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Today I formed my first center rib from .032. Got ready to fluit the edges. I had not yet marked the rivet locations on the edge of my bending form. (On my nose rib I marked red sharpie lines
for the rivets and green bars to indicate the center of the fluit.) Plans say a rivet every 1.5 inches. I lined up the aerolon's cable hole in the bending form with the same mark on the 2X plan sheet. That located the form ( I think) correctly front to back. I then transferred the first couple of rivet marks on the plan to the form. Then I took the form and laid out a line every 1.5 inches
until I got to the rear. (on the top surface) When I got to the rear I notice my marks are 3/8 of an inch off from the rear marks on the plans. This means that my first and last hole on the
tp are NOT equidistant from the edge. (like the holes on the plans. This would seem to mean something is off somewhere. where-- I don't know yet.....
I took my first rib that I made and measured the curved length of the top flange , bottom flange and then the straight length through the plan centerline. I get : 31+5/8, 31.5 and 31.5
The center line measurement seems to indicate that I have about 1/16 slack on each end between the ends of the rib and the spar caps. That sounds like about what I was shooting for.
What I am trying to figure out is------ there must be ( I would think) a sort of anchor point on the rivet positions which I could measure from that wont be variable.
One thought is this----- get out my master rib form---- lay it down flat and set a nose rib on it and slip 2 bolts through the 2 alignment holes. Then set my 1-st main rib down and put a couple
or 3 bolts through its holes into the master form. That SHOULD establish and ABSOLUTE relationship between the 2 ribs------ then I might be able to lay a cloth tape across the top of the master rib form and mark its edge in red - duplicating my rivet positions from the nose rib---- then just continue the 1.5 inch marks all the way back on the edge of the master rib form. SEEMS like that
would ensure my even spacing on the outside of the skin later--- at least externally.
But if my rivet positions don't line up with the plans as I get near the rear of the main rib---- will that cause my rivets back there to miss hitting what they need to go through---- like the rear
spar flange or the false rib flanges ??????? I see on the plans----- Bob same in 3/4 from each end of the main rib and made a rivet hole. Do I NEED to expand or contract my rivet
spacing ( as though I was using a fan) to make the front and rear holes keep that 3/4 margin ????? If YES- that would imply that the first and last hole are sacred and need to stay at
3/4 from the end.
I am guessing that everybodys master rib form will be very slightly taller or shorter (thick) than the next guys due to how we marked lines and how close we sanded to the line.
That would mean that the curved distance measured along the top main rib flange could be slightly longer or shorter. That could cause a little variation in the needed rivet spacing---
a slight variance away from exactly 1.5 inches.
My marks were right on for the nose ribs---no discrepancy---- and the marks for the bottom of the main rib are closer but still off by about 1/8 at the rear (agreeing at the front)
I would think that many of us had noticed this and done something to adapt ……… but WHAT ??????
can someone who just finished bravo ribs or patrol ribs give me a recollection of this measurement discrepancy ????? (mine is Bravo)
Thanks ahead of time for any nuggets of wisdom.....
Tim
PS--- there seem to be 21 rivet holes in the top. took the distance between the end rivets and divided it in two. 21 rivets is 1 in the center and 10 on
either side. That leaves 9 and 9. I just kept dividing the distance in two over and over. Marked that along the master rib centerline. Will next
try to take a square and mark the top and bottom positions.
It occurs to me that the 1.5 inch rivet spacing might have been measured on TOP of the skin. The outside of the skin is at least 2 sheet metal
thicknesses bigger than the master rib. Maybe that makes the 1.5 inch spacing on the master rib seem a little off ?????
Tim
for the rivets and green bars to indicate the center of the fluit.) Plans say a rivet every 1.5 inches. I lined up the aerolon's cable hole in the bending form with the same mark on the 2X plan sheet. That located the form ( I think) correctly front to back. I then transferred the first couple of rivet marks on the plan to the form. Then I took the form and laid out a line every 1.5 inches
until I got to the rear. (on the top surface) When I got to the rear I notice my marks are 3/8 of an inch off from the rear marks on the plans. This means that my first and last hole on the
tp are NOT equidistant from the edge. (like the holes on the plans. This would seem to mean something is off somewhere. where-- I don't know yet.....
I took my first rib that I made and measured the curved length of the top flange , bottom flange and then the straight length through the plan centerline. I get : 31+5/8, 31.5 and 31.5
The center line measurement seems to indicate that I have about 1/16 slack on each end between the ends of the rib and the spar caps. That sounds like about what I was shooting for.
What I am trying to figure out is------ there must be ( I would think) a sort of anchor point on the rivet positions which I could measure from that wont be variable.
One thought is this----- get out my master rib form---- lay it down flat and set a nose rib on it and slip 2 bolts through the 2 alignment holes. Then set my 1-st main rib down and put a couple
or 3 bolts through its holes into the master form. That SHOULD establish and ABSOLUTE relationship between the 2 ribs------ then I might be able to lay a cloth tape across the top of the master rib form and mark its edge in red - duplicating my rivet positions from the nose rib---- then just continue the 1.5 inch marks all the way back on the edge of the master rib form. SEEMS like that
would ensure my even spacing on the outside of the skin later--- at least externally.
But if my rivet positions don't line up with the plans as I get near the rear of the main rib---- will that cause my rivets back there to miss hitting what they need to go through---- like the rear
spar flange or the false rib flanges ??????? I see on the plans----- Bob same in 3/4 from each end of the main rib and made a rivet hole. Do I NEED to expand or contract my rivet
spacing ( as though I was using a fan) to make the front and rear holes keep that 3/4 margin ????? If YES- that would imply that the first and last hole are sacred and need to stay at
3/4 from the end.
I am guessing that everybodys master rib form will be very slightly taller or shorter (thick) than the next guys due to how we marked lines and how close we sanded to the line.
That would mean that the curved distance measured along the top main rib flange could be slightly longer or shorter. That could cause a little variation in the needed rivet spacing---
a slight variance away from exactly 1.5 inches.
My marks were right on for the nose ribs---no discrepancy---- and the marks for the bottom of the main rib are closer but still off by about 1/8 at the rear (agreeing at the front)
I would think that many of us had noticed this and done something to adapt ……… but WHAT ??????
can someone who just finished bravo ribs or patrol ribs give me a recollection of this measurement discrepancy ????? (mine is Bravo)
Thanks ahead of time for any nuggets of wisdom.....
Tim
PS--- there seem to be 21 rivet holes in the top. took the distance between the end rivets and divided it in two. 21 rivets is 1 in the center and 10 on
either side. That leaves 9 and 9. I just kept dividing the distance in two over and over. Marked that along the master rib centerline. Will next
try to take a square and mark the top and bottom positions.
It occurs to me that the 1.5 inch rivet spacing might have been measured on TOP of the skin. The outside of the skin is at least 2 sheet metal
thicknesses bigger than the master rib. Maybe that makes the 1.5 inch spacing on the master rib seem a little off ?????
Tim
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