lot of careful thought and detail went into planning and rationalizing
why a biplane version of the venerable MO-1 control line Carrier
model should fly better than the traditional monoplane platform.
It was January of 1973 when this article appeared in American Aircraft
modeler. Time has shown that the old adage about if something isn't
broken, don't fix it must ring true here. That is not to say efforts
should not be undertaken to improve on a design, just that in this
case going to a biplane configuration was not the answer. Maybe
website visitor Duke J., who wrote to ask for this article, can
pick up where Mr. Gerber and Mr. Higley (yes, THE Harry Higley)
left off. Maybe a MO-Tripe...?
Mo-BipeRequirements for Profile Carrier allow non-scale designs.
biplane can offer several advantages such as reduced weight and
Don Gerber and Harry Higley
the 1920s Martin made the MO-1 monoplane which was used as the subject
for both a Class I and Class II Navy Carrier ship. The Class I version
appeared in the August 1969 issue of American Aircraft Modeler.
The subject of this article was designed for the Profile Navy Carrier
event, and its name was not chosen because Martin made a biplane
variant of the MO-1 - they didn't. It was chosen because the Bipe
retains many of the construction features and the same general appearance
of the MO-1.
In an era when the Scale Navy Carrier events
were dominated by Guardians; the MO-1 was a most unlikely but highly
successful choice for the event. The real airplane was to be a battleship
based observation plane in the early 1920s. Only two ever saw Carrier
service; an old letter reveals they were not regarded as fit for
this service by the Navy. The MO-Bipe may appear an unlikely choice
for Profile Carrier, but for a different reason. Most fliers do
not normally think of a biplane for a Speed event.
the nature of the rules, the biplane configuration, however unlikely
it may seem, offers the very decided advantage of reduced weight
and frontal area. A monoplane with a 36-in. span would require about
an 8.5 in. chord to achieve the 300 sq. in. required by the rules.
A few airfoil sketches will show that the minimum thickness that
will maintain the structural integrity of a built-up wing is about
0.75 in. This gives a frontal area of about 27 sq. in. A wing this
large does not lend itself well to solid construction. The MO-Bipe
used two solid, easy to shape wings with a 28 in. span, 5.7
in. chord and 0.25 in. thickness. These give a total frontal area
of 14 + sq. in., or only slightly more than half that of the monoplane.
The Bipe will also have a shorter fuselage because of the reduced
wing chord. This 15 to 25 percent overall reduction in fuselage
dimensions will provide a substantial weight reduction. One last
advantage for the biplane is the capability of using full span strip
ailerons on the lower wing which eliminates the need for tip weight,
thus saving another ounce. Strip ailerons are easier to install
than conventionally placed ailerons, as there is no need for long
torque rods or clumsy pushrods. The importance of the working ailerons
and rudder cannot be over-emphasized. This plane was designed from
the ground up for Profile Carrier, but the full potential of the
design cannot be realized unless the moveable ailerons and rudder
Unusual construction features shared by the MO-1
and MO-Bipe include solid wings and easy to install semi-enclosed
controls. Another common feature is variable sweep line leadouts.
The less the lines sweep back, the faster the plane will go. However,
the plane will be more likely to come in. By trying different holes
in the tip guide, the most favorable line sweep may be found.
Full credit for the design belongs to Don Gerber. Don and
I correspond regularly and this spring he sent some photos of the
MO-Bipe and asked if I would be interested in a joint article, as
he did not want to devote the large block of time that assembling
an article such as this requires.
All painting was done with linkages removed. This is also handy
when crashes make major adjustments necessary.
The MO-Bipe with its predecessor the MO-1, both in pre-WWII
markings. Only the MO-1 has scale heritage.
Adjustable leadouts provide for windy or calm conditions. Moved
forward line tension is less but speed is higher.
Plans show the hook-drop, elevator and aileron systems graphically.
Note use of adjustable clevises throughout.
The construction procedure
was planned to avoid two problems. First, a completely assembled
biplane is difficult to finish due to the limited space between
the two wings. Second, painting after the controls are installed
at best will look bad because of partially painted rods and other
components; worse yet, the paint may foul the whole system. The
strategy employed is to assemble the plane minus the upper wing
and struts. The controls are then temporarily installed, checked,
adjusted and then removed prior to finishing. The main frame, control
surfaces, struts and upper wing are finished separately, and then
the whole model is permanently assembled.
To begin with,
cut all plywood parts. These include the bellcrank, hook and tail
skid mounts, the struts and the plywood fuselage doublers. The doublers
should be cut a little oversize as they may not end up in exactly
the position they should. The resulting slight overhang is easily
trimmed and sanded flush with the fuselage. Drill the required holes
in the bellcrank mount, inboard strut, and tail skid mount.
Now is as good a time as any to bend the landing gear, tail
skid and hook. Attach the wheels with soldered washers. Attach the
tail skid to its mount with No. 6 x 3/8" sheet metal screws. This
will facilitate easy removal of the skid for painting and replacement,
though the latter will probably never be necessary.
bellcrank on the J. Roberts unit must be shortened. Notice on this
control unit that there are, in addition to the holes provided for
"the leadouts, two dents indicating alternate leadout positions.
Drill at these points, then trim the excess from the bellcrank.
Attach the leadout wires. I personally prefer Perfect brand - they
are a little stiff, but are strong and solder well. Mount the control
unit to the bellcrank mount to verify that the moveable bushing
that is recessed into the mount has adequate clearance. Once this
is established, remove the control system.
The next operation
is fabricating the fuselage. Cut the motor mounts to the correct
length. It will hurt nothing to drill 1/4" holes in them from the
landing gear mount back; it will save some weight. Glue the bellcrank
mount to the upper motor mount. Cut the fuselage from 1/2" sheet
balsa. Choose this piece of wood carefully as a heavy sheet adds
nothing but weight. Cut all slots including the bellcrank hole,
except the one for the lower wing which will be cut after the doublers
are installed. Cut the recesses for the hook mounts and the tail
skid mount, and glue these in place. Glue the motor mounts in position.
Notice on the plans that there is a piece of 1/2" wood on the top
of the upper mount. Cut this from a scrap and glue it in place.
The doublers may be attached with contact cement or Titebond. If
the latter is used, clamp between blocks, remove any excess glue
with a wet rag, and allow to dry overnight.
After the fuselage
assembly dries, it is convenient to drill holes for the motor, tank,
hook and landing gear. If a drill press is used, it will be necessary
to hold the fuselage on the block of wood so that the bellcrank
mount clears the table. Trim the excess from the fuselage doublers
and sand these even with fuselage.
Now the slot for the
lower wing may be sawed. Hold the fuselage on a couple of blocks
so the bellcrank mount clears the jigsaw table. The slot should
be 1/4" and not the shape of the airfoil. The lower wing is left
with a rectangular cross section where it intersects the fuselage.
There are two reasons for this. First, it is difficult to cut a
hole that will mate well with the airfoil. Second, sliding the fuselage
onto the wing would surely nick and gouge the wing if the slot was
a snug fit. Attach the landing gear.
The wings are made
from 1/4 x 6" medium sheet balsa and are no more difficult to shape
than a wing for a hand launched glider. Draw parallel lines on the
top and bottom of each wing 1.75" from the leading edge and 2.5"
from the trailing edge. Also draw lines down the middle of the leading
and trailing edge of the wing blank. Sanding the airfoil should
be done on a smooth surface. Any glue glob will chew up the under-surface
of the wing. This sanding is done with a 3 x 12" block with 60 grit
paper glued on one side and 220 grit on the other.
lines that are drawn on the wing blanks are used as guides to shape
the airfoil. As one looks down on the wing, the wood above a plane
determined by the line on the leading edge and the forward line
on the top of the wing is removed by sanding. The airfoil is shaped
by removing these wedge-shaped sections. The center section of the
bottom wing is left unsanded where it intersects the fuselage. Rough
sand the airfoil by using cross grain strokes with the rough side
of the sanding block. Do not sand below the guide lines and leave
a 1/16" radius on the leading and trailing edges. Use spanwise strokes
with the 60 grit paper to even out any ripples. Now remove any sanding
marks with the 220 grit side of the block. Cut the ailerons from
the lower wing; then cut the hinge slots and glue the lower wing
into the fuselage.
The tail assembly is straightforward.
Cut, shape and slot these surfaces for the hinges, then glue the
fin and the stab to the fuselage.
Efforts have been made
to keep the hardware standard, but there are three pieces that must
be homemade. These are the two horns on the hook and the horn on
the rudder. The hook horns are made from 1/16 x 1/4" brass, available
from any good hobby shop. This heavy a piece is used so there is
adequate contact with the hook to insure a strong solder joint.
Solder the right horn to the hook, but leave the left one unsoldered
until after the final assembly. The rudder horn can be made from
the same material or a lighter gauge. A homemade rudder horn is
necessary as a conventional horn will interfere with the elevator
travel. Attach all horns to their respective control surfaces. Install
the control surfaces but do not glue the nylon hinges in place,
as the control surfaces are removed for finishing.
the bellcrank; bend and install the pushrod. Now epoxy the hook
release guide tube to the fuselage. Bend the hook release wire,
then bind and solder it to the pushrod. The aileron and rudder push
rods are made from 12" Du-Bro "Kwik-Links." Insert the hook into
the fuselage. It will probably be necessary to use one or two between
the hook horns and the fuselage for spacing. Slide the horn on the
left side of the hook, bend the Kwik-Links and temporarily install
them. Solder the catch on the hook. It should disengage the release
wire with about 15 to 20 degrees down. Mount the motor and tank
and bend the throttle push rod to length. The engine we recommend
is the plain bearing Fox 36 RC. This motor is as good as any other
and is by far the easiest to install. The throttle arm is in the
right place and moves in the right direction (i.e., closes the throttle
when moved forward) to permit a straight, short pushrod between
the bellcrank and the throttle. It may be necessary to make a long
throttle arm to slow down the closing action. The Fox has a very
fast throttle. Other engines may require some arrangement to get
the push rod around the tank and perhaps a link to reverse the pushrod
direction. This is the kind of trouble that a new Carrier flier
would be well advised to avoid.
At this point, the plane
is completely assembled except for the upper wing and the struts.
Check to see that all the controls function properly. The left aileron
will not work properly because the horn on the hook is not yet soldered.
It can, however, at least be verified that the pushrods are the
correct length. Remove all the controls, the motor, tank and landing
gear; the model is now ready to finish.
I suppose every
flier has his favorite finishing technique. Plain dope is probably
adequate, but an epoxy finish will hold up longer when high nitro
fuels are used.
The method I use is as follows: Fill any
nicks with vinyl spackling compound. Sand the entire model smooth
with 320 or 400 grit paper. Brush on two coats of clear dope and
sand smooth with 320 paper after each. Apply three brushed coats
of dope and talc filler and sand with 320 after each. Next, spray
a very, very thin coat of DuPont No. 30 auto primer. This can be
thinned with dope thinner. Sand this lightly. Now spray on colored
epoxy. The primer is necessary as the epoxy will not adhere well
to dope. Elaborate spraying equipment is not needed. The PreVal
sprayer coats a dollar and one unit will paint a model the size
of the Bipe. The epoxy should be applied hot. Heat it in very hot
water for half an hour before application - this will greatly speed
the drying and thereby reduce the chance of dust adhering to the
finish. Reinstall the motor tank, controls and landing gear, and
glue on the struts and upper wing.
The lines and handle
are critical parts of the control system, and no matter how careful
a job has been done up to this point, the lines must be cut to the
correct length or only frustration will result. The lines must be
cut so that the distance from the center of the fuselage to the
center of the grip is between 60 and 60.5 ft. First, cut the elevation
lines so they satisfy your feel of level. Next, hold the handle
in a horizontal position so they satisfy your fell of level. Next,
hold the handle in a horizontal position so the elevation lines
run parallel all the way to the plane. The motor is now in its high
speed position. Now with the trigger pulled back, tie the throttle
line so that it sags slightly more than the elevation lines. Slightly
more means "as little as possible without sagging less." Next before
the line ends are soldered, check to see that the system has a full
range of throttle movement. Lines that are not the correct length
in relation to one another are the biggest cause of trouble to a
beginning Carrier flier. Minor adjustments in length can be made
by using different size line clips.
The model is now ready to fly. If this is your first Carrier
ship, it would be wise to contact an experienced Carrier flier,
let him watch you fly and then offer you his suggestions. Carrier
does not require great flying skill and endless hours of practice.
The rules for Profile Carrier are very restrictive in an attempt
to keep the event simple. It is safe to say that if the engine is
well broken in and the control system is carefully adjusted, the
Bipe will keep up with the best. If you would like to send any comments
or suggestions, please send them to me at 433 Arquilla Dr., Glenwood,
111., or to Don at 1119 Parkside Dr. N., Wyomissing, Pa., 19610.
MO Biplane Plans
<click for larger
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
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advocate for model aviation throughout the world. If the AMA no longer has this
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Posted December 11, 2012