Here is unique and sophisticated 1/2-A free flight model designed for and
flown successfully in Half-A payload, Half-A free flight, Class A free-flight,
and it meets FAI gas requirements. By adding a set of floats it can be flown
in R.O.W. events. Chula Vistan's elliptical dihedral and use of a diesel
engine set it apart from many similar models of the era (mid-1950s). As
with many F/F models, the Chula Vistan's framework is a work of art that
is most appropriately covered in a translucent or transparent scheme with
colored trim so that its structure can be appreciated. Not being a free
flighter, I do not know if it meets modern specifications for current AMA
or FAI events.
Chula Vistan PAA-Load Free Flight
Elliptical Dihedral Diesel Powered PAA-Load Free Flight Contest Model
Plane for Five Events
By CPO Tom Henebry
is the second of a series of small gas models with an elliptical dihedral
wing form. It is unique for a payload model in that it retains the high
performance of a true pylon, yet the simple cabin enclosure meets PAA's
Half-A payload specifications. It has been flown in Half-A payload, Half-A
free flight, Class A free-flight, and it meets F.A.I. gas requirements.
By adding a set of floats it can be flown in R.O.W. events. All told, five
events may be entered with this one basic model. The dummy is located exactly
on the C.G., and flying with or without the dummy doesn't noticeably change
the flight pattern.
Rather than repeat at length the construction of the wing jig, I refer
you to page 37 of the January 1954 issue of Air Trails. The jig for Swayback
and the Chula Vistan are the same in type and construction, the only difference
being in the curve line. By comparison you can see the Chula Vistan is flatter
in the center section and rises more sharply at the tips.
Assuming you have the jig, with the plan located properly in the concave
form, install the inner piece of 1/8" sq. balsa that forms the leading edge.
Outline it with pins and weight it down so it stays in contact with the
form along its entire length. Cement the leading piece of 1/8" sq. along
its entire length to the piece already installed; you now have a leading
edge 1/8" high and 1/4" wide. Repeat these steps until you have the leading
edge built up to 1/4" sq. and evenly cemented together at all points of
contact. The trailing edge is made in the same manner except the inner piece
of 1/8" sq. is installed a little later.
When the leading and trailing edges are set up, cement the slotted 1/8"
sheet tips in place. Follow with the 1/8" x 1/32" bottom cap strips, cut
to size and cement the 1/32" x 2" cross-grained sheet in the indicated position
in the center section. After the cap strips and center section strips are
in place, cement the inner piece of 1/8" sq. trailing edge to the trailing
edge as well as to the tops of the cap strips and center section piece.
cutaway drawing is by Douglas Rolfe, nationally known aircraft artist. Mr.
Rolfe's work appears regularly in this publication and in the forthcoming
Cement a piece of tough 1/8" sq. from tip to tip, filling the slots in
the tips and cement securely to all cap strips and center section strip.
You will need to weight the spar down with any small heavy object at hand
to assure even contact with all cap strips. The spar is built up by cementing
successive pieces of 1/16" x 1/8" to the 1/8" sq. already installed. These
pieces are progressively shorter as indicated, so when the spar is complete
it is not unlike an automobile leaf spring, thicker in the center and thinner
at the tips.
To complete the wing, cement in the ribs and the top cap strips, cover
the three center section ribs with cross-grained 1/32" sheet and finally
add the unslotted pair of wingtips on top of the installed pair. When the
wing is thoroughly dry remove it from the jig, shape the leading and trailing
edges and the tips with sandpaper - and of course an overall sanding with
fine sandpaper. The wing is now ready to cover. I believe it is at this
point that the builder realizes the beauty of this type of wing construction.
No weak dihedral joints, no chance of misalignment, and even without covering
its resistance to torsion is amazing. The secret here of course is that
every strength member in the structure is pre-stressed.
Stab construction is the same as the wing except the leading edge and
the spar are not laminated. The spar should be tapered as indicated before
construction is conventional; make the two sides over your full-sized penciled
plan. You will note that the longerons are 1/8" square but the sheet fill-in
is 3/32"; this is intentional. Place scrap pieces of 1/32" sheet under the
sheet parts to bring them flush with the longerons on the first fuselage
side. Make the other side directly over the first, but push the sheet parts
down so they are 1/32" below the edge of the longerons. On assembly be sure
the depressed sheets are on the outside; the longerons are then sanded smooth
with the face of the sheet before covering.
The pylon is made from laminated pieces of 3/32" x 3" overlapping each
other at 60 degrees. The pylon extends through the fuselage to the broken
line on the drawing. After laminating the pylon is cut to shape, sanded,
and lightening holes cut where indicated, and formers F-1, 2, 3 and 4 are
cemented in position on the pylon. The complete firewall assembly containing
the landing gear and engine mounting nuts is cemented in place securely.
Insert a waxed PAA dummy in position between F-3 and F-4 - be certain he
With the dummy in place, cement the fuselage sides to the formers and
firewall, being careful to maintain correct alignment. Cement the 1/16"
x 8" cross pieces in place, then the completed rudder, fill in as indicated
with 1/16" sheet. The 1/16" plywood stab platform is cemented in place with
the fuselage lying on a smooth, flat surface and the stab in place. Be sure
it follows the curve of the stab exactly and that the stab is in line with
the fuselage bottom.
The headrest fairing is carved from soft balsa, hollowed out and installed
as shown. The plastic canopy is cut to size, slotted to fit around the portion
of the pylon that protrudes through it, and cemented in place. Cut the required
holes for the engine timer but do not install it until after covering. Finish
shaping the pylon and add the 3/4" trailing edge stock plus the two layers
of 1/16" sheet, leaving a 1/8" wide strip on the center line for a wing
completed structure is covered with Jap tissue, water sprayed and given
four coats of butyrate dope. It is a good idea to double-cover the stab
bottom; because of its low position it is prone to minor tears and damage.
After covering install the engine timer, wing hold-down wires and the bent
pin hooks that retain the payload dummy. Cement a piece of hard 1/16" x
1/8" on the centerline of the bottom of the wing. Before the cement dries,
secure wing in place and check the distance from each tip to the top of
the rudder - be sure they are equal.
The wire pivot bar and dethermalizer parts are formed and cemented in
place. Cement liberally and use strips of Band-Aid backing (crinoline) to
further reinforce the points of contact between the wire and the structure.
Do not force the wire into the wood but drill holes for it, which results
in a stronger joint.
The McCoy Diesel shown gave me the best Half-A and Payload results, but
any other good Half-A engine could be used. The Royal Baby Spitfire tank
shown needs only minor alterations to fit the McCoy. Filing off a small
flange, a home-made gasket and drilling the tank mounting holes slightly
oversize will make it work. If you care to compete in Class A events, a
Cub .074 or a Royal Spitfire can be attached to the firewall with wood screws.
You may note that there are no provisions On the drawing for any form
of glide turn control. You may use your own favorite method, a tilted stab,
a floating tab on the left wing or maybe you prefer, like me, to use 1/16"
to1/8" wash-in on the right wing. I feel this prevents the right wing from
"digging in" in a tight power turn. Whichever method you prefer, the model
is trimmed to glide smoothly to the left before power is applied. Start
the power flights on low power settings and gradually approach maximum power,
making minor thrust line corrections until a smooth, fast, right climbing
turn and a floating left glide result. Remember the C. G. position is right
at the dummy - if you shift engines, be sure the model balances at the same
The AMA Plans Service offers a full-size
version of many of the plans show here at a very reasonable cost. They will scale the plans any size for you. It is always
best to buy printed plans because my scanner versions often have distortions that can cause parts to fit poorly. Purchasing
plans also help to support the operation of the Academy of Model
Aeronautics - the #1 advocate for model aviation throughout the world. If the AMA no longer has this plan on file, I
will be glad to send you my higher resolution version.
Try my Scale Calculator for Model Airplane Plans.
Posted April 5, 2014