you imagine what four Cox .049 engines running at the same time
on the same airplane sounds like? Keith Laumer and John Simmance
didn't have to wonder once they teams up to design, build, and fly
this 45" wingspan, control line B-17 Flying Fortress. As if that
wasn't enough, they added a custom electrical retractable landing
gear (including the tail wheel), navigation lights, throttles on
all four engines, and flaps! An 800:1 reduction gear box was coupled
with a 3 volt motor to drive the retract mechanism, flaps,
throttles, and light switches. A third control line and a Roberts
3-line bellcrank controlled everything. Operation of the retracts
is a bit dicey since they are triggered to go up at full throttle,
then go back down a low throttle. That means the pilot has to be
careful not to command full throttle while the model is on the ground
or the landing gear will fold up on him. I would not have wanted
the task of trying to get all four Bay Bee .049 engines running
at the same time. Today we have commercially available electric
starters for the small engines, but in 1963 it was either use the
spring starter on the engine or flip it by hand. Boy, do I remember
Retracting Gear B-17G Control Liner
British scale champ and noted American designer team up
to produce fabulous 4-engine bomber with working flaps and landing
gear, lights, even motor control!
By Keith Laumer &
We could begin by discussing the fantastic record of the airplane
that started life as a heavy bomber and ended the war classified
as "light" by contrast with the bigger, more modern aircraft that
had come to supplement - but never to replace it -
won't. We picked the B-17 as our scale project because it's a model
builder's dreamship; sturdy, straightforward, handsome - and a born
flyer that will ride in on one engine just like the big ones.
You can build her with fixed landing gear and two engines
plus two dummies - or go all the way with four operating mills,
retracting gear, operating flaps, navigation and landing lights,
throttle control, and little men in the cockpit. Either way, she's
a project that will keep you off the streets for quite a few evenings
- but she's worth it. The ship is not recommended as your first
scale project. But there are no unusual techniques, tools, or materials
Spend an hour looking over the plans, then begin
construction by laminating main and rear spars and making leading
edge, taking care to build-in correct sweep-back.
B-17 control line model uses four Cox .049 engines.
Side view of B-17 with retractable landing gear.
Working landing gear mechanism is shown above in "down" position.
Designer Laumer went all out on this Flying Fortress project.
Gear is retracted. Mechanism, made up of generally available
parts, presents a real challenge to the advanced U-control fan.
Builder of this B-17 is John Simmance, British free flight scale
champ for past two years; model will fly in '63 C/L events.
Cut out all wing parts, then thread ribs A-E onto component "N"
using slow drying white glue; add L.G. mounting plates and main
and rear spars, then component "0." Align and set aside. When thoroughly
dry, add remaining ribs and leading edge. Add trailing edges in
front of flap and aileron stations, then use 1/16" sheet to cover
the wing on both upper and lower surfaces aft of the rear spar,
on upper surfaces only between main and rear spars, and on undersurface
only forward of main spar to leading edge. Sheeting should be doped
with clear fuel-proofer before installing.
Build the main
gear assembly, using any suitable electric motor and gear train.
Install main L.G. legs and center operating yoke assembly by binding
and cementing brass bearing tubes to supporting plates. Use a stick-anything
glue for this step.
Add both formers 3 and 4 to center section,
then upper fuselage spine and former 2, followed by main L.G. unit
already mounted on its 1/8" ply supporting platform, gusseting everything
well with scrap balsa.
Build up fuselage by half-shell,
add side numbers 15-17, and join to wing, cutting 16 away at main
spar. Cut away bottom keel behind main spar hack to former 4 to
form "bomb-bay" battery compartment. Check alignment of the entire
assembly and allow a few hours for cement to set hard.
linkage from gear unit to L.G. is made and installed along with
tail wheel assembly and push-rod from main gear. Nacelle components
are cut and glued in position - cut away leading edges where indicated
on inboard nacelles only.
Install bell-crank, lead-outs,
elevator push-rod, throttle controls, trigger and limit switches
and L.G. wiring.
Sheet undersurface of wing between spars;
add 1-oz tip weight to starboard panel, then add flaps and linkage
and connect to L.G. push-rod.
Start fuselage planking with
one strip of 1/8" x 1/4" medium soft balsa along each of the upper
and lower spines and side members.
Construct and install
stabilizer unit and elevators and connect to push-rod from bell-crank.
Use lightweight balsa for all tail components.
type "grain of wheat" light on short pigtails are wired in, together
with all wiring and main and landing light switches. All switches
are made from small pieces of printed circuit board and thin brass,
the landing light switch being closed by the L.G. yoke arm when
in "down" position, the main switch being rotary in action operated
by a small screw head. Access with a screwdriver for switching-on
is through an 1/8" diameter hole in the underside of the wing center
Batteries are installed and all systems tested.
If necessary, bolt sheet lead behind former 1 until
model balances one inch forward of main wheels in down position.
Complete fuselage planking, wing sheeting, nacelle
planking; add soft block tail end, fin and rudder, wing tips and
ailerons. Complete the fitting of navigation and landing lights
and glaze landing light apertures in wing leading edges.
Fill in nose section, cabin, and fuselage top glazed sections with
soft balsa, lightly cemented in place so that these parts may later
be cut away to be used as molds for the acetate canopies. Make separate
molds for the gun turrets and tail gunner's station.
Sand entire aircraft smooth, apply 3 coats of sanding sealer, sanding
well between each coat; build up wing and stabilizer root fillets
with Plastic Wood.
Break out balsa canopy mold sections,
mount firmly on 1" x 1" balsa hand grips, dope and polish glass-smooth
and mold all acetate sections.
Cut out all windows
from fuselage planking and dope matt-black all interior woodwork
visible through windows and canopies. Fit cockpit details, pilots;
fit all canopies and gun turrets and glaze windows with acetate
sheet. With masking tape or adhesive-backed plastic sheet, cut out
and fit individual clear area window masks over all acetate sections.
This will take a little time but it's the only way of achieving
a really professional job.
Spray all unmasked acetate
sections light grey or green to give the appearance of internal
paint color. Fill and sand smooth all cracks and imperfections around
From now on all work will greatly affect
appearance of finished model, so take time to insure a good finish.
Build up cowlings from balsa, fit to nacelles and seal and
dope. Sand entire model smooth again. Cover model all over with
lightweight silk or paper, and apply three more coats of sanding
sealer, then at least three coats of clear dope, thinning dope progressively
each coat to achieve a really good basic finish. Dope should be
sprayed, but a careful brush job will do. Use fuel-proof dope throughout.
Apply thinly sprayed color dope in any authentic scheme.
Many photographs are available with either all-aluminum or olive
drab finishes. If you choose an olive drab finish, then another
cry from a scale modeler's heart: do not forget to apply a final
last coat of clear matt varnish - please, NOT glossy!
When all color is on, together with serial numbers and markings,
masks may be removed from glazed areas. Fit guns from aluminum tube,
windshield wipers from straight pins and aerials from thin nylon
thread. Test all systems and free up any working joints that may
be clogged by dope.
With India ink and a fine pen,
draw hatch detail onto model, taking care not to overdo it.
to watch to achieve a good finish: (1) Clean dope. (2) Clean, dust-free
brushes. (3) Clean, dust-free room, not too cold. (4) Clean, dust-free
model - wipe off frequently with clean cloth. (5) Let all coats
dry before applying next. (6) Make certain basic structure and clear
dope finish is really good before applying color, which should be
sprayed on lightly. Two coats of color dope should be enough. This
saves a lot of weight! (7) Don't panic! Take your time! The model
will not go together in three evenings, but the finished job is
worth the trouble.
Final weight trim is achieved if
necessary by drilling a small hole underneath the chin turret, filling
with cement and lead shot, until the model balances on the leading
edge just outboard of the nacelles. This hole is easy to plug without
marring the finish.
Test all systems again on the
flying field, with lines connected and all engines going, once you
have recovered from the effect of those four Cox's running wide
open! This model not only looks like a B-17, it sounds like onel!
Test throttle response, adjusting so that starboard engines throttle
down more than port engines. Open throttles wide, and as soon as
L.G. starts up, close throttles slightly. This will stop L.G. on
limit switches but has no noticeable effect on engines. Bring L.G.
down, stop engines, fuel up and flight test.
model to taxi out and keep her on the ground until speed is well
up, then "up" elevator may be applied on ground run to prevent nosing
over, but neutralize as soon as she lifts off. From then on you're
on your own, but you will find the B-17 easy to fly and "groovy".
And the joy of being able to haul those big wheels up forward into
the nacelles, and as the third engine falters to bring down the
wheels and touch down again for a perfect landing, applying up elevator
again as soon as she rolls. Approaches are easy on low throttle,
the engines still running fast enough to give good control.
Gear B-17 Control Liner Plans: Fuselage
<click for larger
Gear B-17 Control Liner Plans: Wing
<click for larger
Gear B-17 Control Liner Plans: Retracting Gear Detail
<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
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 September 30, 2012