Turbine Pilot: Citation Encore+: The Encore's Encore

Spec Sheet

Tricks of the Trade: Jet Fuel—
Pounds to Gallons, Revisited

Correctly converting at the fuel truck

The February “Tricks of the Trade” in “Turbine Pilot” contained a big error, for which we apologize. We said that 15 gallons equates roughly to 100 pounds of Jet A (based on Jet A’s nominal fuel weight of 6.67 lbs per gallon—rounded off to 6.7 lbs per gallon), but unfortunately that was the only correct advice we provided. The rule for translating Jet fuel in pounds to gallons—which you must do when fueling up at most locations—was in error. Here are some rules of thumb offered by readers.

Bob Darling of Las Vegas wrote, “There is a rule of thumb—it is to drop the zero, and then add 50 percent to that. So, if you need 1,500 pounds you would take the 150 and then add half, or 75, which is 225 gallons (150 + 75).”

William R. Simmons of Atlanta, wrote, “Another rough way to calculate gallons required is to know that 150 gallons is approximately 1,000 pounds. After that gets you in the ballpark, use the 15 gallons per 100 pounds to get you the rest of the way. For example, if I need 3,500 pounds I can get 3,000 pounds by taking three times 150 for 450 gallons. For the additional 500 pounds, multiply five times 15, or 75. So, in total you need 450 plus 75, or 525 gallons. If you have a calculator handy, you can just divide the pounds needed by 6.7 to get the gallons required.

“So how do you convert gallons to pounds? Jet fuel density varies with temperature, but is usually about 6.7 pounds/gallon. Hence, 100 gallons will give you 100 times 6.7, or 670 pounds. Don’t have a calculator? Use seven as a stand-in for 6.7, then drop five percent of the number. For example, 100 times seven is 700 pounds. Five percent of that is 35 pounds, so 700 minus 35 is 665, which is very close to 670. Five pounds difference is negligible since no fuel gauge is that accurate anyway. I believe Part 25 aircraft fuel gauges only have to be accurate within three percent at any given fuel load. Also, most turbine aircraft only use float sensors for annunciator light indications of low fuel condition, say 200 pounds/side left. The main fuel sensors might consist of five or six sensors per side, with one of those having a fuel density correction factor, which is applied to the total sensed in each tank.”

Finally, Jeff Loichinger of Annapolis, Maryland, offers, “Determine fuel need in pounds, add 50 percent to that number and divide the result by 10.

“For example, 5,000 pounds are needed, so add 50 percent (2,500) to that number, ending up with 7,500. Now divide that by 10 to get 750 gallons; 750 times 6.72 equals 5,040. Close enough!”

Thanks to all those who wrote in with their contributions. Members with other rules of thumb for turbine operations are welcome to submit them for publication in this space. Possible topics may deal with flight planning, checklists, operational procedures, or accommodating system quirks.

Cessna’s new Encore+ is the latest entry in the Citation 560 series of “middle-weight” business jets. Like its predecessors in the 560 series (the Citations V, V Ultra, and Encore) the Encore+ brings incremental improvements to this popular straight-wing design. In this case, those increments are quite significant. The Encore+ one-ups the Encore (built from 2000 through 2006) with its full-authority digital engine controls (FADECs), new instrument panel, and greater load-hauling capability. The standard, seven-seat interior (eight, if you count the belted potty), with its dropped aisle, four center-club seats, aft-facing forward seat, and two forward-facing aft seats, differs slightly from the Encore in that new seat designs give passengers a bit more headroom. A double-club seating configuration is optional.

Although most customers fly the Encore and Encore+ as two-pilot airplanes, it is possible to secure a single-pilot exemption to the rules usually governing turbofan airplanes in this weight category. But Cessna says that only about one in 25 owner-pilots earns the qualification to fly the Encore solo. This involves ordering a specific equipment package (to include a yoke-mounted transponder ident button, a functioning autopilot, and a boom microphone) and following certain training and operational guidelines. Five-day-long annual training is required, for example, and circling approaches are not approved.

FADEC power

The Encore+ powerplants have the same, 3,400-pound thrust ratings as those of the Encore, but power management is simpler and more precise with FADEC controls. The FADECs use computers to precisely set optimal power for takeoff, climb, or maximum cruise power, based on ambient air temperature, pressure, and airspeed inputs from the ship’s air data computers. All the pilot has to do is slide the thrust levers into the takeoff, climb, or maximum cruise power click stops and the FADECs automatically calculate and command the correct power setting. Obviously, this lowers workload during takeoff and climb, leaving the pilot more freedom to scan for traffic and maintain control of the airplane.

During takeoff, for example, all you do is shove the thrust levers forward three clicks until they’re in the “TO” notch. Automatically, the fan and turbine speeds come up to the right levels for takeoff. Now you’re able to steer the airplane through the takeoff run without the distraction of having to fiddle with the power settings, trying to reach the exact N1 values. Ditto for climb and max cruise settings. Just dial the power into the appropriate click stop—you can easily do it by feel—and you’re done.

The Pratt & Whitney Canada PW535B engines (the “B” suffix denotes FADEC-equipped) generate enough power for the Encore+ to reach maximum cruise speeds of 438 knots while burning a total of 1,767 pph (or approximately 263 gph)—at 29,000 feet, that is. At more normal cruising altitudes—say, 39,000 feet—true airspeeds drop to 427 knots, but fuel burns are more economical 1,203 pph (or about 179 gph). At the airplane’s maximum operating altitude of 45,000 feet, max cruise speeds and fuel burns are listed as being 414 knots and 892 pph (133 gph). All of those numbers assume standard conditions and a very light, 12,000-pound weight. Subtract five to seven knots for a 16,000-pound airplane flying at max cruise at 29,000 and 39,000 feet—which approximates an Encore+ carrying six passengers and flying with full fuel.

Pro Line 21 panel

The Encore+ features a three-tube Rockwell Collins Pro Line 21 avionics suite that includes two radio tuning units, Rockwell Collins’ FMS-3000 flight management system, an integrated flight guidance/autopilot system, a Garmin GPS 500, dual attitude heading reference systems, and much more.

The Pro Line 21’s primary flight displays (PFDs) and multifunction display (MFD) have active matrix liquid crystal digital displays that are bright and sharp, which is great for daytime visibility, but also help when it comes to displaying the standard-equipment XM WX datalink weather information and Jeppesen electronic charts on the MFD. The charts are geo-referenced, so you can follow your symbolic airplane’s position along an airport diagram’s ramps, taxiways, and runways, or through published approach, departure, or arrival procedures.

Radios can be tuned using either the panel-mounted tuning units, or the center pedestal-mounted FMS keypad. Meanwhile, flight director modes are selected on a small horizontal panel atop the PFDs, and to engage the autopilot and yaw damper, the auto-pilot panel at the base of the center pedestal is used.

In keeping with the Citation strategy of making popular options in past airplanes standard in newer ones, the Encore+ also has a TCAS II (Traffic Collision Avoidance System, with aural and visual avoidance advisories) and a Class A TAWS (terrain awareness and warning system). The TAWS is a Honeywell Mark VIII EGPWS (enhanced ground proximity warning system) that has several alert modes, including: excessive descent rate; excessive terrain closure rate; altitude loss after takeoff; unsafe terrain clearance; and excessive deviation below glideslope. In short, the Encore+ has just about every safety feature you’d expect in a much larger class of modern transport airplane.

On top of all this, the Pro Line 21 enabled a weight savings, much of which was applied toward the airplane’s increased payload (the original Encore has a 16,830 pound maximum ramp weight—200 pounds less than the Encore+). Cessna says that the Encore+ has a 1,170-pound payload with full fuel (with a maximum takeoff weight of 16,830 pounds). That’s approximately 217 pounds more than the Encore’s full-fuel payload.

Flying the Encore+

My flight in the Encore+ was with Steve Workman, a flight supervisor and senior pilot in Cessna’s 70-pilot demo pool. Workman had little explaining to do when it came to firing up. All you do is push a button, then monitor the interturbine temperatures (ITTs) during the start sequence. We computed our V-speeds for takeoff at our 15,500-pound takeoff weight, and at our temperature of 10 degrees above standard. That day at Wichita’s Mid-Continent Airport (and Cessna’s headquarters) V ₁ (takeoff decision speed) came in at 95 knots; V _R (rotation speed) was 101 knots; and V ₂ (takeoff safety speed) was 112 knots. All those numbers were dialed into the “refs” menu on the PFDs, and then were posted automatically on the vertical-tape airspeed indicators.

After lineup and clearance to take off, I advanced the power—click, click, click—to the takeoff detent, and soon we were rushing down Wichita’s Runway 19L. The first two V-speeds came and went in seconds, and after a hefty pull, we launched. The somewhat high stick forces for rotation are because the main landing gear is well aft of the center of gravity. After liftoff, it was time to trim nose down to compensate for all the pitch-up created by those 6,800 pounds of thrust, and dial the thrust levers back one click to the climb setting. Workman pointed out how blue carats on the N1 vertical tape show maximum continuous power levels. Our white N1 tape readouts were snug in the blue carats, indicating that the FADECs were indeed making the engines meet climb power requirements.

We settled into a 247-knot, 3,600-fpm climb, and went directly to 40,000 feet in just under 15 minutes, holding 2,000 fpm even as we passed through 34,000 feet. After levelling off at 40,000 feet I clicked back to the max cruise detent, watched our true airspeed build to 223 knots indicated, then saw a true airspeed of 419 knots on the PFD’s readout. Our fuel burn was 590 pph per engine, or about 176 gph total. Not bad, and right on book numbers, given that the air temperature was now two degrees below standard.

We descended to 10,000 feet for some airwork and approach stalls. As I slowed the airplane and extended flaps to their full, 35-degree deflection, an autotrim interconnect helped by introducing some nose-down trim as the stall approached. The Encore+ has a stick-shaker to announce an impending stall, but no stick-pusher to automatically command corrective, nose-down action. I held the nose up until the stall break, which came with a prompt rolloff to the left that was easily corrected during recovery.

An ILS to the Hutchinson, Kansas, municipal airport, followed by a circle-to-land maneuver to Runway 22, came next. V _REF was targeted as 104 knots, and the landing was pretty good, if I must say so myself—a testimony to the Encore+’s docility in low-speed maneuvering, and its forgiving, trailing-link main gear. (The last time I flew an Encore was in 2001.)

The takeoff from Runway 22 was a bit more exciting, as it involved a V ₁ cut at liftoff. There is no rudder bias on the Encore+, so there is a need for firm rudder pressure to keep the nose straight during climbout. After trimming for the yaw, it was time for a return to the runway for a single-engine landing. V _REF this time was 115 knots for the single-engine condition, but the landing, if anything, was better than the previous one. More focused attention, I guess.

After all that excitement, the return to Wichita was a piece of cake. After 1.4 hours getting used to the Encore+, I was starting to feel at least somewhat at home. Easy to fly, a strong performer at altitude, able to fly five passengers from coast to coast with one stop, and a service center never far away—these are the reasons Citations continue to account for large portions of the business jet market.

Apart from that, the Encore+ has another plus that may appeal to some: It’s the biggest business jet that can be flown single-pilot. The next step up the Citation 560 line is the $11 million, big-cabin XLS+. At $8.2 million, the Encore+ may be out of reach to you or me, but so far, 15 customers have seen fit to take delivery.

E-mail the author at [email protected].