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I already possessed
the recommended Hummel conversion of the 1/2 VW engine that I had planned to
use on another project. How nifty would it be to use it to power an
UltraCruiser?
In January 2001, I
contacted Morry Hummel, the UltraCruiser's designer, and asked about the
plans availability. He told me they were "in the pipeline." I
learned that the UltraCruiser is built mostly of 6061-T6 aluminum-an alloy
that is less expensive, easier to work with, and less subject to corrosion
than other metals. In areas where higher strength materials are
needed, such as the spar caps, 2024-T3 aluminum is used.
Getting Started
Morry provided me
with a rib drawing in early February 2001, and I went to work. The
ribs are constructed of bent-up angles and channels in a form much like
wooden ribs. Each rib station is composed of a main and a nose rib,
and there are 23 stations for a total of 45 pieces...the odd station beefs
up the step area of the port wing aft of the main spar.
The ribs are
constructed of 6061-T6 aluminum on a simple plywood jig. The caps are
an angle formed of .025 inch material, and the interstices are channels of
.016 inch. The nose of the nose rib is formed of .016-inch aluminum. The ribs are riveted with 3/32-inch driven rivets
or all-aluminum 1/8-inch pulled rivets. I formed the caps with a
shrinking tool, but other builders have had success with a stovepipe shrinker or fluting pliers. Hummel Aviation also now has formed rib
sets available.
Conventional or
driven rivets are mandatory for assembly of the main spar and most of the
engine compartment. They are optional elsewhere. Most of the
aircraft's construction is of pulled rivets--aluminum with a steel mandrel
in high-strength areas and all aluminum in the remainder. Brand names
and sources are included in the drawings. An unusual feature of the
steel mandrel type is that it is a flush head rivet. One of the heads
on the rivet tool is countersunk and, when used with these rivets, results
in a very low profile dome head. I used a manual tool throughout and
wore one out!
About the time I
finished the ribs, the outer wing panel drawings were released. The
main spar caps are 3/4-inch by3/4-inch by 1/16-inch 2024-T3, doubled for about half the
span and single for the remainder. The web is .020 inch 6061-T6 with
lightening holes. The rib spacing is 1 foot with a vertical stiffener
U-channel bent up of .016-inch material between the rib stations.
Being the Lone Ranger in my shop, I used a back riveter to drive the
conventional rivets on the spar assembly.
Setting up Shop
My shop has few
major tools. I have a drill press, band sander, and large air
compressor. My brake is a 36-inch, bench-mount model available from
Aircraft Tool, and I cut almost everything with a handheld electric shear.
A sheet metal shop in nearby Salt Lake City has both a 12-foot shear and a
12-foot press brake, so I used them to shear the wing webs and bend up the
8-foot ailerons as well as the lower wing skins. Some parts must be
rolled on the aircraft, and I used the metal shop for those few items.
In addition, I have left, right and center snips as well as two air drills,
a straight and an angle one. The angle drill really winds up quickly,
and I tend to favor it.
Several aircraft
tools are required: a rivet gun, bucking bar, hole finder, rivet cutter,
handheld dimpler, cable cutter, flanging tool, deburring tool, and fluting
pliers. I was able to build the aircraft with 100 1/8-inch Cleco
fasteners and 50 3/32-inch Cleco fasteners along with two pair of Cleco
pliers (these pliers grew feet and scampered away just when I needed them).
My
workbench is 3 feet by 8 feet with a 3/4-inch ply top, and it's on wheels.
(Yes, I said three feet wide! If it's four feet wide, one rubs the old
pot leaning over to reach the middle.) I flipped the top for this
project--nothing like a clean start!
The Details of Construction
The wings are
skinned with .016-inch 6061-T6 using the matched-hole tooling (MHT)
technique originated on the Thorp T-18. The transfer tool is
fabricated from steel banding stock gleaned from a local lumberyard.
MHT tutorials can be found in issues of the T-18 newsletter printed in old,
old issues of EAA Sport Aviation. MHT was also described in the
late Dick Cavin's "Tin Bender" series that appeared in Experimenter
from October 1986 until May 1991. In addition, instructions are
provided with UltraCruiser drawings.
The leading edge skins must be rolled. I rolled mine by hand and, of
course, overdid it on several. All was not lost, however. I set
those pieces of aluminum aside and used them later to fabricate the
empennage.
The lower wing skins have a Z-section at the trailing edge that forms the
aileron cove. The leading edge is skinned first followed by the rear
section. The ailerons can then be fitted, and the hinges drilled and
riveted. Then the flaps should be removed and stored because they are
somewhat fragile.
The center wing panel is integral to the fuselage. The spar caps are
1-inch by 1-inch by 1/8-inch 2024-T3 angles, and the web, again, is .020-inch 6061-T6.
Where the main spar passes through fuselage, the load is carried by a "carry
thru" sawed from 3/16-inch 2024-T3 plate. This sawing job is
accomplished easily using a band saw with a conventional wood-cutting blade
at wood-cutting speeds. One builder cut his "carry-thru" with a saber
saw. Cutting the fuselage to fit the center wing panel may raise the
anxiety level a little--measure thrice, check twice, cut once!
The UltraCruiser's fuselage is semi-monocoque with six bulkheads labeled A
through F, with A being the firewall. The bulkheads are formed of
.025-inch 6061-T6, with the exception of F, which is .040-inch. The
bulkheads are arranged on a "strongback" built of door frame wood, much like
building a boat, and are skinned back to front, one bay at a time. The
skins are .016-inch 6061-T6 aft of bulkhead C. A pair of 3/4-inch by
3/4-inch by 1/16-inch 2024-T3 angles runs from bulkhead A to C on the
bottom.
The wing's rear spar of 3/4-inch by 3/4-inch by 1/8-inch 6061-T6 angle
attaches to a semi bulkhead just aft of bulkhead C. This spar connects
to a short spar of the same angle on each outer wing panel.
The empennage is conventional, and each piece is formed with end ribs and
skins of .016-inch 6061-T6. The horizontal stabilizer is beefed up at
the root with .040-inch sheet and the spar with 3/4-inch by 3/4-inch by
1/16-inch angle for half its span. The stabilizer is ground adjustable
through a few degrees for a semi-permanent trim, while a spring arrangement
on the elevator push rod in the cockpit provides in-flight adjustment.
Both the elevator interconnect and the rudder/tail wheel actuating rods are
4130 steel weldments
The tail spring and wheel mount are 4130 weldments. The main gear legs are 1½
by 1/8-inch 6061-T6 tube and attach to the top spar cap with a 1/4-inch bolt
and to the lower cap via a 1/8-inch 6061-T6 plate and associated .040-inch
2024-T3 fittings with six 3/16-inch bolts. Tracy O'Brien external band
manual brakes are used.
The flight controls are conventional stick and rudder that actuate 1/2-inch
push rods for the ailerons and 3/4-inch push rods running aft.
The engine mount is aluminum with two main strength members of 1-inch by
1-inch by 1/8-inch 2024-T3 angle. Each angle is inside a motor mount
box, triangular in cross section, one on each side. Each box comprises
an inboard side, a top side, and an outer side of .020 sheet. The
lower fixed cowl is of .020-inch, with two braces of .040-inch aluminum at
the bottom and two straps of 3/4-inch by 1/16-inch at the sides. The
removable upper cowl is also .020 affixed with the fastener of your choice. |
