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, [email protected] 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
