Big Flapper Article & Plans
February 1972 American
visitor Iram O. wrote to ask that this article and plans for the "Big
Flapper" be scanned and posted. It appeared in the February 1972 edition
of American Aircraft Modeler. With a 70" wingspan, it was considered a rather
large plane in the day. Big Flapper was designed for lazy Sunday flying.
The original used a home-brew engine (big and heavy per the author) and
sported reeds for control actuation. 'Reeds,' for the uninitiated, were
receivers that used 'resonant reeds' - a type of electromechanical oscillatory
device - to decode channel function. They acted like narrowband tuned circuits
(decoders) for responding to discrete commands from the transmitter. Think
of each reed as one of the fingers on the comb of a music box mechanism
that is resonant at a specific frequency, only instead of emitting a tone,
it vibrates in response to the unique frequency for which it is tuned. When
stimulated by the detected AM signal from the transmitter, it would close
a switch for a particular command, thereby signaling a servo or escapement
to move the airplane's control surface.
By Dave Boddington
airplane won't do the AMA or FAI pattern, it won't take retracts, it isn't
fast, and it is not quick to build. But, here is the plane for the quiet
Sunday flying craftsman who wants a big relaxing model for three or four
Scene: An Eight Air Force
Bomber Group Airfield somewhere in the east of England.
Time: In the late afternoon of an early summer's
The air is full of a mixture of the musty, oily, rubbery
smells only to be found on service airfields, and the clean fresh smells
of newly mown hay and wild flowers. In the distance, silhouetted against
the descending flaming orange sun, stand the metal framework of the water
tower and the sweeping curves of the huge blister hangars. A lark sings
sweetly overhead, its gentle bubbling song the only sound to be heard until,
suddenly, the peace is rent by the harsh crackle of a powerful engine's
In a far corner of the airfield a group of flying personnel are busying
themselves in preparation for the first flight of a newly-delivered aircraft.
Despite the seemingly lighthearted bantering among the pilot, his crew and
engineers, there is a tension, a nervousness that comes when the unknown
has to be conquered and the unexpected can happen at any time. Finally,
the moment of truth arrives and, as the plane accelerates down the runway,
the spectators hold their breath.
Launch of the first flight by hand because of tall grass field.
Inverted engine unique and attractive in cabin jobs.
With a big engine, use a large diameter but low pitch prop,
12-5 or 13-4 would do fine. High pitch props would produce enough
thrust to keep this model flying at idle!
Heavy homemade engine on prototype model. Removable cowl not
necessary with front rotor inverted engine installations if motor
mounts .are relocated.
A small correction with rudder
to keep her tracking straight down the center of the track and, with speed
having built up, a gentle easing back of the stick - she is airborne. Five
minutes of flying around to get the feel of the ship and the controls is
sufficient for this first flight; then it is time to return for the circuit
and landing. Nice and easy does it on the final leg, long and flat, giving
plenty of time for small corrections to direction and the descent angle.
Hold off until the speed drops and then firmly down all the main wheels.
A slight "curtsying" as she touches deck, but no bounce, and an almost audible
sigh of relief from the pilot. After the congratulations and inquest, everyone
retires for a celebration drink.
No, this is not a war story
of the early 1940's, just the first flight of a new model the Big Flapper.
The location is correct though - it is the U.S.A.F. base at Molesworth in
Huntingdonshire, England. Those evocative airfield smells were all there
too, although the airfield had not been fully operational for a number of
years. I suppose I was ten or eleven years old when I first visited an American
airfield (through the woods and fields of course, as the main entrance was
guarded), but my most lasting memory of that day will always be through
the sense of smell.
The Big Flapper, as its name suggests, was developed
from a smaller model called the Flapper - a 48" span single-channel model
that featured a novel form of aileron control It was before the days of
motorized servos and I mounted the rubber-driven escapement in the center
section of the wing with the rubber motor running down the span of the port
wing. The winding hook was let into the tip of the wing. Surprisingly, this
method of operating the narrow strip ailerons worked very well.
With the advent of multi-control or, more truthfully, when I could foresee
the possibility of purchasing this type of equipment, I set about designing
and building a large version of the Flapper for training purposes. The building
went on fine until another project interrupted the progress. I never seemed
to get around to completing the model and eventually let a friend,. Bob
"Flacky" Brightwell, have it. Bob is a perfectionist and he not only made
a superb job of finishing the model, making me wish I had kept it, but also
proceeded to make his own engine and radio gear for it. He incorporated
a number of his own modifications, described in my notes on construction,
as well. Because of these alternatives, please read the instructions carefully,
study the drawings and then decide exactly how you wish to build the model.
The fuselage used is the old-fashioned
"box" type using sheet sides at the front with the rear end built-up from
strip. The engine can be mounted either inverted or, if your motor does
not start happily in this position, upright. Should the latter mounting
be chosen, drop the engine bearers 3/16" to keep the propeller line correct.
Another alternative concerns the shape of the rear top of the fuselage.
Originally the fuselage featured the formers F6-F8 and the two 1/4 x 3/8"
stringers; however, following a mid-air collision causing considerable damage,
the revised outline shown on the drawing was used for the rebuilt fuselage.
There appeared to be little difference in the flying characteristics with
either fuselage, so it is simply a matter of choosing the one whose appearance
Do not omit the 1/16" plywood cabin sides as these strengthen
considerably what is normally a weak area. The 1/4" sq. doublers on the
top of the cabin area should be included. With bolt-on wing fixings the
dowels can be omitted. If you still prefer banded-on wings, try using 3/16"
dia. dural dowels instead of the more normal 1/4" dia. beech dowels. Acetate
sheet for the windscreen should be of a heavy gauge as this is another possible
Admittedly this model is perfectly satisfactory as an ab anitio trainer,
but I think most real beginners will plump for an ultra-simple kit model
or ARF model for their first attempts.
Sketch of undercarriage as used on "Big Flapper" by Bob Brightwell
Remember reeds (type of radio system)? They were used as recently
as the model's first flight last year.
A conventional bent wire
torsion bar type undercarriage is shown in the drawings; this will be quite
adequate for most conditions. Bob Brightwell, however, designed an advanced
form of main undercarriage featuring individual sprung wheels.
extra work involved in making "this unit will be amply repaid - the Big
Flapper can be thumped down really hard on landing without the slightest
bounce. A. steerable twin-wheel nose leg unit was used and this combined
with the sprung main wheels proved to be highly successful.
is nothing unconventional in building the wings - just make sure that you
do not build in any warps. Ribs have to be slid onto the rear spar before
they are pinned into position over the plan. The leading edge is propped
with 1/4" scrap balsa and the lower 1/16" x 1-1/2" trailing edge with suitably
Construct the wing in three sections; center, port
and starboard. The 1/16" vertical webbing is an essential part of the inherent
strength of the wing, forming a box section at the front and the rear or
the wing. Cut the slots for the dihedral braces after the wing sections
are complete, except for capping strips. I usually glue in the dihedral
braces and the wing sections together at the same time, using copious quantities
of pegs and pins to keep everything together. Sheeting to the center section
between the leading edge and trailing edge is not essential unless ailerons
are fitted and a servo installed. The dihedral shown is intended to be used
for wings without ailerons. Where ailerons are fitted, whether of the inboard
or strip type, the dihedral must be reduced to a maximum of 2 percent. The
reason for this reduction? Simple - the ailerons will not be effective unless
you do. Nylon tube and cable connections should be used between the aileron
servo and the center of the strip aileron, otherwise you may suffer from
aileron flutter if the horn connection is at the inboard end of the aileron.
The fin and rudder construction is self-explanatory. The rudder
may look small, compared with current aerobatic models, but was found to
be quite adequate. Increase the area if you want a really snappy response
or if you have plenty of multi experience.
of the tail plane with a simple framework of 1/4 x 3/4", 1/4 x 1/2" and
1/4" strip built over the plan. When this is dry, remove from plan and add
3/16 x 1/4" strips to all "rib" stations, both top and bottom. Note that
the bottom of the tailplane slots onto the top of the fuselage and that
the fin slots into the top of the tail plane. Sand the tailplane to a symmetrical
airfoil section . The 1/4" sheet elevators can be joined either by 3/32"
dia. music wire or 1/4 x 3/8" spruce.
I much prefer covering this
type of model with nylon as this adds tremendously to the model's overall
strength, yet retains a certain amount of flexibility to take up the shock
of hard landing (better known as a crash). It is surprising how strong an
open structure type fuselage, as used on the Big Flapper, can be due to
this degree of shock absorbing capability.
This model can cope with
a very considerable payload so there is no need to skimp on the decoration
and fuelproofing for a change.
Why not assume that the model is
going to last for a long time and really make a superb job of the finish.
However, it is no good making an assumption such as this unless you make
a first-rate job of the radio installation. The type of radio, linkages,
hinges, engine, etc. you use is up to you - just make sure they all operate
With the correct balance
point - the further rearwards, the more tricky it will become to fly - and
a warp-free wing you are ready for that first trip. Hand the transmitter
to an experienced flier if this is your first model; it may hurt your pride
but it will save you a lot of extra work.
Either hand launching
or a takeoff can be attempted for the first flight. You will find it easy
to handle and quite stable. The Big Flapper is not intended as a highly
aerobatic model, but it will cope with the basic maneuvers with varying
degrees of efficiency and style. Should you wish to do a lot of high "G"
maneuvers, then it may be prudent to add wing struts.
struts were experimented with on the prototype and, although it was never
proved that they were structurally necessary, they certainly looked quite
I sincerely hope you will enjoy building and flying
the Big Flapper. It is not a unique aircraft in any way - only an honest
sports model designed to give the maximum of fun and satisfaction.
Big Flapper Plans
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 July 20, 2013
Even during the busiest times of my life I have endeavored to maintain
some form of model building activity. This site has been created to help me chronicle my journey
through a lifelong involvement in model aviation, which
all began in Mayo, MD. There
is a lot of good information and there are lot
of pictures throughout the website that you will probably find useful, and might
even bring back some old memories from your own days of yore. The website began life around
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