wing skin placement

[bransom]

I have both versions of the Rebel MAM -- the one that came with my 1995 kit
and the revision that came out around 1998 or 99.

In the earlier MAM, they make the following note wrt skin placement:
"**IMPORTANT: Ensure the inboard edge of the bottom skin is flush
(underlined) with the inboard ends of both the rear spar and the main spar."
MAM repeats this "IMPORTANT" note twice more -- once for the leading edge
skin and then for the top skin.

The 1998/9 MAM drops this note entirely, which seems correct when looking at
things. On the right wing, the prepunched rib holes start exactly 7/16 inch
in from the end of the skin on the root end. The rib flanges are 5/8", so
the hole line down the middle of those flanges will be 5/16" from each side,
and on the root, this hole line is therefore 5/16" from the flush end of the
spar or root rib. Sooooo, if the prepunched skin holes go on the centerline
of the rib flanges (of course they do), the root end of the wing skin will
not be flush as the "IMPORTANT" note says to do. Rather, it will stick out
1/8" (7/16 - 5/16) beyond or inboard the spars and root rib.

So I guess after botching the leading edge spar from a similar MAM confusion
(to put it politely), I'm looking for some reassurance. I assume the
IMPORTANT note is bogus, that the skin's prepunched holes line up on the few
prepunched holes (and centerlines) on the rib flanges, and that a 1/8" lip of
the skin on the inboard side of the root rib is fine. Correct?

I'm tempted to also ask about span-wise placement of the stringers, as this
is not specified, but I have this close enough. I'll have the root end of
the stringers not protrude inboard of the root rib, and follow the note about
offsetting them 3/4" further out from root end for 4 the rows as specified in
the newer MAM (but not mentioned in the older one). I'll worry about where
stringers end on the outboard ends when I get there, thinking Dremel tool if
I need to trim them later.

If not obvious -- I'm glad I bought the newer MAM -- but it is possible to
feel like I'm following two road maps with different scales, and it's
especially disconcerting when deciding the capital IMPORTANT notes in the
manual must be erroneous. :/
As always, thanks for your help,
-Ben Ransom


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[bransom]

Ken,
Thanks for your msg.
I'll go with the 1/8" skin overlap from root rib. I've already match drilled
the tank skins with 1/2" overlap from the skin edge, so that will end up 5/8"
over root rib edge.

I spent probably 2+ hours on Saturday making sure I had the correct skin
orientations and Sharpie marking them to not goof later. MAM is fairly good
on identifying which end is root vs far end -- although the diagrams for this
come 8 pages *after* they say to match drill the tank skins!! MAM is lousy
about which is front/back, especially with what was their red ink barely
showing faded prepunched holes on a small black and white diagram. Obviously
important , it requires looking things over very carefully and reading ahead,
which of course is good to do anyway, and once you do this, skin orientation
is finally clear.

Yes, the skin edge distance to prepunched rib holes is different at each
end. Root is 7/16" as I mentioned, and far end is maybe double that -- I
forget exact number. I assume the greater distance at far end is for
fastening the fiberglass tips.
-Ben


-> Ben
->
-> On 119R (1992) the rivet centers are indeed 5/16 from the root rib
-> inboard edge. I'm can't recall for sure but I may well have trimmed the
-> skin AFTER the holes were all drilled. I don't think it is essential
-> that the holes are exactly in the center of the rib flanges since the
-> width of the flanges varies somewhat. I actually like to put the holes a
-> shade closer to the rib face than the edge of the flange. That would
-> make your problem worse on the right wing though I guess. Most of the
-> inboard edge of the wing skin will actually be cut away and replaced by
-> the tank skin and you do want a generous overlap (more than 1/2") on the
-> tank skin so that you can fasten the fairings that go between the wing
-> and the fuselage. I don't think a 1/8" skin or leading edge overlap on
-> the root rib will hurt anything and it might even be an advantage when
-> you drill holes into the root rib for the screws and possibly nutplates
-> for the fairings. OTOH an overlap will make it easier to damage the skin
-> during construction and handling and perhaps look a bit odd before the
-> fairings go on. I think MAM is mostly trying to make sure your wing is
-> square which it will be if the edge is flush, and also that the
-> prepunched holes line up with all the ribs with adequate edge distance.
->
-> When I purchased a newer manual on CD, MAM told me that they had seen a
-> number of problems develop from builders trying to use a newer manual
-> with an older kit so I guess it is possible that some dimensions have
-> changed. I know a few of the parts and the thickness of some parts has
-> changed over the years.
->
-> Identifying which wing skin was which and orienting them properly used
-> to be a big deal though and I'm told that a number of replacement wing
-> skins have been purchased or made over the years... Do both ends of the
-> skin have 7 /16 edge distance and are you certain you have the right one?
->
-> Ken
->
-> bransom@dcsol.com wrote:
-> > I have both versions of the Rebel MAM -- the one that came with my 1995
kit
-> > and the revision that came out around 1998 or 99.
-> >
-> > In the earlier MAM, they make the following note wrt skin placement:
-> > "**IMPORTANT: Ensure the inboard edge of the bottom skin is flush
-> > (underlined) with the inboard ends of both the rear spar and the main
spar."
-> > MAM repeats this "IMPORTANT" note twice more -- once for the leading
edge
-> > skin and then for the top skin.
-> >
-> > The 1998/9 MAM drops this note entirely, which seems correct when
looking at
-> > things. On the right wing, the prepunched rib holes start exactly 7/16
inch
-> > in from the end of the skin on the root end. The rib flanges are 5/8",
so
-> > the hole line down the middle of those flanges will be 5/16" from each
side,
-> > and on the root, this hole line is therefore 5/16" from the flush end of
the
-> > spar or root rib. Sooooo, if the prepunched skin holes go on the
centerline
-> > of the rib flanges (of course they do), the root end of the wing skin
will
-> > not be flush as the "IMPORTANT" note says to do. Rather, it will stick
out
-> > 1/8" (7/16 - 5/16) beyond or inboard the spars and root rib.
-> >
-> > So I guess after botching the leading edge spar from a similar MAM
confusion
-> > (to put it politely), I'm looking for some reassurance. I assume the
-> > IMPORTANT note is bogus, that the skin's prepunched holes line up on the
few
-> > prepunched holes (and centerlines) on the rib flanges, and that a 1/8"
lip of
-> > the skin on the inboard side of the root rib is fine. Correct?
-> >
-> > I'm tempted to also ask about span-wise placement of the stringers, as
this
-> > is not specified, but I have this close enough. I'll have the root end
of
-> > the stringers not protrude inboard of the root rib, and follow the note
about
-> > offsetting them 3/4" further out from root end for 4 the rows as
specified in
-> > the newer MAM (but not mentioned in the older one). I'll worry about
where
-> > stringers end on the outboard ends when I get there, thinking Dremel
tool if
-> > I need to trim them later.
-> >
-> > If not obvious -- I'm glad I bought the newer MAM -- but it is possible
to
-> > feel like I'm following two road maps with different scales, and it's
-> > especially disconcerting when deciding the capital IMPORTANT notes in
the
-> > manual must be erroneous. :/
-> > As always, thanks for your help,
-> > -Ben Ransom
->
->




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[klehman]

Ben

On 119R (1992) the rivet centers are indeed 5/16 from the root rib
inboard edge. I'm can't recall for sure but I may well have trimmed the
skin AFTER the holes were all drilled. I don't think it is essential
that the holes are exactly in the center of the rib flanges since the
width of the flanges varies somewhat. I actually like to put the holes a
shade closer to the rib face than the edge of the flange. That would
make your problem worse on the right wing though I guess. Most of the
inboard edge of the wing skin will actually be cut away and replaced by
the tank skin and you do want a generous overlap (more than 1/2") on the
tank skin so that you can fasten the fairings that go between the wing
and the fuselage. I don't think a 1/8" skin or leading edge overlap on
the root rib will hurt anything and it might even be an advantage when
you drill holes into the root rib for the screws and possibly nutplates
for the fairings. OTOH an overlap will make it easier to damage the skin
during construction and handling and perhaps look a bit odd before the
fairings go on. I think MAM is mostly trying to make sure your wing is
square which it will be if the edge is flush, and also that the
prepunched holes line up with all the ribs with adequate edge distance.

When I purchased a newer manual on CD, MAM told me that they had seen a
number of problems develop from builders trying to use a newer manual
with an older kit so I guess it is possible that some dimensions have
changed. I know a few of the parts and the thickness of some parts has
changed over the years.

Identifying which wing skin was which and orienting them properly used
to be a big deal though and I'm told that a number of replacement wing
skins have been purchased or made over the years... Do both ends of the
skin have 7 /16 edge distance and are you certain you have the right one?

Ken

bransom@dcsol.com wrote:

I have both versions of the Rebel MAM -- the one that came with my 1995 kit
and the revision that came out around 1998 or 99.

In the earlier MAM, they make the following note wrt skin placement:
"**IMPORTANT: Ensure the inboard edge of the bottom skin is flush
(underlined) with the inboard ends of both the rear spar and the main spar."
MAM repeats this "IMPORTANT" note twice more -- once for the leading edge
skin and then for the top skin.

The 1998/9 MAM drops this note entirely, which seems correct when looking at
things. On the right wing, the prepunched rib holes start exactly 7/16 inch
in from the end of the skin on the root end. The rib flanges are 5/8", so
the hole line down the middle of those flanges will be 5/16" from each side,
and on the root, this hole line is therefore 5/16" from the flush end of the
spar or root rib. Sooooo, if the prepunched skin holes go on the centerline
of the rib flanges (of course they do), the root end of the wing skin will
not be flush as the "IMPORTANT" note says to do. Rather, it will stick out
1/8" (7/16 - 5/16) beyond or inboard the spars and root rib.

So I guess after botching the leading edge spar from a similar MAM confusion
(to put it politely), I'm looking for some reassurance. I assume the
IMPORTANT note is bogus, that the skin's prepunched holes line up on the few
prepunched holes (and centerlines) on the rib flanges, and that a 1/8" lip of
the skin on the inboard side of the root rib is fine. Correct?

I'm tempted to also ask about span-wise placement of the stringers, as this
is not specified, but I have this close enough. I'll have the root end of
the stringers not protrude inboard of the root rib, and follow the note about
offsetting them 3/4" further out from root end for 4 the rows as specified in
the newer MAM (but not mentioned in the older one). I'll worry about where
stringers end on the outboard ends when I get there, thinking Dremel tool if
I need to trim them later.

If not obvious -- I'm glad I bought the newer MAM -- but it is possible to
feel like I'm following two road maps with different scales, and it's
especially disconcerting when deciding the capital IMPORTANT notes in the
manual must be erroneous. :/
As always, thanks for your help,
-Ben Ransom

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[klehman]

Ben
Sounds like you have this figured out but your comment in the last
paragraph about the hole edge distance at the outboard end caught my
attention. I have 3/8" edge distance there and the wingtips fasten
through the skins and into the outboard rib flanges. (My outboard skin
edge is even with the end of the ribs.) I am starting to wonder if there
might be a problem with your skins. I think they are made out of a 12'
sheet so they are unlikely to be longer than 12' although anything is
possible I guess. It might be worth checking to make sure the rib
spacing in the skin matches the hole spacing on the spars although I
think you've already done that. My rib centerlines are spaced about
1/16" less than a foot apart and I think (but haven't checked) the skins
and spars are all exactly 12' long. At least one person has reported
problems with the pre-punched holes but I think that is very rare...
Ken

bransom@dcsol.com wrote:

Ken,
Thanks for your msg.
I'll go with the 1/8" skin overlap from root rib. I've already match drilled
the tank skins with 1/2" overlap from the skin edge, so that will end up 5/8"
over root rib edge.

I spent probably 2+ hours on Saturday making sure I had the correct skin
orientations and Sharpie marking them to not goof later. MAM is fairly good
on identifying which end is root vs far end -- although the diagrams for this
come 8 pages *after* they say to match drill the tank skins!! MAM is lousy
about which is front/back, especially with what was their red ink barely
showing faded prepunched holes on a small black and white diagram. Obviously
important , it requires looking things over very carefully and reading ahead,
which of course is good to do anyway, and once you do this, skin orientation
is finally clear.

Yes, the skin edge distance to prepunched rib holes is different at each
end. Root is 7/16" as I mentioned, and far end is maybe double that -- I
forget exact number. I assume the greater distance at far end is for
fastening the fiberglass tips.
-Ben

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[Wayne G. O'Shea]

Ken, I found some of MAM's wing skins were 12' 1/4" at various times so
anything is possible here!

Ben, just make sure your spars are even/square and that the prepunched holes
hit the rib centers and start drilling!

Wayne

----- Original Message -----
From: <klehman@albedo.net>
To: <murphy-rebel@dcsol.com>
Sent: Tuesday, April 06, 2004 2:30 PM
Subject: Re: wing skin placement

Ben
Sounds like you have this figured out but your comment in the last
paragraph about the hole edge distance at the outboard end caught my
attention. I have 3/8" edge distance there and the wingtips fasten
through the skins and into the outboard rib flanges. (My outboard skin
edge is even with the end of the ribs.) I am starting to wonder if there
might be a problem with your skins. I think they are made out of a 12'
sheet so they are unlikely to be longer than 12' although anything is
possible I guess. It might be worth checking to make sure the rib
spacing in the skin matches the hole spacing on the spars although I
think you've already done that. My rib centerlines are spaced about
1/16" less than a foot apart and I think (but haven't checked) the skins
and spars are all exactly 12' long. At least one person has reported
problems with the pre-punched holes but I think that is very rare...
Ken

bransom@dcsol.com wrote:

Ken,
Thanks for your msg.
I'll go with the 1/8" skin overlap from root rib. I've already match

drilled

the tank skins with 1/2" overlap from the skin edge, so that will end up

5/8"

over root rib edge.

I spent probably 2+ hours on Saturday making sure I had the correct skin
orientations and Sharpie marking them to not goof later. MAM is fairly

good

on identifying which end is root vs far end -- although the diagrams for

this

come 8 pages *after* they say to match drill the tank skins!! MAM is

lousy

about which is front/back, especially with what was their red ink barely
showing faded prepunched holes on a small black and white diagram.

Obviously

important , it requires looking things over very carefully and reading

ahead,

which of course is good to do anyway, and once you do this, skin

orientation

is finally clear.

Yes, the skin edge distance to prepunched rib holes is different at each
end. Root is 7/16" as I mentioned, and far end is maybe double that --

I

forget exact number. I assume the greater distance at far end is for
fastening the fiberglass tips.
-Ben

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[bransom]

Ken,Wayne,Bob, others,
Didn't work on my plane last night, but did check the hole distance from the
outboard end -- it is 11/16". As I mentioned earlier, root vs outboard end
is clear so I'm not worried about that. And, the skin prepunched rib hole
spacing is the standard 1/16 shy of 12". All is well and will start drilling
some stringers tonight. This whole thing is just needing some help deciding
to ignore the thrice stated "IMPORTANT" warning in the 1995 kit MAM to have
the skin end flush with the root rib.
-Ben

-> Ben
-> Sounds like you have this figured out but your comment in the last
-> paragraph about the hole edge distance at the outboard end caught my
-> attention. I have 3/8" edge distance there and the wingtips fasten
-> through the skins and into the outboard rib flanges. (My outboard skin
-> edge is even with the end of the ribs.) I am starting to wonder if there
-> might be a problem with your skins. I think they are made out of a 12'
-> sheet so they are unlikely to be longer than 12' although anything is
-> possible I guess. It might be worth checking to make sure the rib
-> spacing in the skin matches the hole spacing on the spars although I
-> think you've already done that. My rib centerlines are spaced about
-> 1/16" less than a foot apart and I think (but haven't checked) the skins
-> and spars are all exactly 12' long. At least one person has reported
-> problems with the pre-punched holes but I think that is very rare...
-> Ken
->
-> bransom@dcsol.com wrote:
-> > Ken,
-> > Thanks for your msg.
-> > I'll go with the 1/8" skin overlap from root rib. I've already match
drilled
-> > the tank skins with 1/2" overlap from the skin edge, so that will end up
5/8"
-> > over root rib edge.
-> >
-> > I spent probably 2+ hours on Saturday making sure I had the correct skin
-> > orientations and Sharpie marking them to not goof later. MAM is fairly
good
-> > on identifying which end is root vs far end -- although the diagrams for
this
-> > come 8 pages *after* they say to match drill the tank skins!! MAM is
lousy
-> > about which is front/back, especially with what was their red ink barely
-> > showing faded prepunched holes on a small black and white diagram.
Obviously
-> > important , it requires looking things over very carefully and reading
ahead,
-> > which of course is good to do anyway, and once you do this, skin
orientation
-> > is finally clear.
-> >
-> > Yes, the skin edge distance to prepunched rib holes is different at each
-> > end. Root is 7/16" as I mentioned, and far end is maybe double that --
I
-> > forget exact number. I assume the greater distance at far end is for
-> > fastening the fiberglass tips.
-> > -Ben
->
->




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