SERVICE LETTER #25
Lift Strut Attachment
Kitfox™ Owners, All Models
experience with creation of the Kitfox™ XL manual has allowed us to rethink
the way we answer two commonly asked questions:
How do I make sure my dihedral is set correctly?
What should I do if I find a need to force (lift with pressure) the
forward or aft lift strut, to make
first question, regarding dihedral, is easy to answer through the use of a
4 ft. carpenter’s level. Your first step is to follow the existing
directions by positioning the Lift Strut Bracket onto the spars, so that
the center of the Strut Bracket bolt hole is 96.75 inches from the root
end of the spar for Model IV and XL aircraft. For the Speedster, use an
initial starting point of 97.75 inches from the root end of the spar. The
Lift Strut Brackets should be temporarily held in place with hose clamps.
Follow existing instructions for temporarily installing both wings, making
sure you DO NOT drill the rear spar bottom hole, or either top or
bottom front spar holes, until a final dihedral check is made.
final dihedral check is made only after making sure the fuselage is
leveled both laterally and longitudinally. Once the fuselage is leveled,
with the wings, struts and Lift Strut Brackets temporarily assembled,
simply hold your 4 ft. carpenter’s level up to the bottom of the leading
edge spar at a mid span location. Because of the dihedral, the bubble will
not be centered if the level is held firmly against the spar. Simply lower
the “wing tip” end of the level until the bubble is centered. The
following distance should exist between the “wing tip” end of the
level and the spar:
can further increase dihedral accuracy by also checking the rear spar. After
checking the front spar, simply multiply the value you measured (let’s say
it was 1.1”) by 1.137. In this example, 1.1” x 1.137” =
1.25”, meaning the top edge of your 4 ft. level should be 1.25”
below the rear spar.
these distances are not present, simply loosen the clamps holding the Lift
Strut Bracket and move the brackets inboard to increase dihedral, or
outboard to decrease dihedral. Once you are satisfied with overall wing
alignment, complete the wing installation, as indicated in your Builders
some cases, a gremlin called “weld warp” causes carefully jigged, welded
parts to fit incorrectly when installed on an airframe. This “warping”
results from unevenly heated surfaces acting upon surrounding metal in a
fashion which distorts the intended shape. Fortunately, the flexibility of
4130 steel tubing permits such warping to be resolved, in many cases, by
applying pressure on the part, to rectify the warped condition. The elevator
to stabilizer fit is often subject to such warpage, and requires the builder
to “nudge” parts until a pleasant fit is obtained.
we have seen some wing lift struts exhibit an alignment issue wherein, after
attaching the forward strut to the front spar attach bracket, the rear strut
hangs below the rear spar attach bracket. In some cases, a good deal of
force must be applied to move the rear strut into place. Can anything be
done about this you bet!
By clamping the “fuselage” end of the strut into a vise (with boards on each side to prevent scoring), a twisting force can be applied to the “wing” end of the struts, thereby correcting the misalignment. The diagram below shows the proper placement of clamps and force. The strut must be nudged past the actual point of adjustment required to allow for the natural spring back. This process may be repeated several times until a tension free fit is secured. Absolutely no harm is caused to the struts, and you will have ensured a custom fit to your specific wing dimensions. Please feel free to contact Builder Support if you have any questions.