and Rockets visitor Ray L. wrote to say he has a Biceps model that appeared
in the April 1969 edition of American Aircraft Modeler, and that he would
like to have the article posted. Per Roy, "I bought this model from one
of our club members who is a team race flier and built it on a whim, he
fitted it with electric and had it test flown by one of our aerobatic pilots
and after that he lost interest it and I was happy to give it a good home,
the quality of build and finish is to pro standards." Power in the original
was a Fox .59. AMA Plans Service still prints the
A muscular, big-engine bipe for sport and exhibition control-line
every airplane nut has a soft spot for biplanes. There is something nostalgic
about a two-winger, the whistle of wind through rigging wires and all that
When our local model club began control-line exhibition flying
to stimulate public interest and recruit new club members, I became enthusiastic
about a bipe for that type of flying. It would be an attention-grabber,
an extremely stuntable and flashy aircraft. The ship I had in mind would
be large; a small plane just doesn't get attention. The further I studied
the biplane configuration, .the more intriguing it became.
that the built-in head-wind high-drag characteristic to biplanes might be
used to advantage. A large engine to turn a big low-pitch prop would give
a very high static thrust. In combination with the high-lift high-drag layout
this would result in a relatively slow-flying, extremely maneuverable craft
- like a helicopter with its rotor facing forward! And that's the way it
A few additional design features improved performance,
such as: thick, blunt airfoil sections with full-span flaps on both wings
to help eliminate the wobbling or staggering at low speeds common to biplanes
during tight turns. A large elevator surface proved effective at low speeds.
A large rudder with quite a bit of turn-out kept the lines tight at all
times, since centrifugal force is not much of a factor at low speeds. There
you have it.
The theory sounded good, but the proof came in building
and flying the brute. Biceps is a spectacular performer, a real ball to
fly. Although not a smooth, precision, contest-type ship, it should give
a good account of itself in any contest in the hands of a competent pilot.
For exhibition-flying, Biceps is superb, the hit of any show. It is not
particularly difficult to build. Large size and straight lines contribute
to simplicity. It does take a considerable amount of balsa.
Tail surfaces: Both the fin-rudder and the stabilizer-elevator
assemblies are made from medium-weight sheet balsa; wood grain parallel
to hinge lines. First glue balsa sheets together edgewise to obtain enough
width for entire piece to be cut from. Then shape to a streamline section
similar to that shown on the plan. I have found that sanding boards (sandpaper
of various grits glued to a flat piece of 1 x 2" pine about 8 or 10" long)
make excellent tools for rough-shaping balsa wood before final sanding,
prior to painting and finishing.
This completed Biceps is owned by Ray L., of the UK. He was kind
enough to send me the photo. He bought the model from a fellow club
member. I would never be able to part with such a nice airplane!
(click for larger version)
High-lift, high-drag, with big prop, make the bipe fly like a 'copter
with rotor facing forward.
Oodles and gobs of wing area, thick airfoils and full-span flaps add
up to a precision in flight that must be seen to be believed. You'll
After rough-shaping, thoroughly
sand with progressively finer sandpaper until you are satisfied with the
job. Then seal the wood grain with a couple of coats of clear dope. I use
and recommend Aero Glass products. They cost a little more but the quality
is worth it. A couple of coats of filler should be applied next, again lightly
sanding between coats. Now cut the rudder and elevator apart from their
respective assemblies and sand the cut edges, rounding them slightly and
follow by doping to seal the wood grain.
Now glue the rudder to
the fin with 1" of turn-out measured at the trailing edge. For the elevator,
recess the edge as necessary for the control-horn assembly; I used a prefabbed
unit available at most hobby stores. Cement or epoxy the horn in place.
Next attach the hinges, cloth, metal, or plastic as you prefer - I used
cloth. Dope over them, seal, and fill the surface. A drop of oil applied
to the center of each hinge before doping will keep them flexible. The final
finish coats of dope will be applied after the surfaces are attached to
Wings: There isn't anything unusual
in their construction except for the wing-strut-attachment method, which
will be explained in detail later. First cut out the ribs. You may think
there are a lot of them and there are, but the close-rib spacing really
looks nice on the completed ship; it serves a real purpose too. On a thick
airfoil, close-rib spacing is necessary to prevent the covering from sagging,
which would defeat the purpose of the thick airfoil. Cut the ribs from medium-soft
1/16 sheet balsa. I made metal templates for the W1 and W2 ribs, so I could
cut out about a dozen at a time which helped somewhat.
Make up the
wing spars from hard, straight balsa - 1/4 x 1" for the front spars and
1/4 x 3/4" for the rear. Splice as necessary to gain the proper lengths.
Slide the full-length ribs, one at a time, onto both the front and rear
spar making sure you do not forget the W3 center rib in the top wing and
the W7 rib in the bottom one. When the ribs are in their approximate position,
pin the spars down directly over their corresponding plan, blocking them
up to clear the ribs with balsa scraps - 1/8" thicker scrap under the rear
spar than the front. Next, slide the ribs into their exact positions and
spot-glue them in place. Later you can cement more thoroughly after removing
the wing from the plan.
The trailing edges can be installed next.
They may be shaped either before or after attaching. I used a razor plane
on the original model which worked very well. Next put on the 1/4 x 1 leading
edges after beveling one edge of each so they fit together nicely. Before
trimming the leading edges to final shape (again using a razor plane or
substitute), install all the false ribs (W2, 5 & 6) in their proper
positions and cement thoroughly. Make darned sure you don't forget to put
in the wing strut mounting blocks (made from 1/2" hard sheet balsa). Cement
them thoroughly in their proper locations - bottom of the top wing, and
top of the bottom wing.
Install the wing tips and other finishing
pieces such as top wing center-section trailing edge and bottom wing center-section
trailing edge and bottom wing center-section sheeting. Carefully sand entire
structures, dope and sand again. The wings should now be ready for covering.
I used silk on the original ship for durability although other covering
materials may be used as well. Dope with three coats of clear and two of
color for reasonably good finish, substituting a coat of filler for the
third clear coat if desired.
Fuselage: Make the
engine mounts first, using very hard wood (maple was used on the original
Biceps). Each mount measures 3/8 x 3/4 x 12 1/8". Drill the mounting holes
to fit the engine you are going to use. A Fox 59 was used in the first Biceps
and worked out beautifully - a very powerful, dependable engine. Also drill
the cabane strut in the location shown on the plan. Now mount the engine
on the mounts using #6-32 machine screws. A small amount of out-thrust can
be added at this time if desired, although it is not absolutely necessary.
Next cut out the 1/16 plywood doublers and the 1/8 ply firewall
(patterns are shown on the plan). Place the firewall in position on the
mounts and apply epoxy glue to the joined surfaces. Lay the mounts upside
down on a flat surface with the engine and firewall top hanging over the
edge. Use a piece of wax paper or plastic wrap under the mounts to keep
the epoxy off the surface. Glue the 1/16 plywood doublers to the engine
mounts and firewall with more epoxy and then let everything cure.
Now cut out the 1/8 fuselage sides and 1/16 balsa doublers (grain-vertical
on the latter) from medium-weight sheet balsa. Then cement the 1/16 doubler
pieces against the inner surface of the 1/8 side parts; be sure the cutout
for the lower wing is cut out through both parts. Now cement fuselage side
assemblies to the plywood doublers, putting on formers F1 and F2 at this
time. After allowing the glue to dry overnight, bring the aft ends of the
fuselage together and cement them with a wedge of scrap balsa for reinforcement.
Install the rest of the fuselage formers, bellcrank and mount assembly and
landing gear mount.
Attach a couple of 6-32 nuts to the upper
surface of the gear mount while you can still get at it. Do not put the
top and bottom sheeting on yet. You can, however fit the fuel tank in and
build up a supporting plate of balsa underneath and on top. I used a plastic
"clunk" R/C tank in my Biceps, but a metal control-line tank could be used
as well. One advantage to the plastic tank is that it is removable for repair
or replacement through the round hole in the firewall. If a metal tank is
used, the firewall hole may be eliminated. No fuel tank fill and vent lines
are shown on the plans because of the option of tank type used.
Landing gear: This is made from 1/8 spring aluminum stock.
A Sig landing-gear blank was used on the original model. The aluminum spring
stock is cut to size and bent to shape as shown on the plan, being very
careful to use large radius bends. A small radius bend will very likely
crack the hard aluminum stock, in which case, you've had it. Nothing to
do but start over again with another blank. The wheels are attached with
No. 8 machine screws (see plan for details).
The wheel pants
are built up from three laminations of balsa with a plywood insert in the
side between the wheel and gear leg. Use epoxy glue between the plywood
insert and landing gear leg, and epoxy putty to fillet in for extra strength
to finish off the job. You will probably have to drill out the wheel hubs
with a #19 drill to make them fit a No.8 machine screw since most wheels
have smaller hub holes than that. Mount the gear on the fuselage with two
No. 6 flat head machine screws, countersinking the heads flush with the
Miscellaneous assembly: Install
the lower wing. Before you slide it through the holes in the fuselage however,
put wing flap horn into position. The flap horn is made from 3/32 music
wire. The sheet metal lever arm is silver-soldered to it. Glue the wing
in position and connect the bellcrank to the flap horn. Install the flaps
by attaching the hinges (fabric or metal).
Now install the
stabilizer and attach the elevator to the flap horn. Thoroughly check out
the control system and modify as necessary before going further. Next, install
the tail wheel and mount. Before going further, all four wing struts must
be built and attached. The struts are made from music wire as shown on the
plan. Spiral wrap all tips with copper wire and solder all joints. Now see
if you can fit the bottom ends of the cabane struts into the corresponding
holes in the engine mounts. If you can - great! If not, bend the struts
to fit or enlarge the holes in the engine mounts.
interplane struts into position in the lower wing and fit the top wing onto
all the strut tips. Make a couple of cardboard jigs (shown on the plan)
to align the top wing properly. When everything fits, epoxy the lower ends
of all the struts into their mating holes and allow to cure undisturbed.
Remove the top wing and install the top and bottom sheeting on the fuselage.
Round all corners and edges, install the rudder, and start applying the
finish. At least two coats of clear followed by filler and color coats.
Attach the top wing again, using the cardboard jigs and the old faithful
epoxy. After attaching the top wing flaps, install the flap linkage rods
and make sure they work without binding.
Build the flap linkage
rods from 1/8 brass tubing flattened slightly to an oval shape. Cut length
carefully so the flaps will be even and parallel. Drill 1/16 holes through
the rod tips so they will end up at least 1/16 below the flap surface. The
hinge pins at both ends of the flap rods are 1/16 music wire, 7/8" long.
The tubing pieces that complete the assembly are 1/16 ID x 1/16" long, either
brass or aluminum. Grease the rod tip, hinge pins and tips of the tubing
(not the center) with Vaseline.
Place the assembly in position
in the grooves in the flaps and cover with epoxy. Try to keep the epoxy
away from the oval rods to prevent binding later. It is much easier to do
the lower wing hookup first, then after that is cured, turn the ship over
and repeat the hookup to the top wing. Be certain that the flaps are even
and parallel before the last hookup is made. It is darned hard to correct
Build the cowling from sheet balsa, being sure to dope
generously inside. The cowling may be attached using a couple of screws
through the side into the engine mounts. After completing all the little
details like the spinner, windshield, line guides, etc., it should be completed.
Nothing left but some spectacular flying.
Biceps Plans Sheet 1
for larger version>
Biceps Plans Sheet 2
for larger version>
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.
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Posted July 16, 2012