By: Rick Klages 2-2009
Today’s model helicopter engines vary from their counterparts even just a few years ago. Unless you are very familiar with today’s high quality and high performance r/c helicopter engines, choosing the proper exhaust for you application can be a daunting task.
To explain some differences and help you decide which exhaust to purchase I have put together some information to help you make a better decision.
As with most purchases it usually holds true that if an item costs more it is usually better. This is true with exhaust systems as well. However this does not mean you need to spend top dollar for the best in every helicopter application.
Let me explain about mufflers, tuned pipes, and what is most common today-the tuned muffler. In the early years of modeling it was apparent that some sort of noise control was needed on our model engines. At that time performance was not the issue it is today because flying styles and helicopter evolution had not reached the high performance and the radical styles of flying that we now see. Mufflers of the era where just that; noise control devices with little thought as to maximum engine performance. They were simple heavy and unsightly devices that served their purpose to some degree. Next came the tuned pipe setups that increased the engine performance but at the expense of noise. These devices were shaped to maximize the exhaust flow both to and from the engine using resonating sound waves created by the engine to increase the flow of the fuel/air mixture. They were designed much like the tuned exhaust systems still found on many of today’s high performance two-stroke motorcycles. It takes countless hours of experimentation to create a pipe that works well at high rpm yet still provide a reasonable and reliable idle and transition throughout the entire rpm range. This is related to the final cost of the product. Tuned pipes usually were two piece units that included a header that attached to the exhaust port of the engine and the actual “tuned pipe” that was connected to the header via a short piece of silicon tubing. The pipe was slid in and out of the silicone coupler until the pipe “peaked”. This was at the point where engine performance was maximized and referred to as being “on the pipe”. It usually took several try’s to get it optimized and could become frustrating to many users. The drawbacks were usually glow plug life was sacrificed to a few flights and engine idles were not as reliable as we expect in an r/c helicopter. Also they were usually very large and bulky as well as noisy.
With today’s noise restrictions at most r/c flying sights they are no longer acceptable.
 Fast forward to today. With the introduction of the wild 3-D type flying common today, exhaust engineers needed to design a more compact, lighter and better performing exhaust system that not only gave optimum power and reliable throttle control, but also a system that controlled noise to acceptable levels. This is where today’s “tuned mufflers” came on the helicopter scene.
Tuned mufflers are a hybrid between a tuned pipe and a muffler. Most people today refer to them as just a muffler, which they are not. Engineers at various exhaust manufacturers spend countless hours using very sophisticated computer programs and expensive test equipment to optimize each tuned muffler in regard to each specific engine they are creating an exhaust system for. After the R&D they again spend considerable time “field” testing these exhaust systems to make sure they operate as designed in a real world environment. The systems are tested for not only performance but also durability and longevity. Also they must work with fuels containing various amounts of nitro.
With this small amount of background info lets now talk about which “muffler” is correct for your application.
If you are a beginning pilot the choice is not as critical. You can use anything from the stock exhaust that may come with your kit or purchase any of the inexpensive mufflers available from various manufactures. Of course you may also opt for a premium exhaust that you can grow with as your skills progress.
For the scale pilots, the above is also true for you since most of your flying will be “scale type” and you will not need that last drop of power from your engine. Reliability is your main concern and most of today’s choices will suit your needs.
For the aggressive 3-D pilots your money will be well spent considering the “premium” exhaust systems out there. These offer you high performance, light weight, and consistent engine runs flight after flight. They also have the most aesthetic appeal of any available.
There are many manufacturers today with reputations that are stellar and have been designing and producing high quality mufflers for years. Some companies are dedicated to only muffler production and produce cutting edge muffler systems for each and every engine specifically. This should be your choice for if you want the best available.
 Single piece or two piece design? This is a common question. While most of us prefer a single piece design for their bolt on convenience, do not be afraid if you can only find a two piece design for your specific application. They are a little more work to install and maintain but they also offer more protection to your engine’s manifold and somewhat more vibration protection as well because of the isolated dampening system they utilize. Very few incidents are seen as a result of a muffler failure today. Most companies have very good replacement warranties as far as product failure. This does not include crash damage of course.
Most manufacturers include their choice of a gasket system and some use no gaskets at all. I have found that if a gasket is needed that it’s very hard to improve upon an aluminum gasket. They are leak free and allow the muffler to slightly “embed” itself both to the engines manifold and the muffler itself. Try to stay away from silicon or gasket compounds as they eventually fail and your muffler will loosen and leak. The fiber gaskets provided with some mufflers also work well but do not last as long as an aluminum gasket.
Click here to view our selection of mufflers and exhaust accessories.
Good luck and happy flying.
Rick Klages 2-2009
rick@heliproz.com
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