Between a 1937 Dewoitine D338 and, a 1957 Lockheed Starliner, the difference is obvious. On the ground, the first ‘plane inclines with its tail on the ground, the second is horizontal. Why? Due to their differing undercarriages.
In the late 1920’s, commercial aircraft were equipped with "conventional" undercarriages, i.e. two wheels beneath the wings and a tail wheel, or even like this German Udet Kondor, a skid under the tail. A skid was a sort of metal or wooden bar that protected the fuselage from being damaged. Their inclined attitude meant that these aircraft were easier to build, but had inherent problems during ground related manœuvres, such as during take-off and landing, or even steering.
Patrick Facon, Historian & Project manager - Centre for Aerospace Strategic Studies
"The main problem that arose was the reduced forward visibilty which the pilot had during take-off and landing. At take-off, with an inclined aircraft, and particularly from a closed cockpit, it was very difficult to see whether the area or runway ahead was clear. Some ‘planes required ground guidance."
To solve this problem, engineers then developed commercial aircraft with "tricycle" undercarriage, like the Lockheed Starliner.
Patrick Facon, Historian & Project manager - Centre for Aerospace Strategic Studies
"Tricycle undercarriage, with the provision of a nose wheel under the fore part of the fuselage, neccesitated a much bigger and more complex landing gear, whilst keeping the conventional main undercarriage of the time, under the wings, thus providing the aircraft with a horizontal aspect on the ground."
With the visibility problem then resolved, it remained up to the pilots to get used to landing with the main gear having to touchdown first, because, not being designed to absorb the intial impact of the landing, the nose wheel had a strong possibility of failing. A technique that is now mastered by all pilots, and of course, all large commercial aircraft are nowadays equipped with tricycle gear.