Avro Manchester - Prototypes

The first prototype of the Avro Manchester flew for the first time on 5th July 1939 and it revealed to have some flaws and stability problems apart from being too heavy and exhausting to control.
It also required a very long runway to take-off when fully loaded even when it hasn't installed yet any armament.
It showed, however, a very good internal space arrangement, specially when compared with the smaller Handley Page Hampden.
The second prototype, featured lighter controls and wingtip extensions in order to shorten the minimum required runway. However stability problems weren't solved, specially when flying at low speeds. So Avro decided to take the prototype back to the factory in order to add a third vertical fin, which initially seemd to solve the problem, but it came back when the turrets were fitted. In fact, the frontal turret created a heavy yaw when turned, the rear one created a very heavy vibration and the ventral one was too unconfortable to raise or leave it deployed.
The engine was also a problem, as it was underpowered. It had initially a rate of 2000hp but it turned out that at its peak it could achieve only 1750hp, less than an aircraft of this type needed. It was discovered that it was because of the internal arrangement of the engine made the lubrication system too dificult, causing some engines to break down or overheat.

Sources:
1. https://defenceoftherealm.wordpress.com/2015/03/21/forgotten-aircraft-avro-manchester/
2. https://en.wikipedia.org/wiki/Avro_Manchester