Plane & Pilot
Tuesday, March 9, 2010

Cougar Baron: Most Happy Baron

Rocket engineering offers the world’s most enthusiastic Baron

Our flight didn’t demand such heights—just as well, it turned out. One slight limitation of the Cougar is the pressurization system. Differential is only 3.9 psi, an inevitable consequence of trying to pressurize a cabin that was never designed for it. In essence, you’re trying to inflate a box.

This was the same problem Cessna faced when attempting to upgrade the 210 Centurion and 337 Skymaster. The result was an even lower 3.37 psi differential. Additionally, remember that even the newest 58P is nearly a quarter-century old, so minor pressurization leaks could be a problem on even the best-maintained airplane.

The 3.9-pound Garrett pressurization system may have been adequate on the Beech piston twin that rarely lofted much above 22,000 feet, but it’s a little weak for a turboprop that needs to cruise in the mid-20s to achieve its best speed and fuel economy. Higher always is better for turbines. The pressurization system provides a 10,000-foot cabin at 22,000 feet. That means the cabin will be near the 12,500-foot limit at an altitude of 25,000 feet. Conrad hopes to certify the Cougar for 26,000 feet to take better advantage of the turbine’s high-altitude capability. Supplemental O2 will be required at that height.

By coincidence, FL220/230 is the height where the airplane logs its quickest cruise, right at 300 knots. (Rocket Engineering plans to offer Colemill Foxstar composite winglets, which increase cruise by six knots, for an extra $10,000.) Fuel burn is 33 gph per engine, 66 gph total. Do the math with the original’s 220 knots on 38 gph, and you can see mileage is only reduced by roughly 1 nmpg on the turbine conversion. That’s a small price to pay for cruising at near-jet speeds well above most of the piston traffic. In other words, you can fly very fast but not very far, or moderately fast and farther.

If you’re in a little less of a hurry, you can ease back on the thrust to consume 45 gph, and still manage to speed along at 250 knots. At this burn rate, you easily can manage four hours of endurance for nearly a 1,000 nm range.

Of course, pure, unbridled speed wasn’t the only goal of the Cougar. PT6A engines are phenomenally smooth, as they develop power with turbines that rotate at high speed (typically, 37,000 rpm) rather than multiple pistons that slam up and down. The PT6A series is the most popular turbine engine in the world, and it’s certified on nearly 100 models.

Replacing the Baron’s Continentals with Pratts boosts TBO from 1,600 to 3,600 hours, a major incentive all by itself. Turbines are inherently more reliable than pistons, and though you do pay for that reliability, some pilots feel the security and safety are worth the price.

Further, in addition to the obvious boost to multi-engine climb performance, single-engine climb nearly sextuples from 270 fpm to about 1,800 fpm, providing a more comfortable hedge in the event that one mill goes to sleep. Conrad hasn’t pinned down the exact SE spec at this writing, but he suggests single-engine climb performance will be so good that it will no longer be a safety concern for single-engine operation.

Labels: Turbine Twins

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