Oboe Beam Approach

It seems that no-one can offer a solution to the problem of the Oboe Beam.

The matter is obviously complex, involving the curvature of the earth(?) and variables such as the height being flown, the height above sea level of the transmitter, the height above sea level of the target, the distance from the ground station to the target, and the direction and strength of the wind to arrive at the intended trajectory of the bombs at the release point. All these factors, and probably some others, would presumably be calculated and programmed to fix the beam to be transmitted on a pre-determined radio frequency.

While I have been trying to understand why the course apparently flown differs from the circular arc of the beam, it has occurred to me that the height above the target may influence the flight path. To try and explain what I mean, a comparison with the operation of the Gateshead Millennium Bridge across the Tyne at Newcastle may help (photographs below from the Sunniside Local History Society are gratefully acknowledged). As the semi-circular pedestrian pathway is raised to allow shipping underneath, the arc viewed from above will appear increasingly elliptical rather than semi-circular. If it were possible to raise it to a vertical position, it would appear as a straight line viewed from above. In other words, as the height increases, when viewed from above (or below), its apparent shape would change from a semi-circle at one extreme (when horizontal) to a straight line at the other (when vertical). The intermediate stages would appear as a changing ellipse as the angle of rotation increased.

The diagram below attempts to illustrate this. On the left is the geometry of a rotating arc of a circle viewed from above. On the right this is translated into the geometry of an Oboe beam over the Forêt du Croc transmitted from Hawkshill Down. If the Oboe radio beam is a circular transmission, then as its height above the target increases, would it not gradually appear more elliptical when viewed from above, becoming closer to a straight line than the arc of a circle? Just like the perspective of the Gateshead Millennium Bridge. Is this how Oboe worked?

I’m sure this over-simplifies the problem, but could the fundamental reasoning be sound? It seems logical. If so, it would certainly explain why the flight path was not following the arc of a circle (which would be at ground level), but the shallower angle of an ellipse (from the perspective of 16,000 feet). The height of the aircraft in relation to the radius of the beam is obviously relevant to the extent of the elliptical deviation, but could this create a flight path from the north-west similar to that shown in the aerial view pictured in my last post? It is the only explanation I can think of, and I have managed to convince myself that the scenario portrayed does therefore appear to have a rational explanation!

All this presumes that the Oboe-leader was following the beam! But this is confirmed by the Oboe ground station recording a successful release with no deviation.

Any thoughts, anyone?

Now we wait for some improvement in the weather so that Laurent can resume his search for more wreckage.

Photo-gallery:
https://onedrive.live.com/redir?resid=BCF75E8AD40ADF0D!164&authkey=!AJrxfdmdr6MXSdw&ithint=folder%2cjpg

Index to parts found and annotated illustrations:
https://onedrive.live.com/redir?resid=bcf75e8ad40adf0d!1426&authkey=!AAJOZyTYrN-x0CQ&ithint=folder%2cjpg

Bomb carrier angle stiffener ?

I have at last heard from France following efforts to obtain recollections from more eye-witnesses to the fall of the aircraft. Curiously none have mentioned a second explosion as the aircraft neared the ground, nor at the time of impact, although this would almost certainly have been obscured by houses or trees in the line of sight. There is general agreement that the revised flight path now recorded on the wreckage plan represents a reasonable depiction of what happened.

Last month’s flurry of activity looking at bomb carriers has caused me to look again at some of the unidentified pieces of fuselage in the light of the diagrams in AP1664 and the photographs of the Avro Type bomb carrier.

The wreckage location plan shows a few items from the bomb bay found beyond the forward fuselage, perhaps thrown there from the gyrating aircraft. It is unlikely that there would have been time to close the bomb doors after bomb release, before the explosion almost immediately caused the port wing to detach, so the bomb bay may have been wholly or partially open as the aircraft fell.

At location 14 a bomb hoist point was found, and then at location 15 there was a bomb door frame former and a hydraulic jack attachment for the bomb bay doors. Moving further away from the forward fuselage situated at location 1, there were a few items at location 16 including a distinctively shaped piece which had the general appearance of a fragment of fuselage, but which had no obvious position on the aircraft.

I now wonder whether this may be an angle stiffener from a bomb carrier release unit. The piece can be compared with the photograph of the central part of the carrier (attached below) and the similarities are apparent. (The other piece in the photograph is a lever from a Mae West CO2 cylinder). If this is right, we have a slightly mysterious grouping of items from the bomb bay and fuselage floor some distance apart from other parts from the centre section of the fuselage. This suggests the probability of pieces breaking away from the bomb bay area, perhaps where the fuselage had been damaged by the original explosion, or by a second explosion as the falling fuselage neared the ground.

But as I have mentioned, none of the eye-witnesses have, so far, mentioned a second explosion and more information is being sought. This is odd in view of the blackened earth still visible in the area where the forward fuselage came to rest. Perhaps this may be further evidence that the scattering of wreckage was at least partly caused by the aircraft breaking up as it gyrated downwards, rather than as a result of a second explosion. One witness did refer to the bombs appearing to overshoot the target and exploding in the direction from where pieces from the port wing have been found: maybe the noise he heard was from an explosion in the wing of the falling aircraft rather than from the bombs? This latter view would be consistent with the evidence obtained from the location of the wreckage as shown on the plan. It is difficult to place complete reliance on teenage memories, however plausible, recalled over seventy years later without corroboration from other sources.

Photo-gallery:
https://onedrive.live.com/redir?resid=BCF75E8AD40ADF0D!164&authkey=!AJrxfdmdr6MXSdw&ithint=folder%2cjpg

Index to parts found and annotated illustrations:
https://onedrive.live.com/redir?resid=bcf75e8ad40adf0d!1426&authkey=!AAJOZyTYrN-x0CQ&ithint=folder%2cjpg

Bomb carriers

I have now looked through the copy of AP1664 kindly sent to me by jamesinnewcastl and have gleaned the following information:

The Universal (No.1 and No.2) bomb carriers were intended for use for 50lb to 500lb bomb loads;
the Avro Type (Standard) (Mk.I and Mk.II) was used for 100lb to 1,000lb bomb loads;
there was a Twin adapter, with two carriers on one unit, for the Avro Type for loads of 100lb to 1,000lb, with a maximum of 500lbs on each carrier, enabling four 500lb bombs to be carried abreast;
there was a special carrier for loads of 2,000lbs in the Lancaster;
Handley Page carriers for 250lb to 1,000lb bombs were used in the Halifax and Mosquito;
there was also a Twin adapter for the Handley Page carrier; and
there were other variations for loads of less than 1,000lb for the Halifax, Stirling and Wellington.

It therefore seems that the Avro Type (Standard) carrier would have been used in all aircraft carrying loads with 1,000lb bombs. AP2062A&C, the Lancaster parts listing, indicates that, as expected, the Avro Type carrier would have been fitted as standard to the Lancaster.

We know that two Twin adapters were fitted to ED908 as an Aiming Point photo dated 19 July 1944 shows what should have been four 500lb bombs falling abreast, together with 11 x 1,000lb bombs, but there were only three 500lb bombs falling as one hung up! This picture is near the end of the photo-gallery.

I have edited my earlier post showing AT part numbers to use the nomenclature in AP1664.

Photo-gallery:
https://onedrive.live.com/redir?resid=BCF75E8AD40ADF0D!164&authkey=!AJrxfdmdr6MXSdw&ithint=folder%2cjpg

Index to parts found and annotated illustrations:
https://onedrive.live.com/redir?resid=bcf75e8ad40adf0d!1426&authkey=!AAJOZyTYrN-x0CQ&ithint=folder%2cjpg

James, many thanks – the diagram is very helpful. I’ve sent you a PM.

Old item identified

Laurent tells me that the weather has been dreadful in France recently – he is waiting for a lull in the wind and rain, and rather less mud, before undertaking any more searches.

In the meantime, another item has been identified. Amongst Laurent’s discoveries to date, there have been a few items not related to the aircraft, including a World War I rifle grenade launcher (post #471) and the frame of a 19th century musical box (post #983)! Now we have another: the butterfly valve carburettor-like item found at location 12 (post #380) has been identified. The consensus at the time was that it was probably from a vehicle and that the piece had been discarded on the rubbish heap accumulating at the corner of the forest.

While Laurent was browsing, looking for information on the Stromberg carburettor, he came across the images below from a French business selling spare parts and accessories for Jeeps (acknowledged on the images). Our piece is a “Handy Vari-Speed” Governor manufactured in the USA and fitted to GM vehicle engines used in World War II. The Canadian forces who liberated the area in 1944 may well have used vehicles with American-made engines, so it seems quite possible that this is a wartime relic from an Allied vehicle.

Photo-gallery:
https://onedrive.live.com/redir?resid=BCF75E8AD40ADF0D!164&authkey=!AJrxfdmdr6MXSdw&ithint=folder%2cjpg

Index to parts found and annotated illustrations:
https://onedrive.live.com/redir?resid=bcf75e8ad40adf0d!1426&authkey=!AAJOZyTYrN-x0CQ&ithint=folder%2cjpg