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SERVICE
LETTER #25B 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 obtained from your front spar, and multiply it by 1.137.
Adjust the aft strut attach brackets so that your level indicates
level when the outboard end is below the aft spar to this value. For
example: If you measured
1.1" on the front spar, then 1.1" x 1.137=1.25", so
adjust the lift strut attach brackets until the bubble is centered with
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 trailing 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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