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Andrews Web Site
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Date: 7-14-2010
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Number of Hours: 5.00
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Manual Reference:
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Brief Description: Profile Error Discovered
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Okay, I have had my first big SNAFU. While skinning the aft fuselage sides, I discovered that the contour of the bulkheads will not allow a smooth wrap of the skin. That is, although the top, bottom and sides of the bulkheads fall in a straight line, the upper curve (lower in the fixture) will not create a ruled surface when skinned. That means, the skin has serious gaps when installed. The worst offending bulkhead is 102.625. I laid the form block on the plans to recheck it...perfect... So the problem may be that we build our form blocks to the contour lofted on the plans, but the plans are just paper, and not totally stable. It would be nice if the plans included coordinates along any lofted contour so that we could be sure of the dimensions. The other possibility is that the drawings are just wrong,..but I struggle with that since 2 prototypes have been built. It is noteworthy however, that the forward bulkhead (seatback) angle was changed by Dick (noted on previous log entry) perhaps the resulting change to the skin contour was not fully investigated.
At any rate, I think the solution is to reform new 102.625 and 122.625 bulkheads to accomodate what is needed to make a continuous ruled surface. I have measured the differences and the 102 bulkhead needs to have contour changes as great as 0.19 inches made, while the 122 bulkhead needs about 0.12 max contour change.
This certainly will not be the lat setback, but it does make me question the accuracy of the plans. Perhaps I should take the time to CAD model the entire airplane to make sure this does not happen again. (uggg, a lot of wasted work)
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Showing gap to skin at 102.625 bulkhead
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Showing magnitude of gap
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Stings to assist in defining adjustments to be made to form blocks
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