Model Airplane Engine Types
There are a variety of engine types available to us and every few years a
type we never had before becomes available. I can not predict what
next, but there are already many engine types to choose from.
Actually, I predict that electric power is going to become more popular than
internal combustion. The technology has improved to the point of
having lightweight batteries that provide strong power for reasonable flight
times. Electric planes have power comparable to glow to include
extreme speed planes.
In coming years, the price for what is now considered to be high-end
equipment should come down to where it more affordable. The quieter
propulsion systems, comparable performance and lack of exhaust mess all over
the airframe should make electric much more enticing. In fact, in some
places, E-power may be mandatory in order to keep flying fields.
If you are a beginner and you plan to fly a gas-powered
trainer, then my
recommendation is a two-cycle glow engine for your first plane because
almost anyone at your local club will be able to assist you with it.
However, you may want to go straight to electric power. That way you
will not have spent money on support equipment for glow and then have to go
back and purchase the equipment for electrics.
2-Cycle engines are by far the most
popular type of model aircraft engine. They are simple,
inexpensive, powerful and reliable. These engines are capable of
turning very high RPM and are the engine of choice for propeller
driven speed aircraft. Ducted fan aircraft depend on high fan
RPM to produce their thrust and only a two-cycle can produce these
kinds of RPM.
4-Cycle engines started
becoming popular in the 1980's and have become well-established in the
R/C community. They were originally billed as sounding realistic
which they do not. They do not sound like full scale aircraft
engines, but they are much more pleasant to listen to.
more torque than two-stroke engines while turning lower RPM. That means
they are better for aircraft that require strong vertical climbs and more
consistent airspeeds. Four cycle engines are as reliable as two-cycle
engines but are more complicated with more moving parts.
Lastly, four-stroke engines are more fuel efficient than two strokes. A
given size 4-stroke will run much longer on a tank of fuel than the same size
For many of our applications, a two-cycle is used when a four-cycle would be a
better choice. In fact, it is my opinion that with the exception of models
that need high rpm and trainers, a four-stroke is always a better choice. However, a comparably sized four-cycle engine is more
When large aircraft first started appearing at flying fields they were powered
by converted chain saw and weed-eater engines. Now there are a several
manufacturers building gas engines specifically for R/C aircraft. The fuel
for these engines is much less expensive than glow fuel which (in theory) helps
offset the cost of flying larger models.
Personally, I think that gas engines are the most realistic
sounding engines other than turbines. They have that deep, throaty growl
that reminds me the old Stearmans.
While any engine can inflict serious bodily harm, these
engines in particular can remove limbs and should be treated with extreme
You could fly model aircraft for your entire lifetime and never see an aircraft
with a diesel engine at your field. For whatever reason they just are not
popular. I have no practical experience with these engines, but they sound
like they have a lot of advantages over other types.
For example, they are capable of swinging larger propellers which would be of
great benefit on scale models of early types such as WWI aircraft.
Additionally, they do not require the use of a glow driver and battery.
I would really like to use a diesel on a small Rubber to R/C conversion.
However, the only available choices are far more expensive than a comparable
two-cycle and there usually is not anyone around who can provide guidance to
those of us who have no experience with these engines. Nevertheless, I am
going to have one at some point in the not too distant future. I will let
you know what I learn.
As far as I know there is only one Wankel engine produced for model aircraft.
That is the .30 Wankel manufactured by O.S. Max. I have one and was
pleased with it is performance in every area except fuel consumption. It
burns fuel so inefficiently that I have decided it is strictly a novelty engine
and I display mine in a glass case.
A true turbine engine in a miniature size.
These engines are very powerful and sound exactly like their full-size
counterparts. Although very expensive, they are becoming more
popular among those who like fast aircraft or build scale models of
These engines are very powerful and loud.
They are generally only used for speed models as they have no way to
throttle them. Additionally, they can be very dangerous and are
outlawed by most R/C clubs.
Beck Technologies has a lot of information
about pulse jets as well as plans, videos, a forum and other information. I know jack about pulse jets
so I can't say if the information is good quality or not but the videos give me the impression the man knows
Many multi-cylinder piston engines are being manufactured. They are available as
horizontally opposed , Inline, V and radials. Generally these engines have
less vibration than a comparably sized single, but they also have less power for
the same total displacement.
Selecting the "Right" Engine for Your Model Aircraft
Normally I choose the engine at the top of the range recommended by the
manufacturer. For example, if the kit suggests an engine from .25 - .40
then I will use a .40 or .45. The only real exception to this are 1/2A kits
that I will normally put a .10 or a .15 in if I think the model can handle it.
Because a comparably sized 4-stroke engine is less powerful than a 2-stroke, the
rule of thumb is to use a 2-stroke of about 2/3 to 3/4 the size of a 4-stroke.
For example, if a plane is designed for a .45 2-stroke, a .60 4 stroke can be
substituted. If a plane is designed for a .90 4-stroke, then a .60
2-stroke can be substituted. 4-strokes are more fuel efficient so if you
make a swap like this, the tank size can remain the same.
I also buy name brand engines. They are all good. Aircraft engines
are like cars. Some people swear by Ford and others by Chevy, but they all
work the same. What I do not buy is store-brand engines or clones.
The reason for that is I do not know who actually made them and they all look
suspiciously like O.S. Max engines.
What that means to me is that O.S. spent the money to develop the engine
and then someone else bought one, took it apart and measured it and made a
clone. For them, the development cost is a fraction of what OS paid and I
just do not think it is ethical and it might even be illegal. Regardless, I
just do not buy them, but that is my personal attitude and you can take it for
what it is worth.
I generally do not use tuned mufflers — commonly called tuned pipes which are
closely related, but different. The cost of a tuned system plus the engine
is generally same as or more than the cost of the next size engine. I
do not see the point in adding the headaches and complexity of a tuned system to
an aircraft when I can just buy the next size engine instead. If I already
have the engine, then I may purchase a pipe for it — especially if a larger
engine will not fit the airframe.
Exceptions to my philosophy might be a
competition event where engine size is limited. Another exception might be
if you are building a speed-demon. Speed comes directly from RPM so a
larger engine is not going to get a lot more speed, but it will give a better
climb and more power for hovering, etc. But if you want to go fast, there
is no substitute for RPM — exactly what a tuned system is designed for.
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Copyright © 2003 Paul K.