Introduction
The objectives during this series of tests were:
-(1)To determine the take-off run with a 2-pitch D.H. 3 blade Type P.3-5-5-7 airscrew with a pitch range of 32½° - 45°
-(2)To determine the most suitable fine pitch setting for take-off and initial climb, the best speed to climb away and the height at which the airscrew pitch should be changed to coarse so that the minimum engine speed of 2070 r.p.m. at +6¼ lb. boost would be attained.
-(3)To spin and dive the aeroplane with the changed distribution of loading occasioned by the change in airscrew weight, armour plating and Lorenz blind approach equipment.
-(4)To check the performance in speed and climb.
Summary of Results.
The most suitable fine pitch setting is 32½° at 42" radius, and for this setting and normal take-off procedure the climbing speed reaches 170 m.p.h. (A.S.I.), and the r.p.m. 2850 at 2,000 ft. The change over to coarse pitch at this speed and height reduces the engine r.p.m. to 2070 at +6½ lb. boost. Speed should then be increased to 185 m.p.h. - the best climbing speed in coarse pitch.
The behaviour in spins is satisfactory - the most noticeable difference with the increased inertia due to (3) above is that the irregularity in the spin to the right noted in Part of Report M/292,a. dated 19th October is more marked. Less turns are required for recovery, however, than with the wooden airscrew fitted. With a reducing valve incorporating a balance pipe to the air intake dives up to the limiting speed of 450 m.p.h. were made with no sign of the engine cutting out as reported in Part of Report M/692,a. dated 19th October, without this valve fitted.
The take-off is much improved over that with the wooden airscrew, and the maximum speed is increased from 362 m.p.h. with wooden airscrew to 367 m.p.h. with the 2 pitch metal airscrew. The climb performance with metal airscrew is also better considering the increase in weight.
SUMMARY OF TRIALS
| AEROPLANE | Spitfire | Serial | K.9793 |
| SPEC. N° | 16/36 | ||
| CONTRACTOR | Supermarin Aviation Works (Vickers) Ltd. | ||
| TYPE | Landplane | Duty | Fighter |
| ENGINE | Merlin II | N°1137 | |
| Normal B.H.P. | 998 | At Rated Altitude | 12,250ft |
| At | 2,600 R.P.M | ||
| lb. | |||
|---|---|---|---|
| Tare Weight | 4598 | ||
| Weight light | - | ||
| Fixed military load | - | ||
| Fuel 84 gallons* | 630 | ||
| Service Load | 658 | ||
| Oil | 49 | ||
| Flying weight on trials | 5935 | ||
| *Based on 7,5 lb. per gallon | |||
| At Full Throttle | |||
| Height in Feet | Top Speed M.P.H. | Time To Climb Mins. | Rate of Climb Ft./Min |
|---|---|---|---|
| S.L. | --- | --- | |
| 2,000 | 1.29 | 1625 | |
| 5,000 | 3.0 | 1845 | |
| 10,000 | 5.5 | 2150 | |
| 15,000 | 8.1 | 1725 | |
| 20,000 | 366 | 11.4 | 1305 |
| 25,000 | --- | 470 | |
| 30,000 | 23.8 | 470 | |
| Service Ceiling | 34,400 (Estimated) ft. | Landing speed | M.P.H./Kts. |
| Take off run | 320 yds. Time secs. | Distance from rest to clear 50 ft. screen | 490 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 = 470* | |
| Landing and take off tests corrected to zero wind. | |||
| *This is considerably less than the distance recorded in Part of Report M/692,a for the Spitfire with wooden airscrew.
The difference is probably due to a difference between the braking forces for the two aeroplanes. | |||
1. Weight and centre of gravity.
The aeroplane was loaded in accordance with the Weight Sheet Summary No.715.
The changes of loading due to fitting the metal airscrew are as follow:
I. Increase of airscrew weight 262 lb., that is Wooden airscrew 83 lb., Metal 345 lb.
II. Removal of 135 lb. lead from engine bearers.
III. Fitting 40 lb. lead in the rear end of the fuselagefor normal load, with an additional 22 lb. to give the extended aft position of the centre of gravity.
The above ballasting does not represent armour plating and blind approach apparatus in weight or position but it was estimated by thy Royal Aircraft Establishment that the inertia of the aeroplane about the lateral axis would not exceed this arrangement of ballasting when the above items are subsequently fitted.
| Total weight: |
|---|
| 5935 lb. Centre of Gravity 7.6 ins. aft of the datum |
| 5957 lb. Centre of Gravity 8.4 ins. aft of the datum (the extended aft position). |
| The total weight with the wooden airscrew Drg. No.3001700/A was |
| 5784 lb. Centre of Gravity 7.8 ins. aft of the datum. |
| 5796 lb. Centre of Gravity 8.7 ins. aft of the datum. (the extended aft position). |
| Aircraft | Spitfire K-9793. |
|---|---|
| Airscrews | |
| Direction of Rotation | R.H. |
| Position | Centre |
| Type | 2 Pitch |
| Serial No. | D.H. 55713 |
| Dia Measured. | 9.1 Feet, |
| Dia. Marked. | - |
| Pitch Range. | 20° |
| Basic Setting. | 50° |
| Hub Serial No. | D.H. 55713 |
| Hub Drg. No. | Front P.5300/1 Rear P.5301/1. |
| Radius | Coarse Pitch Setting | Fine Pitch Setting. | |||||
|---|---|---|---|---|---|---|---|
| 42" | Blade No. | 1 | 2 | 3 | 1 | 2 | 3 |
| Setting | 45°-40' | 45°-47' | 45°-47' | 32°-5' | 32°-30' | 32°-40' | |
| Calibration | 45°-6' | 45°-6' | 45°-6' | 32°-30' | 32°-30' | 32°-30' | |
| (.7 Rad). 45.22" | Angle | 43°-20' | 43°-20' | 43°-20' | 30°-40' | 30°-40' | 30°-40' |
| Chord | 8.72" | 8.72" | 8.72" | - | - | - | |
| Thickness | .66" | .66" | .66" | - | - | - | |
CLIMBING TRIALS
| Height in Standard Atmosphere Feet | Time From Start Min. | Rate of Climb Ft./Min. | True Air Speed M.P.H. | A.S.I. M.P.H. | P.E.C. | Comp. | R.P.M. | Boost lb.sq.in. |
|---|---|---|---|---|---|---|---|---|
| Sea Level | 0 | - | - | - | - | - | - | - |
| 1,000 | 0.7 | - | 149 | 150 | -4.3 | -0.1 | 2750 | +6.2 |
| 2,000 | 1.3 | - | 171 | 170 | -4.3 | -0.1 | 2850/2080 | +6.2 |
| 3,000 | 1.9 | 1700 | 189 | 185.5 | -4.3 | -0.2 | 2160 | +6.1 |
| 5,000 | 3.0 | 1845 | 195 | 185.5 | -4.3 | -0.3 | 2230 | +6.1 |
| 6,500 | 3.8 | 1950 | 199.5 | 185.5 | -4.3 | -0.4 | 2285 | +6.1 |
| 10,000 | 5.5 | 2150 | 210.5 | 185.5 | -4.3 | -0.6 | 2400 | +5.9 |
| 13,000 | 7.0 | 1900 | 218.0 | 183 | -4.0 | -0.8 | 2400 | +4.0 |
| 15,000 | 8.1 | 1725 | 220.5 | 179 | -3.5 | -0.9 | 2400 | +2.7 |
| 16,500 | 8.9 | 1600 | 222.5 | 176 | -3.0 | -1.0 | 2440 | +1.8 |
| 18,000 | 9.9 | 1475 | 224.5 | 173 | -2.5 | -1.1 | 2400 | +0.95 |
| 20,000 | 11.4 | 1305 | 227 | 169 | -2.0 | -1.2 | 2395 | -0.2 |
| 26,000 | 17.2 | 800 | 236 | 156.5 | 0 | -1.4 | 2385 | -3.1 |
| 28,000 | 20.0 | 630 | 239.5 | 152.5 | +0.7 | -1.5 | 2380 | -4.1 |
| 30,000 | 23.8 | 470 | 242 | 148 | +1.5 | -1.6 | 2370 | - |
| 32,000 | 29.1 | 295 | - | - | - | - | 2360 | - |
| 9,700* | 5.4 | 2175 | 209.5 | 185.5 | -4.3 | -0.5 | 2400 | 6.1 |
| Estimated absolute ceiling | 35,550 | Greatest height reached | 32,700 | |||||
| R.P.M. stationary on ground | 2470 | Boost pressure lb./sq.in. | +6.3 | |||||
| * Full throttle height | ||||||||
| ** Service ceiling 34,000 (estimated). | ||||||||
SPEED TRIALS
| Height in Standard Atmosphere Feet | True Air Speed M.P.H. |
A.S.I. M.P.H. | Compress.and Position Error Correction M.P.H. |
R.P.M. | Boost lb/sq.in. | Speed at Normal Revs. | |
|---|---|---|---|---|---|---|---|
| P.E.C. | Comp. | ||||||
| Sea Level | |||||||
| 1,000 | |||||||
| 2,000 | |||||||
| 3,000 | |||||||
| 5,000 | |||||||
| 6,500 | |||||||
| 10,000 | |||||||
| 13,000 | |||||||
| 15,000 | |||||||
| 16,500 | 358.5 | 290 | -8.5 | -4.2 | 2930 | +6.2 | |
| 18,000 | 365 | 288.5 | -8.5 | -4.6 | 2980 | +6.2 | |
| 20,000 | 366 | 288.5 | -8.5 | -4.6 | 2980 | +6.2 | |
| 23,000 | |||||||
| 26,000 | |||||||
| 28,000 | |||||||
| 30,000 | |||||||
| 18,600* | 367 | 287.5 | -8.5 | -4.7 | 3000 | +6.2 | |
| Landing and take off tests corrected to standard atmosphere and zero wind | |||||||
| Take off run | 320 yds. | Time | 12.5 Secs | ||||
| Distance from rest to clear 50 foot screen | 490 yds. | ||||||
| Gliding in A.S.I | 98 M.P.H.. | Stalling speed | --M.P.H. | ||||
| Landing A.S.I. | 72 M.P.H.. | ||||||
| Distance to rest (with brakes) after passing over 50 ft. screen | 560 yds. | ||||||
| Landing run with brakes | 235 yds. | Landing run without brakes | --yds. | ||||
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°.>/p>With this setting the measures distances were:
| Corrected to wind yards | Measured in wind 8 m.p.h. | |
|---|---|---|
| Take-off run | 320 | 265 |
| Distance from rest to 50 ft. screen | 490 | 410 |
| Landing run. | 235 |
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:-
| A.S.I. | Height at which pitch was changed (ft.) |
Compress.and R.P.M. in Pitch |
|
|---|---|---|---|
| Fine | Coarse | ||
| 140 | 1000 | 2650 | 2020 |
| 150 | 1000 | 2750 | 2030 |
| 170 | 2000 | 2850 | 2070 |
| 160 | 3000 | 2850 | 2070 |
The proposed method for take-off and climb is:
| I. | Normal take-off, speed leaving the ground 70 m.p.h. A.S.I.; Flap setting zero. Airscrew in fine pitch. |
| II. | Retract undercarriage as soon as possible and increase speed gradually as for a normal take-off, to 170 m.p.h. The height will be about 2,000 ft. by the time this speed is reached and the engine speed will be about 2850 r.p.m. |
| III. | Change into coarse pitch when the r.p.m. will fall from 2850 to 2070 at 6¼ lb/sq.in. |
| IV. | Increase speed to the best climbing speed (185 m.p.h.). |
SPITFIRE L.9793
Gliding tests (Engine-off).
Estimated Mean Weight 5750 lb.
| Air speed m.p.h.  |
Rate of Descent Ft/Min  |
Rate of Descent Ft/Min |
R.P.M. Windmilling. |
||||
|---|---|---|---|---|---|---|---|
| Flaps & Undercarriage Down Airscrew Fine Pitch | Flaps and Undercarriage Up. Airscrew coarse pitch | ||||||
| 90 | 1200 | - | Below the scale on instruments | ||||
| 100 | 1315 | 870 | |||||
| 110 | 1510 | 895 | |||||
| 120 | 1800 | 935 | |||||
| 130 | 2210 | 1010 | |||||
| 140 | - | 1100 | |||||
| 156 | - | 1210 | |||||
| 160 | - | 1345 |
| N.B: | | are dynamic quantities and are the actual values which would obtain at sea level under standard atmospheric conditions. |
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:
| C. G. Position |
Direction | No. of Turns. |
Height at Start. Ft. |
Time of spins. secs. |
Turns to recover |
Ht. out in level flight. |
Remarks on recovery |
|---|---|---|---|---|---|---|---|
| Normal 7.6 ins. aft of the datum |
L | 8 | 17400 | 25½ | 3/4 | 11,050 | Full opposite rudder; control eased forward to just aft of central |
| R | 8 | 17500 | 26½ | 1/2 | 10,600 | ||
| R | 4 | 17800 | 11 | 3/4 | 13,700 | Rudder reversed; control eased forward. | |
| R | 8 | 17700 | 24 | 3/4 | 11,700 | ||
| L | 8 | 18300 | 25 | - | 11,300 | Control forward too far, went into opposite spin. | |
| L | 3 | 19200 | 13 | 1½ | 14,500 | Full opposite rudder; control central. | |
| R | 3 | 19000 | 10 | 3/4 | 15,700 | ||
| L | 8 | 19000 | 26½ | 1¼ | 12,000 | ||
| R | 8 | 19000 | 25¼ | 3/4 | 12,300 | ||
| Ext. aft. 8.4 ins. aft of the datum | L | 8 | 17000 | 27 | 3/4 | 10,900 | Full opposite rudder; control moved to just aft of central. |
| R | 8 | 17700 | 29 | 3/4 | 11,900 | ||
| L | 3 | 17200 | 10½ | 3/4 | 14,200 | Full opposite rudder; control central. | |
| R | 3 | 18000 | 14 | 1/2 | 14,800 | ||
| L | 8 | 18800 | 24 | 3/4 | 12,500 | ||
| R | 8 | 19000 | 30 | 3/4 | 11,500 |
Summary of Results
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.
