and completely break down the causes of the engine derating, but CV felt much of it could be explained due to mismatching of the nozzle and engine due to the pressure losses in the AB. Supporting this conclusion, they pointed to the adverse turbine outlet temperature lapse rate with flight speed being caused by AB pressure losses. This was laid at the feet of the greater variation in nozzle flow coefficient for the AB clamshell nozzle as compared to the conical nozzle of the tailpipe.

16 October 1950: The F6U-1 CV Service Bulletin Progress Chart shows SB No. 16 complete as of that date. This was for the provisions of a tailpipe in place of the AB.

17 October 1950: A contract NOa(s) 8783 stop work order was issued by BuAer. This stopped all work connected to F6U demonstrations, correction of deficiencies and kit fabrication.

26 January 1951: The stop work order was amended to order direct shipment of three tailpipe kit assemblies to the AMES Aero Lab at Moffitt Field, CA as replacement for afterburners.

12 March 1951: Disposition instructions were sent to the CV Dallas BARR for 7 F6U-1 and 2 F7U‑1 defective afterburners, ordering them to be salvage for critical material or scrap as might be appropriate.

30 November 1951: CV wrote a long set of comments on the conclusions of the Naval Air Test Center (NATC) Patuxent River Final BIS Flight Test Trial Report for the F6U-1 dated August 1950. (Note: It is likely the correct date for the CV comments is 1950, as more than a year later than the events being commented upon, would have served little purpose.) The F6U-1 was tested with the AB and also with a tailpipe only, the Solar AB having been removed. The report covered many handling and speed issues raised during the evaluation. In regard to the AB, the overall conclusion of the report was that: “The performance without afterburner is so poor in comparison with current fleet fighters that it is unacceptable.” Various arguments were put forward regarding the reasons for retaining the AB, claiming it was not an auxiliary boost device but an integral part of the basic power plant and as such the use of afterburner in climb and level flights resulted in a thrust increase of 50% and 66% respectively. Other discussion points regarding engine derating due to low TOT, etc. repeated earlier discussions.

No design work had been done to determine the magnitude of the F6U-1 fuselage rework necessary to house the larger AB. The basic F6U-1 airframe had a top speed of about Mach 0.80 and by 1950, the threat of long range Soviet bombers carrying nuclear weapons and with presumed speed abilities matching those of the Boeing B-47 meant much faster airframes were needed to protect the fleet and the country.

Solar’s work beyond the end of the AB work for the XF6U-1, F6U-1 and XF7U-1 show they remained as a constructor of afterburners, particularly for the Westinghouse J46-WE-8 series of engines and others. All reports and materials produced as a result on the early AB development were shared with Westinghouse and the Army.

Fig. 5. Chance Vought F6U-1 in the National Naval Aviation Museum Collection, Pensacola, FL