William, as I understand it the higher speeds associated with perpetual flight are to keep momentum above certain thresholds so the plane doesn't fall out of the sky. You can find several articles (full text) that go into the subject in greater detail here: http://www.dynamicsoaring.lehigh.edu/wiki/index.php/Publications
The one-piece wing assembly is quite an unusual approach, and the reasons for the choice are certainly important. I had not realized that the multi-piece building up approach added much weight, but I can see where it would have to add weight and volume. The method of fabrication sounds quite traditional, except that many structures use the hexcell type of material for additional stiffness.
The one assertion that I did not understand is the claim that a perpetual flight craft would need to fly very fast. IT would seem that flying at the minimum speed to maintain the desired altitude would require less energy because of less drag losses. For fans, at lleast, it seems like the required power goes up as the fourth power of speed, and so I would expect the drag of a wing to increase with speed also. But that is an area that I have not studied.
It's nice to hear about this collaborative design effort. It would be interesting to follow this story through to the actualy finished "perpetual flight" aircraft. Sometimes innovative fabrication techniques find their way into unexpected places. I like the reference to having used this same technique for a marine craft, for example.
This design removes two critical issues of flight, fasteners and metal/composite fatigue. As this is a perpetual flight aircraft, the flexing of the wings upon takeoff and landing is eliminated. B-52 bombers flex about 6-8 feet at the wingtips during their cycles, leading to frequent inspections and replacements.
Lou, thanks for that input on fastener issues: their absence was one of the unusual aspects of this design that piqued my interest in writing about it. And I agree, I thought it was totally cool that the team combines a ME with a CS. In the student newspaper article, the ME Grenestedt is quoted as saying that his partner, Spletzer, "handles the intelligence aspect of the wing and aircraft," which includes controls and flight trajectories.
Nadine, I agree, it would be great if these advancements could be translated to commercial manned aircraft. But in general, the structure design is not as similar as you might think, since manned aircraft usually carry a lot more weight than unmanned, among other factors. The wing described in this article is designed for an unmanned perpetual flight plane, more like a glider than a Boeing commercial jet, and its design has challenges not present in commercial aircraft design. The links at the end of this article can guide you to more articles we've done about composite use in manned craft, since we write about both.
Very good question, Beth. It wasn't mentioned, and it most likely would have been if they'd used it in any way. The reference to layering is to the typical epoxy composite process, where sheets of fiber are laid down in the epoxy matrix.
Ann, this is indeed a great way to proceed. You mention composited in spacecraft. I worked on one, a long time ago, that had composite tubular frame members and titanium hubs. The first design for attaching the tubes to the hubs had the holes aligned. This produced stress cracks and had to be modified to offset the holes. By eliminating the fasteners, and the different materials, I am sure this structure would be superior. We had CAD and CAE back then, but it was very primitive compared to what we do now.
I was also interested in the fact that the researchers included a Mechanical Engineer and a Computer Scientist, who is actually named. Computer Scientists are a necessary part of many projects these days. Especially when they research projects. They often play the role of the mathematician, solving complex numerical problems that have not been solved before.
There is a lot of technical advancement in aviation focused on unmanned aircraft. Can this be translated for larger planes? Maybe it's just the focus here on Design News. Seeing more advancement in "manned" aircraft would be great too.
The one-piece composite structure seems like a pretty big deal for wing design as the fasterners and adhesive joints usually seem to be the areas that are magnets for potential trouble. Question: Was 3D printing involved in any way?
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