033 - Aircraft Turbocharging + More | Aviation Podcasts

This week, we talk about the pros and cons of buying a turbocharged airplane. Then we talk about some recent avionics equipment approvals in this week’s Alphabet Soup. Plus aircraft ownership news, Don’s tip of the week, and your feedback.

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More About Aircraft Turbochargers

Let’s start our discussion about turbochargers with a brief description as to what a turbocharge is and how they work. In a nutshell, a turbocharger enhances engine performance by utilizing otherwise wasted heat energy from the engine’s exhaust to drive a compressor that pumps a higher volume of air into the cylinders to be mixed with more fuel thereby allowing the engine to maintain full-rated performance.  The turbocharger is housed in a circular case with several large pipes on either end. Engine exhaust is sent directly to the turbine side of the turbocharge, often called the hot side. The turbine then converts heat energy into rotational energy, similar to a turbine engine. The rotational energy from the turbine is used to spin an impeller-style compressor wheel attached to the turbine with a shaft. The compressed air is then sent directly to the engine’s intake manifold.

As you may know, many airplanes built by Piper, Cessna, Beechcraft, and others have normally-aspirated and turbocharged versions of the same airplane; for example the Cessna 182, Piper Arrow, and Beech Bonanza. How do you know if the airplane you’re interested in has a turbocharger? No, you don’t have to take the cowlings off to take a peek at the engine; simply look at the aircraft’s spec sheet or listing to find the engine designation. If there’s TS in the engine spec, such as TSIO-520 found on the 210, it’s a turbocharged airplane. The TS stands for Turbo supercharged. The normally aspirated version of the 210 simply has IO-520 in the designation. Also, the aircraft’s model may have a T in the name, such as the T182 for the Turbo 182, or PA-34-220T for the Seneca. Another difference between turbocharged and normally-aspirated aircraft is price. Turbocharged aircraft are typically more expensive due to increased complexity and performance. More cost in a minute.

To understand the true benefits of turbocharging, it’s important to understand how aircraft engines are rated for power. Let’s take a 300 horsepower aircraft with a normally aspirated engine. You might be interested to learn that the 300 horsepower only exists at sea level on a standard day, that is 15 degrees C, 29.92 inches of mercury, where the atmosphere exerts a pressure for 14.7psi. We learned in private pilot ground school that the atmosphere loses pressure with altitude, somewhere to the tune of one inch of mercury per one-thousand feet. That translates to a loss of rated power as the aircraft climbs. Interestingly, the engine’s performance diminishes an astounding three percent per one-thousand feet. That means your normally aspirated 300 horsepower loses 25% of its rated power at just 8,500 feet, a typical cruising altitude for many GA airplanes. In other words, your 300 horsepower engine only has about 225 horsepower with full throttle.

 

I think you get the point here. Now let’s look at some of the pros and cons of turbocharging so you can begin making more informed decisions when it comes to selecting a suitable airplane to meet your unique travel needs.

First and foremost, turbocharging gives you hands-down better takeoff and climb performance in high-density altitude airports thereby increasing your margins of safety because the engine is producing maximum-rated horsepower. Second, turbocharging effectively increases the airplane’s service ceiling enabling you to fly higher and potentially faster, perhaps as much as 10-15 knots true faster. Moreover, you’re able to fly clear of high terrain and most of the weather and turbulence found down low, again increasing your margins of safety. From a mechanical perspective, turbocharging sends more oxygen to the engine allowing for fuel to be burned more completely, more efficiently, and cleaner. One final consideration in the pros category is that some turbocharged airplanes are pressurized. Some examples include the P-Baron, Cessna 414/421, the P210, and Piper Malibu. Pressurization eliminates the need for supplemental oxygen use above 12,500 feet.

While pressurization is a pro, turbocharging for non-pressurized aircraft is somewhat of a con. Turbocharged airplanes want to fly up high to deliver maximum efficiency. However, most turbocharged airplanes are not pressurized. Therefore, you and your passenger will need to utilize supplemental oxygen to be safe and legal. As many of you know, supplemental oxygen is not the most glamorous and comfortable thing in the world, and is definitely worth considering. Not to mention, adding supplemental oxygen increases the weight of the airplane thus diminishing some performance.

A second con to turbocharged airplanes is that they require TLC from the pilot. Turbocharged engines are very sensitive to misuse and abuse from pilots. It’s also possible to over-boost the engine with some turbochargers. One possible solution is getting an airplane with a turbo-normalized engine, where the turbocharger’s wastegate prevents over boosting the engine. Moreover, it’s prudent to get proper training on the correct handling of a turbocharged engine, regardless of the type, to ensure that you handle the engine properly. Improper technique will have a significant and expensive impact on your engine’s overall longevity.

The final con comes in terms of maintenance. A turbocharger, while simple in design, is a fairly complex device. There are a number of critical mechanical components, such as the intercooler, wastegate, controller, bearings, shafts, and wheels that can break, thereby increasing your overall cost of ownership. Moreover, most turbocharged engines have a lower TBO when compared side-by-side to its normally-aspirated brethren. Therefore, your cost per hour will increase accordingly. Also, being that the engine is more complex and has more parts, the cost to overhaul the engine will be about 25-35% more than a normally-aspirated engine of the same size.

Let’s take an A36 Bonanza. The normally aspirated model has a TCM IO-520 engine with a 1900-hour TB. The average cost of overhaul is $35,000. That equates to about $18.42 per hour in engine reserves. Now let’s look at the A36TC model. It has a TCM TSIO-520 engine with a 1600-hour TBO and an average overhaul cost of $45,000. When you do the math, that will cost you about $28.10 per hour in reserves. It’s probably safe to add an additional $2-3 per hour to that cost for additional unscheduled maintenance needed for the engine being that turbocharged engines have more parts, tend to run hotter, and are more sensitive to abuse. That puts you at $18.42 per hour for the normally aspirated engine and $31.10 per hour for the turbocharged airplane. In other words, it will cost you about $12.70 more per hour per engine to take advantage of turbocharging. That’s a difference of about 30%. Also keep in mind that turbocharged airplanes typically burn more fuel per hour than normally aspirated – approximately 1 gallon per hour, so add $5 per hour for fuel costs.

However, thanks to the average gain in speed, you’ll get where you need to go slightly faster, thus reducing trip time. This is especially true for longer trips where the speed advantage and time saved is more pronounced.  So while it cost more gallons per hour, it will take you fewer hours to make the same trip in a turbocharged airplane.

We talk to a lot of customers and prospective buyers that immediately want to purchase a turbocharged airplane without really considering the cost differences. If that’s you, my question is this: what does your typical mission profile look like? Do you need pressurization? Do you typically fly into high-density altitude airports? Do you fly over high terrain that requires higher cruising altitudes? Is speed and performance a greater priority than efficiency? Do you have the budget to properly care for and maintain a turbocharged engine? If you answered yes to any of these questions, you probably need a turbocharged airplane. But turbocharging may go beyond just what you need. Some people simply want the boost in performance for their aircraft. And the increased safety turbocharging offers them, their family, and their passengers. Bottom line is you must know what your mission is and what your priorities are. The last thing you want to do is buy too much airplane to the point that you can not afford to fly or maintain it. You have to decide whether the benefits of turbocharging outweigh the costs.