Guys,
Why is it so hard to admit a simple technical fact? If cloth covered wings are so superior, why are they so out of fashion? Every load carrying aircraft is using a rigid wing covering. Would you accept a cloth covered 747? Or can you picture a F-18 with cloth covered surfaces? Even the DC-3 has metalized wings. There must be a reason for that. One praised characteristic of fabric is that it withstands hail. That is because it flexes. Metal wings are riveted to the ribs, thus creating pretty stiff boxes that as a box transfer the forces on the wing directly to the ribs and spars. If that is a good thing maybe discussed, but one has to admit the different features of each design. One thing is clear to me. A fabric wing should be carefully recovered by a knowledgeable person. As an amateur, I would not be able to decide between a safe wing and a wing that could kill you. http://www.ntsb.gov/ntsb/GenPDF.asp?id=FTW89DPJ02&rpt=fi (for those that can't open the accident file: N99636 Ercoupe (eng & Research Corp.) / 415C, 2 fatally injured, INSPECTION REVEALED THAT THE FABRIC OF BOTH WINGS HAD BEEN INSTALLED IMPROPERLY, AND PART OF THE FABRIC ON THE LEFT WING HAD COME LOOSE IN FLIGHT.) As previously stated, finding someone that does the covering right might be a challenge sometimes. On the other hand it is easy to find someone that can do a great job with sheet metal and rivets. Hartmut To: [email protected] From: [email protected] Date: Thu, 10 Sep 2009 13:54:13 -0500 Subject: Re: {Disarmed} [ercoupe-tech] Metal Wings are stronger..... I would suggest that any engineering evaluation use the correct approach in evaluating "stronger". Adding thin sheets to a wing structure already designed and capable of coping with the normal stresses of flight (plus a considerable safety factor)would add little, if any, to the overall load carrying capacity of an Ercoupe wing in terms of the additional stress said could carry before it failed under load. The materials and procedures utilized by the various STCs presently installed or available does not transform the Ercoupe wing designed for grade A cotton covering into a monocoque structure as would seem to have been inferred. "Monocoque" construction is defined as "an aircraft structure in which the outer covering skin carries all or a major portion of the stresses". The internal structural components, metal skin thickness, rivet type, size, and spacing of a stressed skin wing design would be quite different, and likely lighter. Consider also these questions: 1. What practical purpose is served by increasing wing strength beyond regulatory design requirements? 2. How much has the load capability of Ercoupe wing design increased when covered with modern synthetic fabrics of higher tensional strength abd durability than the original grade A cotton? Regards, WRB -- On Sep 10, 2009, at 13:05, Art Langston wrote: Chris, could you please share the engineering data with us and cite the documentation where we can read it? When finished, I believe the Polyfiber may actually be stronger than the aluminum. I've de-skinned Ercoupe wings, and the metal is very thin. Polyfiber is tough. Thanks Art N2666H Chris wrote:A metal wing is stronger than a fabric one. The metal distributes the loads over the surface. Would anyone want to consider a fabric covered fuselage? Chris Santa Cruz 99674 ‘--o-O-o--’ _________________________________________________________________ With Windows Live, you can organize, edit, and share your photos. http://www.windowslive.com/Desktop/PhotoGallery
