R/C Airplane Engines

Radio-controlled hobbies for me means R/C airplanes, because that is where I got started and at that time R/C airplanes were mainly what was available.  I was fortunate enough to live in a community that had a well established radio controlled airplane modelers club.

    I joined the club after purchasing a kit and started building it.  I soon realized that the kit I had purchased was not only  very difficult to assemble, it was not designed to be a trainer.  I got acquainted with one of the members of the club and he suggested a different model and was willing to work with me all through the building and setup process.  Consequently, I was successful in getting my first model up and flying without any accidents.   This is why I emphasize the advantage of finding an experienced modeler to help you get started.

    I will cover some of the things you need to consider when selecting the engine for your radio controlled model airplane.  First, the manufacturer of the kit or model will have suggestions as to the size and sometimes even the brand and model of the engine that the R/C airplane was designed around.  If you wish to experiment with something different than what is specified by the manufacturer, proceed with caution and get help from your local expert.

The weight of the engine, the physical size, the power rating, and the required propeller size and pitch can greatly affect the balance and thus, the overall performance of the model.  This is not to say that you shouldn’t do your own experimenting, because modelers have been able to improve engine performance and therefore achieve greater overall performance of the aircraft.  But, it is probably advisable for beginners to stick to the basics.

Two-cycle versus four-cycle engines is a controversial subject and it has been since they started making the 4-cycles somewhere in the late 1970’s to the early 1980’s.  The 2 cycle engines have been around for a lot longer and they have been proven very reliable and many models were designed around them.    The 2 cycle or as some folks say “2 stroke” engines run at a higher rpm than the 4 strokes.  Some R/C fliers believe the 2 cycle engines respond quicker to throttle changes.  They also are noisier and in some areas it is a requirement to have them be muffled to reduce noise pollution.  The performance of the time proven 2 cycle engine is very predictable and reliable when the engine is properly  “broken in”  and tuned.  We will investigate how to break in and tune the engine as we get closer to flight time.

    Generally speaking, at least for R/C model planes, the 4 strokes are usually sized bigger than the 2 stroke.  For, example, if the model maker specified a .45 sized 2 stroke for a certain model, you would probably use a .60 size 4 stroke.  However, the 4 stroke will move the plane the same as the smaller 2 stroke by swinging a bigger propellor at a lower rpm.  This gives you the advantage of having a quieter and more realistic sounding model.  They do require a little more technical ability to tune up and maintain.  You will have to decide on which seems to best fit your particular situation.    

Always keep safety in mind.  One of the things I strongly reccomend to consider when selecting the engine is to get one with a remotely adjustable needle valve.  Originally, they all had the needle valve adjusting screw at the front of the engine.  That required your fingers and thumb to be very close (within 1/2 inch) to the spinning prop.  These engines need to be adjusted when running at full throttle and many times people have had their knuckles nipped by the prop.  Nowadays, a lot of manufacturers are mounting the needle valve at the back end of the engine making it much safer to tune.  Another thing you may need to consider is whether the engine has a built-in fuel pump or if it is gravity fed.  Usually for a trainer, a gravity fed fuel system is adequate, but for a high-performance aerobatic or 3D model you may benefit by having a positive pressure fuel system. 

    One last thing on getting the correct size engine for your model.  Radio controlled model aircraft are usually built according to the size of the motor or engine and it is advisable to follow the model manfacturers instructions for sizing and installion.

    Till next time think about what has been covered so far and and check the earlier blog posts just for review.  I have covered a lot of information and I don’t want you to get overwhelmed.   I encourage all readers to comment on the posts and make suggestions, ie, am I missing anything, are the posts to detailed, not detailed enough, etc.  I want to make your experience with this blog as friendly and informative as possible.