PiperJet Launches New Airplane Category

It appears that the PiperJet, assuming it meets its objectives, would create a fourth category of light jet. The first category of the new light jets includes the Cessna Mustang, which is a totally conventional twin-engine jet that meets all of the traditional jet standards, including engine-out takeoff safety standards. The Mustang differs from larger business jets such as the Cessna CJ family only in size and cost, but not in terms of certification standards or levels of redundancy.

The second category includes the Eclipse 500, which is a twin, but does not meet conventional jet standards. Eclipse has certified the 500 to light airplane requirements meaning, for example, that like a piston twin, it will be able to continue after an engine failure in most circumstances. However, unlike all other jets previously certified, it is not required to demonstrate that it can continue after an engine failure at the worst possible time.

A third category of new light jets would be the Diamond D-Jet and what little we know about the single-engine jet that Cirrus is taking orders for. These are truly personal jets with performance and flying qualities more akin to a turboprop than jet. These personal jets, as some call them, are modest in performance but their uncomplicated systems and flying qualities make them ideal for less experienced pilots who want to move up.

But the PiperJet would be in a different category of light jet. With its proposed top cruise speed of 360 knots it is as fast, or faster, than the light jet twins. The announced 1,300 nm IFR range is amazingly long, longer than other light jets and better than many, much larger, traditional jets. And its 35,000-foot ceiling is smack in the middle of the high jet flight levels, and not far from the 41,000-foot maximum of the multi-engine light jets. With its expected performance the PiperJet transcends the personal jets, but because it has only a single engine, it will be much more accessible to pilots without considerable multi-engine experience. Insurance companies have been quite comfortable with lower time pilots moving into the single-engine turboprops such as the Piper Meridian, TBM-700 and now 850, and the Pilatus PC-12. It seems likely that the attitudes will be similar for the PiperJet, particularly when you consider that the TBM-850 is already close in terms of cruise speed and altitude. In fact, much of the expected PiperJet performance can be credited to having only a single engine because that one and only engine requires a lot less fuel than two. That's good news at the fuel truck, but in terms of performance, it's all about weight. With one engine you save the weight and drag of a second engine, but more importantly, you don't need to carry the fuel to feed it. With less fuel the airplane weighs less and is thus more efficient, whether you take that efficiency in terms of speed, or slow down and reap the benefit in range.

But where on the airplane to put that single engine? Instead of burying the turbofan in the fuselage where it could be mounted further forward, Piper has elected to mount the engine on the vertical fin, much like the DC-10's center engine. This engine location simplifies feeding air to the engine because there is no need for ducts in the wing roots or fuselage. But the tail-mounted engine does move the center of gravity far aft, and with the thrust line above the center line of the airplane, power changes can affect the pitch attitude.

There are also potential issues with feeding reasonably undisturbed air into the engine when the airplane is operating at a high angle of attack. The PiperJet engine is mounted far lower on the vertical fin than is the center engine on a DC-10, but Piper's testing and analysis shows that the fuselage won't disturb the air flowing into the engine inlet enough to cause problems. To handle the rearward CG caused by the tail-mounted engine Piper has moved the wing fairly far aft. There is also a large baggage compartment in the nose where the stuff you take along can act as ballast. Conventional business jets all have their engines mounted on the tail cone, not as far aft as on the PiperJet, but far enough aft that when empty most jets are out of the aft CG limits. Virtually everything that goes into a typical business jet is ahead of the CG so the center moves forward as you load them. The same will almost certainly be true for the PiperJet, where the only troublesome weight and balance situation is likely to be a flight with only a single skinny pilot to move the CG forward. That situation may require some ballast in the nose baggage compartment.

The PiperJet fuselage is an adaptation of the PA-46 Malibu/Mirage/Meridian cabin with a four-foot stretch. The structure will be all new because the wing is in a different location, and the cabin must withstand about 7.5 psi of pressure to fly at 35,000 feet compared to the 5.5 psi maximum pressurization in the Malibu family. Also, the PiperJet has a huge three-foot wide cabin door, certainly the largest on any light jet, and that requires substantial structural change in the Malibu fuselage design.

The PiperJet cabin is larger than most of the VLJs with an optional seventh seat or lavatory located behind the copilot's seat. There is a baggage compartment aft of the forward-facing seats in the rear of the cabin, as well as in the nose. Piper has created an entirely new natural laminar flow (NLF) wing for the PiperJet. NLF means that the shape of the airfoil is specifically designed, and then built to extremely tight tolerances, so that airflow remains laminar instead of tripping into turbulent flow over much of the wing. Cessna has demonstrated good success with NLF wings on the CJ family of jets. If successful, an NLF wing can reduce drag markedly, thus increasing speed and range. Piper has not yet announced the engine or avionics suppliers for the PiperJet, but does say that the airplane is designed for 2,400 pounds of thrust. That is almost exactly the rating of the version of the Williams FJ44 that powers the Citation CJ2+. Since Piper has partnered with Honda to market the HondaJet, it would seem obvious that Piper would select the new HF120 engine from the Honda and General Electric partnership. However, the HF120 engine has not been used on any production airplane yet, and will first power the HondaJet slated to enter service in 2010, the same time as the PiperJet. That means the engine will be certified, of course, but have no real world experience. Do you build a single-engine jet with a new engine, or with one proven over many thousands of hours on the CJ fleet? Bet on the Williams.

The selection of avionics supplier seems far more wide open. Piper officials say that they expect some dramatic changes in what technology will become available during the four years of PiperJet development, and they want to keep their options open. Piper is showing sidestick controls in the cockpit mock-up and plans to offer an optional autothrottle system. Piper plans to certify the jet for single-pilot flight, of course, and for reduced vertical separation minimums (RVSM) to qualify for flight above 28,000 feet.

Piper has been conducting detail design work on the PiperJet for about one and one-half years. The characteristics of the airplane resulted from extensive owner surveys Piper conducted before completing the design. Owners of Malibus, Meridians, TBMs and other high-performance singles told Piper they were more concerned about speed, payload, range and cabin comfort than they were about price. When Piper distilled the dreams of their surveyed pilots and owners they found that people wanted what could be called a luxury sport utility jet, not a very light jet. So Piper engineers worked backward, in a way, using the desires of owner-pilots to set the specifications, and the airplane was then designed to meet those specs.

Following the lead of the established jet manufacturers, Piper is guaranteeing the basic performance of the PiperJet. The airplane is guaranteed to meet the 360-knot max cruise speed with a +5 percent/-2.5 percent margin; full-fuel payload of 800 pounds is promised with a +/-5 percent margin; and the 1,300 nm IFR range has the same expected margin of error.

Piper has not released runway requirements for takeoff and landing, or rates of climb. No weights, either empty or maximums, have been announced, but that is becoming typical of jet development programs. What prospective owners really care about is speed, payload and range, not some arbitrary empty weight or maximum takeoff weight. Company officials do say that they plan for the airplane to meet the 61-knot maximum stall speed that is standard for single-engine airplanes, and that they will certify under the normal category one-turn spin requirement, also a standard for single-engine airplanes.

Developing the PiperJet is easily the most costly and complicated project in the company's 75-year history. And so far, no single-engine jet of this size and performance has been certified in the normal category. Piper President Jim Bass says he has the backing of parent company American Capital Strategies, which is fully prepared to fund the program. Piper received orders with deposits for the PiperJet before any details were announced and booked many more after the mock-up and performance goals were revealed at NBAA. The beautifully crafted metal mock-up of the PiperJet drew some of the biggest crowds at the convention, a huge hall full of every size and category of business jet. Now the hard work begins. Making the PiperJet a reality.