Multi-Engine Rubber Power
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by Bob Isaacks and Andy Mitas
August 10, 2005
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SFA
is pleased to present two slightly different
perspectives on the subject of multi-engine
rubber models. Andy Mitas shares his views
as a prolific semi-scale sport modeler, while
Bob Isaacks discusses his point of view as
a competitive FAC scale modeler.
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SELECTING
YOUR SUBJECT |
BOB:
My primary criteria for selection is aesthetics.
I cannot conceive spending hours building an ugly
airplane. For me it has to have visual appeal, a
good color scheme and provide plenty of opportunity
for adding eye catching detail. My A-20
Havoc (Mike Midkiff design) easily supplied
all these factors. The WWII camouflage with invasion
stripes, the nose art and the large (Jumbo) size
supplied plenty of opportunity to add detail.
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Another consideration is potential flyability.
The Havoc has a long nose
moment, nacelles long enough for a decent
motor run, a C/G near the center of the nacelles,
a mid wing, and tail surfaces large enough
to provide stability without the need to scale
“up.” |
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Bob's A-20 Havoc
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A-20 Havoc
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Airplanes that I would avoid are the “Mosquito”
(nose moment too short), Sea Hornet
(nose moment too short), and the Grumman
Skyrocket (nacelles too short and short
nose).
Airplanes that I would consider for construction
are the DeHavilland Twin Otter,
The P-38 Lightning and the DeHavilland
Comet. There are literally hundreds of
others with long nose moments (good for balance),
turbo engines (good for long nacelles), or twin
fuselages (even more room for motors). Many old
time airliners had good moments and the added
stability of high wings, plus fuselage decorations
to die for!
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P-38 Lightning |
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ANDY:
Bob’s suggestion of the DeHavilland
88 Comet is a good one. It has attractive
outlines, good proportions, and long nacelles. If
you’re going to build a scale model you have
to consider the usual limitations – adequate
tail moment and stab size. With multiengine models,
however, you must also consider nacelle length (this
eliminates many airliners) and space between fuselage
and nacelle to accommodate a larger-than-scale prop.
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It’s a question of the length of motor run.
For me to get a pleasing flight of half a minute,
each nacelle must be long enough to accommodate
1000 turns of a motor or more, and the prop needs
to have enough blade area and pitch to get 30 seconds
of running time out of those 1000 turns.
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Andy's Dash 8 |
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On my simplified Dash 8 airliner,
I “cheated” on both of these dimensions.
I made the nacelles longer than they should be,
and placed them farther out on the wings. You can
look at these changes the same way as enlarging
stab area. However, it will likely cost points in
scale judging.
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There’s another unsightly but useful option.
Many flyers build the nacelles to scale and leave
a small hole in the back. This makes it possible
to install a motorstick that extends well beyond
the nacelle. With rubber band or tissue tube devices,
the motorstick may be removable.
What about sport and duration models? Almost all
well-proportioned models can fly under twin-motor
power. You can build nacelles and stick them to
the wings, but it’s even easier to just use
motorsticks. Larger models like P-30’s can
accommodate four motors with no problem. |
I stretched the wingspan, stab span, and fuselage
of the Peck One Nite 28 P-30 to
create my Tremendous Four, a simple
sport model with four motorsticks. |
Andy's Tremendous Four
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DH-10 Bomber |
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WWI subjects:
Almost all twin-engine biplane bombers
had tiny nacelles. If you’re willing to use
motorsticks (explained later in this article), something
with a big stab like a DH-10 would
be good.
Golden Age
subjects:
The Short Singapore
would be a good choice. Not as good are the HP
Heyford (small nacelles) and Dragon
Rapide (small nacelles and small stab).
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Short Singapore
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WWII subjects:
Good choices would be the Yak-2
(short nose but nacelles are long enough to compensate),
the P-38, or the A-20.
Not as good are the Bristol Blenheim
or the B-17 (although the latter
has been done, and very well too!).
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Yak 2 |
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Postwar
Airliner subjects:
The Bristol Britannia would
work well. Also good is the Lockheed Electra
– proven in BMFA competition by Richard Crossley
(but the motors are four times the hook-to-peg length
and motor run is still short). Not as good are the
Martin 202 or the Boeing
Stratocruiser.
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Bristol Britannia |
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Modern
subjects:
Good choices are the Dash
8 (also proven in FAC competition by
the great Chris Starleaf), Antonov turboprops,
Fokker 27, Cessna Titan,
and Piper Cheyenne. Not as good
are the Dash 7, Saab
340, Dornier 328, and
Beech King Air.
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