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SERVICE
LETTER #25A DATE:
March 12, 1993
revised September 12, 1994 SUBJECT:
1) Wing dihedral
2)
Lift strut adjustments APPLICABILITY:
Subject 1) All non-Series 5 Kitfox's
Subject 2) All Kitfox's COMPLIANCE:
As applicable FROM:
SkyStar Aircraft, Engineering Department Subject
1) In
an effort to help you accurately set your wing dihedral, we
offer the following technique: Follow
your existing wing directions to the point where you have
temporarily positioned the lift strut brackets onto the spars
so that the center of the strut bracket bolt holes 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. Temporarily hold
the brackets in place with hose clamps. It is important not to
drill the spar-to-fuselage attach holes (except for the top
rear hole) until after the dihedral has been properly
adjusted. Carefully
level the fuselage both laterally and longitudinally.
Hold a 4'
carpenter's level up to the bottom of the front 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.
Lower the wingtip end of the level until the bubble is
centered, and then measure the distance between the spar and
the top of the level. Adjust
the position of your strut attach brackets until you have
obtained the proper measurements.
For the Model IV and XL, the measurement should be
between 1.1" and 1.4".
For the Speedster, the measurement should be between
.31" and .35". To
further increase the accuracy of your dihedral, check the rear
spar as well. Take
the measurement you attained from your front spar, and multiply
it by 1.137. Adjust
the aft strut attach brackets so that your level is below the
aft spar to this value. For example:
If you measured 1.1" on the front spar, 1.1 x
1.137=1.25", so adjust the lift strut attach brackets until
the bubble is centered when the outboard end of the level
1.25" below the rear spar. A
special note for Speedster builders:
after you have set your dihedral and before you drill all
the spar-to-fuselage holes, check that you have clearance for
the flaperons when the wings are folded.
Carefully fold the wings back by pivoting them on the
attach bolt through the upper rear spar hole.
When the wing is fully folded, you will need a minimum of
5" clearance between the leading edge of the wing and the
horizontal stabilizer. If
you don't have this clearance, increase your dihedral slightly
and equally on both sides as required to allow the wings to fold
without having an interference problem between the flaperon and
the horizontal stabilizer. Subject
2) Due
to a manufacturing problem called weld warp,
occasionally a properly jigged and welded part will fail
to fit correctly. This
is most obvious on parts with very long members, such as the
lift strut. In
some cases, after attaching the strut to the fuselage and
to the forward strut attach bracket on the spar, the aft strut
member hangs below the aft strut attach bracket.
A simple technique can be employed to make a warped lift
strut fit the airframe. Clamp
the fuselage end of the strut in a padded vise, and place two
long boards across the outboard ends of the strut.
Apply torque to the strut through the boards in the
direction required to make the strut fit; be careful not to
apply any torque to the threaded ends of the strut. To allow for
the natural spring back of the 4130 material, you will need to
go slightly farther with your corrective efforts than 'just far
enough'. Repeat the
process as required until a tension free fit is obtained.
Because of the forgiving nature of 4130 steels, the strut
is not harmed by this procedure at all. If
you have any questions about the information in this service
letter, call our Customer Support Department at 208-454-1443 |
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