Nitro RC boat motors
Nitro rc boat motors, also called 'glow plug' or 'gas' motors, can be purchased in several different forms depending on the need for the model.
By far the most common, and the one that you'll find in nearly all RTR (Ready To Run) entry level 'sports' boat, is the 2 stroke nitro motor similar to those used in rc airplanes and rc cars.
The basic body of the engine is the same as those used in planes and cars but there are a couple of noticeable changes; firstly on a nitro rc boat motor the cylinder head is water cooled as opposed to being air cooled and secondly there is a flywheel on the end of the crankshaft.
A fairly typical 2 stroke nitro rc boat motor
is shown below:
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You can clearly see the water cooled head and flywheel. To cool the cylinder head silicon or plastic tubing runs from the water pick-up, located beneath the boat close to the propeller, to the inlet on the head. A second length of tube is attached to the outlet on the head and exits through a small hole drilled in the side of the boat somewhere near the motor.
As the boat speeds along, pressure around the propeller forces water up through the pick-up, along the tubing and around the cooling head before exiting out the side of the boat. As the water passes around the head it takes away a large amount of heat from the engine.
The flywheel on a nitro rc boat motor is there to make starting the motor easier. A groove runs around the flywheel and this is to accommodate a belt which is used with an electric starter.
Some nitro rc boat motors are pull start which is a much better option, because it means that you don't have to use a starter. Pull start motors have a length of cord attached to a sprung-loaded recoil mechanism on the back of the crankshaft, with a handle. To start this kind of motor, you simply grab the handle and pull the cord until the motor fires up.
A pull start nitro motor for an rc boat is shown to the right.
A pull start motor in use is shown in the following picture. You can see that a tuned pipe is being used to improve performance and you can also see the silicon tubing entering and exiting the water cooled cylinder head (the 3rd tube is the fuel line):
Other kinds of nitro rc boat motors
An increasingly popular choice for larger nitro rc boats is the outboard motor. This uses the standard 2 stroke motor shown above but with a few changes to its design.
The motor is 'up-ended' with a flexible prop shaft exiting from the back of the motor. The whole unit of motor and running hardware is simply fixed to the very back of the boat. An example of a nitro outboard motor is shown below, again clearly showing the water pick-up and tubing running to the cylinder head:
And another kind of powerplant is the jet drive. Again, a basic 2 stroke nitro motor is used but instead of normal running hardware and a propeller, the motor drives a very small prop called an impeller that's located inside of a tube, or duct.
The impeller spins at very high RPM and sucks water in through the front of the duct and expels it out the back with an enormous force, pushing the boat along.
Jet drives are becoming more popular and are often used in racing boats. One advantage of a jet drive over a normal nitro motor with propeller is that 'reverse buckets' can be fitted; these drop down over the exit of the duct (requires a 3rd channel on the radio control gear) and so the water being expelled pushes against the bucket and so is forced forwards off the bucket, thus pushing the boat backwards.
Tuned Pipes
When you buy a nitro rc boat motor, the chances are that it will come with the standard muffler. These are fine for general use but they can restrict the power of the motor and hinder performance.
Because of this, 'tuned pipes' are often used instead. These are much longer and greatly increase the power output of the motor compared to how it performs with the standard muffler, because there is far less restriction of the gases trying to exit the motor.
Many different sizes and shapes of tuned pipe are widely available but of course you need to get one that's compatible with the motor that is in your boat. Tuned pipes aren't necessary for your first nitro rc boat, but you may want to upgrade as you gain more experience and start looking for more speed. You can see the difference between a tuned pipe and a standard muffler in the picture below:
Nitro motor sizes
All nitro motors - whether for rc boats, aircraft or cars - are referred to by their size as a number. This number is the cubic capacity of the motor and the most common way is to give the number of cubic inches (cu.in.). The other way is to refer to the motor in cubic centimeters (cc).
A common size nitro motor for an entry level 'sport' boat is the .16 - this means that it's .16 cu.in. but is just referred to as a '16'. Another size often used is the .18, or '18'. These sizes in cc are 2.67cc and 2.99cc respectively.
Nitro rc boat motors can of course be bought in many different sizes, and the size used depends solely on the size of boat that it's going into.
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Related pages
Nitro RC boats - an overview and some examples.
Electric rc boat motors - examples of electric motors for rc boats.
