the tail problem

 

The photograph above shows a MKII Handley Page Halifax bomber - the same type as JP137. The aircraft is fitted with 4 Rolls Royce Merlin engines, and as you can see, triangular shaped tails fins.

This second photograph shows a later MkIII version, which looks very different. The engines are now the more powerful Bristol Hercules radial engines, and the tail fins are much larger, and rectangular in shape.

The dramatic difference between the two types of tail fin can be clearly seen in these next 2 photos.

 

The reason for this significant design change was really very simple: The design of the original triangular tail fin was seriously - and tragically - flawed.

As early as 1941 there had been some concerns about the original tail design, and by 1943 there had been a large enough number of apparently inexplicable Halifax losses for full scale  tests to be carried out, in secret, at Boscombe Down in Wiltshire.
The results of those tests revealed that the triangular tail fin fitted to the Halifax was potentially lethal, in that it had a tendency to overbalance and 'lock' into the maximum rudder offset position, a condition that could only be corrected by allowing the aircraft to dive, at high speed, for some 4000 ft. 

As a result, during late 1943 and 1944 a new MKIII version of  the Halifax was introduced. The tail fin had been completetly redesigned, and was much larger, and now rectangular in shape. In addition, a different powerplant - the more powerful Bristol Hercules radial engine - was fitted to overcome the problem with the Merlin engine being underpowered for this airframe. The resulting aircraft was much improved in both performance and safety, and served with distinction for the rest of the war.

Unlike the Lancaster, the Halifax was more than just a bomber. It also served as a glider tug - especially in the build up to D Day - and with Coastal Command for anti submarine duties. The Halifax was also used as a special forces aircraft, dropping SOE agents and suppies behind enemy lines in Europe. We believe it was in this capacity that JP137 was intended to serve.

Although perhaps rather less glamourous than the more famous Lancaster, the Halifax was a highly respected aircraft - particularly these later versions.

However, this changeover to the new design took time, and although a number of MKII aircraft were modified, and had been fitted with the new tail by the middle of 1944, not all had..... JP137, for example, was still fitted with the earlier triangular tail fins, even though it was a virtually new aircraft.

With the engine failure that occurred soon after take off, the use of the rudder to try and correct for that almost certainly caused a rudder overbalance, and the subsequent fatal stall spin.

Ideally, these earlier - potentially lethal - aircraft should have been remove from service and modified, once the problem had been identified. But this was wartime......

The problem was so significant that Johnson and Heffernan devoted the whole of the first chapter of their book 'A Most Secret Place : Boscombe Down 1939-45' to the problem of 'The Disappearing Halifaxes'. The notes make chilling reading....(you can see a transcript HERE)

The crew of JP137 may not have even been aware of the potentially lethal nature of their 'overbalancing' rudder ... Revealing that kind of design flaw was not going to be good for morale.  As a result, the crew of JP137 - and probably many other Halifax crews - lost their lives when a rudder problem made their aircraft uncontrollable.....