Tag Archives: radial engines

Refresher Lesson: The Difference Between Radial and Turbine Engines

Turbine engines, also commonly known as jet engines, are different than radial engines. Some pilots who fly smaller aircraft find that radial engines are more fun to fly, while pilots of jet engine aircraft find the extra steps involved in flying a radial engine too difficult.

Turbine Engines

Turbine enginesTurbine engines operate similar to a steam power plant, except they use air instead of water. Air flows through a compressor, creating higher pressure, and fuel is sprayed into that air so that it ignites and creates energy. The gas created enters a turbine, expanding and producing shaft work output. The turbine shaft then works to drive the compressor and generator, and energy not used in the process is expelled as exhaust fumes.

Radial Engines

Radial engines, also referred to as “round engines” by pilots, resemble a star when viewed from the front, as cylinders point outward from a central crankshaft. Radial engines were common in aircraft before the development of turbine engines, and many pilots still prefer flying radial engine airplanes. In a radial engine, pistons are connected to the crankshaft using a rod assembly. One piston has a master rod with a direct attachment to the crankshaft. Normally, radial engines have an every-other-piston firing action that makes the motion more uniform.

Main Differences

Radial engines often have a large frontal area, which sometimes made planes—especially those used in battle—less aerodynamic. Turbine engines also fly at higher rates of speed than aircraft powered by rotary engines, but are often less fuel efficient and much louder than rotary engines. Many pilots claim that rotary engines are more challenging to fly, as the steps for take-offs, in flight and landings are much more complicated than turbine engines.

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TBO: Time Between Overhaul. Even the PT6A Needs Maintenance

Covington Aircraft has now been in business since 1979.  Over the last 30 plus years, we have seen some Agricultural Aircraft owners who were riskier than even the most daring stunt pilots. How so? Well, they try, much like those who push the oil change on their vehicle, to put off as long as possible the overhaul of their engine. We focus on what to look for and Time Between Overhaul in this post.


The Ag industry often overlooks FAA Part 91/137 (Agricultural Operations) regarding recommendations for TBO, or Time Between Overhaul.  TBO is overhauling an engine at the manufacturers recommended times.  Often, Ag industry pilots are under the mistaken impression that PT6A engines don’t need these recommended overhauls, when this couldn’t be further from the truth.

SB 14503 (-67AG)

Pratt Service Bulletins governing TBO for this engine indicate that the first stage power turbine blades should be replaced at 12,000 hours, while second stage power turbine blades should be replaced at 5,000 hours.  Compressor Turbine Blades with certain part numbers must be replaced at 6,000 hours.  Main-line rotor bearings #1 and 4 as well as the first stage planet gear set’s sun gear should be replaced at 12,000 hours time.  Considering these low hours, it stands to reason that the PT6A will not fly forever if the recommendations are not followed.

PT6A-34AG SB 1303

pw-pt6aThe 5000 Hour Check, which involves removing the disc from the hot section, removing blades from the disc, cleaning and conducting non-destructive testing, is recommended for the first time at 5,000 hours and at 3,000 hour intervals after that.  This inspection also requires comparison of the actual length of the blade but they cannot be cracked.  Cracked turbine blades or those stretched beyond limits could be devastating to an aircraft.

These two simple recommendations indicate that PT6A engines do not last forever.  Failure to follow these recommendations could result in engine failure.  In addition, Pratt & Whitney places significant importance on maintenance recommendations when honoring warranty repairs.  Therefore, it is important that owners educate themselves on service bulletins and overhaul recommendations to avoid catastrophe.

If it has been too long of a TBO for you or you have general maintenance, sales, or overhaul questions, make sure you visit the Covington Aircraft website!  Happy Flying!


Global Turbine & Radial Aircraft Engine Sales and Overhaul Company has long Local History

Find our more about Covington Aircraft at www.covingtonaircraft.com

It’s pretty cool to say you work for an aircraft company.  Hi everyone, I’m Aaron Abbott and I’m proud to say that I work for a company that has been around for almost 40 years.  When Covington Aircraft first started, it began working on the Pratt & Whitney R-985 and R-1340 radial engines as a way to take care of the air cargo industry.

Now, Covington Aircraft is one of the few OEM authorized MRO facilities in the world.  Still true to our beginnings we continue to overhaul and maintain the radial engines, but in the mid 90’s we added the Pratt & Whitney Canada PT6a series engines to our list of capabilities.  This allows us the ability to take care of the corporate and agricultural markets in a more effective way.

Covington Aircraft is not just a company that specializes in the overhaul and maintenance of aircraft engines, but also sets an example for other companies with its tried and true dedication to being a company entrenched in integrity.  Our word is our bond.  It is our goal as a company to provide the customer with dependable service, at affordable prices, and it is our commitment to do this with exceptional service.

We’re among the world’s leading maintenance, repair, and overhaul facilities, specializing in the PT6A turbine and R-985 and R-1340 radial engines and accessories.  And we are proud to offer the fastest turnaround time and lowest prices in the business.

We also offer 24 hour worldwide aircraft on ground support.

Feel free to contact us today at covingtonaircraft.com

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