Between 23rd and 29th July 1947, a
proving flight of the new Tudor IV was carried out. The flight routed
through the Caribbean to test the suitability of the aircraft for tropical
The Tudor left Heathrow, piloted by Air Vice-Marshal Bennett, at 14:06 on Wednesday 23rd July and followed the route London - Prestwick - Gander - Bermuda - Trinidad - Jamaica. It was originally intended to route via Antigua, but landing rights were not obtained in time for the flight. While in Jamaica it carried out tests required by the A.R.B. and left for Heathrow on the night of 27th July. The return flight called at Bermuda and the Azores and landed at Heathrow at 23:43 on Tuesday 29th July. The total time flown, excluding the tests in Jamaica, was 57 hours 14 minutes, and over the course of the six days, 11,713 statute miles had been covered.
It is worth noting that it was during this proving flight, on the leg between Prestwick and Gander that the serious in-flight emergency occurred which is explained in detail in 'Fly With The Stars'.
The text below is the official technical report of the proving flight.
REPORT ON CARIBBEAN TEST – TUDOR IV
The results obtained on these tropical trials show that:
(a) the performance is satisfactory for operations in the tropics on our present routes, and
(b) the radiator cooling is satisfactory in tropical operations.
(Configuration: the aircraft was fitted with the latest short chord wing root fillets and the propellers had the shortened overshoes. The undercarriage, however, was not modified to the shortened type.)
Aileron controls were light and pleasant at all speeds. Elevator and rudder are, however, a little too heavy to be pleasant. The aircraft has no marked vices but it will swing at take-off if permitted to do so in some circumstances. This swing in the normal case into wind is less than a LANCASTRIAN but owing to the very large fin surface the weather-cocking tendency both at take-off and on landing is slightly more marked than a LANCASTRIAN.
Landings can be carried out normally in almost any attitude but it is desirable to touch with almost more vertical component if some bouncing is to be avoided (with the present, unmodified undercarriage). At 74,000 lbs. A.U.W. the approach should be carried out at a speed not lower than 115 knots, and at such a weight the aircraft should not be held off too high as the drop at this weight comes quite suddenly as opposed to the gentle sink which occurs at the lighter loads.
Two night take-offs and two night landings were carried out and no adverse features were discovered.
A failure of an outboard engine at take-off can be held quite easily on rudder though on these tests this was not attempted at very low speeds (nothing under 110 knots). Up to 5° of bank materially assists rudder control in these conditions and is particularly recommended in the case of a two engine failure.
The aircraft appeared to stall evenly, and the nose dropped away at about the same time as the tail buffet started. The stall and the buffet appeared to be normal.
CRUISING PROCEDURE AND RESULTANT A.M.P.G.:
In order to obtain a high A.M.P.G. it is necessary in this aircraft with its large span to operate at a low Indicated Air Speed of about 155 knots A.S.I. at 80,000 lbs. Decreasing to about 145 knots at the lighter loads. To achieve the best A.M.P.G. at these speeds, the height should be chosen so as to obtain at full throttle the highest permissible cruising B.M.E.P. This is at about 10,000 feet at the full weight at 155 knots in M gear. In the absence of experience, a comparison of the improvement of the Merlin 621 in relation to the Merlin 24, combined with the relevant Maker’s recommendations, must be used to decide what cruising B.M.E.P. to be used. On this basis in initial operations it is recommended that we use 175 lbs. Per sq. Inch B.M.E.P. (equivalent sea level).
The A.M.P.G. obtained in low blower on these trials were all better than those obtained at Boscombe Down for the Tudor I in its final form which are about 2% to 4% worse than the latest A.V. Roe figures for this particular aircraft (See A.V. Roe Report No. FTS/688 IV/I dated 1st June 1947). A test carried out on Flight No. 2 comparing the A.M.P.G. with radiators “auto closed” as opposed to “inch closed” showed the latter approximately 0.75% better.
In order to obtain a high True Air Speed without adversely affecting A.M.P.G. it is, of course, necessary to fly at high level which entails the use of pressurisation. As on this series of flights the pressurisation was not fully serviceable, it was not possible to obtain a full set of figures. It is clear, however, that high level cruising is essential for satisfactory operation of this aircraft.
As a tentative measure the following is the proposed B.S.A.A. cruising procedure:-
“Fly at 155 knots A.S.I. above 70,000 lbs, using the required power obtained with the following combination of boost and R.P.M. :-
It is recommended also as a tentative measure that we should adopt a cruising climb at 140 knots A.S.I. using 2,650 R.P.M. and boost between +7 and +9. The rate of climb using 2,650 R.P.M. and +9 boost (taking-off at 80,000 lbs.) was tested on two occasions (Flight No. 5 and Flight No. 8). The average rate of climb to 10,000 feet was 375 feet per minute in the first case and 397 feet per minute in the second case. The first test was carried out in turbulent conditions.
In common with other electrical instruments fitted two radiator thermometers gave some trouble during the flights. They appeared, however, to be working normally at the time the radiator suitability tests were carried out.
HIGH LEVEL TROPICAL TESTS:
One test was carried out in S gear using maximum permissible continuous power at 20,000 feet. The results are shown in the Appendix to Flight No. 4. The figures obtained are well within the permissible limits. With the outside air temperature 27° above standard atmosphere the highest radiator reading with radiator flaps at manual open was 100° which is 25° below normal permissible maximum and 35° below emergency maximum. With the radiator flaps closed the highest temperature reached on one engine was 116° with the average of the other three at 109°. (NOTE: The thermometer which gave the high reading was flickering and must, therefore, be regarded as suspect). ALL temperatures are within the permissible limits.
The Rolls-Royce brochure figures for the Merlin 621 shows fuel consumptions which have always been regarded as unacceptably high.
The fuel injector pumps in general have been on the high side, and have in any case incorporated tolerances of performance far too wide for acceptance in commercial operation. On this occasion, however, the pumps had been carefully calibrated on the low side of the permitted setting and had small tolerances. The results achieved were most gratifying and in general the figures agreed with the Rolls-Royce brochure almost exactly.
These injector pumps work on a capacity basis rather than a mass basis and therefore deliver the same quantity of fuel regardless of the specific gravity of the fuel used. Figures were obtained on practically all flights and results are plotted in figure No. 1. The A.M.P.G. on the Prestwick/Gander and Santa Maria/London seem to indicate that colder conditions improve the performance by about 2% over the figures obtained in the tropical conditions of the remaining flights. Further figures are required for confirmation.
Oil consumption outward bound averaged as follows:-
P.O .394 G.P.M.
P.I. .382 G.P.M.
S.I. .394 G.P.M.
S.O. .362 G.P.M.
Homeward bound the consumption was:-
P.O .216 G.P.M.
P.I. .284 G.P.M.
S.I. .236 G.P.M.
S.O. .06 G.P.M. *
* Gauge read 30 gallons on ETA London (i.e. 6-7 above others)
THREE ENGINE PERFORMANCE:
Three engine climb and three engine cruising in tropical conditions both appeared to be satisfactory. Three engine cruising is shown under Appendix of Flight No. 5, paragraph (a). Three engine climbs are shown under Appendix of Flight No. 6, paragraphs (a) and (d), and Flight No. 7, paragraph (c).
(NOTE: Two engine cruising was carried out at Jamaica and with both engines on the port side stopped and feathered, level flight was maintained at 6,000 feet at 2,850 R.P.M. and +16 boost with an A.S.I. reading of 130 knots).
The electrical instruments undoubtedly were the source of the greatest trouble during this series of flights. In most cases the fault lay not with the instrument but in the transmitter concerned. Whether this is merely a characteristic of a new aircraft or whether we can expect these instruments to continue to cause trouble is at present uncertain. It is, however clear that drastic steps must be taken to obtain more reliable results from electrical instruments.
At Nassau the port oleo leg deflated overnight, and owing to difficulties of obtaining adaptors and the fact that the compressed air supply was limited a considerable delay was caused before departure. The schrader valve on this oleo leg was found to be slightly loose and as test for leaks otherwise showed negative results, it was assumed that this was the cause of the deflation.
Many minor details of the aircraft are unsatisfactory and must be rectified:-
1. Fuel gauges poor.
2. Tank cocks at present inaccessible in flight must be made accessible.
3. Pilots’ seats so close to pedestal that ingress and egress are difficult, (modify seats).
4. Light intensity of centre instrument panel too low (compared with starboard panel which is on the same dimmer switch).
5. Noise level too high (particularly where no sound-proofing is provided, e.g. in small compartment at the rear of the forward passenger cabin. Tail pipes must be fitted at least to inboard side of inner engine. Escape hatches and entrance door require additional sealing rubbers to improve sound-proofing).
6. Vibration: No carpets were fitted in this aircraft but even allowing for this it appears that more vibration is transmitted to the fuselage than in most modern large aircraft. This is particularly noticeable in the centre section compartment.
7. Ventilation of the lavatories and galley most unsatisfactory.
8. Electrical turn and bank indicators must each be provided with a switch immediately under the instruments.
9. C.S.U’s appear to be sluggish.
10. As there are only two generators fitted, the electrical services would be overloaded if galley services, cabin lights, ventilating fan and radio were all working at take-off and inner engine failed. This overloading would result in a very slow feathering, and it is essential, therefore, that standing orders provide that electrical loads be kept to an absolute minimum during take-off and landing.
11. Electrical generator cut off switches are at present unprotected and can be knocked off accidentally.
12. Refuelling system needs further investigation to determine fuel capacity when refuelling over the top and fuel capacity when pressure refuelling, - consistency of these figures to be checked.
13. The clear view panel on each side of the cockpit jams the control wheel and if the panel is accidentally left open this could be dangerous. Hinging it on the trailing edge of the panel would be an improvement.