Page 10-84 (of my manual) states "to check that there is no forward or aft sweep
(of the wings), stretch a string across from wing tip to wing tip, lining it up
with the rear edge of the port spar and the forward edge of the starboard spar
(remember the spars are off set) and sight along it."
Consider a tiangle, which is what we all have if we string a line from wing tip
to wing tip due to the dihedral. When sighting along the hypotenuse (string
line) it is always possible to ensure that the other sides of the triangle line
up with the string, whether we are sighting vertically or not.
If in doubt, pick up a set-square and try it.
If we follow the factory's method without refinement we could end up with the
wings angled forward or back, which would be contrary to their expectations, or
intentions
When this penny dropped with me, I decided to tie small plumb-bobs to the string
above the port and starboard wing root which helped me to sight vertically, and
I could also sight down the plumb-bobs to make doubly sure.
This ensures that the wings are in line. However, there is still the possibility
that they could be Starboard forward, Port back, or whatever, and the only way
I
could try to ensure against this was to measure from a screw fixed to the centre
of the fin stub on the top of the fuselage lid to the wing tips to get the same
distance.
Of course, it doesn't always work out, but at least you should know what your
wings may be doing! Remember that due to build difference the distance from the
fuselage to your wing tips may differ, Port to Starboard, so measure this and
make a mark before taking the distance from the fin. Also, try measuring from
the centre line of the fuselage, or is this too demanding?
Whilst mentioning the centre line, has anyone else noticed that the starboard
side of the fuselage bulges slightly more than the port side at the point of the
rear cockpit module bulkhead?
My wife tells me that I measure too much - I'm not sure how to take that!
Happy brain-teasers,
Peter.
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