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Miles/HPR Marathon

On 23rd December 1942 the War Cabinet appointed an inter-departmental committee, with Lord Brabazon as Chairman, to prepare outline specifications for new transport aircraft types that would be required post-war, and to also consider the conversion of existing types in the short term. The Committee was also directed to plan for the use of spare design and production capacity as soon as it became available. To complicate matters, the requirements had to ensure that there would be no interference with war production.

By early 1943 the resultant Brabazon Committee was able to recommend immediate action to proceed on the design of five main types, as follows:

Further to a meeting on 22nd February 1943, the Civil Aviation Sub-Committee advised the War Cabinet that, “…British air transport after the war shall be on a scale and quality in keeping with our world position, and that work on the design of new types of civil aircraft and on the conversion of existing military types should proceed under the direction of the Government as and when this can be done without impairing the war effort. We therefore ask the Cabinet to …agree to accept financial responsibility for the initiation of the programme of civil aviation upon a basis adequate to provide a minimum number of essential types of aircraft in the immediate post-war period.”

Woodley
The Miles factory at Woodley in the summer of 1947. The Marathon production line was in the narrow black building running top to bottom at the right of the cluster of buildings.

The War Cabinet understood the need to make an immediate start on these requirements so that a seamless transition from military to civil aircraft production would be achieved when peace was declared. But it also realised that design personnel were fully occupied with the war effort. It was therefore hoped that industry could, “…from time to time make available some designers for civil air transport work.”

Following consideration of the Brabazon Committee’s findings, the War Cabinet directed on 25th February that:

Furthermore, a Second Brabazon Committee was set up in May 1943 to refine the requirements for the types identified by the First Committee. The main aim was to consult industry and airlines to so that the aircraft would satisfy the largest possible market. A subsequent revision to the Type V resulted in two distinct subtypes being identified:

By the Spring of 1944, contracts had been agreed and work had begun on the Brabazon Type I (Bristol Brabazon), Type II (Airspeed Ambassador, Vickers Viscount and Armstrong-Whitworth AW-55) and Type Vb (de Havilland Dove). The Type III, Type IV and Type Va could not proceed until detailed specifications had been drawn up. It was the Type Va that eventually became the Miles Marathon and it is worth noting that at this stage, the War Cabinet estimated (notwithstanding the lack of a specification), that design work on the Type Va could begin in July 1945 with flight trials commencing in February 1947.  

In May 1944, the Air Ministry issued Specification 18/44 for a civil feederliner to meet the Brabazon Type Va requirement, and though Percival and Armstrong Whitworth submitted designs, it would appear that Miles Aircraft Ltd of Woodley (near Reading) had already been chosen for this project.

In his book Miles Aircraft Since 1925 (Putnam, 1970), author and long-time Miles employee Don Lambert Brown recalled that, “George [Miles] on the one hand, was convinced that a low-wing monoplane of about 12,000 lb all up weight and powered by four de Havilland Gipsy Queen engines was the ideal; the author was equally convinced that a high-wing monoplane of about 20,000 lb all up weight and powered by two 1,100 hp Bristol engines was to be preferred. Eventually a compromise was reached, the result being the M.60, a high-wing monoplane with an all up weight of 16,500 lb and powered by four 330 hp Gipsy Queen 71 engines. This was submitted to the Ministry in time for the official Specification, 18/44, to be written round it.”

Prior to this, Miles had assumed itself to be the chosen bidder for the Type Va, but despite now having to compete with other manufacturers, the Miles design won, and in October 1944 instructions were issued to proceed with the design and manufacture of three prototypes. The Miles design was given the type number M.60 and by May 1945 had been named Marathon.

Marathon GA
This early general arrangement shows the small freight door just aft of the flight deck, which was only a feature of the prototype aircraft.

Miles formed an M.60 Design Committee, with George Miles as chairman, but headed by Don Brown. Other members of the team were HS Wilkinson (chief of stress), DS Bancroft (chief aerodynamicist), JH Lowden (chief draughtsman) and Brian Buck (weights engineer). The first prototype, with construction number 6265, was registered as G-AGPD on 5th June 1945 and would be the first Miles aeroplane of all-metal construction and its first four-engined aircraft. The second machine was given construction number 6430, while the third (c/n 6544) became the prototype of a turboprop version, the Marathon 2.

By mid-1945 the design was reasonably well-defined, Miles being able to state that the Marathon would be able to carry 14 passengers plus baggage and 650 lb of freight or mail, a still-air range of 500 miles to tanks empty, or 350 miles with one hour's reserve of fuel. This was based on a recommended economical cruising speed of 175 mph.

The preliminary design followed earlier Miles transport projects and featured a high wing of all-metal construction, allied to a tricycle undercarriage and twin fins and rudders (note the latter). Engines were the quartet of Gipsy Queens earlier alluded to, but the constructor also provided for an alternative powerplant in the form of twin 850 hp Armstrong Siddeley Cougar air-cooled radials. The latter engine was still under development and not expected to be ready for some time. Ultimately this engine was not proceeded with.

Basic dimensions were; wingspan - 65ft, length - 52ft 6 in, height - 13ft 3 in. These basic figures changed only slightly between the initial concept and the final design.

A capital cost of £25,000 per aircraft was estimated, and a cost per passenger mile at full load of 1.39d (1.39 old pennies), based on a utilisation of 2,500 flying hours per annum. The design at this stage envisaged four rows of seats arranged with one to port and a pair to starboard. The fifth row comprised just a single pair of seats to starboard and the aisle was thus offset to the port side.

Unfortunately, life was about to become difficult for the new design. At this time aircraft could only be ordered by the Ministry of Supply (MoS, and later, the Ministry of Aircraft Production (MAP)), who would of course not be the actual customer. The Ministry had little in the way of contact with the operators, mainly reacting to the Brabazon Committee’s requirements and the resultant Air Ministry specification. To exacerbate this situation, the aircraft manufacturer (in this case, Miles) was precluded from having direct contact with the operators (“the Corporations”), with all discussion between parties being conducted through the Ministry. In a 26th November 1946 House of Lords debate on Civil Aviation, Lord Nathan, Minister of Civil Aviation put the case this way,

“The Ministry of Supply is acting as the agent for the Corporations, and the Corporations are the people who decide upon the specifications. The Corporations are in touch with the contractors upon all the modifications, although they will have to consult with the Ministry of Supply if very substantial changes are required. But the Ministry of Supply is acting as the agent on behalf of the Corporations, and the Corporations have the financial responsibility.”

But the operators were the least of the problem. With various Governmental bodies having an interest in the design, their disparate requirements began to make their effects felt. One of the first issues centred on the MAP requirement that the engine installation be interchangeable with the de Havilland Dove (Brabazon Type Vb). Since the Dove was a low-wing design and the Marathon would have a shoulder-mounted wing this requirement was difficult to implement and ultimately proved impossible to meet. Nevertheless Miles wasted many hours proving what they already knew.

The situation of inter-departmental meddling was highlighted in a House of Commons Debate on 11th July 1946 by Air-Commodore Sir Arthur Harvey (Tory MP for Macclesfield),

“On 6th October, 1944, the Miles Aircraft Company of Reading were invited by the Ministry of Aircraft Production to make two prototypes. They were given verbal instructions to build these aircraft. Following this provisional order, a struggle took place between the Ministry of Aircraft Production, BOAC, the Air Registration Board, the Ministry of Civil Aviation and the Royal Aircraft Establishment, none of whom had any coordinating effort, and all of whom issued conflicting instructions. For instance, it was laid down that the radio in the Marathon type should be the weight of three or four passengers. I leave it to the imagination of honourable Members to say what its effect would have been. The Ministry of Supply insisted on pressurisation of these aircraft, although the engines allowed them to fly at a height of only 6,000 or 7,000 feet.”

The pressurization requirement was later rescinded by Lord Nathan, who had learnt of the requirement during a visit to Woodley. However, Miles later received a letter from the Ministry of Aircraft Production which ordered the company to ignore all design inputs expect its own, and to re-state the need for pressurization!

Into the Air

Despite this ridiculous wrangling, construction of the prototype continued at Miles’ Woodley plant and on 19th May 1946, the aircraft took to the air, piloted by Ken Waller, Miles’ chief test pilot. This machine was initially given the Miles test marking U-10 (the Miles test letter ‘U’ was replaced by ‘G-21’ in 1948). It made its second flight on 21st May, again with Ken Waller in command but now with Hugh Kendall as second pilot. On Saturday 1st June it was presented at the Reading and District Royal Aeronautical Society’s garden party and a short flying demonstration was given by Ken Waller. He and Hugh Kendall flew U-10 to Farnborough on 26th June for demonstrations which ran from 27th to 29th June 1946. Repainted with its civil registration G-AGPD, the aircraft was delivered to ‘B2’ Performance Squadron at A&AEE Boscombe Down to begin its Certificate of Airworthiness trials on 26th August.

Marathon prototype
Marked 'U10' for testing by Miles, this is the first prototype Marathon, rolled out at Woodley circa May 1946.

Meanwhile, the Ministry of Supply had canvassed British Overseas Airways Corporation (BOAC) on potential customers for the new aircraft. By June 1946, British European Airways Corporation (BEAC, and later abbreviated to BEA) had agreed to take 25 of a turboprop variant and the MoS wanted to guarantee at least 25 more overseas orders for the piston-engined version so that production could start. BOAC responded that they would be happy to act as agent for the majority of the overseas sales it predicted, as follows:

Iraqi Airways - 3 aircraft
British West African Airways - 3 aircraft
Egypt (Misr) - 5 aircraft
Iran - 2 aircraft
Lebanon/Syria - 2 aircraft
Turkey - 5 aircraft
Malaya - 5 aircraft

None of these airlines or locales subsequently placed orders and the whole issue of procurement for the airlines is covered in the 'BEA' section of the Airlines page.

On 12th and 13th September 1946 the Marathon was shown to the industry for the first time at the Seventh Society of British Aircraft Constructors (SBAC) Show at Radlett. The aircraft was one of four Miles civil types on view and was seen to be fitted with a stick-force test recorder on its starboard control column. Ken Waller and Hugh Kendall both performed flight demonstrations at the show.The Miles stand also included a model of a proposed version of the aircraft with twin Mamba turboprops.

Following the SBAC Show, G-AGPD was returned to Boscombe Down and it then suffered two successive incidents that could easily have ended its flying career. The first occurred on the morning of 28th October 1946 as the aircraft was performing handling tests for its Cerificate of Airworthiness (C of A). Up to this point the Marathon prototype had flown 65 hours. Pilot for the test was Sqn Ldr JA Jarvis, with observers Miss Beryl Edmonds and GW Dearsley.

Takeoff at 10 am was uneventful, with a slight crosswind from starboard; unstick occurred at 85 mph indicated airspeed. However, as Sqn Ldr Jarvis selected the landing gear up, the mainwheels retracted correctly but the nosewheel remained locked down. Flaps were then retracted and finally, at three to four minutes after takeoff, the nosewheel retracted. However it was then realised that the side-slip indicator was inoperative and so the test was abandoned.

Before returning to land, the undercarriage was functioned at 110 mph to obtain further details for the ground crew and again the nosewheel was found to stay down for three to four minutes after the main landing gear had raised. Unfortunately, it was now discovered that the nosewheel would not re-extend when Sqn Ldr Jarvis selected it for landing, and only after a loud bang was heard aboard the aircraft did it eventually unlock, but it did not fully extend or lock in the down position. By now Boscombe Down's control tower had visual contact with the aircraft and they advised that the nose gear appeared to be locked down. A precautionary landing was made onto grass beside the runway, holding the nosewheel off the ground as long as possible, but at the end of its landing run the nose gear finally collapsed and the aircraft slid for more than 30 yards on its folded gear and doors, but damage thankfully was minimal. The crew was unhurt.

On 6th December 1946 the Marathon suffered its second flying incident. The aircraft was again being flown by Sqn Ldr Jarvis on a further C of A handling test. Also aboard were two civilian observers, GW Dearsley and W Budden. The Marathon left Boscombe Down at 15.10 hrs at an all-up weight of 16,500 lb and tests then included the use of full take-off power for periods of 1 to 2 minutes on ten separate occasions. On the third application of power, the port outer (No.1) engine showed signs of cutting out, but no cause could be found and there seemed to be no cockpit indications. Care was then taken when using full throttle to make sure that cylinder temperatures were at least 200 degrees C before applying full power for subsequent parts of the test.

It was on approximately the eighth test that fluctuations on the instrument readings for the the port outer were nted, with the boost gauge fluctuating from 8 lb to 2 lb, but again the crew could not reproduce the symptoms immediately in order to verify the fault. Further tests were completed, but these did not use full power and all temperatures and pressures remained normal. The final test of this sortie was to simulate the failure of the starboard outer engine and on this occasion the port outer engine performed faultlessly. It was not until a return to base had been initiated that problems returned, at which point the warning light in the feather button for the port outer engine illuminated. A visual check showed no sign of fire, but as a precautionary measure the propeller was feathered and the fuel shut off. A safe three-engine landing was made along Boscombe Down's flare path with no damage to the aircraft.

Subsequent investigation of the No.1 engine (Gipsy Queen 71 s/n A550723) showed that engine failure had occurred, and that a hole had been blown in the rearmost cylinder. To quote the Chief Technical Officer's report, "Failure occurred due to severe overheating of the rearmost cylinder. [It] shows discolouration due to excessive heat, the upper cylinder filming was partly disintegrated, the cylinder baffle distorted and ignition lead burnt or scorched. The flame switch adjacent to the rear cylinder had operated". The engine had completed just 68 hours since installation on 25th July 1946. A new engine was installed and G-AGPD continued its test programme. It completed the C of A tests on 15th January 1947. The A&AEE testers were generally in praise of the aircraft's handling, but did raise a few reservations and criticisms. Notable among these were the 'large and clumsy' ganged throttles. They would be redesigned for production.

The second prototype (registered G-AILH on 18th October 1946) flew on 27th February 1947. It would be the final Miles-built Marathon.

Marathon prototype
A fine shot of the highly-polished first prototype Marathon on an early test flight. Note the lack of pitot airspeed probes on the nose section.

Prototype Described

Externally, one of the most prominent features was the expansive forward windscreen area, which was formed by blown perspex panels with near-constant-radius curvature, and supposedly free from distortion. It would seem likely that after a short period of service, and with a few scratches and blemishes, the situation would not have been so rosy. There were small ‘bad weather’ windows let into each side of the main windshield and these could be opened if desired. The aircraft featured curved windscreen wipers which were novel in being mounted horizontally and moved up and down by a mounting tube, through which the de-icing fluid was fed.

The fuselage was of conventional stressed skin construction, with riveted skins applied over a frame of fore-to-aft longerons and intermediate frames and bulkheads. There were two main aluminium bulkheads (aft of the flight deck and aft of the main cabin), and a half-bulkhead forward of the flight deck. Fuselage skins were attached via snap-head rivets and the skins varied from 20 gauge to 24 gauge (0.914 to 0.559 mm) in thickness.

The wing was mounted atop the fuselage so that the main spar did not intrude into useable cabin space as would a more conventional shoulder-mounted wing. Instead it was attached via a box-like structure which projected only slightly into the cabin so that there was still a good 6ft of headroom beneath the wing box. The ailerons were mass-balanced via external lever arms. Flaps were recessed into the inboard wing trailing edge, with the flap track mechanisms neatly recessed into the aft section of each engine nacelle. Miles claimed that the Marathon was the first British four-engined commercial aircraft to be fitted with this type of low-drag flap. Each outboard wing mounted a combined pitot/static tube for measuring airspeed, though on the second and subsequent machines, these were relocated either side of the forward fuselage.

Design Certificate
Dated 20th August 1947 and signed by George Miles, this is the Design Certificate for the Marathon I.

In line with convention, the Marathon wing was divided into a main centre section with separate outer wing panels, which joined up outboard of the engines. The wing gained most of its strength from the front spar, which was constructed as a D-section, braced internally on aluminium riblets. At 70% chord there was a secondary spar, constructed of pressed channel section and bearing only light loading. The outer wing panels were attached to the centre section at the main spar via ‘fork-and-lug’, pin-jointed straps; at the aft spar, simple pin-jointed fish plates were employed. The wing skins were attached with snap-head rivets, apart from the leading edge, back to the 30% chord line, where countersunk rivets were used to maintain a flush surface. The skins varied in thickness from 16 to 24 gauge (1.626 to 0.559 mm). Tail surfaces were from 20 to 26 gauge (0.914 to 0.457 mm) in thickness.

The horizontal tailplane was of conventional construction and mounted to fuselage frames, with the rearmost taking the main loads. Twin fin/rudder assemblies were attached at the extremities of the tailplane, the rudders being horn-balanced and mass-balanced while the elevators were mass-balanced via external lever arms. On the first prototype, a central fin (with no rudder) was fitted, but initially this item was absent on the second prototype.

Fuel storage was taken care of by four separate tanks, with two in each wing giving 120 gallons capacity per side. These tanks were crash-proof, with flexible, bag-type rubberized liners. The four-tank layout made a simplified fuel system possible, whereby each engine was fed by its own fuel tank. Miles claimed an 85% range with one engine out. Fuel cross-feed was possible between tanks on the same wing, but not between wings. This meant that there were no fuel lines passing near the fuselage.

On the prototype, four Gipsy Queen 71s were fitted, and these featured carburettor fuel control, but all production versions would have direct fuel injection. Maintaining the avoidance of fuel in or near the cabin, the aircraft used a remote-controlled, single-shot engine-priming system, which used compressed air to inject a controlled measure of fuel into the engine for starting. In this way, only the compressed air lines entered the cabin area, with single priming buttons in the cockpit controlling the whole system.

The landing gear was a Miles design and emphasised simplicity and ease of maintenance. The main undercarriage was of the levered suspension type and taxy lights were incorporated into each leg, which for the time was another novel feature. The nose wheel could be allowed to freely castor or steered by using the rudder pedals.

Entry to the aircraft (for both passenger and crew) was via a main door of approximately 5 ft 4 in x 2 ft 6in, located just aft of the wing trailing edge, on the port side. At this time, the aircraft was planned for two seating configurations: for 14 or 18 passengers, but up to 20 seats could ultimately be installed, if required. This would have seriously restricted the range of the aircraft however. Seats would be arranged in pairs, either side of a single, central aisle. Just aft of the entry door, a small toilet compartment was located and immediately behind the cabin area, a 164 cubic ft luggage bay was provided. It was accessed via a top-hinged loading door on the starboard side.

In the cockpit, throttles for the four engines were ganged, such that by using one hand the pilot could operate single engine controls, both engines on one wing or all four at the same time. This was a feature seen on a number of WWII American bomber types, notably the B-17 and B-24, and presumably inspired by them. Another (for the time) novel feature was the design of the landing gear and flap control levers, which were hinged to fold down sideways into gated slots for positive locking. Airscrew braking (reverse pitch) was by means of the speed control levers, which were pulled up to the top end of their gates, followed by retarding of the throttles beyond the normal closed position. It wasn’t fully automatic, but did create a modicum of safety to prevent inadvertent operation.

Mounted separately behind the pedestal was a console which mounted the trim selector. Based on a switch of German origin, it had fore-and-aft and lateral movement as well being a rotary selector. Fore-and-aft movement actuated the elevator trim tabs; sideways movement gave aileron trim and rotation provided rudder trim. The trim tabs were operated by Miles electric actuators mounted inside the main control surfaces. Trim tabs were complemented by servo tabs on the starboard rudder and elevator and on both ailerons.

One unusual feature was the way that directional trim in the yaw plane was adjusted by use of the outer tail fins, which could also be 'toed-in' during take-off to provide better control in the event of an engine failure. This feature was not thought necessary for the Gipsy-engined aircraft but for twin-engined Cougar (and later Mamba engine) applications, failure of a single engine would have been far more critical on take-off. The trim controls for the fins were electrically operated from a large multi-position switch to the rear of the main control console.

The Marathon had no hydraulic system, and instead all landing gear and flap actuation was pneumatically operated. The pneumatic system operated at a pressure of 450 psi and emergency lowering of the undercarriage was a ‘free-fall’ operation, initiated by cable-operated unlocking of the gear uplocks. A separate air bottle was provided for emergency operation of the flaps.

Marathon prototype instrument panel
This is how G-AGPD's instrument panel looked early in its brief life. Particularly worthy of note are the dual controls (most Marathons just had the control wheel and rudder pedals fitted on the left side) and the ganged throttle levers at centre. The latter items were criticised when the aircraft was tested at Boscombe Down and were replaced by more conventional levers on production Marathons.

In September of 1947, Flight magazine visited Woodley and reported in effusive terms on the general characteristics of the aircraft, “The present design trend, in the smaller categories, toward a high-wing layout gives the Marathon an entry door threshold which is but 2 ft 5 in above ground, permits an unobstructed floor throughout the cabin, and allows the passengers clear views of the country over which they are flying. An incidental advantage, which is frequently unregarded, is that the wing offers a considerable area of shade and consequently precludes the discomfort of glare for most passenger impositions; it also must help to reduce direct heat transmission when the machine is parked on tropic airfields.”

Flight magazine described the aircraft in flight as, “…[exhibiting] very pleasant characteristics”. It went on to provide some useful feedback for consideration on the production aircraft, “Take-off is remarkably short and the general noise level in the cabin pleasantly low. The fact, however, that the exhaust pipes of the Gipsy Queen engines emerge on the starboard side of each nacelle makes the port side of the cabin noticeably noisier than the starboard. Despite the fact that most operators would prefer maximum interchangeability of engines to the attainment of minimum noise level, it would be worthwhile considering a modification to the port inner engine exhaust to eliminate this drawback.”

G-AGPD was returned to Miles at Woodley from Boscombe Down on 15th January 1947 and Certificate of Airworthiness No.9695 was issued on 4th September, just in time for the aircraft to appear at the eighthSBAC show. For 1947, the show at Radlett was expanded to four days, running from Tuesday 9th September to Friday 12th September, with flying displays for powered aircraft starting at 2.30pm. The final day of the show was dedicated to “Government and industry only” and with no flying display. Miles exhibited six aircraft and again took along the first prototype, for reasons as Flight magazine described it, “The actual aircraft on view was the first prototype with the centre fin, and was, in fact, the same aircraft as that exhibited last year. It had been furnished for an overseas tour, and the company considered it better to show that model furnished than the No. 2 prototype as a shell.” Ken Waller flew the Marathon for the display days.

The De Havilland Gipsy Queen Engine

The de Havilland Gipsy Queen was a 6-cylinder inverted, in-line, air cooled, 4-stroke aircraft engine. It was initially developed in 1936 as the military version of the earlier 9.2-litre Gipsy Six II and eventually replaced the earlier type in both civil and military applications.

The Gipsy Queen I of 1936 developed 185 hp at 2100 rpm (max power was circa 200hp) and was a direct-drive, unsupercharged engine. Subsequent versions up to and including the Gipsy Queen III were improved versions with similar power but with improved strength and reliability.

The Gipsy Queen IV of 1941 was originally developed as a supercharged version of the Gipsy Six engine, known as the Type IIIS. Capacity was increased to 10.2 litres and power was now up to 285 hp at take-off or 230 hp at 2100 rpm in the cruise. Drive was still direct from the crankshaft.

De Havilland now standardised the capacity for its Gipsy Queen engines at 10.2 litres and circa 1944 had three basic models – the direct-drive, non-supercharged Series 30 (175 hp in cruise), the direct-drive, supercharged Series 50 (180 hp in cruise, but with better high-altitude performance) and the Series 70, with geared drive and supercharging (280 hp in cruise).

In 1950, de Havilland introduced the Gipsy Queen 71, which was the military designation for the Series 70 variant.

The Gipsy Queen 71 was constructed with a one-piece aluminium alloy crankcase. The cylinders comprised steel barrels and detachable die-cast aluminium alloy heads. Each head mounted a single inlet valve and one exhaust valve, both actuated by push rods.

The six-throw, one-piece counterbalanced crankshaft incorporated fixed vibration dampers and the whole was supported in seven plain hearings. Reduction gearing was by epicyclic spur reduction gears, the ratio being 0.711:1 with provision for a de Havilland Hydromatic propeller.

Supercharging was via a single gear-driven compressor with a ratio of 11.22:1. Fuel was injected through a single nozzle into the eye of the supercharger impeller from a single Hobson DHG/4 horizontal injection type carburettor. Boost control was automatic.

Ignition was provided by twin 14mm spark plugs per cylinder, receiving their high tension charge from two BTH CGD magnetos and a pair of BTH CD6A 6-point distributors. The engine was fitted with an electric starter as standard. Basic details were:

Bore x stroke4.72 in x 5.90 in (120 mm x 150 mm)
Displacement10.2 litres
Compression ratio6.5:1
Width19.6 in (498 mm)
Height33.2 in (843 mm)
Length71.7 in (1821 mm)
Weight670 lb (304 kg)
Weight/horsepower1.76 lb/hp (0.80 kg/hp)
Fuel consumption0.46 lb/hp/hr (210 g/hp/hr)
Oil consumption0.015 lb/hp/hr (20 g/hp/hr)
Rating (take-off)380 hp at 3000 rpm
Rating (normal) at 4400 ft (1340 m)355 hp at 2700 rpm
Rating (cruising) at /8000 ft (2440 m)   265 hp at 2400 rpm

 
Gipsy Queen engines were installed in a number of aircraft, including the de Havilland Dove and Heron, Percival Prentice and Proctor as well as the Fiat G.46. A total of 1,889 Gipsy Queens were built.

Gipsy Queen 70
A Gipsy Queen 70 engine. Cylinders were positioned beneath the engine to aid forward visibility in single-engine applications.

End of an Era

Early in 1947, a period of harsh winter weather had seen temperatures drop below zero and brought with it prolonged bouts of snow. Road and rail networks were badly affected and coal supplies, already severely reduced by the war effort, struggled to get through to the power stations. Many of the latter were forced to shut down and the government introduced emergency measures to cut power consumption. For domestic users, electricity was restricted to 19 hours per day, but for industry the effects were even more draconian, with some supplies being stopped completely.

For a company like Miles, still making the majority of its aircraft from wood, and with glued joints requiring reasonable temperatures for curing, it was a disaster. Allied to this, the company had slender financial resources and with production priority being given to the Monitor target tug (which was subsequently cancelled), even the production of the smaller civilian aircraft became difficult. When the gluing of structure was attempted at low temperatures, the failure of joints led to more wasted effort and so the company was sent into a spiral of rising production costs and reduced income.

To address this situation Miles secured a £400,000 overdraft via Barclays Bank but that was soon reached, and though subsequent increases in the facility were made, each time the company quickly began to exceed these renewed borrowing limits. To reduce expenditure, staff redundancies were introduced, first with small numbers of production staff, then in larger numbers and finally even the designers began to be stood off.

On 27th September 1947, Samuel R Hogg was appointed as receiver and manager for the troubled company. He had full executive authority and ultimately he had to discharge the remaining employees and bring aircraft production to a halt. One of his first actions was to write to the company’s creditors, explaining the situation, and his letter pointed out that the early 1947 period had coincided with the beginning of full production of the Gemini and Aerovan types. Production costs had been in excess of estimates and the civil aircraft sold for the 1947 year to that point had resulted in ‘considerable loss’ for the company. Hogg added that he was now negotiating to reinstate production and had consulted four principal trade creditors (Blackburn Aircraft Ltd, De La Rue Extrusions Ltd, Smiths Aircraft Instruments, Ltd and Sperry Gyroscope Co Ltd).

Marathon 2nd prototype
Life goes on. Despite being subject to bankruptcy proceedings, the Marathon carried on its testing schedule. The second prototype was transferred to RAE Farnborough on 25th April 1947 and fitted with an astrodome above the flight deck around this time. G-AILH is seen at Farnborough during the 1948 SBAC show, still in its 'twin fin' guise (what appears to be a central fin is in fact that of the AW.52 flying wing, parked to the rear). (GS Collection photo via Peter Amos)

Concurrently, suppliers were paid off as far as possible, but despite this in November 1947, the Titanine paint company brought a petition for the winding-up of Miles Aircraft Ltd. The case was brought before the Law Courts on 24th November, where Mr Justice Wynn-Parry adjourned the petition until 19th January 1948 on the grounds that the company had showed prima facie reasons for not yet having formulated a reorganization scheme. An affidavit put before the court showed that a loss of £630,000 had been incurred up to 31st October, but this sum was still subject to audit. Furthermore, negotiations were not yet complete with respect to obtaining fresh finance. Further adjournments continued the saga into 1948, but finally in April of that year, creditors and shareholders in Miles Aircraft agreed to accept a scheme for reconstruction of the company, along with partial remuneration for all parties. Sadly one condition of the agreement resulted in the departure of the Miles family from any interest in the company, and a new management team was put in place, including Mr Hogg and Mr AF Jopling. The winding-up petition was thus dismissed, Mr Hogg stating in an affidavit that assets in the balance sheet amounted to £596,457, representing aircraft still in production. Gradually the name ‘Miles’ disappeared into history, but there was a bright spot on the horizon.

Handley Page Production

Throughout this period, negotiations had been conducted to ensure continued aircraft production at Woodley and finally in June 1948 the receiver was able to announce that a wholly-owned subsidiary of Handley Page Ltd would take over the manufacture of Marathon aircraft, the repair and servicing organization for all types of Miles aircraft and the running of the flying school at Woodley. Handley Page (Reading) Ltd took possession of Marathon production on 21st June. From a caretaker staff of 200, HPR rapidly expanded it up to around the 2,000 figure that had been employed prior to the Miles collapse.

Sadly, while this regeneration was still under negotiation, tragedy struck the programme. The first prototype Marathon had been transferred to Boscombe Down on 20th April 1948 to begin Ministry of Supply acceptance trials, at which point it had completed 106 hours of flight time. On 20th May it was destroyed in a flying accident near to the airfield , killing MoS test pilot Brian Bastable and flight test observer Miss Beryl Edmonds. View synopsis of the crash.

For the next year, there was just one Marathon – the second prototype – airworthy and this aircraft was heavily involved in flight testing, including C of A trials at an increased 18,000 lb all-up weight. Thus HPR was left with no choice but to concentrate its efforts on getting the production line running.

The surviving prototype, G-AILH, was loaned by the Ministry of Supply back to Handley Page for exhibition at the Farnborough SBAC Show from 7th to 13th September 1948 and it then remained with the company for exhibition purposes as Handley Page attempted to find a market for the production machines, which had begun to roll down the line at Woodley.

Meanwhile, by May 1949 the first production machine was standing on its landing gear, engines fitted and expected to fly within a month. The second aircraft was due in the air during September and it was hoped to have four production machines flying before the end of the year. Thereafter the remainder of the 40-aircraft production run was due to be completed at the rate of two per month, increasing to four.

The Marathon 1 was not included in the flying display for the 1949 SBAC show, Handley Page instead showing an aircraft in the static display in BEA colours and with seating for 20 passengers.

G-AILH was transferred to A&AEE at Boscombe Down on 19th October 1949 to check compliance with specification requirements prior to a period of tests in Africa. By this time the aircraft was fitted with non-adjustable tail fins, though it would appear to have initially flown with this feature. The aircraft (which had also by this time been fitted with a central fin) was not at Boscombe Down for long however, and left for two months of tropical trials at Khartoum and Nairobi on 7th November. This series of tests permitted the scheduling of performance under ICAO maximum conditions to suffice Air Registration Board requirements. Among the trials were take-off and landing distance measurements, rates of climb and engine cooling tests. The trials were complete by 3rd December but a defect in the front false spar web of the tailplane was discovered just prior to the return flight and repairs delayed departure from Khartoum until 20th December. G-AILH arrived back in the UK a week later; it was handed back to HPR on 2nd January 1950.

Modifications for Production

Handley Page put a number of changes into effect for productionising the Marathon; one of the most prominent was that the type became known as the HPR.1 under new ownership.

Material changes were extensive, with the third, central tail fin being standardised (this item had been present on the first prototype, but was initially omitted from second). The external mass-balances were removed and there was a slight revision to the shape of the rudder horn balance. The elevator was also altered by moving its hinge point further aft, with a corresponding nose extension to effect internal balancing. The lower portion of the fin and rudder was also flattened out slightly to reduce the likelihood of tail scrapes on take-off and landing.

On the forward fuselage, the small freight door on the port side was deleted and the air intake scoops for the engines were altered in shape.

To simplify production, Handley Page brought in a number of detail changes and one example was that on production aircraft the fuselage was divided horizontally so that more workers could get access to the structure at an earlier stage. Though not designed to ease construction, the main fuselage frames were stiffened with additional straps on their four sides to allow for the newly-increased 18,000 lb all-up weight.

The prototype aircraft did not feature wing de-icing, but for production aircraft it was thought necessary. Initially a thermal de-icing system, using hot air from the engines as its medium, was considered, but it could not be incorporated until the sixth production machine. The first five aircraft instead featured provision for Goodyear de-icer boots, with the possibility to modify these, if necessary, to the thermal system by replacing the wing and tailplane leading edges. The first five Marathons were due for delivery to West African Airways and the thermal system would have been introduced on the first BEA machine.

Marathon 1st production
Under new ownership. The Handley Page-built first production Marathon, with HP logo on its nose at the 1949 SBAC show. (photo courtesy of Peter Amos)

The final big change for production was the addition of four extra fuel tanks, comprising separate 15 gallon extensions to each tank, which were then interconnected through the wing ribs. Total fuel capacity was now quoted at 280 gallons, though inexplicably, (despite the capacity increase of 60 gallons), a 240 gallon capacity had previously been declared. A sale price of £43,000 was now stated for the machine, minus radio and special equipment, but fully-furnished in 18-seat configuration.

As part of the marketing campaign, on Saturday 14th January 1950, the first production Marathon left Woodley on a 35,000-mile sales tour to Australia and New Zealand. It was flown by Hugh Kendall, with RA Constantine as navigator. There were three others in the party - Commercial Manager Group Captain AF Bandidt, RC Hobbs in charge of servicing the aircraft and J Parker, an employee of de Havilland Engines, who would provide support for the Gipsy Queens. After a short hop to nearby Blackbushe, where the crew spent the night and cleared Customs, the aircraft departed for a series of fast outbound legs to New Zealand, from where the tour would commence. Two 170-gallon fuselage fuel tanks were fitted to G-ALUB to extend its range during this tour, an especially important requirement for the stage across the Tasman Sea. Nearly 2,000 lb of spares and luggage were also loaded aboard.

The route out was via Nice, Brindisi, Athens, Nicosia, Baghdad, Bahrain, Sharjah, Karachi, Calcutta, Rangoon, Singapore, Koepang (East Timor), Sydney and finally to New Zealand’s North Island. G-ALUB reached Sydney on 27th January and flew on to New Zealand on 2nd February, completing the 13,500 mile flight on schedule. The aircraft was then handed over to the New Zealand National Airways Corporation for testing over the airline’s network and flown by its own crews.

The Marathon then departed for Sydney and operated from Melbourne, Adelaide, Perth and Broome on a month-long series of demonstrations in Australia. In both New Zealand and Australia, pilots were converted onto the Marathon, and were said to have been pleased with the aircraft’s handling qualities, stalling characteristics and spacious cockpit. Passengers also praised the temperature inside the cabin, effected by the aircraft’s high wing.

Whilst in Australia, keen interest was shown by a number of airlines and so the tour was extended to enable in-depth assessment. Following a Qantas Empire Airways Limited (QEA) request, G-ALUB was flown from Sydney to New Guinea, where four days were spent, operating in mountainous jungle terrain, among peaks rising above 14,000ft and through passes that rarely were less than 8,000ft. The airfields used in New Guinea were often rough-surfaced and short in length, with difficult approaches in typical rainforest weather. QEA’s pilot for these trials, Captain Orme Denny said that the aircraft had, “…given every satisfaction”.

Upon its return to Australia, the Marathon was also operated by Australian National Airways (ANA). Captain Ivan Holyman, Manager of ANA was quoted as saying that a Marathon-type aircraft could fill a definite need in Australia. Sadly, neither airline made an order.

For return of the Marathon to the UK, a route was planned similar to the outbound legs, but with reduced haste in order to demonstrate the aircraft to interested parties. Four days were planned in Singapore around 17th March; two weeks in India and Pakistan around 25th March and two weeks in the Middle East during April. As it transpired, the demonstrations were done in Egypt, Malta and France, the aircraft reaching Woodley on 2nd May, having flown more than 35,000 miles, made in excess of 300 take-offs and landings, and completed approximately 300 flying hours. The tour was seen as a great success and the crew received an official welcoming ceremony hosted by Sir Frederick Handley Page at Londonderry House in Mayfair on 6th July.

But no sooner had this tour finished than another began. To mark the opening of Livingstone Airport in Northern Rhodesia on 12th August 1950, Handley Page decided to send G-ALUB so that it could take part in the flying display, but also used the opportunity to visit nations on the way back and give demonstration flights. These were planned at Portuguese West Africa, Leopoldville, Lagos and Casablanca, with European visits to Lisbon and Madrid. The aircraft received a white-painted fuselage upper surface for this tour, aimed at reducing cabin temperatures.

Back in the UK, Handley Page now set about producing the balance of the production run, and once this had been completed their activity on the aircraft moved to the support of those in service as well as the conversion of unsold aircraft into trainers for the RAF. But progress was slow, as shown by the calendar of first flights: G-ALUB, the first production aircraft, had first flown in June 1949, but it was not until 14th November that year that the second production machine (G-ALVW) flew, and only in January 1950 that the third machine took to the air. Production continued into 1952.

Marathon GA
The caption that accompanied this photo would probably qualify as an early example of 'spin'. Taken from an HPR brochure, it shows a few of the unsold Marathons in storage at Lasham, awaiting conversion to T.11 trainers. (via Peter Amos)

Altogether 42 Gipsy-engined Marathons were built - two by Miles and 40 by Handley Page. The initial disposition of the production aircraft was thus: 28 to the RAF (two not taken up), 6 to West African Airways, 3 to Union of Burma Airways, 2 to Far East Air Lines and one to Germany.

Marathon 1 Data (Four 330 hp DH Gipsy Queen)

Span65ft (19.8m)
Length52ft 3in (15.9m)
Height14ft (4.3m)
Wing area, gross500 sq ft (46.5 sq m)
Aspect ratio8.4
Aerofoil SectionNACA 23018 at root, NACA 23009 at tip
Weight Empty11,460 lb (5198kg)
All Up Weight16,500 lb (7484kg - later 18,000 lb (8165kg))
Wing loading36.14 lb/sq ft (0.02bar)
Max fuel capacity280 gal (1282 l)
Rate of climb (18,000 lb at sea level)683ft/min (208m/min)
Rate of climb (18,000 lb at sea level on 3 engines)240ft/min (73m/min)
Time to 10,000ft (3048m)14 min
Service ceiling18,400ft (5608m)
Max level speed (6,750ft (2057m), 17,100 lb)232.5 mph (374km/h)
Best range speed at 10,000ft (3048m)157.5 mph (253.5km/h)
Take-off distance (18,000 lb (8165kg) AUW)461 yards (421m)
Take-off distance (18,000 lb (8165kg) AUW) to clear 50ft     841 yards (769m)
Take-off speed (18,000 lb/8165kg) 82.5 mph (133km/h)

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