by Tandy Walker, Arlington, Texas
I have long been a proponent of removable vertical and horizontal tail surfaces on my models, however, I never documented the design that I have developed and employ. So I apologize for the detail in this lengthy report, but it does clearly show my approach. Bruce, you had asked me about this some time ago.
For this big Bomber, I am using three countersunk 2-56 Phillips Head nylon screws to hold the fin down in the stabilizer slot and six 4-40 Allen Head nylon screws to attach the stabilizer to fuselage stab platform. This Part 1 presents the following series of sequential pictures that illustrate the design and construction of one of the three stabilizer attachment base plates use to accomplish the removable feature of the stab.
STEP 1
This shows the 1/16" plywood plate base (5/8" X 3-3/4") and the
two 1/8" plywood pieces, which will be used for wooden blind nuts. |
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STEP 2 The 1/16" plywood base plate has 1/16" sheet balsa epoxied to the back side
STEP 3 The two 1/8" plywood pieces have been bonded to the plywood plate base.
STEP 4
The two 1/8" plywood pieces have been drilled through from the back side
of the base plate with a No. 43 bit and threaded with 4-40 tap as shown.
STEP 5
This shows the edge of the 1/8" plywood/balsa base plate
and one of the 4-40 nylon screws screwed into the base plate.
STEP 6
A 2-56 Cap screw is inserted into the No. 44 center hole.
STEP 7
A length of brass tubing with an ID that will just slip over
the head of the Cap screw is cut and file sharpened on one end.
STEP 8
The sharpened end of the brass tubing is slipped over the head of the Cap screw
for centering and is twisted like a cookie cutter to cut down into the 1/16" balsa.
STEP 9
This picture shows the circular cut performed by the brass tubing cutter centered on the hole.
STEP 10
An Xecto No. 11 knife blade is used to pick out and remove the balsa inside
the circular cut leaving the clean 1/16" deep recessed hole shown below.
STEP 11
Finally a 2-56 nylon screw is inserted into the countersunk hole, which will be used to hold the fin down in the stabilizer slot. The countersinking of the head of the 2-56 nylon screws prevents any interference between the bottom of the stab and the fuselage stab platform.
STEP 12
After fabricating all three stabilizer attachment base plates, they were integrated into the center section of the big Bomber's stabilizer by gluing them to each of three 1/8" X 1/4" bottom spars. The picture below also shows two center section ribs installed which will later receive 1/16" sheet planking. A 1/2" square balsa beam was put in place to line up the inside edge of the center section rib used to form the right side of fin slot. The outside of this rib was braced with four equally spaced triangular braces.
STEP 13
This shot shows all four center section ribs in place. The stabilizer slot for the fin is now identifiable. You can also see the holes in each of the three base plates along the stab's center line along the bottom of the stabilizer slot that will be used to hold the fin down in the stabilizer slot
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