Piston vs turboprop is a very important consideration in the aviation world. Although these power sources are easy to compare using many different criteria, power output is what most aviation professionals think of when making this comparison.
Each type of engine has different advantages and disadvantages. Knowing where each of these engines has the advantage will help you select the better option for your aviation needs.
Piston engines, on one hand, are highly efficient in power output and cost less. Turboprops are also highly efficient, have a reputation for greater reliability, and perform better in higher altitude settings.
In many cases, the definition of which engine is better is subjective and based on the aircraft owner’s particular needs and what type of plane are we talking about. Planes flying cargo have one set of needs, while planes carrying passengers have another set of needs.
Taking a closer look at the features of these engines is a good way to make the right choice. Although the number of factors to consider may seem overwhelming, keeping these factors in mind helps you make a better choice.
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Do Piston and Turboprop Engines Work Differently?
Understanding the basic operating principles of piston and turboprop engines is vital to know the answer to this question. Both types of engines can be defined as air pumps, driving propellers from energy originating in combustion.
These engines have mechanical differences in their operation. However, one thing that both engines have in common is a four-stage engine cycle that consists of intake, compression, combustion, and, lastly, exhaust.
The engine cycle provides the power that the plane requires to take off and reach optimal cruising heights. Because planes need this power, engine quality is an essential component.
How Do Piston Engines Work?
These engines use a combination of fixed cylinders combined with reciprocating pistons. The components all connect to a common driveshaft to ensure operation, which helps keep the engine operating as smoothly as possible.
Most typical plane engines occur on separate engine rotations or strokes. For this sequence to work, a camshaft actuates the valves on each cylinder, which allows fuel and air to enter the engine.
To help increase the intake air pressure, turbochargers and superchargers are used that permit flying at lower-than-usual altitudes. Turbochargers use exhaust gases, while superchargers use the engine’s crankshaft’s power.
How Do Turboprop Engines Work?
Turboprops are best described as jet engines that use exhaust gasses to drive the propeller. These engines have a simple form of operation that involves:
- Air being drawn into the engine
- The compressor increasing the pressure and temperature
- Air being mixed with fuel and ignited
- Turbines controlling exhaust expansion
- Driving the propeller with the gearbox
To determine the output, combustion temperatures and torque are taken into account. For most of these engines to work as intended, intake air is required to reverse direction before it enters the compressor.
Understanding the engine cycles makes it easier to understand why everything needs to work together. If a single stage of the cycle were to break down, engine failure would be a distinct possibility.
Are There Differences Between Piston and Turboprop Engines in Safety?
When you closely look at both engine types, turboprop engines have a solid history of reliability and safety. A turboprop engine’s construction eliminates or reduces reciprocating mass, which reduces wear and tear from fatigue factors and vibration.
The increased number of moving parts rotate in a single direction, with well-balanced mass, and at consistent speeds.
With the exception of gearboxes, there are no parts making physical contact with each other, creating excellent safety records and reliability that have contributed to these engines being in everyday use.
This increased reliability and safety has helped make turboprops a fixture of commercial planes. Alaska Airlines and FedEx have both adopted planes that use turboprop engines for their short-haul flights, citing their reliability combined with overall safety.
An important safety feature of turboprop engines is generating more air, which is beneficial for de-icing systems in use at airports that see a lot of winter traffic. Turboprop engines can also withstand operator errors more easily than piston engines, making these engines an asset in high-performance settings.
What Are Some Safety Downsides to Turboprop Engines?
The gearbox is the greatest mechanical downside to a turboprop, creating a difference in the operating power of the propellor versus the amount required.
Turbine components that deliver propeller power operate at 30,000 rpm in contrast to the 1,500-2,000 rpm speed that the propeller requires.
Although heavy lubrication and propeller speed governors help protect the gearbox, the failure of this component is a leading cause of turboprop engine failure. Warning systems help play a crucial role in alerting pilots to potential trouble.
What Efficiency Differences Are There Between Pistons and Turboprops?
Piston and turboprop engines are combustion engines that work by compressing and burning air while expelling the resulting gas. Piston engines become less efficient with a larger size, while turboprop engines become less efficient with a smaller size.
Are There Such Things as Piston to Turboprop Conversions?
The light aircraft market has a few examples of piston-to-turboprop conversions, with Cessna and Bonanza planes involved for specific purposes. A crossover point between the piston and turboprop engines occurs in the 400-500 hp engine range.
What Types of Expenses Are Involved With Pistons and Turboprops?
One thing that piston and turboprop engines have in common is that they are both expensive.
However, the engine purchase and its accessories tell only part of the story; maintenance issues play a leading role in the overall costs that influence many pilots’ decisions on which planes to buy.
What Are the Purchase Costs of Both Engines?
Piston engines with four cylinders may cost around $25,000, while six-cylinder engines may cost as much as $100,000.
Turboprop engines, like some Pratt and Whitney models, might range from $700,000 to over $1,000,000.
As you can see, these engines cost very little in comparison to how much you’ll pay for a jet-powered private plane.
What Overall and Maintenance Schedules Should You Have?
The overhaul value for piston engines ranges from 1,800 to 2,000 hours. Overhauled engines are often preferred as replacement engines because of the lower cost.
Engine cylinders cost $1,000 or more each, one of the costs that many aircraft owners consider more alarming. Replacing individual cylinders can be preferable to having the entire engine replaced, as far as costs are concerned.
Turboprop engines have longer overhauls that are also more costly. The overhaul value for these engines could range from 3,600 to 8,000 hours.
Although turboprops are more expensive to purchase and maintain, they have greater cost-effectiveness relevant to performance. In this area, turboprops make financial planning for your plane maintenance easier.
What Types of Fuel Costs Do These Engines Have?
Piston engines usually average $65.78-$116.38 in fuel costs per hour. Turboprop engines, by contrast, have average hourly costs of $159.12-$288.42 an hour.
Despite piston engines seeming “cheaper” in terms of hourly fuel costs, turboprops have a greater power output that helps balance out the costs. The overall output will be just as serious a consideration as the base fuel cost for budget-conscious aircraft owners.
An explanation for this difference is that turboprops have a better efficiency rate. Regardless of the engine type, proper engine operating habits and a consistent inspection and maintenance schedule make a difference.
One thing that aircraft owners would do well to remember for both types of engines is that they are complex equipment requiring a certain level of care. The wear parts on piston engines are easier to service, despite more of these parts being present.
Piston engines make cam or valve replacement relatively easy. Replacing turbine blades, by comparison, is a more complicated, expensive type of service.
How Do Piston and Turboprop Engines Perform?
Piston and turboprop engines operate in similar ways, with turboprops being the obvious winner in operation. Two of the most important indicators of performance are takeoff and cruise performance.
Horsepower is the measurement of the output value of both kinds of engines. In measuring performance, it is important to look at maximum continuous power up until critical altitude, as the performance reduces above this rate.
Piston Engine Performance
The maximum continuous power output of a piston engine averages around 75% of the maximum rated power. In most cases, the power output is maintained until 7,000-9,000 feet in pressure altitude.
Turbocharged engines can improve this altitude from lower levels up through the teens. The improvements in cruise altitude with turbocharging are most impressive.
Piston engines have a somewhat limited cruise speed averaging 200-230 knots. Although some experimental aircraft approach speeds of 300 knots, going above 230 knots is more difficult for a piston than a turboprop.
The takeoff performance of piston engines depends on the available power output. When a plane has a specific pressure altitude, this means the plane achieves power and efficiency consistent with this altitude.
The engine will have sufficient energy to help the plane take off using available air.
Turboprop Engine Performance
Turboprop engines, like piston engines, are affected by atmospheric pressure and density. One of the main differences is that turboprops have more efficient power generation and have higher baseline power outputs.
Turboprops can also reach something called critical altitude, the point where Inter-Turbine Temperature (ITT) is more of a limiting factor than torque output. The altitude will vary across different engine models.
One thing that aircraft owners need to be wary of is manufacturers de-rating their engines by limiting torque output in favor of a higher ITT margin. One of the results of this technique is a critical altitude that is artificially higher.
Pilots must balance flying over most weather while maximizing efficiency and maintaining cruise speeds. These conditions make all the difference in how well a plane can carry extra cargo or more passengers.
The overall turboprop advantage is in the form of maintaining maximum power at higher altitudes. There is also an advantage during landings, with feathering and reversing propellers improving overall landing performance.
Piston vs Turboprop Performance Overall
Whether a piston or turboprop engine is better will depend largely on the aircraft’s function. However, there are a few important areas where turboprops maintain distinct advantages.
Pilots intending to fly at higher true speeds and rise above the weather will likely find turboprops more desirable. Piston engines, on the other hand, may have limited performance at lower altitudes.
The increase in turboprop usage signals a desire for better altitude, speed, and efficiency of aircraft. These features enable planes to carry larger, heavier loads and fly over longer ranges.
Is a turboprop better than a piston?
Turboprops are less expensive to operate and purchase, as well as more efficient in power output. In most cases, turboprops perform better at high altitudes, are more efficient, and are more reliable.
Why are turbine engines better than piston engines?
Turboprops can fly at higher speeds due to a greater overall power. Planes using these engines can fly at higher altitudes because the cabins are pressurized.
What advantages do turboprops offer?
Turboprop engines have an increased power output because of their lighter weight. These engines also maintain excellent fuel efficiency at low altitudes, allowing flight at higher altitudes that are lower-cost.
Are piston engines still considered reliable?
Most piston engine technology is over 30 years old, giving it a distinct disadvantage compared to turbines. A common comparison is that automotive propulsion systems are more reliable in comparison to piston engines.
Can private pilots fly turboprops?
A pilot with a private license can fly a turboprop. However, pilots must have the appropriate Instrument Rating, as well as a high-altitude/pressurized endorsement and complex and high-performance endorsements.
Despite the similarities, there are enough differences in piston vs turboprop to give the respective engine types advantages and disadvantages. The most important thing for aircraft owners to keep in mind is that the aircraft’s overall function is of vital importance.