Turbo-normalization : A Summary

There are distinct advantages to flying at high altitudes. These include decreased drag, faster true airspeed, and higher tailwinds (when applicable). However, these advantages bring with them a major disadvantage for any aspirated engine: a lack of air. Air pressure decreases at higher altitudes, and does so quickly. For example, at 18,000 feet elevation, 50% of the entire atmosphere is beneath your aircraft. This means there is much less oxygen for your engine to burn, resulting in a deficiency of horsepower. So, how do aspirated engines, engines that require oxygen to function, solve this problem? There are multiple ways, one of which is called turbo-normalization.

Turbo-normalization is the process of using a gas turbine to power a compressor which increases the engine intake manifold pressure. A turbo-normalization system automatically limits manifold pressure to that of sea level at all altitudes up to the system’s maximum functional altitude. This does not mean that at this altitude the system will not operate, but it will not be able to maintain sea level manifold pressure. Therefore, maximum sea level engine power is available up to this altitude, sometimes called the system critical altitude. Above system critical altitude, manifold pressure will decrease, subsequently decreasing the system power as well. Most turbo-normalization systems have a critical altitude of roughly 20,000 feet. Above 20,000 feet the manifold pressure will decrease approximately one inch for every 1,000 feet of altitude.

Turbo-normalization is often confused with turbo-charging. While they do share certain characteristics, they have major distinctions. First, let’s look at their similarities. Both turbo-normalizing and turbo-charging systems involve compressing outside ambient air to make it denser and provide the engine with more power. Second, in both systems, the degree to which the air is compressed relies solely on design choice dependent on characteristics such as horsepower needs, expected altitudes, and more. Lastly, both turbo-normalization and turbo-charging systems use an exhaust driven turbine to drive the centrifugal compressor. Some units feature compressors rotating at rates as high as 120,000 RPM. The compressor is perhaps the most important of an aspirated engine as it essentially creates air where there is none.

So, what is the difference between turbo-normalizers and turbo-chargers? It is quite simple. While turbo-normalization systems are used to bring intake manifold pressure down to sea level, turbo-charging systems are used to bring intake manifold pressure above sea level. Simply put, because the air to fuel ratio within an engine must be maintained within a relatively small range to maintain constant combustion, internal combustion engines are considered ‘air burners.’ By increasing the amount of air in the engine cylinders, an increased amount of fuel is burned. As power is created through burning fuel, the engine horsepower increases. The tradeoff of this is increased engine wear due in part to both higher operating pressures and increased heat creation.

In turbo-normalization systems, though engine brake horsepower remains relatively constant (up to system critical altitude), the available thrust horsepower also incorporates propeller efficiency, as represented in this equation: ThPa = nBhPa. This equation denotes that thrust horsepower (ThPa) is equal to propeller efficiency (n) plus brake horsepower (BhPa). A similar concept to turbo-normalizing is ground boosting. Ground boosting is essentially the same, though it uses more pressure. Ground boosted systems usually run at manifold pressures between 31 and 45 inches, which is much higher pressure than turbo-normalizers.

The turbo-normalizer is a critical system in aspirated engines, which require sufficient intake oxygen to operate properly. Without enough air pressure, an engine cannot create the necessary horsepower to maintain flight. This would greatly limit the altitudes an aircraft could fly at, or ground an aircraft completely. While the turbo-normalizer is a less commonly-known system, its importance cannot be overstated. Despite this, the turbo-normalizer is not without its drawbacks. Because of increased fuel consumption at higher operating powers, range is often decreased, sometimes significantly. Furthermore, consistent operation at higher power will expedite the process of engine wear. Just as with all aviation components, turbo-normalization requires compromise. Given their important role, all turbo-normalizer parts should come from reliable and trustworthy sources. If you are in need of turbo-normalizer components or other crucial aircraft components, look no further than Fulfillment 3Sixty.

At Fulfillment 3Sixty, owned and operated by ASAP Semiconductor, we can help you source all types of turbochargers, cirrus heat shields, gaskets, and other general aircraft parts and deliver them with some of the industry’s best lead times. Additionally, as we are the only independent distributor with a strict No China Sourcing Policy, we can ensure that each part you buy from us will come from a trusted manufacturer. We’re always available and ready to help you find all the parts and equipment you need, 24/7-365. For a quick and competitive quote, email us at sales@fulfillment3sixty.com or call us at 1-480-504-1299. Our team of dedicated account managers is standing by and will respond to you in 15 minutes or less.


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March 11, 2021

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