GREAT PLANES Super Sportster 20, Instruction Book

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SUPER SPORTSTER FOUR-CYCLE CONVERSION INSTRUCTIONS
Our popular Sportster series is a "natural" for 4-cycle experimentation. The unique looks of a Sportster
just screams "4-Cycle" and the lightweight air-frame and symmetrical airfoil means the Sportster design
will make the most of the 4-cycle fun. Whether you want to just "putter" around the sky, or loop, roll, and
snap, the Sportster/4-cycle combination is unbeatable!
Four cycle engines offer many benefits — their quiet, realistic sound is pleasing to modelers and non-
modelers alike. High torque allows the use of high pitch or large diameter propellers for a new style of flight
characteristics. They are also very fuel efficient for economical operation.
On the other side of the coin, 4-cycles are larger and heavier than equivalent power 2-cyles. That means
some special care must be taken to avoid a nose-heavy airplane, such as moving the firewall and radio far-
ther back than normal. We'll help you with that task with these instructions.
Because of their similarity in design, we are writing these adaptation instructions for all three Sportster
designs (Super Sportster 20, 40 and 60). Where dimensions or measurements differ, read the appropriate
section for your Sportster.
CHOOSING YOUR ENGINE
It's difficult to say exactly what the optimum engine size is for your Sportster. The old rule of thumb was
to choose a 4-cycle engine with 1-1/2 times the 2-cycle displacement for equivalent horsepower. But recent
advancements by engine manufacturers have brought the power of 4-cycles way up, and the weight of the
engines down. One good example is the Enya .46 Four Cycle. This engine weighs just a fraction more than
most 2-Cycle .40's and it produces comparable power and thrust.
SUPER SPORTSTER 20: For this airplane a Saito .30 will give comparable power to a 2-Cycle but weighs
more and is larger than a 2-Cycle. See page 33 for a drawing of the Saito .30 in a Sportster 20.
SUPER SPORTSER 40: For this plane you can choose between .40 and .60 size 4-cycle. A .40 will give
docile flight performance. A .60 provides plenty of thrust, but with a significant increase in weight and size.
The .60 will fit but it's going to be tight. See page 34 for a full size drawing of the Enya .46 mounted in the
Super Sportster 40. The OS FS-61 is shown on page 35.
SUPER SPORTSTER 60: This model is well suited for the .60 to .90 size 4-cycles. Some of the new .60 size
engines are putting out high thrust that will make a light Sportster 60 perform nicely. For maximum thrust
with a small increase in weight, there are several small case .90's on the market that will fit in the Sportster
60. Pages 36 and 37 show the OS-FS 61 and the Enya .90 mounted in Super Sportster 60.
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