Classic Airframe, Cutting-Edge Powerplant: Upgrade and Overhaul Options for your 206Written by Steve Ells
With so many STCs you have many alternatives, and all of them offer technical and operational improvements for your 206.
Cessna’s 206 is a very fine airplane. The 206 series evolved from the Cessna 205 that hit the market in 1963. Model 205s were equipped with a six-cylinder fuel-injected 260 hp IO-470-S engine from Teledyne Continental Motors (TCM). Maximum Take Off Weight (MTOW) was 3,300 pounds.
The 205 was suspended after two years and 577 airplanes, and replaced in 1964 by the Super Skywagon 206 that maintained the 3,300-pound MTOW of the 205 but got a power boost of 15 hp (to 285) due to the installation of a normally aspirated TCM IO-520-A.
In 1965 the U206 line was introduced and stayed in production for 23 years. MTOW was boosted to 3,600 pounds within a year with the introduction of the TU206A in 1966. A turbocharged TCM TSIO-520-C powered the TU206C.
Cessna marketing renamed the airframe often in the first few years. First the 206 was the Super Skywagon. Within a year or two the turbocharged version was the Turbo-System; the normally aspirated version was the Skywagon for two years before Stationair (station wagon of the air?) became the name for seven years. Then in 1978 it was again rebranded as the Stationair 6 and Turbo Stationair 6 until the last one of slightly more than 7,000 206s had rolled off the line in 1986. Cessna Aircraft currently offers the 310 hp Turbo Stationair.
Aged airframe, new powerplant options
Prior to the introduction of FAR Part 33, “Airworthiness Standards: Aircraft Engines,” certification standards for piston engines were contained in Civil Air Regulation 13.
Part 33 standards mandated that all piston engines certificated under this newer standard produce the rated power, minus zero, plus five percent. In other words, the new rules required that new engines put out the rated power, no exceptions.
The 550 series engines, but not the 520 series engines they replace, are Part 33 engines.
Increased TBOs for new or factory rebuilt CM Gold Standard engines
Continental Motors, Inc. (formerly Teledyne Continental Motors) recently extended the TBO of Gold Standard engines. In April of this year, Continental Motors released an update of Service Information Letter (SIL) 98-9B. The subject of this letter is “Time Between Overhaul Periods.”
A press release dated April 9, 2013 shows:
“Continental Motors has increased TBOs up to 400 hours on Gold Standard Factory produced engines. The majority of engine models manufactured after February 2012 will see TBOs increase by 200 hours with frequent flyers receiving up to 400 hours.
“In 2012, Continental Motors introduced its Gold Standard Factory Rebuilt and New Engines. These engines incorporate improvements in technology and manufacturing processes that have allowed us to increase the TBO. The increased TBO is affective on nearly all Continental Motors Factory produced engines beginning in February 2012 as designated by serial number 1006000 and higher. Nearly all models will receive the benefit of a 200 hour increase over the existing TBO. Aircraft owners that fly 40 hour per month will receive up to 400 hours.
“Additional information is available at www.ContinentalMotors.aero/TBOExtension.”
The IO-550 series of Continental engines meet the new Part 33 power standard due to a number of factors. The first is slightly more displacement by increasing the stroke by ¼ inches to 4.25 inches. Only 550-G and later engines have crossflow (CF) heads and a balanced flow induction system. The IO-550-F does not utilize the crossflow cylinder heads; the IO-550-N does. The advantage of the CF design is better economy.
Crossflow heads and balanced induction
In a crossflow head, induction air and fuel enter the combustion chamber from one side of the head: the top, in the case of the 550 series of engines.
After the compression and power strokes, the exhaust and combustion by-products flow out of the cylinder head through the exhaust port on the opposite (bottom) side of the head. This configuration is a more efficient than head designs where the inlet and exhaust ports are on the same (i.e., bottom) side of the head.
Separating the inlet air from the heat of the exhaust system also greatly lessens preheating of the inlet air before it enters the combustion chamber, thereby maintaining air charge density.
The balanced flow induction system incorporates individual intake air tubes that lessen the possibility of unmatched airflows into adjacent cylinders. Non-balanced flow engines have two common induction tubes or logs: one below the left and one below the right row of cylinders. Induction air from the log is pulled into the cylinders one at a time; these intermittent
“gulps” of air from the common airflow affects the airflow into each of the other cylinders common to the log. The result is uneven air quantities delivered into each cylinder in the row.
The uneven airflow in the common log induction system can be compensated for by adjusting the flow rate (tuning) of each fuel injection nozzle. More even airflows equal more uniform power pulses from all cylinders and a smoother engine.
Instead of just replacing the existing engine, 206 operators now have several options to upgrade to more powerful engine and better engine designs. The following are companies that provide these options.
Atlantic Aero, Greensboro, N.C.
John Ackerman at Atlantic Aero told me that the company holds two re-engine STCs for the 206. The older of these approves the installation of a 300 hp IO-550-F in all 206s beginning at serial number 657 (beginning of 1967).
The newer STC approves the installation of the IO-550-N engine. This “N” engine is the latest IO-550 iteration (permold case), is rated at 310 hp and features a crossflow head configuration.
The sandcast engine cases have a belt-driven alternator on the back of the engine. The permold engine case has the gear-driven alternator mounted in a right front position on the engine case.
The 550-F upgrade, being a sandcast engine, is straightforward. The 550-N upgrade kit—Atlantic calls it the 550TI for tuned induction—also includes two additional improvements that are required to install the permold case “N” engine in airframes with the existing sandcast mount system. The conversion also includes a brand-new Hartzell 82-inch Super Scimitar propeller.
The kit is available for T206s and removes the TSIO-520 engine and all of the turbocharging components. This deturbo kit includes a complete new exhaust system along with sheet metal to close up the old exhaust hole, along with sheet metal to close up the cowl flaps (the new engine does not have any heating issues).
Both kits give you a new induction system to include alternate air along with new engine controls, a fuel flow/manifold pressure gauge and a new tach.
Another Atlantic Aero innovation is the Smooth Ride engine mounting system. The Smooth Ride system is available on both upgrades and adds two additional engine mount pads and vibration absorbers adjacent to the existing forward two mounts. This greatly reduces the amount of engine vibration felt in the cabin and stops the need to periodically replace engine vibration absorbers due to engine sagging (commonplace with the original mounting system). The installation of a set of STC’d mount legs is required on the IO-550-N upgrade to adapt the permold case to the Smooth Ride system.
Ackerman said that each 550 engine upgrade kit includes a factory rebuilt Gold Standard engine (a new engine is available for an additional $6,000), new hoses, new engine controls, new instrumentation, and a new induction system with alternate air system.
Today’s price for the kit is $66,844. According to Ackerman, installation man-hours average about 125 for the engine and an additional 25 to fit the new mounts in the airframe for the Smooth Ride system.
Davis Aviation, Bristol, Tenn.
Davis holds an STC to replace the IO-520-A or -F engine in all serial number 206s with the 300 hp IO-550-F engine. In addition, it offers a separate STC for replacement of the turbocharged TSIO-520 engines in turbo model 206 airframes with the normally aspirated IO-550-F model (deturbo modification).
Davis also holds STCs for prop-only upgrades for both Hartzell and McCauley props. As Donna Jones explained it, “This mod is an option that lets owners replace the older threaded hub props with a new prop that fits both the 520 and 550. You can upgrade your prop first, then use the same prop with a low pitch blade angle change at a later time.”
The IO-550 STC installation allows a way for owners of pre-1978 (serial number 4075 and below) 206s to install an extended hub propeller without modifying the existing cowling. This upgrade moves the empty weight center of gravity (EWCG) forward about 1 ½ inches. Cessna made the extended hub prop standard beginning in 1978.
Davis Aviation purchased the STCs developed and held by Bonaire at the end of 1998.
Davis STC installation kits do not include an engine but Jones said that she will do the research required to “spec out” the engine for buyers to make sure they order the correct engine, and does work with other STC holders to make sure each customer gets the package that best fits their needs. Other prop-only options can be installed outside the Davis STC in conjunction with the engine installation. Jones works with other STC holders to make sure each customer gets the package that best fits their needs.
Jones added that Davis has a worldwide network of distributors and have upgraded many aircraft in foreign countries. Most of the Davis STCs are approved in Brazil and the European Aviation Safety Agency (EASA) countries.
RAM Aircraft, Waco, Tex.
RAM aircraft is known for quality engine overhauls of Continental big bore 520 series engines. RAM’s overhauls are among the most thorough and best overhauls in the industry.
RAM holds STCs for engine modifications to the 300 hp IO-520-F in normally aspirated 206s beginning with serial number 657. RAM also has a STC for replacing the 285 hp TSIO-520-C engine in 1976 and earlier T206s with a 310 hp TSIO-520-M or -R engine in T206s beginning with serial number 657.
RAM-developed upgrades to these engines include fine-tuning the reciprocating balance of each crankshaft to two to four grams (a one-dollar bill weighs about a gram), smoothing oil system passages, volumetric and flow match checking of RAM “Nickel New” cylinders, heavy crankcases with seventh-stud modifications, and installing new lifters and new RAM high efficiency camshafts with lobe profiles that reduce cam train loads and improve fuel economy.
Bob Collum at RAM said that the company usually keeps 25 engines in stock that can be built up to ship within three days. In addition to high-quality overhaul skills, RAM also stands behind each engine with one of the best warranties in the business.
Texas Skyways, Boerne, Texas
Jack Johnson of Texas Skyways has been modifying and upgrading Cessnas for decades. The Texas Skyways upgrades are STC’d for installation on all 206 models up through the U206G models (through 1986 production). Buyers can choose from the IO-520-F (300 hp for five minutes; 285 continuous) or the IO-550-F (300 hp continuous) engines.
Both of these engines use the sandcast case and therefore no changes are required to the mounts, baffles, or wiring; this keeps costs low and makes it easy to swap out with the original engine.
Johnson strongly recommends—based on vibration and performance surveys done at Texas Skyways—the installation of a Hartzell PHC-J(C) (G)3YF-1RF/F8068 propeller. Texas Skyways calls this the “Buccaneer” prop.
The price for a factory rebuilt engine and the STC is $44,472; the prop and spinner add $11,461. These are exchange prices with Texas Skyways. Upgrades/installations can be done at the Texas Skyways factory in Boerne, Texas for $3,500 over a two-week period.
Johnson says, “When we’re done, it looks like a new airplane firewall forward.” The Texas Skyways upgrade can also be done at a local maintenance facility after purchase of the STC and kit.
Vitatoe Aviation, Chillicothe, Ohio
Larry Vitatoe obtained an STC to install a turbo-normalized IO-550 in the P210. Vitatoe also did the work to obtain a STC to remove the original 520 cylinders and install a set of crossflow cylinders and the crossflow induction system on IO-520 engines, and to install CF cylinders on IO-550 engines.
These mods provide a step up in engine efficiency and are quick and easy to accomplish. Prices for the CF mods to both the 520 and 550 series engines start at $33,000.
Vitatoe also has STCs for the installation of improved Hartzell and McCauley propellers.
Wipaire, South St. Paul, Minn.
Wipaire manufactures floats and specializes in floatplane maintenance and upgrades. Floatplane operators always need more power.
Wipaire holds an STC for the installation of the 300 hp IO-550-F in the 206. The change is easy and one advantage of the 550 upgrade is lower noise since the 550 makes 300 hp at 2,700 takeoff rpm versus 2,850 rpm from the 520.
Prices start at $2,300 for the STC and $4,700 for the installation kit. The price for a new Hartzell prop and the Wipaire 550 upgrade kit is $15,000. The propeller from the 520 may be used on the 550, but it’s not ideal—and it must be sent to a certified prop shop to have the internal stops reset.
Put in an IO-550 and you can ditch that pesky turbocharger
Increasing numbers of these normally aspirated engine upgrade kits are being installed on turbocharged versions of the 206. The turbocharger and related systems are removed and replaced with a new exhaust system. Modifications made to the cowling and cowl flaps complete the change.
One advantage of replacing the turbocharged engine with a normally aspirated engine is that normally aspirated engines are more thermodynamically efficient than the turbocharged engines because of higher compression ratios.
The IO-520 and -550 series engines have a compression ratio of 8.5:1 while the TSIO-520 has a compression ratio of 7.5:1. The reduction in compression ratio is required to protect the engine due to the elevated turbocharger compressor discharge air temperatures that are pumped into the engine air inlet at high power settings.
Secondly, the IO-550 engines do not have a five-minute max power restriction like the 520 series engines and since the power numbers are true in accordance with the requirement of FAR 33, the owners I know who have elected to ditch the turbo system and upgrade to the IO-550 have not been disappointed.
Do the numbers
The costs of any upgrade should be considered whenever it’s time to overhaul or replace an existing engine. Upcharges are likely when exchanging a 520 for a 550 series engine. There may also be upcharges if the exchange engine is an older-style light case and/or the crankshaft is a non-VAR crank. (“VAR” is short for vacuum arc remelting, a secondary melting process used in high value applications to improve the quality of the metal. —Ed.)
All of the upgrades listed above will provide both technical and operational improvements for your 206. Powerplant upgrade options range from a straight engine upgrade to the 550, on to the Vitatoe crossflow cylinder swap on an existing 520 or 550 series engine, and finishing up through the 310 hp Atlantic Aero IO-550-N.
Each of these companies offers its own package of benefits to buyers. And there’s no need to go to one shop for the engine and then on to another one for the prop, etc.—all of these shops can put together and install the upgrades as a complete package.
Be sure to ask about core charges, upgrade charges, freight costs, kit contents and propeller options when putting together your ultimate 206 upgrade package.
|Atlantic Aero, Inc.||atlantic-aero.com|
|Davis Aviation Services, Inc.||davisaviationservices.net|
|RAM Aircraft, LP||ramaircraft.com|
|Texas Skyways, Inc.||txskyways.com|
|Vitatoe Aviation, LLC||vitatoeaviation.com|