Seafire F Mk. XV NS.493 which is representative of production Mk. XV aircraft subsequent to about the 100th aircraft was sent to this Establisment for measurement of level speed performance and position error, and the results of these tests are dealt with in this Part of the Report. It differed from the first prototype Seafire F Mk. XV NS.487 which was described in the 2nd Part of this Report in having a curved windscreen and "tear-drop" sliding hood.
2. Condition of aircraft relevant to tests.
2.1 General. The principal features of the aircraft were:
A Griffon VI engine
A 4-blade Rotol hydraulic propeller Mk.XH54 of 10'5" diameter
Individual ejector exhaust stubs
No iceguard over air intake, which incorporated an alternative intake with an air cleaner
Radiator under starboard wing, and radiator and oil cooler under port wing.
2 x 20 guns and 4 x 0.303" guns fitted, muzzles and leading edge ports sealed and ejection chutes open.
Folding wings with bulge over 20 mm gun mechanisms, and foding tips.
No navigation lights on wing tips or rudder.
Deck landing arrestor hook beneath fuselage
Retractable tail wheel
Whip aerial above fuselage
No IFF aerials fitted
Curved windscreen and "tear-drop" sliding hood
The aircraft skin was flush-rivetted throughout, all joints were filled with compund, and the whole aircraft was polished to give a smooth finish.
2.2 Loading. The aircraft was flown throughout the tests at a take-off weight of 7955 lb. with the centre of gravity position 6.7 in. aft of the datum, this being representative of normal Service loading.
2.3 Engine numbers and limitations. The aircraft was fitted with a Griffon VI engine Nos.358/241476 and the following operating limitations were relevant to the tests made:
RPM Boost lb/sq.in. Max. for combat (5 mins. limit) 2750 +15 lb/sq.in.
3. Tests made.
(a) The position error with flaps and undercarriage up was measured by the aneroid method over the speed range 120 mph ASI to 370 mph ASI.
(a) Maximum level speeds were measured at heights up to 32,000 ft. with the radiator exit duct flaps in the closed position.
4. Results of tests.
The results of the level speed performance tests have been corrected to ICAN standard atmospheric conditions by the methods of Report No. A.& A.E.E./Res/170, using a supercharger constant of 0.002, and to 95% of the take-off weight, viz:7565 lb. by the methods of the Addendum to Report No. A.& A.E.E./Res/147.
The position error correction is given in Fig.2. and the correction to be applied to the altimeter when connected to the static of the airspeed system is given in Fig.3. The results of the level speed tests are given in Table I and Fig.4.
4.1 Summary of results.
(i) Position error correction.. The position error correction varied linearly from +4.3 mph at 120 ASI to -12.4 mph at 370 mph ASI.
(ii) Maximum level speed performance..
Maximum level speed at sea level 356 mph TAS MS supercharger gear Maximum level speed at 4500 ft. 380 mph TAS (FTH) MS supercharger gear Maximum level speed at 12000 ft. 378 mph TAS MS supercharger gear
Maximum level speed at 8000 ft. 373 mph TAS FS supercharger gear Maximum level speed at 12800 ft. 395 mph TAS (FTH) FS supercharger gear Maximum level speed at 20000 ft. 390 mph TAS FS supercharger gear Maximum level speed at 30000 ft. 366 mph TAS FS supercharger gear
For the optimum maximum level speed performance use FS supercharger gear if the boost in MS supercharger gear would be less than +10 1/2 lb/sq.in.
4.3 Propeller tip Mach number. In level flight at 20,000 ft. the propeller tip mach number reached a value of .916 and at 30,000 ft. the value was .93. No corrections for any consequent effects on the propeller efficiency have been made in correcting the results to standard atmospheric conditions. The range of air temperature difference from standard above 20,000 ft. during the tests was from -3 ½° C to +3 ½° C