1.    Introduction.

                          Level speed measurments have been carried out on this aircraft to assess the affect of fitting a 500 lb bomb on an unfaired rack beneath the fuselage. The installation was one designed by Fighter Command personnel.

2.     Condition of aircraft relevant to tests made.

                2.1.   General. The principal features of the aircraft were:-

A Merlin 61 engine
A four bladed propeller, Type R3/4F5/3.
Individual ejector stub exhausts
No ice-guard over air intake
Fuel cooler air intake in port wing root leading edge.
Armament:- One 500 lb. bomb on a univerwal bomb carrier No. 1.
Mk.1., modified as described below
2 x 20 mm. guns with muzzles sealed and ejection chutes open.
Hemispherical blanks over remaining 20 mm. gun stubs
.303 Browning guns and accessories removed.
A balloon type cockpit hood
Internal bullet proof windscreen
No rear view mirror
Wireless mast behind cockpit
No W/T aerial
I.F.F. aerials

                          The bomb carrier has been shortened by cutting off the beam just forward of the front crutch bracket, removing the front fusing unit and modifying and repositioning the junction box to the rear of the beam. The bomb carrier was supported by a special frame built from mild steel angle and strip. The assembly was suspended at the drop tank attachment points beneath the fuselage.

                  2.2.   Engine number and limitations. The aircraft was fitted with a Merlin 61 engine Nos. 82245/A331615. The limitations applicable to the tests made were:-

.R.P.M.Boost lb/sq.in.
Maximum for all-out level flight (5 minute limit)3000+15

                  2.3.   Propeller Details.

Type of PropellerRotol hydraulic R3/4F5/3
Diameter10 ft. 9 ins.
Number of blades4
Direction of rotationR.H.
Serial No.38682
Serial No. Blade No.1.A 30483
Serial No. Blade No.2.A 30484
Serial No. Blade No.3.A 30485
Serial No. Blade No.4.A 30486
Coarse pitch setting65 deg.
Fine pitch setting30 deg

                  2.4.   Loading. The tests were made at a take-off weight 7805 lbs. with the bomb on. The estimated c.g. position was 5.0 ins. aft of the datum, undercarriage down.

                          The take-off weight with the bomb and carrier off was 7250 lbs.

3.     Tests made.

                          Level speed performance was measured between 11,000 ft. and 21,000 ft. using all-out level power conditions in M.S. suprcharger gear with the radiator flaps closed:-

                          (i) with one 500 lb. bomb fitted
                          (ii) with external bomb installation removed.

4.     Results of tests.

                          The level speed measurments were corrected to 95% of the take-off wieght and to standard atmospheric conditions by the methods given in Report No. A.& A.E.E./Res/170 (which incorporates A.& A.E.E. Memorandom dated 27.8.42). The position error correction used was that measured on Spitfire IX B.F.274, which had an identical pressure head installation; in each case this was corrected to the appropriate weight.

                          The full results are given in Tables I and II and Fig 1. and are summarised below.

M.S. Supercharger gear

ConditionMax. True Air
Full throttle
  With one 500 lb. bomb fitted36314,500
  With external bomb installation removed38514,700

5.     Conclusions.

                          The reduction in maximum true air speed in M.S. supercharger gear due to fitting a 500 lb. bomb and a bomb rack without fairing is 22 m.p.h.


Level Speed performance with one 500 lb. Bomb
M.S. Supercharger gear

Corrected to a weight of 7420 lbs.Radiator flaps closed.

P.E.C.C.E.C. Boost
12,000352   301.5-5.4-3.2+15.25"
13,000357   301.5-5.4-3.6+15.25"
  14,500*363.5300   -5.3-4.1+15.25"
16,000362.5292.5-5.1-4.4+13.5  "
18,000360   281.5-4.6-4.5+11.5  "
20,000357   269.5-4.2-4.7+9.7"
21,000355   263.5-3.8-4.8+8.3"

*Full throttle height


Level Speed performance with external Bomb installation removed
M.S. Supercharger gear

Corrected to a weight of 6890 lbs.Radiator flaps closed.

P.E.C.C.E.C. Boost
11,000368   321.5-6.4-3.6+15.252980
13,000377.5320   -6.4-4.4+15.25"
  14,750*385   318   -6.3-5.1+15.25"
16,000384   311   -6.0-5.3+13.9  "
18,000382   300   -5.6-5.6+11.9"
20,000379.5288   -5.2-5.7+10.0  "

*Full throttle height

Fig 1. Level Speed Performance

WWII Aircraft Performance     Spitfire Mk IX