The manifold pressure and propeller rpm wound down abruptly on the engine in front of me. I lowered the nose a little and continued to climb. There was no roll or yaw change, and the only pilot task was to stay on climb airspeed, the same value I had been holding before the power loss. This straight-ahead climb on one engine is the reason the Adam A500 exists. It is a twin that any competent single-engine pilot can fly after an engine fails.
The centerline thrust concept with one engine pulling while the other pushes is nothing new. Cessna built more than 2,000 Skymasters between 1963 and 1980 and the push-pull twin still has many fans. But the Skymaster, though its design was focused on engine-out ease of flight, came along at a different time. The Skymaster was pushing uphill against a large fleet of conventional twins at a time when the industry believed that all twins were safer than singles, particularly at night, over rugged terrain or in instrument conditions.
Now, it's a different environment for the piston twin. Insurance companies, and many pilots, assume that a piston twin is more risky than a single unless that twin is flown by a pilot of extraordinarily high experience, and one who receives regular recurrent training. The piston twin is the bad boy of perceived safety these days, while the Skymaster was simply, as all prophets must be, ahead of its time predicting attitudes that were to come. You will still need a multiengine rating to fly the A500, but it can be restricted to centerline thrust only so you won't need to go through all of the Vmc control demonstrations and other engine-out maneuvers that just don't apply to this airplane.
Back in 1998 Rick Adam correctly identified the need for a new type of twin if the typical pilot was ever going to have a chance to move up from a single, and the A500 was born. Centerline thrust with its total simplicity of engine-out flying qualities puts the question about pilot capability and experience to rest. And Rick also thought the time was right to transition to an airframe made from carbon fiber instead of aluminum or the less costly but heavier fiberglass some other manufacturers were using.
Rick is an experienced pilot with lots of time in turbines as well as pistons, and he feels most comfortable with a second engine, particularly since he has spent much of his time flying over the hostile terrain out west. But he also understood that 350 hp is the practical limit of piston aircraft engines at this time, so if cabin size and performance were to be increased, the power of a second engine was necessary.
What Rick didn't grasp-and nobody else has-is how complicated, even overwhelming, a job it is to design and build an all-new airplane, and a new airplane manufacturing company, all at the same time. Adam expected the A500 to be in service five years ago, but just now the airplane has won approval for pressurized flight to its ceiling of 25,000, operating air conditioning and workable avionics. The basic airplane has been "certified" for more than two years, but that time has been needed to complete work on winning approval for the full flight envelope.
Burt Rutan was a consultant for Adam on initial design work for the A500 and you can see his influence. The twin booms sweeping up to grasp a horizontal tail between them, the slender 44-foot wing, and the pod type fuselage are all elements Rutan has used before. Tail booms are almost a necessity for a centerline thrust twin to allow space for the rear propeller, and getting the horizontal up and out of the prop wash reduces overall vibration and stress on the tail. The booms provide a handy place to locate the main landing gear, and the fuselage shape is ideal for containing pressurization loads.
The ramp presence of the A500 is dramatic. It's a big airplane that sits high off the ground. The wing is a foot longer than Piper's Malibu and Meridian, the wingspan kings before the A500. And the Hartzell propellers are aggressively swept, giving the airplane a powerful appearance at rest.
The carbon fiber construction yields very smooth surfaces that are, of course, free from skin laps or fastener lines. But the first complete production A500, serial number seven, is still rough around the edges. The company acknowledges that it has details to work out to make fairings and access hatches fit as they should. To this point Adam has been a development company and is now working very hard to transform itself into a manufacturing company. It has the FAA production certification so the big things are all being done correctly, but Adam is now concentrating on the dozens of little things that make an airplane look right.
The engines are twin turbocharged and intercooled Continental TSIO-550s rated at 350 hp each. Continental provided a great deal of guidance on engine installation and cooling, and those issues are not a problem.
Adam made an interesting pressurization design choice that was not obvious, at least not to me, but makes a lot of sense. The airplane taps cabin pressure air only from the forward engine turbochargers. Using pressurization air only from the forward engine saves a great deal of complexity, and thus cost and weight. If the forward engine fails you descend. Actually, you are not going to stay at 25,000 feet on one engine in any case because not enough thrust would be available. And the cabin leak rate is low enough, combined with a prompt descent, that there is no concern about hypoxia, any more than there would be in an unpressurized piston airplane that experienced a failure of its oxygen system while flying at 25,000 feet.
The rear engine is assigned the task of turning the air conditioning compressor. Again, this simplifies the plumbing by keeping the air conditioning equipment in the rear of the cabin, while the pressurization lines and connections are forward.
The A500 cabin is bigger than other six-seat piston airplanes. It's a full foot wider than the Baron cabin and nine inches longer. The A500 cabin is a couple of inches wider than the Malibu, but several inches taller. One issue with the A500 is that the wing spars intrude into the cabin floor. Most recent designs place the fuselage on top of the wing and its carry- through spars.
The A500 avionics package has been in transition but now with production rampup has settled on a three-tube Avidyne Entegra flat glass display system, with S-Tec autopilot and Garmin GPS and other avionics. The airplane is fully approved for IFR and night flight.
The pilot seats are easy to access with the cabin airstair door ahead of instead of behind the wing as it is in other cabin-class pistons. The cockpit is roomy enough for comfort, and the panel is modern looking with its big glass displays and sidestick controls. The engine and propeller control levers are arranged in the normal way with the left set of levers operating the forward engine. It seems natural to me that the left levers would be for engine number one, even though number one is in the nose instead of on the left wing. In any event, that's how Cessna did it with the Skymaster.
