By David Brown
Many years ago, I was involved in production testing of a jet trainer in the UK. Initially we had unpressurized jets and used to climb to 30,000 feet for our production testing as a matter of course. With the exuberance of youth, we ignored the occasional sinus problems, the bends, fatigue, and other such inconveniences, while accepting the rock-hard cushions of the Martin-Baker ejection seats as part of the cost of doing business. A couple of years later, we had progressed to a pressurized version of the same jet, as by now the powers-that-be had realized that the Royal Air Force CFIs were having problems with the day-after-day effects of climbing to high altitude two or more times a day without the benefits of pressurization. From our flight-test point of view, we soon realized that life was much better in a pressurized aircraft.
Fast forward a decade or two, and I was ferrying a military turboprop trainer west across the USA, part of a two-ship formation. Again we were unpressurized, and at 24,000 feet, I was monitoring my oxygen blinker rhythmically opening and closing. Occasionally, I would have to give control to my colleague in the other cockpit, unclip my military-style oxygen mask, blow my nose, eat a sandwich, take a sip of water, etc. before clipping the mask back on. Again, we were on the same Martin-Baker ejection seats, and again the cushions were rock hard after a couple of hours droning west over Texas and the Arizona desert.
I liked the speed, as we were covering the ground at a true airspeed of almost 300 knots, better than doing the trip at low altitude in a general aviation aircraft with TAS of just over a hundred knots, as I was doing on weekends. But the discomfort of mask, bonedome, seat, harness, and parachute straps was a different matter
“One day,” I said over the intercom, “We will be able to do this trip in pressurized luxury and comfort.”
“But not today,” came the answer from our imperturbable test pilot in the front cockpit. A moment later, he resumed humming Willie Nelson’s “ …on the Road again…”
I have news for the world. That day has arrived with the introduction of the pressurized Evolution.
I first saw the Turbine Evolution at Reno last September when it was used as the pace plane for the Sport Racing class. I was impressed by the speed and intrigued by the fact that this was a kit-built plane.
In February, I was fortunate enough to meet up with Evolution Aircraft’s President, Kevin Eldredge, at Cable Airport in Southern California, get the inside story of the Turbine Evolution, and take a short flight in between the storms battering Southern California.
Background to the Turbine Evolution
The Evolution is the latest in a long line of speedy composite aircraft, which originated with the Lancair series of aircraft. Originally piston-powered and available in kit form, the design has evolved into a mature, pressurized, turbine-powered aircraft, which the Evolution Aircraft Company of Redmond Oreg. produces. There is a big emphasis on ease of production. The aircraft was designed using 3-D digital computer-aided design. This ensures interchangeability. Components and systems are built to Part 23 specifications. Wing design has been optimized using Xfoil analysis software and validated by wind-tunnel testing. The small wing is optimized for cruise performance, maneuvering, efficient climb, and low-speed handling.
The engine is a 750SHP Pratt & Whitney PT6A-135A. A four-blade Hartzell propeller has electrical ice protection and 698W is fitted with an optional wing and horizontal thermal system from Kelley aerospace thermal anti- ice/de-ice system. (An alternate system has de-ice boots on the leading edge, with the boots inset into the leading edge to preserve the smooth contours). A glycol spray is used on the windshield.
The tricycle landing gear is robust, and the trailing link main gear is forgiving on landings.
The cabin pressure vessel uses close-tolerance carbon components with Hysol epoxy bonding. Doors have inflatable pressure seals. The pressurization system operates automatically and provides 6.5psi cabin pressure differential giving an 8,000-feet cabin altitude at 28,000 feet
Avionics include the EFC900X avionics suite with synthetic vision and an integrated autopilot. An L3 Trilogy electronic standby instrument is mounted high on the glareshield, and a Radiant touch-screen display controls the environmental, pressurization, and lighting.
Walk around of the Evolution
The Evolution is one of the most aesthetically pleasing aircraft I’ve flown. It’s all swooping curves and subtle contours, made possible by its composite construction, which gives an absolutely smooth surface without the usual panel lines and joints of a metal structure. It has small wings with Fowler flaps.
Entry is via a step below the left wing root then through the gull wing door over the left wing. The cabin has a classy leather interior. Avionics are the twin PFD/MFD displays of the Evolution Flight Control system 900X. Flaps and gear controls are handily on the glareshield. Pressurization and cabin temperature controls are on a touchscreen to the right of the two main displays. As backup to the PFD and MFD, an L3 Trilogy is mounted high on the glareshield in the pilot’s line of sight.
Building the Evolution
The Evolution is built to FAR 23 and registered in the Experimental Category
This specifies that the owner/builder must do 51 percent of the effort. In practice, this usually involves the owner working alongside the factory for two weeks, then working for four to six weeks over an eight-month period with an assistance shop with professional guidance. Typical time to first flight is six to eight months.
The Evolution Aircraft Company has an approved list of builders.
When it comes time for first flight, an Evolution approved test pilot will do the initial flying and complete the required 40 hours of initial flying, which covers the whole flight envelope out to Vne and speeds down to the stall at all cgs.
Then the owner gets to fly his aircraft. An owner needs the usual Instrument Rating with high performance and complex endorsements together with a high-altitude training (The 28,000 foot service ceiling is set by RVSM requirements. The Evolution has the performance to go higher).
The EXPERIMENTAL placard only means two things in practice, the first being no flying for hire and the second no Flight Into Known Icing (FIKI). N698W has de-icing on the wing-leading edge, and propeller de-icing in case of inadvertent flight into non-forecast icing. This is one of the options available for Evolution owners.
Kevin Eldredge said that the anti-ice system on 698Wsystem works well in clearing the wing and prop from ice, and the maximum rate of climb of 4,000 feet/min gets the Evolution through any layer of cloud before ice has a chance to build.
Normal cruise speed of the Evolution is 275-290 knots burning 30 to 39 gph of Jet A. Pulling back to best economy gives 27 gph. Eldredge usually has flight plans for a cruise of 260 knots TAS and flies up to Flight Level 230 on his flights between Oregon and California.
Full fuel payload is around 800 pounds, depending on the final weight set by the options selected by the owner.
Range is around 1,100 nm with IFR reserves. Pressure differential is 6.5psi and gives a cabin altitude of 8,500 feet at FL280. Bleed air is used for cabin conditioning.
The week before my flight, Evolution #72 had taken to the air for the first time at the Redmond Factory.
With more than 70 Turbine Evolutions built, the investment in facilities and workforce at the Redmond factory is paying off.
Flying the Evolution
It’s time to go fly the Evolution. Eldredge climbs aboard and I follow, climbing into the left-hand seat. Once the gull-wing door is closed and locked, I adjust my seat fore and aft, then check the rudder pedals are adjusted, and strap in.
Engine controls are on a quadrant between the two front seats.
Startup and taxi are standard for a PT-6. The Evolution maneuvers well on the ground and has a small turning radius using the rudder pedals.
We taxi to runway 24. Occasional use of Beta keeps the speed down. Simple pre-takeoff checks are completed, we select takeoff flap, announce that we are taking off on Runway 24 (Cable is an uncontrolled field), line up and open the throttle. The full 1,200 feet of Torque is used for takeoff. After a commendably short run of 1,500 feet, we come off the ground, raise the gear and flaps, and then accelerate to best climb of 105 knots. We turn south to clear the pattern and throttle back. A glance across the cockpit to the pressurization display shows that the pressurization is already working.
We fly south over the Chino Hills. Chino airport with its busy airspace is off to our left. The map display lets us keep track of our position in the crowded airspace. Even at three miles every minute we cover the ground pretty quickly.
Early Evolutions produced complaints of heavy roll controls. The Evolution Company has been working the problem by changes to the trim tabs.
Maneuvering within the limits of the restricted airspace available to us with weather all around provides no surprises. Handling is good.
After a quick tour of the local airspace, I come back into the pattern at Cable, slow the aircraft and drop half flap, retrim with the electric trim on the sidestick, drop the gear, and then bank onto a curving base leg finals and lower the rest of the flap. Continuing to slow, we are on final approach with speed decreasing through 85 knots, with a good view of the runway. The trailing link gear provides a soft landing.
We land on the numbers, use moderate braking, and turn off at the mid-field taxiway (about 1,700 feet).
The PT-6 is a well-proven turboprop. It has a TBO of 3,600 hours. The Beta mode, with throttle to the aft position on the quadrant, moves the prop to a reverse pitch and slows the aircraft rapidly.
Span 36 feet 8 inches
Length 29 feet 5 inches
Height 10 feet
Wing area 133 square feet
Wing loading 32.3 pounds/square feet
Max TOW 4,300 pounds
Empty Wt 2,550 pounds
Useful load 1,774 pounds
Fuel 186 gals (698W has an extra aux tank in the rear fuselage, but this would only be used with the rear seats empty for cg reasons).
Full fuel payload 632 pounds
Best ROC 105 knots
Best Angle of Climb 85 knots
Va 190 knots
Vne 256 knots
Max cruise 300 knots
Normal cruise 285 knots
Max ROC 4,000 feet/min
Vstall clean 76 knots
Vstall (flaps) 61 knots
Takeoff run 1,500 feet
Landing run 1,500 feet
The basic kit cost in the region of $600,000, which includes all the parts for the Evolution except for the engine. Eldredge reckons a typical cost will be around $1.4 million, depending on the options chosen, which might include an auxiliary fuel tank in the rear fuselage, the anti-ice option, or a ballistic parachute.