The P-47 N was designed as a long range fighter-bomber, differing from other P-47 airplanes in that it has more powerful engine, a new turbo-supercharger, more fuel, an automatic pilot, homing radio and a tail warning radar. Flight tests were run on P-47N airplane, AAF No. 44-88406, from 1 January 1946 to 1 August 1946. During this time 67 hours were flown in 39 flights, by Captain J. Jaskot, of the Fighter Operations Section. These tests were requested by the Fighter Branch, Production Engineering Section, Procurement Division, and by the Flight Data Branch of the technical Data Laboratory to check the guaranteed performance and Technical Order 01-65BD-1. Stability tests and complete performance tests including take-off, landing, climb, speed and range were originally requested at all power setting from seal level to 40,000 ft. for seven different drag configurations (bombs, tanks, rockets, etc.). Tests to determine angle of attack vs airspeed were also requested by the Armament Laboratory. The first airplane assigned to this project crashed when approximately half way through the program. Some parts of the original program were cancelled, other portions were completed on other P-47N airplanes and have been reported separately.

          1.     Performance of P-47N with and without Special Rocket Installations. Report No. TSCEPE5E-1916 dated 26 June 1945.

          2.     Take-off and Landing tests on P-47N airplane, AAF No. 44-87785. Report No. TSCEP5E-1935 dated 2 August 1945.

          3.     Zoom Characteristics of P-47N-2 airplane AAF No. 44-87785 Report No. TSCEP5E-1892 dated 4 July 1945.

          4.     Range Survey through simulated tactical missions. Report No. TSCEP5E-1835 dated 9 February 1946.

          5.     Take-off tests with two 165 gallon wing tanks, one 110 gallon belly tank and ten, five inch rockets. Report No. TSCEP5E-1918, dated 28 June 1945.

                  This report includes pilot’s comments, speed, range, and climb performance at various powers, weight and altitude for the clean airplane. Some additional data is included for two combinations of external wing tanks.

II        Summary

          The P-47 N airplane has performance and handling characteristics very similar to the early P-47 airplanes, but due to heavier weights caused by greater fuel capacity, performance is lower when using equal power settings. The rate of roll is slower, due to the weight being farther from the longitudinal axis of the airplane.

          Control forces are good, but as in the earlier model P-47 airplanes large changes in trim are necessary for a change in airspeed.

          The principal performance in the various configurations is summarized in the following table. Military power is the power available at 2800 rpm and 53.0” Hg and normal rated power is the power available at 2600 rpm and 42.5” Hg. Cowl flaps are closed in level flight and full open in climbs.

          At high power settings considerable maintenance was involved because of oil leaks, cracked vacuum pump housings, exhaust collector rings burning out and oil leaks. At war emergency power these malfunctions become excessive and operation was restricted at this power. In military power climbs high oil and cylinder head temperature above 30,000 ft. were experienced and made it necessary to reduce power after ten minutes of operation to cool the engine.

III      Condition of Aircraft Relative to the Tests

          A.     The P-47N airplane, AAF No. 44-88406, had a bare metal finish. Wing racks were installed, and it was loaded to 1640 lbs at 30.7& MAC which includes 267 rounds of ammunition per gun, (eight guns with full fuel, oil and water). The airplane was also flown with two 165 gallon wing tanks at a take-off weight of 19,250 pounds at 30.6% MAC, the third configuration tested was with two 165 gallon wing tanks and one 110 gallon belly tank at a take-off gross weight of 19,880 pounds and 30.0% MAC. Details of these three drag configurations may be seen in the photographs included in Appendix III to this report.

          B.     The power plant is a Pratt and Whitney R-2800-57 air cooled engine. In addition to the internal blower, a General Electric type GH-5 turbo-supercharger is installed. Automatic controls are provided for supercharger, carburetor-air, cylinder head and oil temperatures. An injection type carburetor type PR-58E2 is installed.

          C.     Test Equipment.

                  Cockpit instruments calibrated for the test included altimeter airspeed indicator, engine tachometer, manifold pressure gage, torque meter, exhaust back pressure gage, free air temperature, carburetor air temperature, fuel flow indicator, oil temperature and cylinder head temperature. In addition to the cockpit instruments a photo panel was installed which included a clock, altimeter, torque meter, carburetor air temperature, carburetor deck pressure, fuel flow meter, turbo-tachometer and exhaust back pressure gage.

IV     Flight Characteristics

         A.     Taxiing and Ground Handling.

                  Forward visibility is poor although no worse than “D” models and “S” turns are necessary when taxiing. The tail wheel is not steerable so that turns are made by the use of brakes. No difficulties were encountered in taxiing and ground handling in cross winds up to ten miles per hour.

         B.     Take-off and Initial Climb.

                  After lining up on the runway prior to take-off the tail wheel may be locked in the forward position. This helps to keep the airplane going straight until enough speed is obtained for the rudder to become effective. With about 5° right rudder trim the torque effect is unnoticeable . A slightly longer take-off run is necessary for this airplane than is needed for the average fighter type and with a full load of fuel including two wing tanks of 165 gallon capacity each and one bely tank of 110 gallon capacity practically the entire length of a 6000 ft. runway is needed fro take-off with 54” manifold pressure. Depending on the load, the airplane will take-off between 115 and 120 mph IAS with no undesirable take-off characteristics. If more than 54.5” Hg manifold pressure is desired on take-off, the water injection switch should be placed in the manual position (above 30” Hg) at the beginning of the run to prevent a slight loss of power when the water automatically cuts in. Ordinarily no flaps are used for take-off but under adverse conditions such as muddy of short runway, 20 to 30 degrees of flaps will shorten the take-off run.

                  The initial climb is poor and below 150 mph the airplane feels sluggish so that it should be allowed to accelerate to at least 150 mpg before a climb is attempted.

          C.    Handling and Control.

                  The handling and control characteristics of the P-47N were similar to earlier models of the P-47. There were o control force reversal tendencies noticed over an IAS range of 150 to 400 mph. Below 150 mph IAS and with high power, uncoordinated use of aileron and rudder will cause the rudder forces to decrease and in extreme cases will become negative. Recovery is accomplished by coordinating the controls, reducing the power and increasing the speed by nosing down.

          D.    Stability.

                  Qualitative stability tests were not made but there appeared to be no undesirable static or dynamic stability characteristics. With full external wing tanks the directional stability seemed decreased. With full auxiliary tank the longitudinal stability appeared to be neutral especially in the climbing attitude, becoming normal again when auxiliary fuel is used up.

          E.    Trim.

                  Flight Adjustable trim tabs are provided for all three controls and there is sufficient trim for all normal flying. Above 54” Hg manifold pressure, right rudder trim is insufficient for speeds below 150 mph IAS but the forces are not great and may be maintained by the pilot.

                  As in earlier model P-47’s, large changes in trim are necessary for changes in airspeed.

          F.     Maneuverability and Aerobatics.

                  Maneuverability and aerobatic characteristics are similar to earlier P-47’s in the clean configuration. With wing tip tanks filled the rate of roll and radius of turn of the P-47N is poor. No aerobatics were performed at the high gross weights (wing and belly tanks), but the rate of roll was slow for this condition.

          G.    Stalling Characteristics.

                  There was no bad stalling characteristics noticed on the P-47N. All stalls were preceded by slight buffeting 6 or 7 mph above the stalling speed and as speed decreased the buffeting increased until the stall which usually resulted in dropping the left wing. There was no tendency to spin after a stall and the airplane would recover by itself after airspeed was regained.

          H.    Longitudinal stability of the P-47N decreases with an increase in altitude and becomes objectional at high altitudes.

          I.     Noise and Vibration.

                 The noise level of the P-47N was low for a fighter type of airplane and was not objectionable. Slight vibration was noticed at 2250 rpm but at rpm’s above or below 2250 rpm the vibration was negligible.

          J.      Approach, Landing and Wave-off.

                  Approach is made with 50% rated power, full flaps, 0° rudder and aileron trim and approximately 5° nose up elevator trim. Recommended IAS for approach is 140 mph with a minimum of 120 mph. There is no ground looping tendencies due to the locked tail wheel. Going around is not dangerous but flaps should not be raised below 400 ft. and then gradually.

          K.    Vision.

                  Visibility in taxiing, take-off and climb is poor but no worse than earlier P-47’s. Landing visibility is good with the exception of power landings. No distortion was noticed in the windshield, canopy or bullet-proof glass.

          L.    Cockpit Layout.

                  Access to the cockpit is made from the left side where suitable steps and handles are provided. Controls should be unlocked before entering cockpit because the control lock is a strap latch arrangement which extends across the bottom of the seat and would be difficult to unlock after the pilot is seated. Some difficulty is experienced in unlocking controls before entering cockpit.

                  With few exceptions, the cockpit is similar to earlier P-47’s. Pilot’s of “D” series Thunderbolts will feel at home in the “N” model. In general, all the controls and instruments are well laid out for a fighter type aircraft. Some of the differences noted from earlier model P-47’s are:

                  The main switch panel is located on the left side of the cockpit, just above the flaps and landing gear levers. An internal wing fuel and oil quantity gages are provided, the auto-pilot controls and instruments are added to the front panel and the manual primer had been replaced by an electric switch.

                  The P-47N is better than average for comfort since the cockpit is large and does not cranp the pilot. Heating appeared normal although no long range flights at high altitude were made. Ventilation is provided by two cold air inlets, one on each side of the cockpit just below the arms. However, at low altitudes on warm days the cockpit is too hot and air conditioning would be required to provide cool air under these conditions. For long range flight and auto-pilot is provided and for leg comfort the rudder pedals may be folded aft enabling the pilot to place his feet through the spaces thereby provided.

          M.    General Functioning.

                  Due to the high power consistently used during the tests, considerable maintenance trouble was experienced with this specific airplane. Some of the more common malfunctions were:

                  Oil leaks, exhaust collector rings burning off, tachometer generator leads breaking off and in one instance the valve push rods broke off. With the exception of one burned out generator no trouble was encountered with the electrical and hydraulic system.

                  The emergency system for the extension of gear and flaps is satisfactory. No emergency system is provided for the brakes, For bailing out, the canopy may be jettisoned.

V        Performance Data

          A.     All performance data has been corrected to NACA standard atmospheric conditions. Observed flight test data for all tests are tabulated in Appendix II of this report. Performance curves corrected to standard conditions are grouped in Appendix I of this report.

          B.     Airspeed Calibration.

                  Airspeed calibrations were obtained by flying with a P-51 pacer airplane and were run for each of the three drag configurations tested. The resulting curves are plotted in Figure I of this report. Although there was a slight difference in calibration for the airplane with the auxiliary tanks installed it was less than 1 mph and the position error correction of the P-47N airplane is given in the following table.

          C.    Altimeter and Free Air Calibration

                  Altimeter and free air calibrations were flown past the power and the curves are shown in Figure 2.

          D.    Level Flight Performance.

                  Speed, power, and fuel consumption runs were made at various altitudes and curves of speed vs power in the clean configuration from 3500 ft. to 38,000 ft. are shown in Figure 4. This same data has been reduced to P-w vs Via form in Figure 6. Considerable decrease in propeller efficiency at high altitude is indicated for this airplane as has been true of other P-47’s. A summary of level flight performance of the P-47N including engine data such as turbo rpm, exhaust back pressure and carburetor air temperature at military rated power, normal rated power and 2250 rpm, 40.5” Hg is given in Figure 3, and is tabulated below:

                  All level flight runs were made with cowl flaps closed, oil flaps closed and intercooler flaps flush, at take-off gross weight of 16,400 lbs.

                  Several runs were made at war emergency power (2800 rpm, 72” Hg manifold pressure, water on) on the first P-47N airplane tested before it crashed and the high speed was increased by approximately 30 mph at 10,000 ft. Tests were not completed at this power because of excessive maintenance trouble encountered after each flight on which war emergency power was used.

          E.     Cruising and Range.

                  Speed vs power curves in the cruising power range were obtained at 3500 ft, 10,200 ft, 14,400 ft and 24,00 ft and are included in Figure 4 with other level flight data. Engine operation throughout these tests were according to a power schedule based on the propeller load curve and 140 b m e p. Curves of air miles per gallon vs speed are given in Figure 5 for the 10,200 ft, 14,400 and 24,000 ft. The data at 24,000 ft was not obtained at 140 b m e p. and probably des not represent optimum cruising conditions. A summary of these curves is tabulated below:

                  Cowl flaps closed, oil flaps automatic, intercooler flaps flush. Take-off weight of 16,400 lbs.

                  Airplane clean – wing racks only.

                  Similar tests were made at 14,400 ft with two combinations of external auxiliary fuel tanks installed. The first consisted of two 165 gallon auxiliary tanks mounted on under each wing rack. These tests were flown at a take-off weight of 19,250 lbs at 30.6% MAC. Level flight data has been corrected to an average weight of 17,400 lbs. The second combination consisted of two 165 gallon auxiliary tanks mounted one on each wing rack and one 110 gallon auxiliary tank mounted under the fuselage. These tests were flown at a take-off gross weight of 19,880 lbs at 30.0% MAC and the level flight data has been corrected to an average weight of 18,000 lbs. Comparative speed vs power curves are shown in Figure 7. Corresponding air miles per gallon curves are shown in Figure 8. The same data has been reduced to Piw vs Viw curves in Figure 9, so that a direct measurement of the additional drag of these tanks may be obtained. The effect of the tanks on speed and range at 14,400 ft is included in the following table.

                  In order to determine the best intercooler flap position for level flight performance a series of speed points were obtained at normal rated power at various intercooler flap positions at 20,000 ft. The results showing the effect of intercooler flap position on speed and carburetor air temperature at this altitude and power is given in Figure 10. The minimum drag position is with flaps flush with the fuselage and not in the full position.

          H.    Climb Data.

                  Sawtooth climbs were made at several powers and altitudes to determine the optimum IAS for rate of climb. The resulting data is plotted in Figure 11. 165 mph, IAS was used for all normal rated power climbs and 175 mph for all military power climbs.

                  A number of rated power climbs were obtained in the process of climbing to altitude for the speed runs and additional rated power climbs were made to 25,000 ft with two combinations of external auxiliary fuel tanks to show the effect of these tanks on the climb performance of the airplane. Results of these climbs giving brake horsepower, turbo rpm, carburetor air temperature, exhaust back pressure, fuel flow, rate of climb and time to climb are plotted in Figure 13. Similar data for military power climbs is plotted in Figure 12. A curve of gross weight vs altitude to which all performance of this airplane has been corrected is shown in Figure 14.

                  A summary of the climb performance of the P-47N airplane is tabulated below.

                  All climbs were made with cowl flaps wide open, intercoolers wide open and oil flaps automatic.

          I.     Comparison of test results with existing operating instructions in Technical Order 01-65BD-1 for P-47N airplane shows the following:

                  1.     The airspeed calibration given in the Technical Order is correct as published.

                  2.     The climb performance in the clean configuration agrees reasonably well with the climb performance in the Technical Order. However, the climb performance listed in the Technical Order for the airplane with external tanks installed is approximately 25% high.

                  3.     Speeds in level flight for a given power setting agree reasonably well with the data in the Technical Order.

                  4.     Fuel consumption was from ten to fifteen percent less than that given in the Technical Order and the corresponding published range data was conservative by the same amount.

IV      Conclusion

          1.     Due to the large quantity of fuel it can carry, the P-47N is a good long range fighter-bomber. Although the performance is not too good at high gross weights, it improves as the external fuel is used and by the time the target area is reached it compares favorably to earlier P-47N’s.

          2.     Although a longer take-off run is needed at high gross weights than is usually required for a fighter type aircraft the airplane has no undesirable take-off characteristics.

          3.     Undesirably large changes in trim are necessary for a change in airspeed.

          4.     The present control lock due to its location and type is difficult to operate.

          5.     The performance obtained in these tests indicated that the operating information published in Technical Order No. 01-65BD-1 is approximately 5% conservative for speeds and 10% conservative for fuel consumption in all configurations, 25% optimistic for climb with auxiliary tanks installed, and agrees reasonably well with climbs of the clean airplane.

VII     Recommendations

          It is recommended that Technical Order No. 01-65BD-1 be revised with a view towards reducing the discrepancies between the performance given in the Technical Order and that obtained in these tests with particular attention to the climb performance with auxiliary tanks installed.

          Speed vs Altitude
          Military Power Climbs