This is an interesting discussion, but,as it relates to Bob Palmer, and his Smoothie design, some often heard "facts"are being reported..
I have some insight to the questions, as I drew the CAD plans for Brodak's Smoothie kit. Bob sent me his originals, plans drawn in pencil on "Butcher Paper". In those days, creating drawings on Butcher Paper, was in style with scratch builders. As the CAD Drawings progressed, the question regarding the airfoil difference came up.
Here's Bob's answer, as correctly as I recall it.
He told me that the fellow doing the kit, and who also had major impact on the published article, ( I wish I could remember his name.Hi comes to mind, but I don't believe that's correct, (must be early Alzheimer's). Anyway, this fellow was anxious to get the design published, and get the kit out on the Hobby Shop shelves. The problem was Bob was out of the country. He told me where, but my memory tells me, he was either in England, or Africa, on tour. Bob had built the first Smoothie previous to leaving, so the only plans at the time were for the thinner, aft high point, airfoil we all are familiar with, in the published and kitted version.
Bob was still showing signs of agitation after all these years, as he explained his Smoothie being published and kitted without his final blessing. He wanted the airfoil changed closer to the normal 4 digit version. He was upset that they had released the design before he returned and before he had made his final changes. Thus the skinny wing being in the original published and kitted design. In a moment of clarity, Bob reported That the money made a difference0in paying some orf his bills, that's why He didn't push things too hard back then.
He told me that after his return from his tour, he revised his design to reflect his final desires for the Smoothie. He wasn't happy with some aspects of performance with the skinny wing. In decent stunt winds, the normal symmetrical airfoil flew better shapes. This was what he wanted the design to be.
He said that he would go to contests at venues such as Santa Anita parking lot on a Sunday Morning. He would have both versions, in identical paint schemes. in the trunk of his car. He would check out the wind conditions, below a certain limit, he would use the 4 digit Smoothie. Windy,over the limit, he would use the skinny winged version. He was tickled, very few folks ever caught onto his selection process.
You may question the use of such sneaky methods in stunt practises in those days.
Remember, in the 50's through some of the 70's, it was common to have your special little Stunt Secrets. secrets such as handles, lines, wing styles, (such as the Detroit style, or I Beam wing.) engines, Push rod Geometry, on and on.
In the early 70's, as PAMPA formed and grew, we started sharing and teaching what were formerly secrets.
I believe, after spending many hours talking with Mr. Palmer as we collaborated on the Creation of the Cad Drawings, used with the Brodak Smoothie version. That what was being drawn in CAD, was the Smoothie as Bob wanted it, and as he peferred to fly on most occasions.
Bob was happy, as he said the new Smoothie drawings represented what he wanted the Smoothie to be, and was what he flew, (except those very windy days).