This article reproduces the “Final Report on Flight Tests of Prototype F6F-5K High Speed Target Drone with Eclipse-Pioneer P-1K Auto-Pilot,” Report No. R-0168, produced by the Naval Air Material Center, Naval Aircraft Modification Unit located in Johnsville, Pennsylvania in 1947. The following paragraphs reproduce the main conclusions of the report, a high resolution version of which can be purchased below.
This report covers a flight test period from May 24, 1946 through April 10, 1947, in the prosecution of project TED NAM 1881. It discusses the major problems encountered in the adaptation of the basic P-1K automatic pilot installation and related features of the overall drone configuration comprising the Grumman F6F-5K Hellcat target drones as approved for the production program under TED NAM 4451. Results of the flight tests showed the following:
The F6F-5K demonstrated much smoother operation for all air work maneuvers than was obtainable with the F6F-3K with the air pick-off type automatic pilot. Performance included good coordinated (ball-center) turn up to 60° of bank. As indicated previously in the report, the aircraft maintained altitude in coordinated turn up to 45° of bank and thereafter lost some altitude in steeper turns up to 60° of bank. Sixty degree dives up to 360 kts IAS could be accomplished with smooth straight entry, dive, and pull-out. The elevator speed was so adjusted as to give approximately 5½ “g” recovery from dives. All maneuvers were smooth and fast, making the drone easy to handle under radio control.
The take-off characteristics of the F6F-5K were considered superior to the F6F-3K. They were accomplished under all wind conditions and easily met with the performance specifications outlined in the original project. While the existing method of employing brakes in the accomplishment of take-off was satisfactory, there were flight tests then underway under project TED NAM EL-701 in an attempt to accomplish take-off on the automatic pilot alone without the use of brakes.
The F6F-5K was catapulted on the automatic pilot with normal operation.
It was stated that the landing characteristics of the F6F-5K were satisfactory and they were deemed slight superior to the F6F-3K, in spite of the fact that the elevator action would be improved somewhat in order to get the utmost in performance from the automatic pilot. However, slightly more than 1/3 of the landings were considered unsatisfactory. This did not mean that the F6F-5K was a doubtful quantity where landings were concerned. Many of the landing attempts were made with the original servo installation which did not provide fast enough elevator action. Others of the so called unsatisfactory landings occurred in the process of adjusting and proving feasible the control surface position indicator lights as a means of properly engaging the automatic pilot for drone operation.
As previously stated, a development program was then underway for accomplishing take-off on the automatic pilot alone. There was being developed in conjunction with this, a system of automatic brakes to control directional heading during the landing run. It was felt that successful completion of this development would improve greatly the overall landing characteristics of the F6F-5K.
P-1K Automatic Pilot Maintenance and Discrepancies
As noted in the Summary Flight Data section of the report, there had been a total of 236.4 hours of flight operation on the P-1K autopilot. In addition to this, there had been 180 hours of ground operation necessary in the preliminary phase of flight test work for making pre-flight adjustments. During this time the following failures occured:
- One failure of mechanical servo disconnect (under load the disconnect pins would not remain engaged).
- One failure of Rectifier Tube in the Servo Amplifier, causing the Power Transformer to burn out.
- One questionable “Flux Gate” transmitter (would not cage properly).
- Several Rate Gyro Excitation Leads reversed.
The above noted failure of a rectifier tube and power transformer occurred in flight and started a small electric fire. Obviously, this would have resulted in failure of the autopilot and loss of a nolo drone. However, it did not cause any embarassment to the safety pilot as the fire ceased immediately when the power was shut off from the automatic pilot. One high altitude test at 35,000 ft was conducted with this installation and proved satisfactory in every respect.
Summary of Operations
A total of 236.4 flight hours were accumulated on the P-1K autopilot between May 29, 1945 and April 1, 1947. All phases of drone work were simulated, including high altitude operation. Very few take-offs and landings were accomplished in the F6F-5K aircraft designated as X-4. This aircraft was bady out of trim in the landing condition and therefore did not, in the preliminary phases of flight test, provide a good vehicle for evaluation of the P-1K automatic pilot.
Very few flights were made in the F6F-5K aircraft designated as X-5. This aircraft was in the shop for long periods of time for modification and correction of difficulties in the aircraft itself. When this aircraft did become available for flight there was no P-1K controller on hand for installation. It was noted that the 25 flight hours reported on X-4 were flown in connection with project PA-501 as authorized by the Bureau of Aeronautics.
This summary is only a small portion of the report, which goes into much greater detail concerning flight tests of the F6F-5K target drone. The document features many high resolution photos and schematics of the equipment installed in the F6F-5K, as well as photos of the pilotless aircraft control truck used in conjunction with the aircraft. These images are ideal for the modeler wishing to build a super-detailed replica of these modified Hellcats.
All images from NARA Archives II, College Park, MD, RG 72
Readers may purchase a high resolution PDF download of the report previewed above for $1.99 from our shop on Gumroad.com; a sample high resolution image is shown to the left.