Structural strength has many factors. The covering process is only a portion of that. Comparing apples and oranges with regards to different airframe designs is naive. Metal covered wings *may* be slightly stronger, but they are, in fact, heavier. They are also, for whatever reasons, more prone to problems and corrosion. The general concensus - amongst those of us who have flown both - is that fabric covered wings just seem to fly better for whatever reason(s). If properly done with today's processes, fabric covered wings will last many years even if parked outside without cover. I don't see why anyone would want to metalize fabric wings just from the weight angle alone, but to each his own.
Tom Graziano A&P; I.A.; Commercial Pilot On Thu, Sep 10, 2009 at 5:16 PM, William R. Bayne < [email protected]> wrote: > > Are we getting away from the original "issue"? > > The assertion that "a metal covered wing is stronger than a fabric one" is > a bit of a "red herring". So long as the original strength was suitable for > the purpose intended, extra strength is like fuel carried in excess of the > appropriate "minimum"...unless an exceptional event occurs the extra weight > added by metal wings reduces operational efficiency and the airfoil change > adds frontal area (drag). > > Also, there are persons who should be physically restrained from handling > tools...let's call them "mechanically challenged". Any mechanic with much > experience has seen the work of such persons on Ercoupes before. It would > seem well within the realm of possibility that there are some metal covered > wings "out there" that are less safe, in terms of strength today, than the > "average" fabric-covered wing. > > State of the art glider wings are incredibly strong (i.e. for the purpose > intended). If "fashion" were a determining factor these would be metal > today too. > > The DC-3 cruises at over four times the speed of the Ercoupe and its > contemporaries. Mentioning the 747 (in terms of sheer size) and the F-18 > (in terms of being designed for combat) merely makes a total of three > airplanes inappropriate to compare with Ercoupes. Quoting from the Service > Manual: "In its outward appearance the Ercoupe resembles a commercial or > military airplane. But in servicing it cannot be treated in the same light > as heavier aircraft, for the metals used...are of much lighter gauge. > ...these solidly designed light-weight Ercoupeparts are relatively > inexpensive to manufacture..." > > There is no doubt that aircraft design made great leaps between the late > thirties, when the Ercoupe was designed, and the end of World War II. Even > so, neither Fred Weick nor Erco apparently believed it necessary or > desirable to change the wing design from a fabric covered one to a metal > covered one. The difference between a safe wing from one with a fatal flaw > is likely independent of how it is covered, and most usually evident in > hindsight. > > It may well be that it was easier for Forney, Alon and Mooney to use metal > wing covering because between 1946 and 1956 the pendulum of skilled labor > swung from doing fabric to metal for covering wings. Why Monday morning > quarterback the issue some 40-60 years later? > > It would be my considered opinion that either fabric or metal wing covering > on an Ercoupe is intended to and does contribute to the structural > capability of a complete wing under normal stresses of flight. I would not > speculate as to how much less strength an uncovered wing has in comparison > to a covered one. Obviously both lift and structural integrity are equally > essential to go and remain aloft. > > Regards, > > WRB > > -- > > On Sep 10, 2009, at 14:54, Hartmut Beil wrote: > > >> >> 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. Click >> here. >> >> >>
