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.