I am looking at the history of wing planforms, and I am having trouble finding reasons for why the wright flier and other early aircraft were built with rectangular wings. I thought it was due to being more structurally secure, but I can't find any sources that explicitly say that, or describe the thought process of early designers.
Is my reasoning correct, and are there any other reasons for the decision to use a rectangular wing (vs a tapered wing)?
The benefit of tapered wing lies in its proximity to the elliptical lift distribution while retaining much of the structural benefit of a rectangular wing. But we owe this knowledge to a few things:
The Wright Flyer flew in 1903. By all accounts, the Wright brothers designed it through trial and error. As a result, the insight of tapered wing couldn't have been known to them during the Flyer's design and through much of the First World War.
In any case, most of the early airplanes were bi/triplanes with external struts being their structural members. The drag from the struts would've overwhelmed any benefit gained from tapered wings.
Wing ribs are usually made with the aid of a template or tool. For metal wings, it could be the male and female parts of a mould used in a press. For wooden wings it's a board with blocks of wood that hold all the pieces in place while the glue dries. Either way, a rectangular wing only needs one tool for each rib, while a tapered wing needs a different tool for every two ribs (assuming you can reuse it for port and starboard wings)
In these days of CAD and CNC machining, it's easy to forget how much effort it took to scale drawings by hand, and build tools and templates that accurately matched those drawings.
The rectangular "Hershey Bar" is a safe reliable, and yes, easier to build design.
But if you look more carefully at the Wright Flyer wings, you can see they were already rounding off the trailing edges to decrease drag. Tapering to a point serves the same function, and also enables one to build a bit more lightly due to reduced torque stress from the end of the wing. Same reason a prop is usually tapered. It evens the load along the wing.
The common sea gull is a good example of tapering done nearly to perfection.
But aircraft mimicking this design lack the fine control gulls have of their wings and trade decreased drag for increased probability of often fatal "tip stalling".
"Washing out" (reducing) the wing tip angle of attack helps remedy tip stalling, as well as deploying slats at lower speeds.
The rectangular wing is fine for many recreational aircraft. Another drag saving device that can be used is the Hoerner wing tip. Basicly, it angles the bottom of the wing to more of a point when it meets the top, helping push the downflow of the vortex away from the top of the wing.
Tapering can be seen on gliders, and even on the Cessna 172, but it is not absolutely required in aircraft design if fuel savings or optimal glide range is not an issue.
A rectangle gives the maximum area for a given span, and for something like the Flyer, running on 12 hp, they needed all the wing area they could get in the lightest possible package, so rectangular it is. Plus it's the easiest structure to build with minimum weight, since all the joints are simple 90 deg ones and the simple cross braced ladder structure is easy to make. There are some (Fokker DVIII springs to mind), but overall you don't see many tapered wings prior to the 1920s.
The Wrights weren't engineers, just bicycle mechanics, but they really were geniuses. They taught themselves all the math required. They weren't really building on the work of others; they started out using Lillienthal's theoretical framework during their glider experiments, discovered that it was deeply flawed so as to be unusable, and built their own wind tunnel to work out their own numbers, to develop their wing from scratch. On top of that, they designed and built their engine from scratch because nobody made one light enough. Pretty amazing.
