...........Brief handling trials have been carried out on Spitfire F.Mk. XIV RB.141, one of the first production aircraft. The handling characteristics have been compared with those of the prototype Mk.XIV. JF.319. Special attention was paid to directional behaviour as this aircraft incorporated a fin and rudder different from that fitted to JF.319, but of the type that is proposed for production.
2. Condition of aircraft relevant to tests.
....2.1. General. The main features of the aircraft were:-
|A RG5SM engine.
A Rotol 5-blade Jablo propeller, Type No. VP.R19/5F5/1.
Individual ejector exhausts.
A tropical air intake: a Vokes wet air cleaner element was incorporated which could be bypassed for normal use.
Universal wings with small bulge over 20mm. guns.
Armament :- 2 x 20mm. guns, 4 x 0.303" machine guns. Gun ports and muzzles sealed, relevant ejection chutes open.
................"Streamline" blanks over unused 20mm. gun stubs.
Whip aerial behind cockpit
V.H.F. aerial beneath starboard wing.
V.H.F. blind approach aerial beneath fuselage.
No IFF aerials.
Fin and rudder shown as in Fig. 1. The rudder incorporated a combined balance and trimmer tab.
Retractable tail wheel.
|....2.2. Loading. The aircraft was flown at a take-off weight of 8490 lb., with the centre of gravity 4.6" aft of the datum (undercarriage down) which represents service load.
...........The practical limits of the centre of gravity range, obtainable by dissipation of load are 3.9 ins. and 4.8 ins. aft of the datum. With a 90 gallon auxiliary drop tank fitted the aft limit becomes 5.5" aft of the datum. All these centre of gravity positions are with the undercarriage down. Raising the undercarriage moves the c.g. 0.4" aft of this loading.
3. Tests made.
...........Brief handling tests were carried out with particular attention to directional behaviour.
4. Results of tests.
....4.1. Cockpit layout. The cockpit layout was generally similar to that on other marks of Spitfire, but there were a few changes. A new type of box for the engine controls was fitted which gave a much bigger throttle lever travel and incorporated the carburettor cut-out control and a new type of friction locking device. The throttle controlled the boost smoothly and fine adjustments were possible. The controls were so arranged that the throttle and propeller control levers could be grasped and moved together, enabling power changes to be made quickly. The friction lock worked well and the cut-out control was in a more convenient position.
...........The usual mechanical visual-indicators that protrude through the wing when the undercarriage leg is down and which are usually fitted on Spitfire aircraft had been deleted, leaving only the cockpit electrical indicators. This is considered a pity, as a direct indication of the undercarriage position was a great help in times of emergency, and their reintroduction is recommended.
...........As on other marks fitted with engines with a Bendix carburettor starting the engine was a matter of practice and dexterity. After priming the engine, the wobble pump must be used to obtain the required fuel pressure, which however drops on ceasing to pump and requires to be kept up by periodic repumping. Then the cut-out, which is spring loaded, must be held back whilst the Coffman starter button is pressed, and as the engine fires the throttle requires adjusting. At the same time the stick must be held back with the knees. This process should be simplified.
....4.2. Handling characteristics. The general handling charcteristics were similar to those of JF.319. The principle differences in behaviour are included in the following paragraphs.
...........4.21 Controls and general flying. The type of fin and rudder incorporated in this aircraft caused a decrease in the change of directional trim with speed compared with JF.319. Rudder forces were of a similar magnitude. The ailerons, despite an absence of reflexing, were noticeably heavier. Variations in the weight of ailerons on Spitfire aircraft are common and are due to manufacturing differences between individual sets. This aircraft presumably had an inferior pair of ailerons; it is desirable that such ailerons should be rejected during production testing.
...........As on JF.319 the elevator was heavier than desirable and showed the same tendency to hunt at slow speeds, particularly in rough air.
...........In other respects, including stability charcteristics, the aircraft was the same as JF.319.
...........4.22 Stalls. The stalling speeds obtained were:-
|Flaps and undercarriage up||87 mph ASI|
|Flaps and undercarriage down||75 mph ASI|
|The characteristics were similar to those observed on JF.319.|
|...........4.23 Dive. The aircraft was trimmed for all-out level flight and dived to 470 mph ASI.
The characteristics were as on JF.319 except that with the decreased change in directional trim with speed the footloads on the rudder bar in the dive were sufficiently small to make retrimming unnecessary.
5. Conclusions. There was little difference in the handling qualities when compared with JF.319 and they were satisfactory. The type of fin and rudder now fitted decreased the change of directional trim with speed and retrimming on the dive to limiting speed was no longer necessary.
...........The new throttle box was found to be a definite and satisfactory improvement.
...........The aircraft would be improved if some or all of the following points received attention:-
...........(i) The procedure for staring the engine should be simplified.
...........(ii) The mechanical undercarriage indicators in the wings should be re-introduced.
...........(iii) Ailerons as heavy as those now fitted should be rejected during production testing.
...........(iv) The elevator could with advantage be lighter.
...........(v) The elimination of the elevator hunt at slow speeds is desirable.