The Lancaster Bomber

Pictured is aircraft from the Battle of Britain Memorial Flight (BBMF) in the skies above Lincolnshire. Lancaster PA474 wearing 460 Squadron (RAAF)
Cpl Phil Major ABIPP, OGL v1.0OGL v1.0, via Wikimedia Commons

Most will know about the Lancaster Bomber, that it was designed by Ray Chadwick to carry a huge bomb load a very long way and was probably the best bomber in WWII, certainly the most famous. Few will know how this came about, they know the middle part of a long story. They will not know the beginning and the end of the story

This article will attempt to remedy that and to ‘fill out’ the Lancaster story

The Lancaster was not designed to fly to Berlin and back with a huge bomb load, it was a product of serendipity, the occurrence and development of events by chance in a happy or beneficial way. It was a lucky random happenstance.

The design process is a long road with twists and turns along the way, seldom does a designer sit at a drawing board and sketch out a finished design. The potential customer, the RAF will issue a requirement, a committee will specify what they want the aircraft to do, the designer then sets to work to find a workable solution to the problems the committee has set.

In the 1930s the committees responsible for guiding the direction of aircraft development had many, it seems to us now, very strange ideas of what was needed in a bomber. Each of these odd requirements contributed, quite unintentionally, to the very good final design of the Lancaster.

The Lancaster was developed from the Manchester bomber, that was a twin engined aircraft but each RR Vulture engine having twice the horse power of existing engines, it was thought that one large engine had proportionally less frontal area and drag than that of two engines and that would benefit its carrying capacity and range. That is good as far as it goes but the problems encountered with development meant that the engines never met their potential. The Germans followed the same line of reasoning with their heavy bomber and that was a failure too, and for the same reason. The Manchester was not a success, many of the design aspects of the aircraft were right but with poor engine performance the plane was doomed to failure.

Many of the design features of the Manchester contributed to the Lancaster’s final success story.

The Lancaster had many features which made it a success.

Huge bomb bay

Long range fuel capacity

Very strong fuselage construction.

Robust undercarriage

Strong wing construction allowing it to carry large ‘overload’ stresses.

The huge bomb bay was a requirement from the original specification, the aircraft was to carry torpedoes,  torpedoes have to travel through water so have to be long and slim, already long at the time of writing the specification it was thought that the torpedo would develop to be longer and heavier so allowance would be made for future loads.

Lancaster area bombing load
Clarke (Plt Off), Royal Air Force official photographer, Public domain, via Wikimedia Commons

If you consider the fuselage to be a long tube it can be seen that if you cut away the bottom of the tube for the bomb bay the rest of the fuselage will need to be beefed up to carry the redistributed load.

Original bomber specifications proposed that bombs should be carried in cells within the thickness of the wing. Bombers of the time were designed to that specification and, although the Manchester never did carry bombs in the wings, the initial stress calculations for the wing design allowed for it. Fortunately the unobstructed space allowed for bomb stowage could be repurposed for the installation of large fuel tanks.

The original specifications called for the facility to be catapult launched. Airfields at the time were grass and the thought was that bigger and heavier aircraft should be helped to get into the air by catapult launching. Although specified it seems that little was done to develop the idea, research turns up very little on the subject however, the aircraft had been designed to take the considerable loads imposed on the structure by the ‘dragging’ forces of 2.5 g on take off. The structure and undercarriage was beefed up to cater for these loads. As it happens the airfields were enlarged, a far simpler solution to the problem, runways were lengthened and paved leaving the catapult idea to become just a note on a few obscure websites.

In the 1930s bomb aiming was a hit and miss affair, indeed it stayed that way far into WWII, so the though was more towards dive bombing as a more effective way of dropping the bomb load on the target. This requirement, diving from height, aiming the whole aircraft plus bombs at the target then letting the bombs go meant loading the wings to high ‘g’ forces on the pull out from the dive. High g forces put huge stresses on the aircraft. Once again, the structure had to be beefed up to compensate. The dive bombing requirement was soon dropped but not until after the structural designs were completed.

It should be noted that the German design philosophy, no doubt at Hitler’s insistence, retained the dive bombing requirement right through the war, to the detriment of some very good aircraft.

You cannot just bolt wings onto the fuselage of an aircraft, the joint would put huge stresses on the fuselage so the fuselage would need to be very much stronger and, heavier, it can be done but it is easier to make a wing that passes through the fuselage, you will note that few large aircraft are ‘mid wing’, they either have the wing structure passing under or over the fuselage. There we find a problem with the Manchester/Lancaster, the bomb bay is where the wing support beams would pass through, the wing has to go above the bomb bay. This put the wing nearer the mid wing, which is ‘cleaner’ aerodynamically but meant that passage through the aircraft was impeded by the beam and, to give the crew room, the cockpit had to go on top, like a greenhouse on the fuselage. This would carry a drag penalty which is a loss, it’s more difficult to push that through the air than one snug in the fuselage, but on the win side of the equation the crew were given a good all around view which is useful when being hunted by fighters..

As has been said, the Manchester was not much of a bomber, there were problems with the engine and the aircraft could not climb to the ceiling required to be out of range of flak. The ceiling of an aircraft is influenced by the wing design, high flying in thin air requires a greater span, the specification for bombers in the thirties required a span of less than 100 feet. Why the 100 ft limit was imposed is unclear, the popular hanger at the time was the Bellman which was only 95 feet wide having a clear span of about 88 feet. To add to the confusion the specification stated that the construction should allow for maintenance and servicing in the open.

It was obvious that the Manchester needed a major redesign. By this time the Merlin had been given an accelerated development programme to iron out any faults and a huge manufacturing facility had been built for its mass production, it was therefore expedient to fit four of these to replace the two troublesome engines. To do that the wing had to be lengthened and because of the previous design requirements this was fairly simply done by re-spacing the existing  wing ribs, thickening the aluminium skin and adding six feet to the outer part.

Initial trials of the Lancaster were favourable, pilots found it easy to fly and it all looked promising, however on the 20th on March 1942, Lancaster L7570 took off from Woodhall Spa and ended up on the beach at Frieston after a crash landing.

The official report reads;

T/o Woodhall Spa for a mine laying sortie off the Frisian Islands. Visibility was poor at the time and as the Lancaster climbed away, so the starboard wing tip grazed the roof of a house. This resulted in a crash landing at 1500 on the beach at Frieston, 4 miles E of Boston, Lincolnshire. The crew escaped injury, and although little damaged, the bomber was swamped by the incoming tide and written off.

What was odd was that Ray Chadwick the designer was soon on site, odd that a designer was interested in an event which was fairly routine, crashes were a regular part of flying. Or not. The pilot reported to Chadwick that after climbing out of heavy cloud in foul weather the engineer noticed that one wing tip was missing, leaving a ragged edge, and the other tip was bending up at ninety degrees. In the next couple of months other aircraft had failures of the outer wing where the aircraft skin detached. There was obviously a problem, investigation showed that the method of pop riveting developed by Avro would not cater for the stresses involved so another method had to be used to stop the wing skin from peeling from the leading edge spar. It is not recorded how the pilot felt for being blamed, in the official record, for hitting a house when the failure was the aircraft and not the actions of the pilot.

The Lancaster then had the well known illustrious war service lugging big bomb loads long distances and returning home despite damage. There are tales of an aircraft having a hole punched in its wing by a bomb dropped by an aircraft above it and flying home. The performance of the aircraft when it was light, having dropped its bomb load and used half of its fuel, gave pilots the confidence to throw the plane around in fighter type manoeuvres to evade fighters. One German fighter pilot was amazed to lose what he thought was an easy target when the Lancaster performed a loop and dived away. Pilots amused themselves on the long slog home by taunting pilots of the American B-17s by overhauling them and shutting down the two engines nearest them, feathering the props and staying alongside.

After the war the Lancaster was used as a transport to repatriate troops and PoWs, and then as a test bed for various new jet engines such as the RR Nene and new aircraft systems.  Civil versions, the Lancastrian, a Lancaster with military gear stripped out and with seats and door added, and the York, which was a more comprehensive redesign with a high mounted wing, served as a stop gap airliners and transports until the new generation of civil aircraft came on stream.

The ‘Nene’ Lancastrian on Nov. 22nd, direct from Le Bourget to Heathrow, was made in only 49 min, including landing, actual flying time from point to point being 41 min—an average speed of 322 mph.  This remarkable performance was in spite a beam wind and the dead weight and drag of the two inboard Merlins, which are only used for take off and landing.

In Canada, where many Lancasters had been built, one was fitted with jet engines in place of two of its four Merlins. (There is scope for an article on aircraft and aero engine design in Canada in the post war years but we will consider just this one example.)

Canadian built Avro Lancaster Mk. 10C, RCAF (Serial No. FM209)  was modified by removing the outer merlins and installing Avro Canada jet engines in their place.

FM209 was taken on strength with the RCAF as a Mk. 10U on 21 Aug 1946. FM209 was loaned to Avro (Canada) in the latter part of 1948 and converted to designation Mk. 10O (Orenda). The bombadier’s position and nose turret were removed, and the tail turret was replaced by tail-cone and observation windows in each side of the fuselage for photographic test recording. The two outboard Merlin engines were replaced by various Orenda engines with the first test flight on 13 Jul 1950 with pilot Don Rogers at the controls. Flying on its jets alone, with the inboard props feathered, was as fast as a stock four engine Lancaster bomber. One incident with Mike Cooper-Slipper at the controls took place at an air show in which Mike asked the engineer to start the Merlin engines and a mix-up occurred and the Lancaster became a glider. The jet engines were started in time. The aircraft became an ideal engine test bed and was able to fly on either jet or Merlin engines or both. The crew of pilot, two engine test observers and a navigator were normal with over 500 hrs logged up till Jul 1954. FM209 was lost in a fire on 24 Jul 1956 in Avro’s wartime flight test Hangar at Malton, Ontario.

Jet powered Avrao Lancaster From Canadian Warplanes 5: Avro Lancaster, RCAF, post-war

The aircraft flew from an airfield at Malton near Toronto which is a few minutes flying time from the US border half way across Lake Ontario. There are anecdotes of the pilots flying the plane along the fringe of US airspace where US P-47 Thunderbolt fighters would come to intercept them only for the Lancaster, with the jet engines and the Merlins in operation,  to pull away from them. There is a mention of the Lancaster doing a barrel roll as it pulled away, boys will be boys even if they know they will get reprimanded when landing.

The Lancaster was developed further to become the Lincoln bomber which became operational just in time to miss the war in the Pacific. There was a Lincoln at Farnborough in the early fifties sporting a large tail fin fixed atop the fuselage to test de-icing equipment. The Lincoln was then developed to be the workhorse of Coastal Command, the Shackleton, a grumbling beast with four Griffon engines, described by someone as “a hundred thousand rivets flying in close formation.”  It performed maritime patrols and airborne early warning duties for many years ending its service as recently as 1991.

The Shackleton was favourite of mine at air shows, at a Farnborough show early on a Sunday afternoon in the fifties I was surprised to hear the commentator inform us that the weather report he’d just given was from a Shackleton out over the Atlantic and if we wanted to see it land it would be back sometime late Monday morning.

From the Manchester’s first flight in 1939 to the Shackleton’s last flight fifty two years later, the Avro bomber family did sterling service for this country.

Feature image: Photo by Daniel Cooke on Unsplash

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