O.S. 120AX Special
When airplanes get to, or exceed, the 90- to 100-inch-span range, you really
want to think reliability when it comes to power systems. For me, nothing says
quality and reliability like an O.S. engine. Sure, you can go with an electric power
system, but by the time you add a 5- or 6-cell LiPo pack (or two) plus a high
voltage ESC and a good battery charger, you might as well keep it simple and
stick with a glow engine. All you need is a glow plug and a gallon of fuel, and
you’re good to go.
For the Rascal 110, I wanted a high performance, 2-stroke engine with plenty of power but
compact in size enough to enable it to fit into the Rascal’s narrow cowl. ;e O. S. 120AX Special
is just the ticket.
;e 120AX Special is a ringed engine and it comes with an O.S. no. 8 glow plug, a 70D
carburetor with a velocity stack, a needle valve extension, and an excellent instruction
manual. It also features a 0.1mm head gasket to increase the compression ratio. ;e stock
engine requires an E-5020 Power Box Mu;er available from Tower Hobbies.
For the review plane, I used a Master Airscrew 16x8 propeller and fueled the engine with
a Morgan Cool Power 15% nitro and 17% synthetic oil mix. ;e combination is extremely
satisfactory and the engine has been a joy to operate ever since I pulled it out
of its box. A really nice feature is that the E-5020 Power Box Mu;er is much
like a standard setup with an exhaust extension and expansion chamber
that’s clear of the cowling. ;is makes for a clean appearance with a
minimum of cowling trimming required. With a max rpm of 9,300, the
firewall-forward portion of this project proved excellent performance
with a minimum of fuss. So, what’s not to like?
Bore: 1.197 in.
Stroke: 1.083 in.
RPM range: 1,800-9,500
Output: 3.155hp at 9,500rpm
Crankshaft size: UNF5/16-24
projects, I have been using the relatively
new servos from Savox USA. I like these
servos a lot and so far, they’ve performed
extremely well. For the Rascal 110, I used
five Savox 0254MG servos and one JR servo
for throttle. As far as installing the servos,
I would change the way Sig orientated the
flap servos. They have the output shafts
of the servos going in opposite directions,
which means if you have a computer radio,
you have to mix the channels together and
reverse one of the servos. You can also use
a servo reversing Y-harness like I did. This is
a quick and easy way to deal with the con-
trol direction issues. I used one from Expert
(EXRA325), as I had it on hand.
Safety first! Al ways have someone help hold your plane while you crank up the engine.
;ere are two servos in each wing panel to control
ailerons and flaps. Installation is quick and easy.
the engine cowl. The muffler and throttle
linkage are nothing to worry about, and
to help get to the needle valve within
the cowl, I used a flexible cable extension
attached to the main needle and threaded
it through a small hole in the side.
As with everything else, the landing
gear is nice and sturdy, easy to install, and
comes painted to match the covering. I
also love the fact that the wing struts have
scale-like fairings on the ends for a clean
appearance. Yes, they are functional so
don’t even think of flying without them.
If you want to treat yourself to a very good-quality product from a company that has
a reputation for producing great-looking
and easy-flying planes, then I think the
new Sig Rascal 110 ARF is a great way to get
into the air. As with all good things, you
get what you pay for. And this one is worth
every penny. ;