I did the majority of my PPL training in a PA28 Warrior and I've recently started transitioning over to a C172 and one thing that amazes me is how convenient it is to have a door either side of the aircraft.
My question is: Why does the PA28 only have one door on the passenger side of the aircraft?
I've never seen the schematics of a PA28 but my assumption might be that there's equipment that runs down the left side of the fuselage preventing a door from being added.
Having one door is just a design preference which makes the aircraft simpler, and lighter to build.
There are many other light aircraft with only one door. Besides Piper, most Mooney, Beechcraft, and Bellanca aircraft only have one door. Even the high wing Cessna 195, 206, P210, 337, and low wing Cessna 310 and 340 have only one door.
It reduces weight and increases the structural strength of the fuselage, particularly with the typical design of a low wing aircraft. Later low wing aircraft like the Cirrus make use of an internal crash rollcage in the dorsal spins of the fuselage which adds extra strength to accommodate the second door. Diamond uses a semi monocoque tub-like design with a single swing up canopy enclosure to facilitate ease of entrance and egress.
Piper's early low wing plane history, the best info I have found has been this:
http://www.pilotfriend.com/aircraft%20performance/Piper/11.htm
In 1954, Bill Piper was looking for a design to compete with the Bonanza. The engineers at Piper were busy with other projects at the time, so Bill Piper asked his friend Al Mooney if Piper could buy the new Mooney MK-20 design that Mooney had not yet started producing. Al wouldn't sell the design, so Bill Piper asked Al Mooney to come up with a totally new design. Al submitted a design to Piper that was an all metal 4 place monocoque construction with retractable gear, a 180 HP Lycoming, and a stabilator in place of an elevator. The stabilator was a new design, an all flying horizontal tail.
The cabin size of Al Mooney's design was a bit small, so the engineers at Piper increased the cabin size and the first Prototype PA-24, N2024P, was created in 1956. As you can see in this photo, the trailing link landing gear on the prototype is not what we have on our Comanches. It is suspected that Bill Piper decided that the trailing link landing gear would be too complex and expensive, and in an effort to undercut the cost of the Bonanza, he decided on the straight tube oleo strut landing gear that all Comanches are equipped with. Although it is much more difficult to make a good landing with the straight oleo strut landing gear than with the trailing link gear, that decision by Bill Piper is why Comanche Pilots have skills much more superior and a highly qualified group of Pilots than the Bonanza and Mooney bunch!!
The second prototype PA-24-180 flew in 1957. The first production 180 was delivered in January of 1958. It cost $14,500. The 250 HP Lycoming was meanwhile being tested in the original prototype PA-24, and the first production 250 Comanche was delivered in April of 1958.
And from Wikipedia:
Piper PA-28 CherokeeI have
At the time of the Cherokee's introduction, Piper's primary single-engined, all-metal aircraft was the Piper PA-24 Comanche, a larger, faster aircraft with retractable landing gear and a constant-speed propeller. Karl Bergey,[12] Fred Weick and John Thorp designed the Cherokee as a less expensive alternative to the Comanche, with lower manufacturing and parts costs to compete with the Cessna 172, although some later Cherokees also featured retractable gear and constant-speed propellers.
