by Rick Durden
The world of general aviation has seen impressive new-age single-engine airplanes from Cirrus, Diamond and Lancair but new piston twins have been relegated to the back of the developmental hangar. Adam Aircraft hopes to change that.
In Englewood, Colorado, Adam is seeking to certify the first new piston-engine twin since the FAA approved Cessnas T303 more than 20 years ago. The company, founded by Rick Adam, is following the lean business practices he learned while making a tidy sum of money in the information technology business.
Accordingly, Adam Aircraft is near certification of the A500, the first of what is intended to be a family of piston, turboprop and jet aircraft in which as many parts as possible are common to all models. Parts count is minimized and the A500, as the first model, is substantially overbuilt so as to simplify the certification of larger, more advanced follow-on airplanes. Further, the airplane is being kept simple so that manufacturing doesnt have to be carried out by rocket scientists getting paid more than the $895,000 asking price for the airplane.
The Adam A500 is well along in certification, so much so that it may have occurred by the time this reaches print. The A500 began as the CarbonAero proof-of-concept vehicle built by Scaled Composites of Mojave, California under contract specs outlined by Rick Adam. Adam knew all about the safety advantages of redundant powerplants coupled with centerline thrust but he makes it clear that hes not breaking new ground. Tandem-mounted engines were pioneered as early as World War I and, of course, Cessna carried on the tradition in the 336 and 337.
The CarbonAero flew some 300 hours and, with modifications, lead to the first and second A500 prototypes. Both of the prototypes were built from what will be production tooling. Relatively small changes have been made and the third prototype A500, considered the conforming airplane, will be used for the certification flights during late 2003 and early 2004.
Rick Adams professed approach to designing and building an airplane is to stick with the proven. The A500s structure is primarily composite-the control surfaces are aluminum-of pre-impregnated carbon-fiber produced by Toray, the same material and supplier that has been used for some time on airliner components. Obviously, composite structures are no longer new in aviation with Beech, Cirrus and Lancair paving the way for FAA certification. So on that count, Adam isnt faced with showing the FAA anything new.
While the FAA has been so conservative with structural strength of composites that the weight saving promised a decade ago hasnt happened, the benefit is a significantly stronger airframe than would be the case with metal with a much lower parts count, reducing the cost of manufacturing. And the airframe can be assembled by unskilled labor.
Adam is keeping much of its manufacturing in house, including tooling. Engineers design the needed tool and an in-house CNC milling machine cuts it out of high-density foam. If and when a change is needed, the milling machine makes it. Turnaround for tools is less than a week versus months for outsourcing. Because he was using his own money initially, Adam set up his company to run 24 hours a day, six days a week, using techniques learned in the computer industry to communicate project status to the next shift.
Adam thus pays straight time but gets about three weeks of work done each week, which is part of the reason the company has gone from start-up to certification in about five years. Its about year away from certifying its A700 jet, while having spent only $60 million, far less than other companies who are not as far along.
This Thing is Big
The A500 is a larger airplane than the photos suggest. It stands tall on its wide-track landing gear and at 36.7 feet long, 9.5 feet high and with a 44-foot wingspan, think Cessna 414/421 to get the feel. At 6500 pounds gross, its lighter than a 421 and will carry something like 230 gallons of fuel. Powerplants are 350 HP turbocharged TCM TSIO-550-E engines, giving it a range of 1100 miles, with IFR reserves.
As with most composite airframes, the surfaces are smooth and clean but heres a twist: the wing leading edges are removable, making damage repair less expensive than on other aircraft, as well as allowing quick installation of TKS deicing. The winglets are actually ventlets, elevating fuel vents to preclude siphoning.
The landing gear is hydraulic, actuated by two electrically driven pumps. Theres a separate set of lines for a back-up nitrogen blow-down system so a broken hydraulic line wont prevent extension. Interestingly, the design of the twin booms means little damage should occur on a gear-up landing, as the undersides of the booms are lower than the fuselage.
Fuel is carried between the C-channel wing spars, providing good protection in the event of impact. The fuel system is dirt simple. Virtually all fuel lines are outside of the pressure vessel, something we applaud. A single fuel line connects the tanks to a center shutoff valve that is normally off.
Starboard of that valve is a fuel pump and a line that provides fuel to the rear engine; to port is a pump and a line running fuel to the front engine, so the left tank feeds the front engine, the right tank feeds the rear. Return fuel from the respective engine-driven pumps goes front-left tank; rear-right tank and theres a shutoff valve for each engine. Thats it.
If one engine should give up and the flight has to be continued long enough to require crossfeed, all the pilot does is open the valve on the line between the tanks and turn on the fuel pump for the tank from which more fuel will be drawn. Most twins require two fuel lines for crossfeed, the A500 needs only one, so only one fuel line crosses under the cabin.
From an occupant-protection standpoint, the fact that fuel lines must pass through the pressure vessel for a short distance to get both engines is a concern. Adam handled the problem by routing the lines most of the way in a tunnel below the center of the cabin. The tunnel is at a lower pressure than the cabin and has drain holes to expel leaked fuel. Where the fuel lines exit the tunnel into the pressure vessel, theyre encased in hoses that will drain any leaked fuel back into the tunnel.
In the spirit of simplicity, there are no cowl flaps, further reducing pilot workload. The location and shape of the rear engine air inlets required tweaking to reduce duct rumble, Adam told us. The three-bladed Hartzell scimitar props are long-bladed and turn at 2700 RPM, making noise a concern. But testing indicates that the airplane will comply with flyover takeoff noise requirements at 2690 RPM, which is where the engines may be redlined.
Entry is via a single plug-type airstair door thats retained with six pins. The door sill is higher than were accustomed to due to certification requirements that the aircraft float after ditching. Given that a composite pressure vessel is far different than a metal one with regard to leaks, we suspect that if an A500 ever ditches, it will float until the Coast Guard sinks it with gunfire. There are two overwing exits, giving an almost unheard of-for a GA airplane, at least-three ways out of the fuselage.
The cabin is about the size of a Cessna CJ1, with plenty of space for four passengers plus the crew and a pressurization goal of an 8000-foot cabin at FL250, max operating altitude for the airplane. Unfortunately, baggage must be stored in the cabin, aft of the seats, something that will engender complaints. (A belly pod will be optional.)
With full fuel, the probable real-world cabin load will be about 700 pounds. With six 200 pounders aboard, theres capacity for about 146 gallons of fuel, enough for about three hours flight at 40 GPH with 45-minutes of reserve. While opinions vary on the fuel-versus-cabin payload tradeoff, taking three big people 1100 miles or six big people more than 600 miles isnt bad.
Having been shoehorned into uncomfortable cockpits over the years, we were pleasantly surprised by the size of the flight deck on the A500. However, the floor under the rudder pedals is raised, badly restricting knee room and causing the side stick to impinge on ones legs. That will be corrected on the production A500, were assured.
From a crashworthiness standpoint, the lack of a yoke yields open space thats a big positive for protecting the pilots, as is the use of a side stick for the flight controls. We much prefer side sticks instead of yokes, which can do ignominious damage during impact, not to mention blocking the view of the panel. The restraint system for all seats is a four-point harness and the seats themselves meet the most recent dynamic impact requirement of 26Gs forward and 18 downward. Adam is evaluating new shoulder harnesses that contain airbags and may offer them as an option.
We were impressed that Adam had remembered the panel design lessons of the 1960s and put all of the switches and gauges in front of the pilot rather than on overhead panels where they can open up a skull during an accident and/or cause bifocal wearers to expand their repertoire of profanities as they try to read switch labels.
Adam will certify the A500 with steam gauges because these will sail through the FAA hurdles. But immediately after initial certification, a glass cockpit will be on the agenda. The Avidyne Entegra line will be used because Adam feels these work well and the FAA has experience with them on other certificated airplanes.
For now, avionics are Garmin, the autopilot is from S-TEC and the engine gauges are Vision Microsystems displays. Radar is an option, although with the developments in datalink, we wonder whether many will order it. The basic airplane is priced at $895,000 with the avionics described above. We were told that with the most common avionics upgrades and options, the airplane will invoice right at $1 million, which means that a slower, smaller, unpressurized twin-the Baron-is more expensive.
Adam intended to certify the aircraft with FADEC (full authority digital engine controls), but we were told that TCM continually missed its development deadlines, so the first several airplanes will have three levers per engine, rather than the hoped-for one.
The electrical system is straightforward. To avoid using vacuum pumps, the all-electric flight instruments have the needed redundancy via an individual bus for each engine, each with a 100-amp alternator and a battery. Should something go wrong, theres a single switch to tie the buses. In addition, load shedding requires toggling only one switch to reduce electrical load to the essentials of lights and avionics.
The only complaint we had concerning the flight deck was limited visibility upward. It caused loss of sight of the runway on the turn from a right base to final, something that could be a problem in low weather. We were advised that the U.S. Forest Service is considering the A500 to replace its P-Barons in the FAC role for fire fighting and that more upward visibility was a requirement for that mission. Adam has expressed its willingness to provide it and we believe it wouldnt hurt to have it on the off-the-shelf airplanes as well.
To get underway, the front engine is started first, allowing the pilot to visually clear the area and use its noise to alert bystanders to clear the rear prop.
The engines are so well annunciated-the panel is directly in front of the pilot, just below the glareshield-that theres no need to start the rear first to determine that its running.
To put it bluntly, with all the engine performance gauges and annunciator lights on the A500, any pilot who cant tell that either engine is not running is either suffering from the blind staggers or is stunningly incompetent.
We noticed that while the annunciator lights were easy to see in direct sunlight, the master caution and warning lights were not. It was difficult to tell when those two lights were on. We recommend that be addressed in the production aircraft. Ground steering is via differential braking, as seems to be the standard these days.
Takeoff acceleration is what one expects of a good-sized piston twin, brisk but not eye-watering and a reminder that theres some mass to be put into motion. With the wide gear stance, tracking is shamelessly easy and the pusher-tractor engine combination nicely cancels torque and P-factor effects.
The rudders are outside the propeller slipstream and are only needed if theres a crosswind, becoming effective at about the time the airspeed indicator comes alive. The side stick is angled inboard about 20 degrees with zero aileron deflection. It takes about one takeoff to determine the precise spot so that both main wheels stay on the ground during the roll.
The nosewheel is raised at 81 KIAS and A500 feels much like an Aero Commander as the flight deck rises slightly with the nosewheel while the mains roll until unsticking at about 95 KIAS. It flies off smoothly; with the flex of the trailing beam gear making it nearly impossible to identify the actual moment of liftoff. Gear retraction takes about 7 seconds and induces no pitch change, although flap retraction does.
Vy is 110 KIAS and produces a steep deck angle, eliminating forward visibility, so we doubt it will be used often. Accelerating to 130 KIAS for better visibility didnt diminish the climb rate by more than a few hundred FPM. One of the advantages of a tandem twin is that the control surfaces are not deflected in a climb, helping the rate. At about 300 pounds below the 6500-pound gross weight, we observed an all-engine climb rate at Vy of 1800 FPM from the 5500-foot elevation departure airport through 10,500 feet, where one engine was pulled to idle.
To our mild amazement, the airplane easily held altitude and may have climbed slightly while holding Vyse of 105 KIAS, again partially due to the fact that it was not necessary to deflect the rudders and ailerons. Once zero thrust was set, we saw just over 300 FPM upward at 11,500 MSL in some turbulence. We were advised that because theres no need to establish flight with zero sideslip, the drag curve on the A500 with one engine out is not as steep as in wing-engine twins. Therefore, a pilot who has difficulty holding blue line precisely, either due to skill deterioration or turbulence, wont face an abrupt loss of climb rate, as in wing-engine twins.
The ease with which a positive rate of climb was held reminded us that the loss of one engine on a twin is an emergency. However, the challenge of maintaining directional control in a wing-engine twin may in itself create a second emergency that you dont face in a tandem twin: risk of control loss. In the A500, it appears that the only thing a pilot has to do after an engine crumps is to suck up the gear and hold blue line.
Once thats accomplished, the airplane will climb at most weights when below 10,000 MSL. If the pilot feathers the prop on the dead engine, the climb rate will approximate that of a loaded light single, although at about a 30 percent higher airspeed. With appropriate initial and recurrent training, we think the A500 will be an easy step-up for operators of high-performance singles.
In flight, we found the controls, other than the ailerons, to be pleasantly harmonized and appropriate for the size and weight of the airplane. Its not, however, one thats going to be tossed about the sky.
We were warned in advance about the friction in the aileron circuitry and the resultant break out force. It was indeed unpleasant; small corrections in roll were difficult to make. A rudder-aileron interconnect doesnt help things as it introduced some adverse yaw when trying to make small corrections.
We had previously observed that the ailerons in the A700 jet had noticeably less system friction and do not have the rudder interconnect. We were advised that the A700 system will be installed in the production A500. We hope so. If thats the case, the A500 should approach the Cadillac feel of a 400-series Cessna.
Precise airspeed and altitude control is easier in the A500 than in most airplanes we have flown. The airplane could comfortably be trimmed to hold speed to plus-or-minus 2 knots. Slow flight is solid, including turns, with up to the 40-degrees of landing flaps. A power-off stall with 1 knot per second deceleration resulted in getting the stick full aft, a bit of nose bobbing, the airspeed cycling between 76 and 80 KIAS, no tendency to roll and a 1500 FPM rate of descent.
We were advised that a faster deceleration would produce a straight-ahead break. Adding power generated a positive rate of climb before we had the throttles three-quarters of the way forward. Theres noticeable pitch change with flap extension and retraction, easily trimmed out.
We did a two-way cruise speed run at 17,500 feet and recorded 195 KTAS while burning 42 GPH in a prototype that had no gear doors. We expect the production airplane will probably meet the goal of max cruise of 230 KTAS at 25,000 feet; almost as fast as a 90-series King Air.
Descending for the airport, we discussed speed brakes with the chief test pilot, Glenn Maben. He said they are anticipated so that large power changes arent needed for a descent when ATC does its slam-dunk thing. Pulling the power back too much, unfortunately, means loss of pressurization. The gear and flap speeds are planned to be 150 KIAS, not fast enough for the gear to serve as a speed brake. Instrument approaches are flown at 120 KIAS with approach flaps, generating a deck angle that makes picking out the runway easy.
In the pattern, target 110 KIAS on downwind with approach flaps and 105 KIAS works out well on base, with landing flaps and 100 knots on final, with no more than 95KIAS over the fence. Because the wing is clean-no engines out there, remember-you have to close the throttles prior to the flare, otherwise the airplane will float. The A500 seems to land well out of a full stall, rather than an attitude landing, something unusual for cabin twins. Even though the elevator is above the prop arc, its quite effective and the nosewheel can be held off a long time in the rollout.
Can Adam Aircraft make money selling the A500 to the owner-flown market? Rick Adam says 80 percent of deposits are from owners of big singles that want to go into a twin but dont want wing-mounted engines and who find the Skymaster too slow, too small and, facing the facts here, too old. Just as Adam is not targeting the A700 jet at the owner-flown market because he believes buyers cant get insurance, he has worked with aviation insurers to make sure that they can insure the A500.
He told us that insurers will insure cover owners in the A500 if they have an instrument rating, are current and take initial and recurrent training. For the time being, Adam will have an in-house training program.
Given that the A500 is easy to fly and has decent performance on one engine, cruises only 10 or 20 percent faster than big singles and has a slow approach speed, its a good bet that a pilot whos willing to stay current can take advantage of the safety benefits of a tandem twin and make the transition successfully. At least thats Adams bet.
Yes, the Cessna Skymaster did not have a better accident rate than its peers, but we think the problem was pilots who didnt train periodically and knuckleheads who intentionally tried to take off with only one engine running.
Adam Aircraft is planning to offer a 24-month/1000-hour warranty and says it will aggressively pursue customer service. It may tie in with the growing number of FBOs that service Cirrus aircraft due to the commonality of TCM engines and composite structure.
Positive feedback from the initial buyers will be critical, but as Adam only expects to deliver about 40 aircraft the first year, we would expect the company can keep that number happy. Well be watching and listening to see if Adam can meet its goals.
Also With This Article
Click here to view “Checklist.”
Click here to view “Adam A500: All But Alone in the Market.”
-Rick Durden is an Aviation Consumer contributing editor. Hes an aviation attorney and a CFII. You can contact Adam at 303-406-5956 or www.adamaircraft.com.