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2-Stroke or 4-Stroke?
The first choice you must make in selecting an engine for your Cub is to decide whether you want to use a 2-stroke or 4-stroke
motor. From the reports that we have received from our customers, 4-stroke engines have proven to be much more popular for
the Cub than 2-strokes. In fact, a 4-stroke engine seems to bring out the best in a slow flying airplane like the Cub. That's
because a 4-stroke model engine produces its maximum power at a relatively low r.p.m., just like the full-scale Cub's engine. In
other words, it more closely duplicates the power curve of the full-scale motor. While a typical 2-stroke R/C sport engine will
normally run at between 10,000 to 13,000 r.p.m. in high throttle, a 4-stroke model engine runs about 7,000 to 9,000 r.p.m. in
high. That enables the 4-stroke to turn a larger, more scale size propellor than the 2-stroke model engine could. The large, slow
turning prop provides more pulling power for a slow flying airplane like the Cub, giving it an excellent rate of climb without
having excessive airspeed in level flight. A 4-stroke engine is the best choice if you want your Cub to have super realistic flight
performance.
In testing 2-stroke engines in the Cub, we found that a .78 - .90 size 2-stroke provided the best all round performance. Fly it
throttled back for realistic speed in level flight and go to full power for aerobatics. We also tried a schneurle-ported .60 2-stroke
in one of our Cubs. While it provided very realistic airspeed, most modelers would feel it was underpowered. Even though it
would loop out of level flight with no preliminary dive needed, and would cruise in level flight at near scale speed with 3/4
throttle, the climbouts and turns had to be kept very gentle to avoid a stall. A .78 - .90 size 2-stroke provides an extra margin of
safety. In conclusion, while a 2-stroke engine can fly the 1/4-scale Cub very well, they do tend to fly the model faster in level
flight than a 4-stroke would. You have to run them fast in level flight in order to have good climb performance.
We do not recommend converted "chain saw type" gas engines for this model. They tend to vibrate more than a precision made
glow engine and are usually too bulky to fit inside the cowling.
Regardless of what size and type of engine you decide to use, strive to keep your Cub as light as possible for best flight
performance.
ENYA .90 4-stroke
represents typical
installation of a single-cylinder 4-stroke
engine in the Cub. Motor is sidemounted
for easy starting and dependable Idle.
Uses a J'Tee #JT-64 Aluminum Engine
Mount, J'Tee #JT-ENS Muffler, and 15-6
prop. No dummy engine needed on this
side of the cowling.
O.S. GEMINI 1.20 twin-cylinder 4-stroke
engine mounted in the Cub. Note 3/8"
thick spacer between back of engine
mount and firewall, to provide correct
firewall-to-prop distance. Cowl is modified
to come apart In two pieces, ala the full-
scale Cub (upper section is removed in
pboto).
Webra .91 2-stroke
engine mounted
inverted in the Cub. C.B. Associates
15310 Aluminum Engine Mount, Slimline
#3401 Sport Scale Muffler with homemade
copper tubing exhaust extensions
(plumbing variety copper tubing from
hardware store). Inverted engines can be
difficult to start.
Mounts
No motor mounts are supplied in this kit because of the wide range of engines that can be used. A suitable radial firewall-type
mount (such as Tatone, Fox, CB, Hayes,etc.) should be available for just about any mass produced engine. The distance from
the front of the cowl to the firewall is adequate for most all .60 to .90 glow engines. Less common engines may require some
preplanning and modification in this area.
Mufflers
There is no one type of muffler that is best suited for the Cub. It all depends on the particular engine that you've elected to use.
You will have to figure out your own muffler installation. We have had good luck adapting the "exhaust manifold" type mufflers
(such as made by Tatone and Slimline) to most .60 to .90 glow engines. Usually they can be made to fit with just slight
alterations. Use copper or heat-proof rubber tubing to extend the exhaust pipes to the outside of the cowling.