Bill, Thanks for the detailed reply. I honestly don't know if it came from a particular S/N or was made from parts. The 3-bead skin does not match the holes on the CS in any case, so it would be better to know where he got the 3-bead skin.
The statement, "If you have a 3-bead skin...you can cut the holes wherever you need to as long as they don't impinge on the spar", actually came from me; paraphrasing what Mike from Univair was saying. I wish we had more correct tech data to back that up, but I'm afraid that's all the data Univair can provide. I did get Mike to confirm that the smooth skins were NOT thicker, they are 0.020 thick according to their specs. As for my project, I have decided to go with the smooth skins. We have tried to keep working the beaded skin we made, but we are seeing too much "oil canning". We could probably get it right eventually or we might have to re-do the skin, but we don't have an unlimited supply of time or Alclad to keep working on it until it's perfect. Thanks, Dave --- In [email protected], William R. Bayne <ercog...@...> wrote: > > > Hi Dave, Prof. Ed > > Dave-what was the N# or Serial # of the bird the center section you > bought from Mr. Webb came from? > > I tried to help out Dan Currier in late April (2849H, serial no. 3474 > manufactured 8/9/46) with this problem and USB-31. Could not offer Dan > much help at that time. I spoke with a Univair FAA designee who had no > information whatsoever as to when or by whom the three bead skins were > produced. He was of the opinion that later skins without beads were > produced of thicker aluminum to achieve the same strength. Serial 404 > has smooth belly skins. > > Don't know how Dan's efforts panned out, but today I noted that Forney > used .020 2024T3 Alclad for the tri-ribbed skins. ERCO almost > certainly used an equivalent sheet for the E and G models...no idea > what they used for their earlier belly skin designs. Since Univair has > not been able to locate production information for three-bead belly > skins for use with their USB No. 31 over the years subsequent to > issuance of same, I took several hours today to see how much could be > determined from information in my files and similar prior research. > > It would appear that Univair's reference (below) to the "13047-1 L/R (2 > bead)" is to skins on Service Assembly 3 for Ercoupes through Serial > No. 812, as shown in the Parts manual, p. 43. I don't have a copy of > that drawing. Ercoupes through Serial No. 813 and up with the MLG > mounted to back of main spar use Service Assembly 3A and 415-13147 > skins. > > I found a print of drawing F-13147 L/R, Rev. "B" of a three-bead belly > skin. According to Forney E.O. 1078, on or about 7/2/58, it was > determined that ERCO's drawing 415-13147 was unreproducible and said > drawing was redrawn with Change "A". Since Change "A" is not entered > in the column for "Changes", it would be my presumption that the > redrawing itself was considered "Change A". Change "B", Forney E.O. > 1210, on or about 9/29/58, merely changed some dimensions pertaining to > the location and attaching rivets of angle reinforcements F-14046-1 and > 13159-L. > > All this leads me to believe the three-beaded belly skins were factory > production on (at least some) E Model Ercoupes and all G models. > Serial number 4902 has them (manufactured 5/18/48). If Univair has the > original vellum or brownline of ERCO's drawing 415-13147 (or late > forties print therefrom), the revisions block should show the date > engineering was completed for production of the three-ribbed belly > skin. I never noticed whether Alons and M10s used the tri-bead design > belly skins or not. > > Univair's suggestion that all belly skins were manufactured without > beads (smooth) following the ERCO Engineering Order of 11/23/45 is not > consistent with what we know to exist in the field. A change such as > this would not have been implemented on the production line before the > great majority (if not all) of the skins previously produced had been > installed in production or sold as parts. Perhaps the most obvious > example of this practice was when postwar Ercoupes serials 113-186 came > out of the factory sporting prewar ERCO double-fork nose gear and the > Hayes D3-164M double-bearing 5.00 x 4 nose wheel. > > It is almost certain that any belly skins which originally came to > Univair from Sanders and any of those still unsold which later > transferred to Forney were of the three-ribbed type. Any shop ordering > a belly skin for a repair would have been furnished a three-ribbed one. > That general practice would explain the profusion of presently > installed skins, and why some ships have two different designs. > Whatever was "in the bin" got shipped out and was installed. > > The record shows both ERCO and Sanders engineering to have been > professional and thorough throughout the period that Ercoupes were > produced. The odds are close to zero that three-ribbed belly skins > were an undocumented production change, done by somebody in the field > because they felt the skin needed stiffening, or a screw up that got > conveniently ignored. Such speculation is wholly inconsistent with the > consistent history and record of changes suggested, investigated, > reviewed, and, when implemented, incorporated into production drawings > over the years (even though there is, as of yet, no evidence that these > skins predate Fred Weick's departure from ERCO). > > After much measuring, calculating and interpolating I have come to the > conclusion that the instructions on page 8 of USB 31 in the right-hand > illustration (for aircraft with beaded bottom skin) are adequate to the > intended purpose but a dimension is needed where it says to "SEE NOTE > 2". To make sense of what follows some may want to tape a printout of > page 8 of USB-31 to the bottom of the wing for reference (oriented with > the main gear leg cutout). Keep in mind that for one illustration to > serve the purpose intended, you are looking at the bottom of the skin > on one side and the bottom of the skin on the other side. > > Draw a line running spanwise (left-right) 10" forward from the aft edge > of the belly skin (as shown for the bottom left 4" dia. opening and for > the bottom right 3" opening). Place a 4-1/2" reinforcement ring such > that said line goes horizontally through the center with the outboard > edge of said reinforcement ring inboard and almost tangent to the > innermost of the three beads in the belly skin. Trace the 3" hole in > the reinforcement ring onto the skin and that is where the lower right > inspection hole should be located. Mark the horizontal centerline of > this hole and measure the distance per the arrows with the words "SEE > NOTE 2". Project this centerline upwards to intersect the line drawn > 23" up from the bottom per the diagram such that the two 3" inspection > holes running fore-aft have a common vertical centerline. NO ONE > SHOULD CUT METAL until the preceding layout is done and aligned (and > you have verified that nothing has been installed inside the wing that > interferes with installation of the new inspection hole or its > reinforcement ring. > > It would be nice to have Univair's suggestion "If you have a 3-bead > skin...you can cut the holes wherever you need to as long as they don't > impinge on the spar" incorporated in some form into a new revision of > USB-31 but, in my humble opinion, the present version of USB 31 does > allow the desired result to be achieved following Note 2 on p. 8 with > triple-beaded skins locating a 3" inspection hole with a 4-1/2" > reinforcement ring as described. > > Regards, > > William R. Bayne > .____|-(o)-|____. > (Copyright 2009) > > -- > > On Nov 28, 2009, at 17:55, bigbrownpi...@... wrote: > > > When Prof Ed first brought up the issue of inspection holes in 3-bead > > skins, I asked Mike Sellers at Univair to comment. I've edited his > > two e-mails on thh subject, but the bottom line is this-- when SB-31 > > was issued, they did not explain how to do inspection holes in a > > 3-bead lower wing skin simply because they were unaware of that > > configuration. After that, late-model Erco and Forney owners started > > asking for more information, and Univair started trying to track the > > airplanes that had the 3-bead skin, but they were unable to correlate > > them. If you have a 3-bead skin, I think the message is that you can > > cut the holes wherever you need to as long as they don't impinge on > > the spar. > > > > I have examples of all three types of skin in my "collection". My > > airplane has a smooth left lower skin and a 2-bead right lower skin. > > I also have a 3-bead skin with the center section I bought from Weston > > Webb in Idaho. > > > > Don't know if that helps, but the subject of how lower wings skins > > came in so many configurations sure is interesting Ercoupe history! > > Maybe Bill Baine can add more information. > > > > "Service Bulletin 31 does not address a three bead skin because we > > have no reference in any of the original data that even suggests the > > possibility of a 3 bead skin. We simply were not aware of a 3 bead > > skin when we wrote the bulletin. It wasn't until the Service Bulletin > > hit the streets did we have people mentioning that they had a 3 bead > > skin. So to that end we don't know what serial number break there is. > > > > It has been a while since the big rush of kits went out the door. When > > we were in the middle of this, I believe we had started a list > > somewhere to see if there was a particular run of serial numbers to > > see if we could come up with some sort of correlation. By the time we > > decided to start keeping track, a number of contacts had been made > > inquiring about the 3 bead skin, and we weren't anticipating the > > issue. So, a number of folks went by us before we started collecting > > numbers. By the time that rush had passed, we didn't have enough data > > to make any conclusions. Since then we here of somebody else about > > twice a year. The only thing we have been able to come up with was the > > total numbers out there weren't great. I don't think the total number > > of contacts we had on the matter would have even amounted to 50. > > > > In trying to figure this out, we wondered if this was an undocumented > > change on the production line, if it was done somebody in the field > > because they felt the skin needed stiffining, if it was a screw up > > that got conveniently ignored or what. > > > > Mike" > > > > "Dave, > > > > Sorry for the delay I took some time off to help a family member move > > to another state. The original number of the skin was 13047-1 L/R (2 > > bead). It was replaced by 13147-1 smooth skin via an Engineering order > > dated 11/23/45. According to my records serial numbers 136, 137, 138 > > were completed on 11/23/45. S/N 139 was built on 11/24/45. > > > > While I do not know the exact serial number break, I would say that > > the smooth skin appeared on aircraft somewhere around that s/n > > 139-140. Going back and looking at margin notes in my parts book, I > > have noted that some later aircraft "i.e. Forneys" had the 3 bead, but > > we have no engineering record of it usage. > > > > Regards, > > Mike >
