All Grown Up: The Cessna CJ4

New wing and engine designs, plus advanced systems and avionics, make Cessna's newest light jet its best ever.

The controls felt like a Citation CJ, but the numbers on the new Collins Pro Line 21 displays didn’t belong to any CJ I had ever flown. Level at 45,000 feet, the true airspeed was 425 knots. And it had taken only 23 minutes to reach that rarified altitude after a near-maximum weight takeoff. How had Cessna’s entry-level light jet grown into such a performer? Well, it took about 17 years and four big steps to grow the original CitationJet into the CJ4 I was flying.

In the early 1990s, the cost of the Pratt & Whitney JT15 engine that powered the light Citations had increased to the point that the company could no longer continue to build its Citation 501 entry-level airplane at a price that made sense. But then Williams International entered the market with its all-new FJ44 series of turbofan engines with thrust ratings and prices well-suited for entry-level jets.

Cessna engineers realized that the new engine also provided an opportunity to improve the aerodynamic efficiency of the Citation 500 series, and the CitationJet — later shortened to just CJ — was born. The CJ had a cabin and cockpit very similar in size and shape to the original Citation 500, but it flew on an all-new wing that achieved a significant amount of laminar flow.

Laminar flow is, of course, the smooth, undisturbed passing of air over a surface, and it creates far less drag than the turbulent flow that is typical over most wings. The new wing was so efficient that the CJ, with about the same thrust, cabin size and weight as the Citation 500, cruised 30 to 35 knots faster.

Williams created ever more powerful versions of the FJ44 engine, and Cessna stretched the CJ cabin and increased the performance with the CJ2 and CJ3 models. The wingspan grew along with the fuselage length, but the same basic wing design, primary systems and avionics flowed into the new models.

Still, pilots and owners wanted more speed and range than the CJ3 could provide but didn’t necessarily want to move up into the midsize cabin category of jet. So Cessna’s mission became to preserve the excellent flying qualities of the CJ family, and its low operating costs, while giving owners an airplane with more speed, range and cabin room to move up to, and the CJ4 was born.

It’s easy to focus on the cockpit and cabin of an airplane because that is where we sit and work, but all successful airplanes start with a wing specifically tailored for the mission. Cessna enjoyed huge success with the unique wing it created for the long-range midsize cabin of its Sovereign several years ago, so it was natural to start with that basic design to create the performance necessary for the CJ4.

The wing is unusual because it has a very noticeable sweep — 12.5 degrees — of the leading edge but a straight trailing edge. Wing sweep reduces drag when an airplane is flying at Mach .70 or faster because the sweep makes the slipstream behave as though the wing were thinner than it actually is. In general, a swept wing gives up some low-speed lift and can produce unpredictable behavior at the stall. The CJ series of jets is rightly noted for low speeds on takeoff and landing, and docile stall behavior, and Cessna didn’t want to give any of that up, so it split the difference by sweeping only the leading edge.

However, the performance of the new wing is more complicated than just its leading-edge sweep angle. The airfoils are proprietary to Cessna and continuously change shape along the span of the wing to optimize performance at each station. The trailing edge of the wing is absolutely blunt and squared off. The edge itself is about half an inch thick and seems to defy what is logical about how a low-drag wing should look. When you run your fingers under the trailing edge, you can feel a subtle concave hollow ahead of the trailing edge, a design that Cessna has sought to protect. The unusual shape of the trailing edge cut overall drag in testing but was most effective in drag reduction during climb. I am constantly amazed by how such seemingly insignificant shape changes can alter the performance of a wing.

To qualify for the maximum Mach operating limit (MMo) of .77, Cessna dived the CJ4 to Mach .84, and the experimental test pilots reported that the dive test was one of the smoothest they had conducted. The wing seemed ready for even more speed, but the trim forces trying to push the nose back up reached the test limits.

The CJ4 wing is also significantly larger than those on the earlier CJs. The new wing has 330 square feet of area compared with 294 square feet for the CJ3 wing. More wing area is effective both at high-altitude cruise and on takeoff and landing. And a bigger wing provides space for more fuel, 1,118 pounds more than the CJ3. The new wing is a home run with the capability for faster climb, low-drag cruise at high altitude and higher airspeed, and more fuel capacity. The result is a 2,002 nm — no kidding, flight testing has demonstrated that the extra two miles are really there — IFR range at the high-speed cruise of 425 knots.

The CJ4 wing has two other features new to the light Citations, ground spoilers and modulated speed brakes. Others in the family have only two speed-brake panels per wing, one on top and one below, and they can only be either fully deployed or fully retracted. On the CJ4, the speed brakes are controlled by a lever next to the throttles and can be extended as much or as little as needed to meet descent requirements.

The three spoiler panels per side are for ground use after touchdown and, unlike the speed brakes, which are drag devices, the spoilers effectively kill residual lift to plant the CJ4 on the pavement for improved braking after landing, or during a rejected takeoff. Ground spoilers are the norm on all larger jets but are new to the light Citations.

When designing the new wing, Cessna engineers were able to move the main landing gear inboard, reducing the track. A narrower track makes all aspects of ground handling smoother, and the long-stroke, trailing-link landing gear that has been on all CJs smoothes any reasonable landing into a greaser.

When you first see a CJ4, I think you will find it to be a more sleek and stylish airplane than others in the Citation 500 family, but you may not immediately know why. The swept wing certainly adds a look of speed, but the real change is to the windshields and canopy. The new windshields and cockpit side windows are heated glass and sweep back gracefully into the canopy, while the windshields on the other CJs are high-strength plastic and are much more upright.

When the first Citation was developed about 40 years ago, the technology to make curved and heated glass windshields was in its infancy, so Cessna, like Learjet, used acrylic material and then blew hot engine bleed air over the outside of the windshield to prevent icing. Those plastic windshields and bleed-air heat systems have served well on thousands of Citations over the decades, but the bleed-air blast is noisy and can require fiddling with the manual control valves to get it just right.

The heated glass windshields in the CJ4 are on all of the time, so fogging and ice are simply not an issue. The glass area is somewhat smaller than on the earlier models, but I found the visibility in flight and on the ground to be great. And with less windshield and side window wrapping up into the overhead, there is less space for the sun to beat down on you.

Cockpit Redesign
The CJ4 cockpit is what I would call current in terms of human factors design. Except for a half-dozen switches on the avionics and electrical power control panel, all toggle switches are gone, replaced by on-off push buttons that light up to indicate their position. Toggle switches are OK in daylight, where it’s easy to see if the switch is up or down, right or left, to indicate the state of the system it controls, but at night toggles are hard to see, and thus it’s difficult to know what has been selected off or on.

For many years cockpit designers assumed the annunciator panel, with its rows of lights that indicate both major and minor system failures, was the most important thing in the instrument panel and placed the annunciators in the top center, where they are easy to see. Over the years it became apparent that pilots can fly their entire careers without ever seeing a significant system failure annunciated, but on every flight we change heading, altitude, altimeter setting and airspeed commands, turn the autopilot off and on and select flight director modes dozens of times. It became apparent that these so-called flight guidance controls should be front and center, where both pilots can see and reach them without diverting their attention down to the center pedestal, or worse yet, back to the aft end of the pedestal. I am happy to say that all the controls you normally use to fly the CJ4 are arrayed across the glareshield, where they are always in your normal field of vision and are easy to reach.

Closing the Hydraulic System When the first Citation was developed in the early 1970s, Cessna opted for an open center hydraulic system for reasons of simplicity and weight and to allow use of a hydraulic fluid that was less flammable than the standard fluids in use at the time. That same open system has been used in the 500 series of Citations, including the CJs, but not in the new CJ4.In a conventional hydraulic system, variable displacement pumps on the engines maintain a constant pressure, typically around 3,000 psi. The hydraulic pressure operates flaps, landing gear, speed brakes, spoilers, flight controls on larger jets, and wheel brakes. In the open center system of Citations, the fluid flows around in a circle and remains unpressurized until it needs to go to work. When the pilot asks for the gear to extend, for example, electrical commands from the gear handle close a valve to pressurize the system and send that pressure to the landing gear actuators. When the gear has completed its cycle and locks up or down, the valves open again and the hydraulic system opens up and is unpressurized.An open center system works fine and has demanded very little maintenance in Citations over the years, but it can accomplish only binary functions. In other words, it must fully extend the gear, or speed brakes, or move the flaps to a preset position. There can be no intermediate actions because the system would need to remain pressurized. In order to have variable speed brakes in the new CJ4, Cessna needed to go to a conventional pressurized system.The CJ4 does, however, have the dedicated and separate power- brake hydraulic system common to other Citations. An electric motor pumps up pressure in the brake hydraulic system whenever the landing gear is down. Because the system is isolated, failures of the main hydraulic system will not change the power-brake and anti-skid functions.

The CJ4 is also the first CJ to have a full crew advisory system (CAS) that replaces the idiot lights of the annunciator panel. Instead of an annunciator with a cryptic message coming on to alert the crew, plain-language messages appear on the multifunction display. For example, in other CJs, the annunciator light “wing anti-ice” could mean the wings are too hot, or too cold, depending on circumstances. Those kinds of confusing messages are replaced with a simple statement that the wing is too cold or too hot. Messages are color-coded according to priority and are stacked in order of urgency. Really critical messages appear in red letters, and the master warning light comes on to call the pilot’s attention to the CAS display. Aural alerts, also in plain English, announce certain important failures.

The CJ4 has the autopilot emergency descent mode that is becoming standard in newer jets. If cabin pressure is lost while flying above 30,000 feet and the autopilot is engaged, it will automatically begin an emergency descent to capture 15,000 feet and hold it. It is up to the pilot to pull the power back and extend the speed brakes for maximum descent performance, but if he conks out from lack of oxygen, the autopilot will get him down without flying into the ground.

The CJ4 is the first Citation I can think of without any knobs for radio tuning. The dual Collins flight management system control-display units are used to manage all data entry including radio frequencies. It would be rare to actually enter a navigation frequency, because they are all called up automatically from the flight management system database, but comm frequencies are simply typed into either of the keyboards.

The flight management system uses GPS with WAAS capability for navigation and also mixes in data from the rapidly scanning DME to enhance the navigation solution. The Pro Line 21 system contains the technology to meet required navigation performance (RNP) requirements that are rapidly becoming the norm in major terminal areas. Of course, traffic alerting and terrain awareness are all standard components.

The Collins integrated flight information system — often called the file server — is a fundamental part of the Pro Line 21 system and allows the display of Jeppesen approach charts, XM satellite weather, enhanced map overlays and a cursor control to manage the information available for display.

Cessna and Collins have also created a new dispatch switch that powers up the No. 1 comm radio, the flight management system and the file server so pilots can get ATIS and the clearance and load all data prior to engine start. After the generators are online, the full avionics system is powered up.

Advanced Electrical System
It’s going to be really tough to be left without an electrical power source for all normal items in the CJ4. There are, of course, two starter generators, and either one can power the entire airplane. But if both of those were to somehow fail on the same flight, the CJ4 has two aces up its sleeve in the form of an alternator on each engine that is independent from the generators.

The primary function of the alternators is to produce wild-frequency AC current to heat the windshields. However, Cessna has installed rectifiers that can convert that AC into DC power with enough amps to operate all avionics and basic systems. Flying the “black tube” approach in the simulator will still happen, I’m sure, but the FlightSafety International instructors will have to stand on their heads to concoct a scenario in which all four power generating sources fail.

The electrical system, as in other recently designed jets, has been significantly automated. Half or more of the circuit breakers that were in the cockpit of previous models is missing in the CJ4, banished to the main power panel in the tail cone. The current thinking on circuit breakers is don’t mess with them if they trip, so they are now out of reach of pilots. If a breaker pops, there are alternate load paths to keep the equipment and systems working. And moving the breakers to the tail gets big, heavy load wires out of the cockpit and back where there is room.

The CJ4 is the first jet to use a lithium-ion battery as standard. The battery has more capacity than the lead acid or nickel cadmium unit it replaces but weighs 30 pounds less. The technology is not the same as that in the lithium-ion batteries in portable electronics that have sometimes overheated. In fact, Cessna engineers couldn’t cause the new battery to fail. Certification rules require that it be overheated and exploded, if possible, to prove that the metal container withstands the pressure. No matter how much voltage or amperage the Cessna engineers put into the lithium battery, it would not overheat or come apart. And the life-cycle cost of the lithium battery should be lower because it requires no routine replacement as lead acids do, or the regular deep-cycle maintenance that nickel cadmium requires.

Longer Cabin
The CJ4 cabin is about two feet longer than the CJ3’s, with most of the stretch being ahead of the cabin door. There is more room in the cockpit to slide the pilot seats aft, and the stretch allows room for expanded refreshment centers and storage areas just aft of the cockpit. The cabin door has been redesigned, patterned after the Mustang’s, and is now square instead of wider at the bottom. The inflated door seal has been replaced by redundant passive seals, so one more maintenance issue is gone.

The cabin windows have been moved up so passengers can see out more easily without bending over. And the central seating area of the cabin is larger at the floor, even though the overall fuselage cross section is the same as that on other CJ models. Using a new construction technique, Cessna has been able to move the lower fuselage frames from inside the skin to outside. I know this is difficult to envision, but it’s true. The external frames are behind the wing-to-body fairing, where they add no drag, while passengers get to spread out more.

Flying the CJ4
By last December, Cessna had completed all testing for the FAA, a task that required more than 1,800 hours of flying in three airplanes. I was invited to fly the first production airplane, which had participated in the flight testing along with the prototype and the No. 2 production airplane. Even though it was built on production tooling, it was still laden with test equipment and ballast, so with just engineering test pilot Peter Fisher and I on board, we could bring the weight up to 16,650 pounds for takeoff, just about one or maybe two passengers short of the 16,950-pound takeoff limit.

Climbing into the CJ4 cockpit, you will immediately appreciate the short pedestal while clamoring into the seat. The CDUs and most other controls have been moved to tilt panels forward of the throttles, which cuts the pedestal length dramatically.

The CJs have had fadec engine controls for several years, but the CJ4 is the first to not have mechanical fuel-cutoff positions on the throttles. Cessna and Williams have acknowledged that the computer is in charge, and it will put fuel into the engines when it’s ready during start and will shut it off when you push the engine button from run to stop. It’s an important cultural step and one that recognizes automation is here to stay.

The CJ4 checklist is somewhat shorter than those for others in the family, thanks to more automation. For example, as in many other newer jets, the pressurization system looks up the elevation of the destination you have loaded into the FMS and enters it, saving pilots an unnecessary step.

Every light in the CJ4 is some sort of an LED, so turning on any and all lights that can help in visibility won’t shorten bulb life. The LEDs could last as long as the airframe, and maybe even outlast CJ4 pilots.

Cessna seems to have gotten the steering and brakes just right on the CJ4, and smooth, precise taxiing is easy. The flight control and throttle positions are totally familiar to anyone who has flown any CJ. And the takeoff speeds of 107 knots for V1 and VR and 116 knots for V2 are just about the same for a near-maximum-weight takeoff in the others.

The new, bigger wing and more powerful Williams engines teamed up to give an initial climb rate of near 4,000 fpm. Normal-climb airspeed target is 240 knots until reaching Mach .64. With one brief level-off on the way up, the CJ4 was through 30,000 feet in just over 10 minutes. There was moderate turbulence as we climbed through 37,000 feet in under 14 minutes. Air temperatures were within a degree or two either side of standard, and we arrived at 45,000 feet before the clock hit 23 minutes. Those are climb rates pilots of the first CJ could never have imagined.

At the certified ceiling of 45,000 feet, the CJ4 quickly accelerated to Mach .75, which equals about 425 knots true airspeed. Total fuel flow was 1,040 pounds per hour (pph). That is more than 10 knots faster than Cessna engineers predicted, but the fuel flow is on target, so the range is longer than forecast. Flying faster on the same fuel flow is a very good thing. If you had a big tailwind, you could pull back to the long-range cruise of around 390 knots and stay up longer and thus go farther, but in light winds or with a headwind, the maximum power cruise comes close to matching the slower long-range cruise in distance covered.

I made some steep turns at 45,000 feet and couldn’t make the wing buffet until the angle went well past 45 degrees, and I pulled pretty hard, and then there was only a very small rumble of complaint. The new wing clearly has lots of margin even at its ceiling.

The new variable-position speed brakes are a delight to use, making it easy to stay right on airspeed limits while still achieving the necessary rate of descent to meet controller demands. Down at 31,000 feet, where the CJ4, like most turbofan-powered airplanes, hits its maximum cruise speed, the air was three degrees below standard, and with max cruise power set, the jet blew right through its Mach .77 limit. With power pulled back to keep the speed right on the Mmo maximum Mach red line, the colder temperatures held true airspeed down to 448 knots, clear evidence that the airplane easily makes the brochure maximum of 453 knots with air temperature at standard.

Despite having an all-new wing, the overall flying qualities of the CJ4 seem to match the rest of the family with totally predictable and docile behavior. The new all-electric trim system matches its speed perfectly to the airplane configuration, so there is little pushing or pulling with speed change and flap extension or retraction. Some pilots may miss the trim wheel spinning against their right knee, but I never touch the thing except to grab and hold on when it runs away in the simulator. If the primary trim fails in the CJ4, there is a second system with a rocker switch on the pedestal under your right hand.

Cessna has done a great job of establishing easy-to-remember speed limits, and there are really only two. For all gear actions the speed limit is 200 knots, and the same for approach flap setting. Landing flaps can go out at 160 knots. None of that 197 knots, or 154 or whatever, that is such fodder for oral exams on type-rating checks.

Around the airport the CJ4 is as easy to fly as any airplane, jet or propeller. Landing approach speeds will usually be just over 100 knots, and the trailing-link landing gear that Cessna perfected many years ago smoothes every touchdown. The lift-dump flap extension of the other CJs is eliminated because the six panels of ground spoilers are so effective. It is perfectly natural to move your hand from the throttles to the longer speed-brake lever on touchdown to extend the spoilers.

Though all testing was complete at the end of last year, Cessna was still awaiting FAA certification, which undoubtedly will have happened by the time you read this. Single-pilot eligibility had been established, and it certainly looked like the CJ4 would qualify to be flown by pilots holding the CE-525 type rating assigned to all other CJs. If I had a vote, I would certainly put the CJ4 under the same type rating with a few days of required “differences” training to learn how to use the system and avionics advances.

In an otherwise dismal market for light jets, the CJ4 is a bright spot with a big order book with essentially no cancellations. Deliveries are expected to begin early in the second quarter. With its longer cabin, advanced avionics and systems, 2,002 nm range and 425-knot cruise speed, the CJ4 delivers what other light jets can’t. That, along with the rock-solid reputation of Cessna and the CJ family behind it, is the recipe for success in any market condition.


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