Hi Keith:
Your new Newtron looks fantastic! Very nice indeed. I'm sure it will be a winner.
I was looking at the photos of your wing construction, however, and had a huge hit of Déjà Vu... I'm sorry if the following sounds like stealing your (or Tom Dixon's) thunder, but that is the same exact wing construction that I developed (sans the take-apart feature...) back in the early 1970's at Control Specialties. Actually we made several of them before discarding the idea. One was built for Gene Schaffer and with it he constructed the stable mate to his famous Hallmark design, which featured a normal, fully-sheeted foam wing.
Gene flew both ships back to back several times and concluded that the Hallmark was by far the better of the two. In typical Gene Schaffer fashion, he then started a wingover with the foam/rib ship, but neglected to pull out... (You just had to know Gene; he did this same maneuver with deficient ships many times over the years...)
We also built a couple of Hal deBolt designed Stunt Wagon wings for use in OTS using this same method. They flew okay.
In the interest of full disclosure and honesty, Mike and Arnie Stott at Foam Flite also had developed a variant of the Foam-Rib wing even before I did. They didn't sell too many of them as I recall...
I did a bit of investigating and found that cutting the wood and foam out between the "ribs" yielded a much weaker wing. In a foam wing, the strength is not derived from either the foam itself, or the balsa itself. The strength comes from the product of the lamination of the two. It is called stressed skin. The balsa attached to the foam prevents the foam from bending, and the foam attached to the balsa prevents the balsa from bending. The actual term for the applied stress is, I believe, “racking.” During an inside loop the top skin is being moved inward, or compressed toward the centerline of the wing, and the bottom wing is being moved outward, or stretched. Because there is a lot of contact area between the skin and the foam on a normal foam wing, this “racking” motion is diminished greatly and the result is a very rigid wing. If you cut away a significant portion of this continuous skin on either side, or both sides, then you have greatly diminished the ability of that panel to resist racking and the two surfaces (top and bottom) will try to meet! (That’s bad…!). In such foam-rib wings the only truly stressed sections are the leading edge and the trailing edge. The addition of a robust spar, or in your case a boxed section that accepts the take-apart hardware, might supply enough rigidity to prevent the wing from failing, but there will still be bending and even twisting stresses in the non-stress skin areas. Under load there are stresses and they have to be transmitted somewhere… The result is usually that the wing panels will twist or “warp” a bit.
I was witness to a catastrophic failure of a wing made in this manner at the Nats one year. It was in a top competitor’s airplane, and it took him out of contention. Up to that point I had been toying with the idea of reprising and improving upon my earlier experiments with the foam-rib wing.
The combat guys have used a variant of this idea very successfully over the past several years, but they did it by making the leading edge section incredibly strong with the use of Kevlar, carbon fiber and other composite materials, and then they use balsa ribs and standard built-up wing construction aft of the LE section to insure rigidity. Perhaps it’s time to take a page from their engineering manual and try this on our ships.
I have been trying to get away from any type of wing construction that requires a shrinkable covering material. It seems that the new silkspan is just crap, and I just have never developed any affinity for Polyspan. For that reason I have gone back to all-foam surfaces that are constructed in the traditional manner. I have found ways to make them lighter, and certainly light enough to come in under the break point where we have to use the heavier .018 lines – even in an electric powered model.
Please do not misconstrue this as a criticism of you outstanding work; I just wanted you to know a bit of the history of the type of construction that you have chosen. There is really nothing new under the sun…
By the way, I am anxious to give your timer a try; I’ve heard nothing but good things from many about it!
Bob Hunt
Topic: My new competition stunter the Newtron (Read 2167 times)
