Wing Rib Mylar Drawing 4 Questions

[kilohotel]

I used a square on my mylar wing rib drawing to check/confirm that the design is based on the assumption that the spars are oriented at a right angle to the center-line of the chord. My check confirmed that the drawing includes precise 90 degree angles at the main spar, flap spar, and aileron spar intersections.

However, the intersection of the rear spar is drawn slightly off of 90 degrees (see attached photos). The angle is off enough to result in slightly more than 1/16 of an inch difference between center-line and upper surface of the airfoil.

Is this a flaw in the drawing?

I realize this would result in only a minor difference in the aft side of the center rib that would be addressed when adjusting the ribs to fit the spars during wing assembly, but I assume the main and rear spars should be assemble parallel to each other...

Should I adjust the rear spar line to a precise 90 degrees before i fabricate the forms for my center and short ribs??

[Battson]

90 degrees to the lower surface of the wing sounds likely to me? From an ease of construction perspective? Just a wild guess.

[Chewie]

Correct, the spars should be parallel to each other on all three axes. The flap and aileron support frames set the position of the spars, and the jig used to make those frames needs to be dead nuts square.

[way_up_north]

Correct, the spars should be parallel to each other on all three axes. The flap and aileron support frames set the position of the spars, and the jig used to make those frames needs to be dead nuts square.

I assuming you have plans B set?
My B plans are packed away at this moment so I can't double check what you found....but what does not seem like a big deal should be double checked with Bob....you want to make sure you're inline with what the factory is doing...so when you order factory hinges or hardware they fit correctly.

not trying to to make a big deal of it, Bob should be made aware of it, there might be other discrepancies to be found if it's a software glitch related to the airfoil modification from the A plans....lots of novice builders like me might not have double checked like this guy did and cut on the line assuming the Mylar plans to be dead accurate.

[kilohotel]

I did email the pictures and question to Bob... (actually I accidentally sent it to Mark Goldberg first, and he jokingly suggested this would not be a problem if I had ordered a QB kit....haha!)

Bob confirmed it should be 90 degrees.

It is a very minor difference that would have been addressed when fitting the ribs to the spar during assembly.

I have attached a picture of the revised line (the line on the right is the correct one) on my master rib block. I only modified the upper segment as the lower segment was so short it made no significant change...

[way_up_north]

I did email the pictures and question to Bob... (actually I accidentally sent it to Mark Goldberg first, and he jokingly suggested this would not be a problem if I had ordered a QB kit....haha!)

Bob confirmed it should be 90 degrees.

It is a very minor difference that would have been addressed when fitting the ribs to the spar during assembly.

I have attached a picture of the revised line (the line on the right is the correct one) on my master rib block. I only modified the upper segment as the lower segment was so short it made no significant change...

I pulled mine from the shelf and had a look, mine are one and half year old version B plans. All the lines were 90 degrees to the centreline.

[fairchild]

KH--- I have B model plans and JUST finished making my main rib forms. I will go check my master rib and see If mine is off a little too. If it is-- I will have some sanding to do.
I will let you know--- I have plans # 1462B.
Tim

PS---- I just checked my mylar on the master rib-- my line is pretty close to 90 degrees. If it is off - it might be about the width of the ink line.(at the top) so its
all most at the edge of my ability to read the square reliably. All the other lines appear to be that close or closer.