Bill, You may want to read page 2 of SB53A. It covers replacement of the rear spar. This is the manufacturers suggested procedure for the rear spar replacement and calls for a new, stronger spar, with pilot holes size#30(1/8") the final hole size being -6 rivets, and the reinforcement you refer to. 'I was surprised by suggestions that airframe alignment could be affected by rear spar work; and others now discussing main spar work seem to have been similarly led mentally astray.' Para. 3 on page 2 refers to the alignment issue when replacing a rear spar. While it is common practice to use a used part in a case like this, I can assure you from long experience that a new part with only pilot holes is much better. "Matched hole tooling" is what you refer to and is great but not perfect. The holes were predrilled undersize and final drilled one size larger after being clecoed to the mating part. This proceedure is still used by cessna and to a lesser degree by piper. If you will refer to page 19 of the service manual, it describes this process in the "NOTE:" at the bottom of the first column. Because during final drilling a dull or poorly sharpened drill can "walk" (or a new employee drilling) I will assure you that a used riveted part from one airplane will rarely fit another exactly. The normal proceedure is to use an oversize rivet or in a worse case a next larger size. It is interesting to note that there is an STC to use next size rivets in a cessna 172 spar repair specifically because of this problem. Cessna originally did not allow for oversize rivets(probably helped their sales of new spars and skins) Would I use a used spar? probably if the holes were close enough on prefitting and I would purchase it with that understanding. I have seen some real "butcher" jobs when someone drilled apart a used part. Vernon Gregory is very sticky about this and you can expect a part without oversized or wallowed holes. Again, not rocket science but requires a skilled craftsman. Bill
To: [email protected]: [email protected]: Fri, 16 Jan 2009 14:36:13 -0600Subject: Re: [ercoupe-tech] New Rear Spar Or A Used One Tom,I understand the frustration you must feel, and yet it is likely the result of many trying to oversimplify a discussion that requires precise words and understanding of those words.It helps if everyone will start from and maintain the presumption that no one volunteeringassistance wants anything other than the quickest, simplest and most inexpensive resolution to your problem and gets any compensation other than such gratitude as may be earned.First off, your problem is with the rear spar. Reinforcement of the rear spar is covered in detail in Ercoupe Service Memorandum No. 53A. Hartmut's attachment did not come thru (for me). Not having been personally involved with such, I was surprised by suggestions that airframe alignment could be affected by rear spar work; and others now discussing main spar work seem to have been similarly led mentally astray.Ed is right that ERCO made and sold "state of the art" aircraft production machinery long before they made and sold the Ercoupe. While it is true the first ten Ercoupes were handbuilt, even then every attempt was being made to standardize parts and assemblies. The level of standardization achieved in the first 112 (prewar) airframes was totally eclipsed by postwar airframes because wartime government contracts to produce gun turrets and other warbird accessories and components had enabled ERCO to acquire (at government expense) extensive machinery for automated sheet metal work, and their design and engineering capability was very, very good.There are three possible "John"s in this discussion, which can confuse. I don't think John Wright Jr. (commonly considered the "man" for fuel tank repair, but fully capable beyond that) has been involved. I would suggest that ERCO's production sophistication and expertise would suggest that John Wright Sr.'s belief that purchase of a good used pre-drilled assembly is the best way to proceed.It would appear that buying a new piece and drilling it to fit (in place without the jigs that ERCO used to pre-drill parts before final assembly) could result in the sort of misalignment Paul Anton (an IA) ascribed to an unidentified Alaskan coupe airframe; therefore use of a pre-drilled used unit would allow "adjustment" of support pressure on the airframe as a means of MAKING the holes line up as they should.An expert understanding all of this could be willing to undertake it, but unwilling to invest the uncompensated time necessary for an owner to make an informed choice as to how to proceed...sort of "I'll do it, but you have to just trust me" ;<) I, personally, seldom have such trust in anyone.I don't see any "black hats" here, but a continuing need for mutual respect and patience.Best regards,William R. Bayne.____|-(o)-|____.(Copyright 2009)-- On Jan 16, 2009, at 13:04, Hartmut Beil wrote: Tom Service Bulletin covers in detail how to replace a rear spar. I attach the file for you and others that might not have access to the Service Bulletins right now. Hartmut _________________________________________________________________ Windows Live™: Keep your life in sync. http://windowslive.com/explore?ocid=TXT_TAGLM_WL_t1_allup_explore_012009
