Plane & Pilot
Tuesday, October 23, 2012

The Epic LT


Do It Yourself Rocket Ship


Taxi, Blast Off And…Wow
Starting the big PTA-67A is standard Pratt & Whitney. First, check to make sure there's plenty of battery juice. Next, engage the starter motor, ignitors, wait for Ng to pass 12% minimum, then bring the fuel-condition lever to low idle and wait for the power to climb through 50%. The prop then comes out of feather while the condition lever goes to high idle. The whole process normally takes less than a minute. With two standard ship batteries, all of the avionics stay on, engine temperatures stay cool and the start sequence happens quickly. The batteries also provide ample backup power to get back on the ground should the starter/generator fail in flight.

Taxiing feels precise with a "big-airplane" feel, and the castoring function of the nosewheel allows tight maneuvering. Like most turboprops, it's absolutely necessary to put the prop into beta to reduce thrust so that taxi speeds stay reasonable and the brakes stay cool.

The single air-stair door provides easy access to a comfortable, bright cabin with large windows.  The spacious area behind the rear seats can handle up to 300 pounds of baggage.
Before we take the runway and push the throttles forward, Finley reminded me that this engine is flat-rated to "only" 1,200 hp for five minutes during takeoff, and that it's important to watch all of the engine parameters to avoid exceeding any torque or temperature limits. Keep in mind that all that power produces a strong tendency for the airplane to want to go left, so a good amount of right rudder and attention to where you're going is important while you set the engine power. Finley suggested that we use 80% torque for the power setting and rotate at 80 KIAS. I held the brakes as I ran the power lever up, and we started to roll as torque passed 30%, so I released the brakes while Finley called out torque and I watched the runway. The airspeed reached 80 knots very quickly, and we lifted off while still rapidly accelerating. The gear-up speed limit is 135 KIAS, so I quickly lifted the gear handle as the end of the runway approached. Raising the flaps and lowering the nose a bit produced 170 KIAS with the VSI showing nearly 3,000 fpm. By FL 200, we were climbing over 1,000 fpm indicating 160 KIAS, using 58% torque and 757 ITT. We didn't work very hard to minimize our time to climb and still reached FL 270 in less than 15 minutes, which is pretty impressive.

Once stabilized in cruise at FL 270, the outside temperature was ISA+5, and we saw a true airspeed of 303 KTAS with torque showing 52%, ITT at a cool 760 degrees C and fuel flowing at 54.3 gph. Bumping the torque up to 58.7% produced an ITT of 800 degrees C (the limit is 840 degrees C), and the speed quickly increased to 315 KTAS with a fuel flow of 60.5 gph. It always takes more fuel to go faster, so if you want speed, the LT will do it. The published top speed is 325 KTAS. At normal cruise power settings, the LT can cover 1,385 nm, and if you pull the power back to long-range cruise (about 270 KTAS,) you can cover a whopping 1,628 nm with reserves. That's extraordinary performance—kit plane or not.

The ride feels solid, the cabin stays warm, and with noise-cancelling headsets, it's a dreamy ride. Without headsets, the particular airplane we flew seemed a bit loud up front compared to other single-engine turboprops I've flown. Finley explained that current airplanes include additional sound insulation, which cuts noise levels by 4 to 5 db—more than half. So, newer airplanes should be pretty quiet. As in most fast single-engine turboprops, ANR headsets make for a quiet, jet-like experience.

Deice And Pressurization
This kind of turbine flying involves high altitudes and lots of weather. So, the LT is equipped with deice boots on the wings and tail and incorporates the same heated, four-blade Hartzell propeller used on the Pilatus PC-12. The windshield has an effective defrost blower, and the extreme rake angle of the windshield prevents ice buildup. Finley also explained that the engine incorporates a large intake plenum, minimizing the chance of ice-related FOD and the need for an inertial separator. The prototype inertial separator is flying in the newest LT out the door. Of course, as an experimental kit plane, the LT isn't FIKI certified, so icing conditions must be avoided and operators are advised to exit any unexpected icing encounters. For weather avoidance, the airplane we flew had NEXRAD data supplied through XM satellite downlink. Onboard radar is an option two foreign builders have installed.

The pressurization system holds a 6.5 psi differential, which yields a comfortable cabin altitude of 7,300 feet at FL 280. An inflatable door seal keeps the cabin tight and a built-in bottle supplies oxygen in the event that pressurization is lost, though there were no quick-donning masks in the cockpit. The good news is that they probably aren't needed since the LT can achieve an impressive 10,000 fpm in an emergency descent. Simply pull the power, point the nose down and run the speed up to Vmo of 280 KIAS (0.64M), and you can get from FL 270 to 12,000 feet in only about a minute and a half.



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