Performance measurments have been made on Tempest V JN.731, the third production aircraft fitted with the Sabre IIA engine. The results of these tests, together with the position error correction are given in this report.
2. Condition of aircraft relevant to tests.
|2.1 General. The relevant details of the aircraft are listed below:|
|Normal air exhaust without ice guard.
Multi-stub exhausts with close fitting shrouds.
Four Mk. II 20 mm. guns, muzzles sealed and ejection chutes open.
Fairings round the portion of the gun barrels which projected foward of the wing leading edge.
Blisters on top of wing over each gun.
Retractable tail wheel with twin contact tyre.
Whip aerial behind cockpit.
Type 90 &VHF-BA marker aerials under fuselage.
No. IFF wire aerials.
The Mk.VIIID pitot-static head was situated beneath the port wing.
|2.2 Engine details. The relevant operational limitations at the time of the tests of the Sabre IIA engine fitted to the airframe were:|
|Max. for climb (1 hr limit)||3700 RPM||+7 Boost|
|Max for combat (5 min limit)||3700 RPM||+9 Boost|
|2.3 Propeller details. A 4 bladed de Havilland propeller of 14 ft. dia. with metal blades, was fitted.
2.4 Loading. The tests were made at a take-off weight of 11,400 lb. with C.G. 14.1 ins foward of the datum, flaps and undercarraige down. The represents the normal fighter load.
|3. Tests made.
Partial climb tests were made at normal and combat rating to determine the best climbing speed.
The climb performance was measured at combat and normal climbing power with the radiator exit duct flap open. The supercharger gear was changed so as to obtain the optimum climb performance.
Full climbs could be carried out using combat power since the rpm limitation is the same as for normal climbing power, and the combat boost of +9 lb/sq.in. falls off to the normal +7 lb/sq/in. within the permitted time of 5 minutes.
Level speeds were measured at combat power with the radiator exit duct flap closed between sea level and 28,000 ft., changing supercharger gear at the optimum height.
The position error of the MK.VIII underwing pitot static head was measured by the aneroid method over the speed range of the aircraft, flaps and undercarriage up, with the radiator flap closed.
4. Results of tests.
|4.1 General. The performance results have been corrected to standard ICAN atmospheric conditions
and the level speeds to 95% of the take off weight i.e. 10,900 lb.
In correcting the level speeds, the compressibility correction has been calculated by the methods given in the Addendum to Report
No. A&AEE/Res/147. A strut correction to the IAS, based on ARC.6420 has also been applied.
4.2 Position error. The results of the position error measurments is given in the form of a correction against IAS in Fig.3
The correction to the altimeter when connected to the static of the airspeed indicator system, is given in the form of correction curves against indicated altimeter height at various indicated airspeeds in Fig.4.
4.3 Climb. The full results of the climb are given in Tables I and II and Fig. 1. A summary of the results is given below:
The partial climb tests showed the best climbing speed for normal and combat rating to be 185 IAS up to 18,000 ft. reducing 5 mph per 2000 ft. thereafter.
|Normal climb rating||Combat rating|
|Max rate of climb in M.S. gear||3815 ft/min @ 3500 ft FTH||4380 ft/min @ sea level|
|Max. rate of climb in F.S. gear||2680 ft/min @ 15800 ft FTH||3000 ft/min @ 13500 ft. FTH|
|S/c gear changed when boost in M.S. gear was||+2.9 lb/sq. in.||+4 lb/sq.in.|
|Time to 10,000 ft.||2.9 mins.||2.8 mins.|
|Time to 20,000 ft.||6.85 mins.||6.55 mins.|
|Time to 30,000 ft.||14.3||14.0|
|Service ceiling||34,000 ft|
|Estimated absolute ceiling||35,600 ft.|
|4.4 Level speed. The full results of the level speed measurments are given in Table III and Fig.2 at the end of the Report. A summary of the results is given below:|
|Speed at sea level M.S. gear*||376 mph true airspeed|
|Max. speed in M.S. gear*||411 mph true airspeed @ 6,600 ft. FTH|
|Max. speed in F.S. gear*||432 mph true airspeed @ 18,400 ft. FTH|
|Speed at 28,000 ft.||405 mph true airspeed|
|To obtain optimum speed performance use F.S. gear when the M.S. gear boost would be less than +4 lb/sq.in.
* The full boost at +9 lb/sq.in. was not obtained during the test. (See para.5)
|5. Discussion of results.
As stated in para.4.4 the full nominal boost of +9 lb/sq.in. was not obtained in the level speed tests at combat power. This was due to inaccurate functioning of the automatic boost control. If the full +9 lbs/sq.in. had been obtained instead of +8.5 in M.S. gear and 8.7 in F.S. gear the speeds would be as follow:
Climb performance at combat rating
Climb performance at normal rating
Level speed performance at combat power
corrected to 10,900 lb. (95% take-off weight)
Radiator flap closed.