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.
|The airplane flown for this report is serial number seven and is the first to have all systems installed and approved. It did not have the new three-tube Avidyne Entegra avionics systems that will be standard on A500s soon. The information here is from airplane flight manuals and represents performance at maximum weight and standard day conditions at sea level unless noted.|
As in all airplane development programs, the A500 has gained weight. The airplane I flew, serial number seven and the first with complete systems, had an empty operating weight of 5,460 pounds with a maximum certified ramp weight of 7,050 pounds. Four years ago empty weight was expected to be 4,200 pounds with a maximum takeoff weight of 6,300 pounds. Some of the weight gain came from the unanticipated little things that add up to a lot when the airplane is complete. But some of the empty weight can be blamed on too much unusable fuel which is now at 30 gallons, the weight of a full-size passenger. Adam expects to trim that down to five gallons per side with more testing to show that the fuel is in fact usable even in uncoordinated flight.
With about 175 gallons of the available 230 gallons in the tanks, and two onboard, we were close to the 7,000 pound maximum takeoff weight, though after taxi we would be down to somewhere around 6,950 pounds for the actual takeoff weight.
It makes sense to start the aft engine first so that you can hear it respond even though you can’t see the propeller. The starting techniques are typical for any big turbocharged Continental, and the engines fired immediately.
The A500 has a castering nonsteerable nosewheel, which is odd in this size airplane. I found it natural and easy to taxi using differential brakes-though I did keep trying to lead a turn with an engine as in a normal twin, to no effect, a habit experienced twin pilots will need time to break in the A500-but on a long taxi with a crosswind a lot of brake pressure, and thus brake heat, would be needed. The company will probably add nosewheel steering in the future.
It was a hot day at Adam’s home base on Centennial Airport near Denver, but the initial acceleration and takeoff roll were surprisingly quick given the airport elevation and our maximum weight. I needed about two seconds to be comfortable with the sidestick control after rotation. The forces are on the heavy side so you need to keep the airplane in pitch and roll trim. As with all sidesticks, the left roll input is where I notice the effort most. Pushing the hand, wrist and forearm away from the body is not a natural motion, particularly for a right hander operating the side stick with his left hand.
Initial climb rate was around 1,000 feet a minute, even though we were starting from a density altitude of nearly 10,000 feet. And the A500 held the rate well as I climbed toward its certified ceiling at FL 250. There are only three recommended power reductions on the way up, and in 29 minutes we were level at 25,000 feet. I was most impressed by the smooth and cool engine operation. Both engines remained within a couple degrees head and oil temperature of each other, and always comfortably in the green. Pilots with memories of hot rear engines in Skymasters can put them to rest with the A500. To get two engines mounted on wings to operate that uniformly would be a challenge, but to accomplish it with fore- and aft-mounted engines is truly remarkable.
At FL 250 the air temperature was 21° C above standard and, with 20 gallons per hour going through each engine, the A500 showed a true airspeed of 208 to 210 knots. I could have shaved two to four gallons per engine and slowed down to 190 to 195 and been able to stretch out the range. We descended to FL 220 where the A500 hits its top airspeed and saw 220 knots true on 44 gph total fuel flow. In the early days of the program Adam had hoped for a top speed of 250 knots, but that was with an airplane weighing considerably less and a program full of youthful optimism. The reality of 200 to 220 knots for an airplane of this size is pretty good.
The A500, as many airplanes do, had a problem with rolling off at the stall, particularly in the so-called “accelerated” stall test where speed is decreased at five knots per second. The solution, which is also a popular one, was to add drooping leading edge cuffs ahead of the ailerons along with vortex generators. The drooped leading edge operates at a lower angle of attack and thus continues to fly while the wing inboard of it stalls, so the ailerons remain active and effective through the stall, allowing the pilot to counteract any roll off. The vortex generators create a high energy wake that helps keep air streaming aft at high angles of attack instead of tumbling off in a span-wise flow that can reduce aileron effectiveness.
I stalled the A500 with no aileron or rudder input and it sort of mushed straight ahead. Even with the stick held full aft the airplane showed no tendency to roll at all, so the wing design is clearly a success.
Landings will be one of the greatest delights of an A500 pilot. The airplane has very long stroke trailing-link main landing gear and very powerful pitch stability, so it is extremely easy to put the airplane in the landing attitude and let it roll on. The greaser will be the typical A500 landing, which is great for the ego.
Adam hopes to begin testing to earn flight into icing condition approval this winter. The company had initially planned to install a weeping wing TKS ice protection system, but will probably go with inflatable deice boots, as it plans to on the A700 light jet. The windshield, propellers and pitot tubes are heated electrically.
The A500 is what I would call a specialty airplane for the pilot who wants the redundancy and performance of a twin, but is uncomfortable with or lacks the experience to be insured in a conventional twin. And it’s also for the pilot who simply wants a pressurized piston twin that is less than 22 years old. The last of the pressurized twins from Cessna, Beech and Piper rolled out in the mid-1980s and since then the only choice for piston and pressure was the Piper Malibu/Mirage single. At $1.25 million the A500 is not cheap, but the Mirage comes in at nearly $1 million with one less engine, and the Meridian at nearly $2 million is the lowest priced turboprop single.
For Adam the A500 is important because it is the company’s first airplane, and to pave the way for the A700 jet. Adam says about 65 percent of the airframe components are common to both airplanes, and even a higher percentage of the suppliers are the same. The lessons learned in developing the A500 will help push the A700 program along immeasurably.
Adam is under totally new management since founder Rick Adam retired earlier this year, and the new team is focusing its energy on developing production methods that can take much of the man hours and cost out of building both airplanes, while at the same time attacking issues of cosmetic quality. It has taken 15 months to build the first few A500s, but the goal is to shrink that process to 14 weeks. Adam is building subassemblies in Pueblo, Colorado, and will soon begin final assembly of A500s, and then A700s, in a new facility just completed in Ogden, Utah. Adam has raised more than $200 million dollars in the capital markets in the past year and has the funds to see its way into volume production.