How Does a Tuned Exhaust System Impact My Aircraft’s Engine Performance?
Your plane’s exhaust system greatly influences the fuel efficiency, power, and performance of your aircraft’s engine. For this reason, no aircraft owner should skimp on the quality, design, and maintenance of their exhaust system.
A tuned exhaust system is an option for some aircraft piston engines. The installation of a tuned exhaust system improves an aircraft’s engine efficiency, power, and overall performance. To better understand how it works and differs from a traditional engine, we need to know how a traditional engine works.
How Does a Regular Aircraft Combustion Engine Work?
Your aircraft’s engine goes through four “strokes” during the combustion process: the Intake, compression, combustion, and exhaust strokes.
An “intake” valve is located at the top of the cylinder. During the intake stroke, the piston moves down the cylinder, sucking a new fuel/air mixture through the open intake valve.
The intake valve then closes, and the piston moves back up the cylinder, compressing the fuel-air mixture, at which point a spark from the spark plug ignites and explodes the compressed mixture. This explosion forces the piston back down the cylinder, producing the necessary power to turn your prop.
Lastly, the exhaust valve opens as the piston pushes out most of the spent fuel-air mixture, and the cycle starts all over.
As the spent fuel-air mixture leaves the cylinder, it is routed through a set of headers, into a common collector area, and pushed out the tailpipe by the remaining pressure.
Like a garden hose with a kink in it, pressure builds up throughout the exhaust system, making it more difficult for the spent gas mixture from the next cycle to leave. So now, the exhaust isn’t flowing as freely as it should, leaving some exhaust in the cylinder, taking up space better used for a clean fuel/air charge.
Traditional Exhaust System vs. Tuned Exhaust System
Traditional exhaust systems were originally designed to remove gases from the cylinder and out of the nacelle. But later on, manufacturers added muffle and heating systems.
General manager Darren Tillman, an A&P and test pilot for Power Flow Systems said “Traditionally, the exhaust system on an engine was purely functional. It removed gases from the cylinder and got them out of the nacelle. Then the FAA came along and said ‘we need to muffle it’ and so they got rudimentary exhaust systems. And then you got pilots that didn’t like to freeze, so the manufacturers had to come up with a heating system. So they wrapped a piece of metal around the other metal and came up with a heating system. But everything was sort of a band-aid approach. It was an afterthought.”
While the traditional exhaust system works out fine, there is still some room for improvement. For instance, with the standard design, only about 80% of the cylinders are emptied with gas, meaning the remaining 20% goes to waste.
By contrast, a tuned exhaust system allows the gases from the cylinders to evacuate more efficiently thanks to the “ideal” length of tubing, which is longer than the traditional system.
Take note that both heat and pressure create waves that escape every time the exhaust valve opens. However, making the tubing longer gives these waves and pulses more time and space to travel, so they have no or very little influence on one another by the time the valve is open.
The optimal measurement for the tubing depends on the exhaust system. Additionally, the four tubes meet at one collector, and after this point, they are of the same length. These tubes then connect to the muffler and out the system.
What is the Main Benefit of a Tuned Exhaust System?
A tuned exhaust system allows an aircraft engine to empty and suction out the cylinder more effectively, resulting in less gas that goes to waste just to overcome the inertia.
The engine also enjoys a more efficient fuel burn and needs less throttle to get the same RPM or travel distance as the traditional exhaust system.
But since more of the exhaust gas is being emptied from the cylinder, the EGT (which is the temperature of the gas turbine engine’s exhaust system) is a bit higher compared to the traditional exhaust system.
Maintenance Tips For Aircraft with Tuned Exhaust
If your engine has a tuned exhaust, the inspection items should include the engine control cables, cowling, and similar components.
Pay close attention to the external surfaces, check them for dents, cracks, and other signs of wear and tear. The same rule applies to the hoses, leads, flexible air ducts, and fuel lines, which should all be protected with heat shields.
During an inspection, also pay close attention to the weld points, the heel of each bend, and the spots prone to leaks and cracks, which you can pinpoint by conducting a pressure test.
Other components you should check on during an engine analysis: the muffler’s removable insert, the clamp attached to the muffler, and the first-generation heating shrouds.
Additionally, you should always keep your exhaust system clean and in its best condition through regular inspections and timely maintenance and repair.
A Final Word About The Tuned Exhaust System
The traditional exhaust engine has worked fine for years. There is always room for improvement, which is where the Tuned Exhaust comes into play.
The main goal of the tuned exhaust is to more efficiently evacuate the exhaust gases from the cylinders. With a tuned exhaust system, you are always suctioning out and emptying out the cylinder more effectively. So less gas is wasted to overcome the inertia.
The engine gets a more complete fuel burn. The effect in the cockpit is that it will take less throttle to get the same rpm than you are used to. This means less fuel flow.
The EGT ends up going up a little bit because more of the exhaust gases are being emptied from the cylinder. But overall a tuned exhaust will help save fuel, promote a smoother, cooler, and finally more powerful running engine.
Source: Aviation Pros