...........Level speed and climb performance has been measured on Beaufighter VI X.7542. During the course of the tests, the engines were re-rated. At the later rating the following performance figures were obtained at a weight of 19,750 lb.
|Maximum rate of climb||2,325 feet/minute at 4,600 feet.|
|Time to reach 15,000 feet||7.5 minutes|
|Time to reach 25,000 feet||19.0 minutes|
|Service ceiling||28,000 feet|
|Maximum level speed in M.S. supercharger gear||327 m.p.h. at 8,500 ft.|
|Maximum level speed in F.S. supercharger gear||333 m.p.h. at 15,600 ft.|
...........Performance measurments were required on Beaufighter VI, fitted with the Hercules VI engines.
2. Scope of tests.
...........The performance of the aeroplane on climb and in full throttle flight has been measured. Partial climb tests showed that the best climbing speed was 120 m.p.h. A.S.I. Subsequent climbs made at an initial climbing speed of 140 m.p.h. A.S.I., to give improved cooling, showed a nearly equally rapid rate of climb compared with the climbs made at 120 m.p.h. A.S.I. At 120 m.p.h. A.S.I., the aeroplane climbs at a very steep attitude, and pilots much preferred to climb the aeroplane at an initial speed of 140 m.p.h. A.S.I. Since there is no measururable loss of performance our results are quoted at the higher climbing speed.
...........After these tests had been completed, information was received that the Hercules VI engine had been re-rated and that the R.P.M. boost limitations had been increased. Climb and level speed performance tests were repeated at the new limitations. The climbs were made at the higher climbing speeds.
...........The old and new engine limitations are:-
|Old limitations||New limitations|
|R.P.M.||Boost lb/sq.in||R.P.M.||Boost lb/sq.in|
| Maximum permitted for take-off|
and full throttle level speed.
|Maximum permitted for climb||2400||+5||2400||+6|
...........The performance results under each condition are included in the Report. The tests were made between 28.10.41 and 10.4.42.
3. Condition of aircraft relevant to tests.
...........This aeroplane is the prototype Beaufighter VI. Externally it is similar to the Beaufighter I, the main difference being the installation of Hercules VI engines and larger oil coolers and oil cooler ducts.
...........Tapered shrouded slotted flame damping exhausts were fitted on both engines.
...........The aeroplane was painted with the normal green and brown camouflage, not night fighter black. It had undercarriage doors and not skirting pieces as on some previous Beaufighters. 4 x 20 m.m. guns were fitted in the nose and neither the gun tunnels nor the ejection chutes were sealed for these tests. The holes for the 6 x .303" guns in the wing were covered over, but the ejection chutes remained uncovered.
...........The aeroplane had a "straight" tailplane, not the 12 1/2 deg. dihedral version. There was no camera gun above the cabin roof. A W/T aerial was fitted between the aerial mast on top of the fuselage and the tail. Neither A.I. nor I.F.F. aerials were fitted.
4. Loading: The tests were made at a weight of 19,750 lb. with the centre of gravity 49.1 inches aft of the datum, measured with the undercarriage down. Raising the undercarriage moves the centre of gravity aft by 0.6 inches at this loading.
...........The design centre of gravity limits are from 41.0 inches to 51.0 inches aft of the datum, or to 52.0 inches aft including the 1% S.M.C. aft extension (undercarriage down)
5. Results of tests:
.....5.1 Climb: The results of the climb tests are given in Tables I and II and in Fig.1. These show that at the new limitations the maximum rate of climb is 2,325 ft./min. at 4,600 feet and the time taken to reach 15,000 feet is 7.5 minutes and to 25,000 feet, 19.0 minutes. These times are less than 1/2 minute shorter than the times to height at the old limitations. The service ceiling is 28,000 feet.
.....5.2 Level Speed: The results of level speed tests are given in Tables III and IV and in Figure 2. These show the following:-
|Old engine limitations||New engine limitations|
|Maximum speed in M.S. gear||325 at 9,900 ft.||327 1/2 at 8,500 ft.|
|Maximum speed in F.S. gear||334 at 16,400 ft.||333 1/2 at 15,600 ft.|
...........In calculating these speed the same position error correction has been used as for the Beaufighter I.
(Table I., Climb results at old engine limitations, omitted)
Climb results at new engine limitations
|* Full throttle height in M.S. supercharger gear|
|**Full throttle height in F.S. supercharger gear|
|+ Service ceiling|
|Estimated absolute ceiling = 29,000 feet.|
(Table III., Level speed measurements at old engine limitations, omitted)
|* Full throttle height in M.S. supercharger gear.|
|** Full throttle height in F.S. supercharger gear.|
6. Discussion of results.
...........It will be noted, as would be expected, the rate of climb has been increased below full throttle height in both M.S. and F.S. supercharger gear, due to the increase in boost at the new limitaions.
...........In level flight in M.S. supercharger gear, there is a small increase in speed (2 1/2 m.p.h.) due to the increased r.p.m. and boost limitations. In F.S. gear, however, there is a decrease in speed of about 1 1/2 m.p.h., above full throttle height at the new limitations. It wouild appear that the increase of power due to increasing engine r.p.m. is small and that the decrease in propeller efficiency at the higher r.p.m. produces a nett decrease in thrust horse power in this case. It seems doubtful in view of these results, whether the increased R.P.M. limitations are worth while, in view of the probable decrease in engine life.
Fig. 1 Performance on climb.
Fig. 2 Level Speeds and Boost at Heights
Main Beaufighter T.F.X. Performance