Cessnas 177 Cardinal can best be described as one of those should-have-been products that just never…was. Sleek, good looking and with decent payload and speed, it never quite nudged the Skyhawk into retirement, as Cessna had hoped it would. Nonetheless, the airplane still has a loyal following of owners, many of whom pine for additional speed.
That wish is now grantable in the form of a new turbonormalizing system now in the final certification stages at Tornado Alley Turbo in Ada, Oklahoma. TAT is we’ll
known for its Bonanza and Cessna 185 TN systems, not to mention its hot selling (at least until recently) turbo system for the Cirrus SR22. The new Cardinal conversion-which retails for about $40,000, all in-adds to TATs lineup.
In mid-March, we visited TATs Ada skunkworks to examine and fly the TN Cardinal RG. (Only RG owners need apply; the STC doesnt cover the fixed-gear version.) The airplane we flew was equipped with what will be the actual TN hardware, although the final dots and crossed-Ts on the paperwork were expected to be done before summer 2009.
Old STC
Tornado Alley acquired the Cardinal turbonormalizer when it bought the STCs from Flightcraft, which developed the systems during the 1990s. Although the Cardinal is a good candidate for turbonormalizing, the Flightcraft version left some engineering boxes unchecked. For one thing, that system lacked an intercooler and had plumbing and induction issues. It had a wastegate, but no induction pop-off valve and Flightcraft inherited a Cardinal problem that it never really corrected: an undersized oil cooler. Even normally aspirated Cardinals tend toward higher oil temps, despite the cowl inlets and flaps being sized sufficiently.
In stock form, the 200-HP Lycoming IO-360 in the Cardinal RG series delivers performance in the 145-knot range, give or take. Thats not stinkishly sluggy, but a Mooney J-model beats it by at least 5 knots and probably more on the same engine and fuel flow. The Cardinal is a bit draggier than the Mooney and has a slightly larger frontal area, but thats a fair compromise for having a largish cabin and more elbow room.
Although the speed was there for the taking, Cessna never bothered to turbo the Cardinal, probably because when the airplane was introduced in 1971, Cessna sales in entry level airplanes were strong and turbocharging was an upsell reserved for twins or at least singles with six-cylinder engines. Further, turbocharging was a bit
of a dark art in the good old days. In our view, the really good turbo systems didnt appear until the 1990s. And even then, Flightcraft didnt exactly flood the world with its turbonormalizer for the Cardinal. TAT estimates there are only about three dozen of the original systems flying.
Clean Sheet
Although TAT owns the original STC, the new turbo system is more of a clean sheet project re-engineered from the inside out. Interestingly, buyers of TN Cardinal systems will benefit from what TAT has learned in its years of building these systems. TATs George Braly told us the company essentially has an Erector Set of parts-or, more appropriately, universally applicable knowledge and expertise-so its not re-discovering fire when it tackles a new installation. It has, for instance, lots of reliable data on intercooler and turbocharger performance.
For the Cardinal, TAT used the Kelly Aerospace turbo, the same model used in the Piper Mirage in a pair. Thats plenty of boost for the four-cylinder IO-360 and, in any case, the Cardinals cowl isn’t large enough to accommodate two turbos.
But it is small enough to require some creative engineering to make everything fit. We noticed that the induction snakes around the Bendix RSA fuel-injection system on the bottom of the engine and finds its way to the right side of the aircraft, where a large intercooler is mounted vertically on the firewall, the only place it would fit practically. From there, the upper deck air is routed through nicely white-painted piping into the Lycomings induction system. The piping and connectors have been revised to improve flow and mechanical robustness and TAT added an upper deck relief valve.
As with all turbonormalizing, the TAT system doesnt ground boost, but will maintain sea-level manifold pressure all the way to the TN-modded certificated ceiling of
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20,000 feet. Because of that limit, the system doesnt have a critical altitude-the point at which the wastegate is fully closed with the engine delivering its rated power. If did, it would probably be somewhere in the mid-20s.
The idea of intercooling is to substantially reduce the temperature of the induction air to increase its density and to also provide additional detonation margin. Aircraft and engine companies have spent small fortunes trying to get intercooling right-it requires a not-so-simple relationship between heat exchanger size, airflow and position in the cowl. If the intake flow comes from the wrong place, it can rob the cylinders of cooling air and tank some of the intercoolers gain, not to mention impacting cooling drag.
The critical measure of an intercoolers efficiency is temperature drop across the inlet and outlet. On our test flight in Ada, the Cardinal was instrumented with a JPI engine monitor to measure both compressor discharge temperature-the warm side where the compressed air has exited the turbocharger-and induction temperature, after its been cooled by the intercoolers heat exchanger. At 17,500 feet, with the airplane settled into cruise, we recorded an intercooler temperature drop of about 84 degrees F. At 30 inches of manifold pressure-thats worth about 6 percent more air density than would be available without intercooling. Moreover, since the engine retains its stock 8.5-to-1 compression ratio, the cooler air provides a considerable hedge against detonation and makes it practical to lean aggressively.
Other Mods
With the Cardinal uncowled, we noticed several other changes. The oil cooler is larger-its the same type and size used in O-540 installations-and it has been reoriented on the right-side firewall. It draws downdraft air from a fat SCAT hose routed from the rear baffling. And speaking of baffling, TAT also installs improved baffling as part of the package.
The engine retains the RSA-5ADI fuel servo system, but its modified to provide higher fuel flow.The IO-360-A1B6D the airplane was certified with had the much-reviled Bendix D-mag which combines both mags in a single housing. That mag doesnt require pressurization to prevent cross-firing at high altitude. But some Cardinals have been converted to the IO-360-A1B6 (or had the engine originally) which uses a pair of separate mags, which do require pressurization. The conversion price includes this option.
The mags are equipped with a kit that pumps filtered bleed air into their housings to keep them near sea-level pressure. Dual mag airplanes also get an Airwolf remote oil filter mount.
Performance
Whats your best guess on how fast a four-cylinder turbonormalized aircraft can fly at altitude? Ours would be the mid-160s, given the engines horsepower rating and the drag profile of the Cardinal. Actually, on our trial flight in the Cardinal, we saw 177 knots-nice resonance there-at 17,500 feet, burning about 10.8 GPH, leaned to about 50 degrees lean of peak EGT. That pencils out to 16.3 NMPG, which is respectable economy for anything going faster than 200 MPH. In climb, we recorded a highest CHT of 399 degrees F and an oil temperature of 195 degrees F.
In cruise, these trended sharply downward, although because of time constraints, we didnt have an opportunity to run in cruise long enough to observe whether the cylinders trend slowly upward or slowly downward. Weve seen both in turbocharged engines. The response is to either lean more if the engine retains acceptable smoothness, fiddle with cowl flaps or run on the rich side of peak and take the economy hit.
At lower altitudes, the TN Cardinal is more or less stock. At 6000 feet, for example, the POH calls for 146 knots at 10.7 GPH and turbocharging doesnt help that much. But the airplane begins to hit the sweet spot above 8000 feet, where the normally aspirated engines power trails off enough to offset any altitude-derived true airspeed gains.
At 12,500 feet-a good compromise altitude when into a headwind-the stock POH calls for 140 knots at just under 10 GPH. (Thats 59 percent power.) At the same altitude, we noted that the TN Cardinal trued at 165 knots on 11 GPH, lean of peak, with CHTs in the 370s. Thats a solid 25-knot gain and, in our view, more than a worthy trade-off for the additional gallon of gas.
The normally aspirated IO-360 performs respectably at altitudes we’ll into the teens, but it gets wheezy trying to get up there. The TN version, on the other hand, retains 500 to 700 FPM all the way to its max 20,000-foot limit.
Weight wise, the system extracts a 35-pound penalty and biases the CG forward somewhat. It remains within the forward envelope, but with heavy occupants in
the front seat, pitch up forces may be noticeably heavier on landing.
Economics
As mods go, the TAT Cardinal installation is at the upper end of what some owners are willing to spend on a 40-year-old airplane. But its typical of the major mod that adding a turbocharger represents.
Cardinal owners love these airplanes because they represent a well-considered compromise between cabin size, speed and payload. On the used market, Cardinal RGs are excellent buys, with early models in the high 40s to mid 50s and latest-model 1978 RG II versions in the mid-70s, depending on equipment.
So we think the right way to look at the TN Cardinal is to add up the all-in cost-say from about $90,000 to $115,000-and compare it to what else will go as fast and carry as much comfortably for the same budget. This list is short enough to be non-existent. The stock Mooney 231 comes to mind, but it doesnt carry as much, it doesnt go as fast and the turbocharger system is crude compared to TATs effort.
The Cessna T210 is also an option. It carries more, but isn’t as economical. Then there’s the Piper Turbo Arrow at perhaps two-thirds the price of converting a bought Cardinal. By comparison, however, the T-Arrow is a relative slug, unless equipped with aftermarket intercoolers, which the original didnt have.
According to owners and the Cardinal Flyers Online (www.cardinalflyers.com), the 177RG remains we’ll supported by Cessna, although some parts arent readily available and may require hard hunting or a long wait. If owners have a persistent complaint about the Cardinal RG, its the landing gear. As GA gear systems go, its not particularly we’ll designed, robust or reliable. If properly maintained, its less of a headache, but it does require care.
For owners looking for an inexpensive, 200 MPH cruising machine with good altitude performance, range and payload, we think the TN Cardinal is worth adding to the list.
