A simple question. What principals made for a good bomber aircraft during WW2? Why were some aircraft outstanding and others mediocre or just plain usless? Leave aside tactics and crew proficiency - let's concentrate on the machine. For every ying there has to be a yang - heavy bombloads affected range, more defensive weapons affected speed etc. If you had to design your own bomber aircraft what would you consider the most important features? Designs must within acceptable limits of what was available during the war, and certain considerations must be taken into account. For example, designing a six or eight engine to allow for greater speed, range, bombload etc will limit an aircraft to fewer airfields that have runways long enough to accomodate them, etc
If using during the day, the main requirement was that it had to be jolly fast, i.e the Mosquito. If it was slower than enemy fighters it was dead meat; the Americans tried to overcome this by massive defensive armament which meant that in the case of light bombers such as the B25 &, B26,they had six or seven man crews doing what two men in a Mossie did. At night, so long as the aircraft was reliable, its survivability was largely down to chance. From this point of view it didn't matter whether you were in a Stirling, Halifax or Lancaster (once the Halifax's tendency to spin was sorted out). But the Lanc had the biggest bomb load, which was the whole point of the exercise.
I think the greatest effect design in a light bomber was int he Mossy: wooden frame which made it flexible and light. Powerful engines which gave it speed, a design that made it manouvreable, and just overall a classic understanding of what a fighting aircraft should be. Ina heavy bomber then again its good reliable powerful engines such as the Merlin, then a strong yet flexible air frame. In the medium Wellington the geodetic frame gave it everything it need and more besides. A heavy had to have speed, carrying capacity and above all manouvrability to get it out of the search light cones or evade a fighter attack. For me the Lanc did this perfectly with the ability to corkscrew and dive and pull up, almost as well as a fighter.
