The above aeroplane is the first of the type fitted with two 20 m.m. cannon guns and electrically heated Mark VIII pitot static head. In other respects the aeroplane was similar to Spitfire K-9793 reported on in the First Part of Report M/692,b dated the 12th July 1939.
The cannon gun installation, one gun in each wing, was very neat and except for two slight bulges on the upper and lower surfaces of the wing at the rear spar, the standard wing section was maintained.
The aeroplane is fitted with a 2-pitch 3 blade metal airscrew and it was desired to compare the handling and the performance of the aeroplane with that of Spitfire K-9793, fitted with Browning guns and 2-pitch metal airscrew.
Summary of Results.
(1) The position error of the electrially heated Mark VIII pressure head which was situated in the same position as the Mark VA head on previous Spitfire aircraft, is the same at high speeds and practically the same at low speeds.
(2) The handling of the aeroplane in normal flight, at the stall, in aerobatics and in dives, is unaltered by the cannon gun installation.
(3) The effect on the handling of short bursts from the cannon guns was detected but was negligible.
(4) The top level speed is about 3 m.p.h. less than the Spitfire fitted with Browning gun installation.
The following Table shows the comparison in speed and climb for the Spitfire fitted with 2-blade wooden airscrew and Spitfires fitted with 2-pitch 3-blade metal airscrews and differing only in their guns installations.
|Engine:-||Merlin II||Merlin II||Merlin III|
|D.H. Type 5/21*|
|Time to 20,000 ft.||9.4 mins.||11.4 mins.||10.7 mins.|
|Speed at 18,500 ft.||363 m.p.h.||367 m.p.h.||364 m.p.h.|
|Service ceiling||31,900 ft.||34,400 ft.||34,500 ft.|
|Log book H.P. for|
2600 r.p.m. at 12250 ft.
*The same pitch setting were used for K-9793 and L-1007.
|ENGINES.||Merlin III||Normal B.H.P||953 at Rated Altitude 12,250 ft|
|At 2,600 R.P.M.|
|Fixed military load|
|Flying weight on trials.||5925|
|At Full Throttle|
|| 20,000||362||10.7 ||1320
|| 26,000||354||16.4 || 820
|Service Ceiling||34,500 ft.||Landing speed||M.P.H./Kts.|
|Take off run||yds. Time secs.||Distance from rest to clear ft. screen||yards|
|Stalling speed||M.P.H./Kts.||Gliding in A.S.I.||M.P.H./Kts.|
|Best landing A.S.I.||M.P.H./Kts.||Distance to rest (with brakes after clearing 50 ft. screen yds =|
|Landing and take off tests corrected to|
|Estimated absolute ceiling 35,800||Greatest height reached 25,600|
|R.P.M. stationary on ground 2500||Boost pressure lb./sq.in. +6½|
|* Full throttle height|
|** Service ceiling (estimated) 34,500 ft.|
|Landing and take off tests corrected to
||Take off run yds. Time Secs
||Distance from rest to clear foot screen yds.
||Gliding in A.S.I. M.P.H.||Stalling speed M.P.H.
||Best landing A.S.I. M.P.H.
||Distance to rest (with brakes) after passing over 50 ft. screen yds.
||Landing run with brakes yds.||Landing run without brakes yds.
|*Full throttle height|
|1. Weight and centre of gravity position|
|Weight light|| 4599 lb.|| 4599 lb.
||Oil.|| 49|| 49
||Total weight|| 5936 lb.|| 5925 lb.
|Handling trials were made at the following centre of gravity position:-|
|1. Normal C.G. position 7.5 ins. aft of the datum||The same as|
|2. Extended aft C.G. position 8.4 ins. aft of the datum|
|by the same pilots who tested Spitfire K-9793.|
In normal flight, at the stall, and in aerobatics, the handling of the aeroplane was the same as Spitfire K-9793 (see First Part of Report M/692,b. dated 12th July, 1939) at both of the above centre of gravity positions.
Handling in the dive which was only checked at the extended aft position of the centre of gravity, was also the same as for Spitfire K-9793.