Meticulous Testing

Meticulous Testing on a BSAA Tudor lV

SUMMARY: 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. All Up Weight. 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 2 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 2 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.

In order to obtain a high AMPG 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 AMPG at these speeds, the height should be chosen so as to obtain at full throttle the highest permissible cruising Brake Mean Effective Pressure.  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 BMEP to be used. On this basis in initial operations it is recommended that we use 175 lbs. Per sq. Inch BMEP (equivalent sea level).

The AMPG 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 AMPG 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 AMPG 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 BSAA 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.:-
R.P.M. Boost
2,650 +7
2,600 +6.7
2,400 +6
2,200 +5.6
2,000 +5.3
1,800 +5.1
It is recommended also as a tentative measure that we should adopt a cruising climb at 140 knots A.S.I. using 2,650 rpm and boost between +7 and +9. The rate of climb using 2,650 rpm 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 1st case and 397 feet per minute in the 2nd case. The 1st test was carried out in turbulent conditions.
In common with other electrical instruments fitted 2 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.
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.
File:Im19450927FL-AvroTudor.jpgFUEL CONSUMPTION:
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 AMPG 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 climb and 3 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 (shock absorber) 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 2 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.

Avro 688 Tudor ll
The 2nd Tudor II to be completed, G-AGRY, went to Nairobi for tropical trials as VX202 (see this photo which may have been taken on its way to or from the trials), but these were unsatisfactory and Tudor II orders were reduced to 18. Eventually, only 4 Tudor IIs were completed including the prototype. Avro’s Type 688 Tudor was a British piston-engined airliner based on their 4-engine Lincoln bomber, itself a descendant of the famous Lancaster heavy bomber, and was Britain’s 1st pressurised airliner. Despite having a reasonably long range, customers saw the aircraft as little more than a pressurised DC-4 Skymaster, and few orders were forthcoming, important customers preferring to buy US aircraft. The tail-wheel undercarriage layout was also dated and a disadvantage. Avro began work on the Type 688 Tudor in 1943, following Specification 29/43 for a commercial adaptation of the Lancaster IV bomber, which was later renamed Lincoln. The specification was based on recommendations of the Brabazon Committee, which issued specifications for 9 types of commercial aircraft for post-war use. Avro first proposed to build the Avro 687 (Avro XX), which was a Lincoln bomber with a new circular section pressurized fuselage and a large single fin and rudder in place of the predecessor’s double ones. During the design stage, the idea of a simple conversion was abandoned and the Avro 688 was File:Im19450816FL-Tudor.jpgdesigned, which retained the 4 Rolls-Royce Merlin engines. It was designed by Roy Chadwick who, due to wartime restrictions, could not design a completely new aircraft, but had to use existing parts, tools and jigs using the Lincoln’s wing, Chadwick, who had worked on the Lancaster, designed the Tudor to incorporate a new pressurized fuselage of circular cross-section, with a useful load of 3,765 lb (1,705 kg) and a range of 3,975 miles (6,400 km). Two prototypes were ordered in September 1944 and the first, G-AGPF, was assembled by Avro’s experimental flight department at Manchester’s Ringway Airport and first flew on 14 June 45. It was the 1st British pressurised civilian aircraft, although the prototype initially flew unpressurised. The prototype Tudor I had 1,750 hp (1,305 kW) Rolls-Royce Merlin 102 engines, but the standard engines were 1,770 hp (1,320 kW) Merlin 621s.

Variants: All except the prototype built by Avro at their Chadderton factory and assembled and test flown from Woodford Aerodrome (above).

688 Tudor 1 Production variant, 12 built, later conversion to other variants.


The prototype Tudor I, G-AGPF, with modified fin and rudder, lengthened engine nacelles and shortened oleo legs.

689 Tudor 2 Stretched version, 5 built.

The prototype Tudor II, G-AGSU, before the fitting of an enlarged rudder and extension of the inner engine nacelles. It was in this aircraft that Avro’s chief designer Roy Chadwick and Chief Test Pilot S. A. Thom were killed on August 23, 1947.

688 Tudor 3 Tudor 1 modified by Armstrong Whitworth Aircraft as executive transport aircraft. It could seat up to 9 passengers, 2 built.

688 Tudor 4 Stretched version of the Tudor 1 (but not the same as the Tudor 2 with the fuselage lengthened by only 6 ft/1.83 m). It could seat up to 32 passengers, 11 built.

688 Tudor 4B As Tudor 4 but retained the Tudor 1’s flight engineers station. Small number of Tudor 1s were converted into Tudor 4Bs.

689 Tudor 5 Tudor 2 for BSAA, powered by 4 x 1,770 hp (1,320 kW) Rolls-Royce Merlin 621 piston engines, six built. One aircraft Star Girl crashed in South Wales 1950 killing 80 Rugby supporters in the Llandow Aerodrome Disaster.
Passengers and crew before the Llandow air disaster in 1950 (Pic: South Wales Police Museum)
Llandow air disaster close to Sigginstone village, Vale of Glamorgan, in 1950 Aerial scene of Llandow air disaster close to Sigginstone village, Vale of Glamorgan, in 1950

The Crash was a scene of indescribable chaos. The front part of the plane was stuck in the ground. The central section was a wreck with both wings ripped off and the fuselage completely destroyed, but the tail, although damaged, was still intact.  The bulk of the 78 passengers and 5 crew were huddled in a mass in the fore part of the wreckage.  Most were still strapped in their seats, which had been ripped away from their moorings by the force of the impact, and piled in a mass among the dead and injured. The possibility of pilot error was investigated with Air Vice Marshal “Pathfinder” Donald Bennett, Managing Director of the owners, “Fair Flight,” commenting that: “It is a simple case of the pilot’s seat slipping back with acceleration and the pilot took the joystick back with him.”
Crash of an Avro 689 Tudor in Cardiff: 80 killed

689 Tudor 6 Ordered by the Argentinian airline FAMA, but the order was cancelled. None of the airframes were completed.
689 Tudor 7 Tudor 2 fitted with 4 x 1,750 hp (1,305 kW) Bristol Hercules 120 radial piston engines, 1 prototype only.

688 Tudor 8 Jet-engined version of the Tudor 1. Tudor 1 VX195 was fitted with 4 Rolls-Royce Derwent Mk.V turbojet engines. Tudor 9 Jet-engined version of the Tudor 2, became the 706 Ashton.

Super Trader 4B Re-engined version, fitted with 4 x 1,760 hp (1,312 kW) Rolls-Royce Merlin 23 piston engines.

Tudor Freighter 1 Freight and cargo version, 3 aircraft were used by BOAC during the 1949 Berlin Airlift.

G-AGRH Avro Tudor Freighter 1 – (c/n 1256) with its original short nose, as used by British South American Airways before being converted by ATL into a long-nose Super Trader for Air Charter service in 1956. Despite its good range, the tail dragger Tudor was vastly outclassed by more modern American airliners like the Douglas DC-6.

711 Trader Proposed freighter development of the Tudor 2 fitted with a tricycle landing gear; not built.

Specifications: (Avro 688 Tudor 1) Data from Jane’s Fighting Aircraft of World War II.
Crew: 5 (2 pilots, flight engineer, radio operator, navigator);
Power-plant: 4 x Rolls-Royce Merlin 100 12-cylinder V12 engines, 1,770 hp (1,320 kW) each; Capacity: 24 passengers;
Length: 79 ft 6 in (24.23 m) – Wingspan: 120 ft 0 in (36.58 m); Height: 22 ft 0 in (6.71 m);
Wing area: 1,421 sq ft (132 sq m); Loaded weight: 66,000 lb (30,000 kg); Max. take-off weight: 76,000 lb (34,500 kg);
Performance: Maximum speed: 320 mph (512 km/h) at 8,000 ft (2,440 m);
Cruise speed: 283 mph (453 km/h) at 12,000 ft (3,660 m);
Range: 3,630 mi (5,840 km);
Service ceiling: 30,100 ft (9,180 m);
Rate of climb: 990 ft/min (5 m/s); Wing loading: 53.5 lb/sq ft (261 kg/sq m).