Avro Lancaster

Strange as it may seem when some types of aircraft are 'loaded' the increased mass dampens out many of the smaller stresses of flight with a reduction in fatigue and a more comfortable ride for the crew.

Chris wrote:

I had nice view when the BBMF Lanc flew over my garden yesterday.

What a suprise!!

I think your house & garden must be a beacon for airshow acts Chris.

PETERTHEEATER;149895 wrote:

Almost certainly a fabricated (rivetted) box section from light alloys with internal formers. The outboard wing spars would have been tapered fabrications attached at the start of the dihedral. The metal thickness (gauge) would have been selected to provide the required strength using the minimum acceptable to conserve weight.

As the main structural component to which everything else was attached directly or indirectly it would be the target for fatigue and, therefore, given a life in flying hours. Landings too would stress the mainspar through the landing gear attachments and should have been factored in. They didn't install Fatigue Meters in operational service so the assessed life would have been quite conservative due to the need to apply a generous safety margin.

I discussed this with my son, who is a recently retired Chief Technician (Airframe), and he did some of the work on the BBMF Lanc when it had a major overhaul some years ago. He remarks that a big problem faced by restorers these days is getting sheet metal in the correct old Imperial measurement thickness, which was expressed as SWG (Sheet/Wire Gauge). Some of the SWG thicknesses are no longer made due to the move to Metric measurements, and approval to remanufacture in a Metric thickness is not easily obtained. In addition the metallurgy has changed over many decades, and the various alloys may not be the same as they were all those years ago. Use of a different alloy to the original is another big stumbling block. Somewhere in the shed I have a piece of a Zeppelin, the second to be shot down, which crashed at Billericay in Essex, and it would be interesting to see what spec the alloy is !

An update on the engine situation (Courtesy of faceache)-

We would light to take this opportunity to thank everyone for their support and understanding as we continue our engine repairs. A special thanks is extended to both Andrew Panton and the Battle of Britain Memorial Flight who immediately offered us loaner engines! Our plan is to remove the No. 4 engine today. For logistical reasons, we will be installing the BBMF engine which is is expected to arrive in Durham Tees later today. Assistance with the conversion is also being provided by Retro Track & Air (UK) Ltd. We are putting forth a maximum effort to make the SOLD OUT event of 3 Lancs on Tuesday at East Kirkby.

Even with the use of a loaner engine, we have incurred significant costs to swap out the engine plus facilitate the repairs to our engine, which will need to be ready for the end of September for our return to Canada. Donations to HELP KEEP THE LANCASTER FLYING can be made here: www.warplane.com/about-cwhm/donate/donationsform.aspx .

She is currently sat in Hangar 1 at Teesside Airport and was tucked up for the night at 9:30pm when the four Canadian engineeers called it a day after preparing the offending merlin for removal . The new or newer merlin arrived from East Kirkby just after 8pm and will hopefully be fitted later today ready for a ground run on Monday .

I think VeRA's date with Jane and Thumper on Tuesday will be a close call but if she does make it then it is down to the hard working , un-sung ground crew rather like it was back then !

I'm afraid that the so-called 're-sparing' of PA474 has, over the years, become surrounded in folklore and mythology. I visited the aircraft at St Athan when the work was being carried out. It was not resparred, if by that term you think that the whole of the main spar from wing tip to wing tip was replaced. It was not.

What was actually replaced was sections of the rear spar top and bottom boom. This work was carried out by Contractor's Working Party from BAE Systems at Chadderton, using parts machined by BAE Systems from raw material stock obtained for similar work on the Shackleton. At the Lincolnshire's Lancaster Association event day at the BBMF about two years ago BAE Systems had a display which showed the drawings of the parts of the rear spar that were replaced, together with test pieces made by the Chadderton technicians because a special riveting technique is used to attach the wing skins to the top and bottom spar booms.

The fatigue status of the RAF's Lancaster is underwritten by BAE Systems using data obtained from the long term support of the Shack, which is read across to the Lanc and adapted using data from its on-board fatigue meter and other data recorders.

It is true to say that the use of certain loads can mitigate fatigue damage, with such techniques being quite widely used today. For example, fuel maight be left in outboard wing tanks to help reduce wing bending moments. In modern fighters it is often the case that various pods and drop tanks are carried for much of the time, even though they are not required for the specific sortie, because of the way they help reduce wing bending. However, anything that is carried by the aircraft add to its all-up mass, and that is the still the killer.

As for the difficulty in obtaining old-style materials, that is certainly the case today. It is for that reason that all aircraft, irrespective of their design, size or use, need active design support so that appropriate material substitutions can be agreed which will not compromise the strength or fatigue resistance of the structure.

WJT ~ thanks for the additional detail as the guide at Kirkby did make reference to the memorial flight using Shakleton parts ~ however not being an air frame conversant person the significance of the comment had not registered.

I must admit that it did strike me at the time as a major task ~ when we had to climb over what they called the main spare ~ to get into the front of the aircraft.

My Mothers old school friend who had worked in Birmingham during WW2 had pictures of them being assembled in the factory where she worked ~ one of them showed a main fuselage section on the production line where the wings were to be attached as a major stand alone component ~ it appeared to the untrained eye ( mine ) that the whole aircraft would have to be taken apart to replace the major component that we had to climb over.

If I had understood the assembly process correctly ( which I doubt ) from looking at the pictures ~ the cock pit section would be added to the front of this wing fuselage section and then the tail section before moving on down the assembly process for the wings etc.

Would be interested to hear some more about the on board fatigue monitors ~ assume that they are real time recorders ?

Dave.

H77: Fatigue recording on the Lanc, as on other still flying military aircraft of the post-war era ranging from the Bulldog and Chipmunk through to the Jet provost, Hunter and Canberra, use a devise known as a 'Fatigue Meter'. This fiendish mechanical device was developed by Negretti & Zambra Ltd and is most probably in use in its Mk 19 incarnation.

The fatige meter has a number of counters which are displayed in windows on the front of the box which is mounted as close to the Centre of Gravity as possible. As the airframe encounters applications of 'g' the internal mechanism trips each counter depending in the level of 'g' applied. Thus, in any one sortie for a fighter type aircraft there might be a large number of clicks on the counters which represent say 1.75g and 2.5g but fewer clicks are likely to be recorded in the 5g and 7.5g windows unless the aircraft was doing full-on combat training or display aerobatics.

These readings are recorded after every flight and fed into a formula to determine the units of 'fatigue index' or 'FI' consumed. When the approved limit is reached the aircraft is scrap or major structural repairs are required. This limit is determined by a full-scale fatigue test or other means by the aircraft design authority (ie BAE Systems in the case of the Lancaster) and the formula to be used and the patterns of flying are reviewed annually to make sure that any change of operation does not go un-noticed. The Buccaneer accident on the Nellis Ranges in the late 1970s had a lot to do with that.

The fatigue meter is essentially clunky clockwork and a lot of work is now being done to validate the performance of solid-state devices such as Minature Structural Recorders (I know them as MSR - but I'm not wholly sure what it means!). These are being operated alongside fatigue meters and are downloaded periodically for the data to be analysed and compared with that from the fatigue meter. It will be a bold step, but I suspect it will not be long before MSR takes over totally from the fatigue meter.

Peter wrote:

My wife has just come back from a cliff walk between Folkestone and Dover and said the Lancaster flew by at head height just off the edge of the cliffs. Eager to see the photos I was somewhat shocked to see the Lanc was sporting only two engines and radials at that! It was a B-25! Odd really as she knows the difference in sound between radials and inlines! Still, a Catalina flew over the house yesterday and the Dakota the day before that so it must be twin radial weekend.

They where all displaying at Shoreham Airshow over the weekend. The B-25 is from the Royal Netherlands Historic Flight.