Take-off and Initial Climb Tests

                   Take-offs and initial climbs were made with different settings of the fine pitch of the airscrew, and the most suitable was found to be 32½°.

                   With this setting the measures distances were:

                   The best climbing speed in fine pitch is about 140 m.p.h. A.S.I. and in coarse pitch 185-190 m.p.h. A.S.I.

                   Initial climbs at 31¾° were made at the best climbing speed in fine pitch to determine the height at which 2070 r.p.m. in coarse pitch were obtained and further tests were made by climbing at a high speed (slightly throttled within the limit of 2850 r.p.m. in fine pitch ) and changing pitch at a low height. The results from these tests showed that the optimum rate of climb was given when the normal climb procedure from the ground was adopted, that is, when the speed at take-off was gradually increased to the best climbing speed. For a two pitch airscrew this speed is between the best climbing speeds for fine and coarse settings. Tests were then made to determine the height to which the climb should be prolonged to give the minium r.p.m. in coarse pitch when the change over was made.

                   At a pitch setting of 31¾° initial climbs were made to various heights and at various speeds showed first, that a greater speed than 160 m.p.h. is required at 2,000 ft. before changing into coarse pitch if the minimum r.p.m. were to be obtained and secondly that a greater speed than 170 m.p.h. in fine pitch is not permissible unless the engine is throttled.

                   The results of climbs for the recommended setting of 32½° with the engine at full throttle are:-

                   The proposed method for take-off and climb is:

Spins.

                   Right and left hand spins up to 8 turns have been made to determine the effect of the increased load and inertia occasioned by the metal airscrew and ballast to represent the inertial loads of armour plating and Lorenz blind approach apparatus.

                   Observations taken during the spins:-

Summary of Results.

(1)              The behaviour in spins is satisfactory. The most noticeable change with the increased inertia is the irregularity in the spin to the right, which has now become very marked. This is not serious but extremely uncomfortable for the pilot, especially when the centre of gravity is in the aftmost position. Spins to the left are unchanged and are smooth and steady.

                   The turns to recover are less than with the wooden airscrew.

                   The same method of recovery should be used as that given in detail in Part of Report M/692,a dated 19th October, 1939. Recovery is by full opposite rudder followed by a slow forward movement of the control column. If the control column is moved forward too soon, or too quickly, a considerable loss of height during recovery results.

Handling. (Compared with lower weight and wooden airscrew, c/f Part of Report M/692a, dated 15th June 1939).

                   Loads used:-

                   1. Weight 5935 lb. Centre of Gravity 7.6 ins. aft of the datum.

                   2. Weight 5957 lb. Centre of Gravity 8.4 ins. aft of the datum.

                   The take-off has been improved in that there is less tendency to swing to port, and the general feel of the controls is more satisfactory.

                   In the air, no great change in flying characteristics is noticeable. The engine runs a little on the harsh side above 2600 r.p.m. and this may be due to the lesser shock-absorbing qualities of the metal airscrew.

                   Gyroscopic effect is apparent but not very pronounced. The nose drops when yawed to port and rises when yawed to starboard. The correction necessary to overcome this during turns is small.

                   The stability characteristics appear to be unaltered, as is also the behaviour of the aeroplane in aerobatics.

                   The aeroplane has been dived to 450 m.p.h. A.S.I. and becomes more tail heavy when fitted with the wooden airscrew but not excessively so.

                   The glide in fine pitch is steeper, but the ground cannot be seen over the nose. The control and feel on the glide have also been improved. The landing remains unaltered.

Dives.

                   At 400 m.p.h. A.S.I. engine cutting out was experienced on this aeroplane the same as was reported on K.9787 before a modification to eliminate it was introduced. This modification was incorporated on K.9793 to determine whether it gave the same satisfactory results.

                   The fuel system was altered by fitting a reducing valve with a balance pipe to the air intake. This increases the fuel pressure to the carburettor in proportion to the air intake pressures.

                   Dives were made to the limiting air speed of 450 m.p.h. without any cutting out of the engine. The maximum engine speed attained was 3450 r.p.m.

                   As in previous diving trials on production Spitfire aircraft the ailerons became very heavy at 250 m.p.h. and almost immovable at speeds over 300 m.p.h. A.S.I. The aileron heaviness is decreased when flush strung ailerons are fitted as described in Part of Report M/692,a. dated 29th June, 1939.