Monday, March 13, 2006
VLJs and Air Taxis: The Contenders
While the net number of platforms seems to be growing on the list of contenders, I’ll focus on only what I see as the three most viable at this time: The Eclipse 500, the Cessna Mustang, and the Adam 700. Some of the other possibilities could warrant more consideration very soon.
This post will compare aircraft design and performance, and acquisition costs. Sometime later, posts will explore some of the less glamorous but no less important aspects of the designs: often referred to as the ‘ilities’ and in still later posts I plan on giving an appraisal of the major “players” as well as some high-level observations concerning possible Air Taxi operational concepts.
The Aircraft: Eclipse, Cessna & Adam
Assuming that all the designs ‘fly right’ and there are no handling abberations associated with any of the aircraft, there are three ‘most important’ VLJ contender performance design elements to evaluate: structure, propulsion, and avionics.
Structure. An evaluation of the contenders from Eclipse, Cessna and Adam pretty much cover all the salient factors (‘Marketeer’ hair-splitting aside) that would apply to any other contenders, as these three manufacturers’ offerings represent all the key discriminating technical approaches in areas of airframe, propulsion, and avionics.
The Eclipse 500 and Cessna Citation Mustang are both conventional wing-body-tail configurations, while the Adam 700 is a twin-boom design (see graphic). The Eclipse and the Cessna are optimized designs tailored for their target range/payload specifications, while the Adam is a follow-on design optimized for maximum commonality with another version of otherwise basically the same aircraft, the Adam 500. The Adam’s planform was originally designed as a twin propeller-driven aircraft with one engine in front and another at the back of the center fuselage, commonly called a ‘push-pull’ arrangement. The primary advantage to the Adam’s planform in the prop version is there are no asymmetrical thrust or adverse yaw problems encountered in single engine-out scenarios.
The Adam is (by a nose) the largest (dimensionally) of the three designs and is of all-composite construction. The Cessna and the Eclipse are of primarily sheet-metal construction, although the Eclipse makes use of new technology that greatly reduces labor-intensive rivet construction techniques. The weights for the Adam and the Cessna are not yet ‘published’ from what I can determine, but the Cessna is supposed to be approaching 8000 lbs gross weight and the Adam 700 should be the same or heavier than the Adam 500’s 6500 lbs. The smaller Eclipse 500’s much lighter maximum takeoff weight is now expected to come in at family’ as the Cessna Mustang’s engines, although rated at a slightly lower thrust than the Cessna’s. This might also indicate a slightly better reliability for the Eclipse engines, if the major differences between the two thrust ratings boil down to how hard P&WC works the same components: differences in operating temperatures and associated stresses can cause different failure rates and modes.
The Adam 700 uses a Williams FJ33 engine. The FJ33 is not closely related to the Williams FJ22 engine that was a setback for Eclipse, but the FJ33 design is closely related to the well-respected Williams FJ44 engines now flying on many other aircraft including larger Cessna business jets.
Avionics. All three aircraft use the latest generation of avionics. Adam is teamed with Avidyne and utilizes their most advanced system available. Cessna uses a Garmin avionics suite, with one of the best display configurations I’ve seen in any non-military aircraft. Eclipse is employing a highly-integrated system from Avio.
While I cannot tell from the material available how integrated the systems are on the Cessna or the Adam, the Eclipse’s “Avio” system reaches far beyond traditional avionics capabilities. This is not at all surprising, since one of the three key tech goals of the Eclipse has all along been to field just such a system that takes a lot of the workload off the pilot/crew and enhances aircraft safety. The “Avio” is the product of a partnership involving Avidyne, BAE Systems and General Dynamics that:
“...is designed to replace nearly 30 individual boxes with 4 identical chassis units. Its major components are the electric power distribution system and the aircraft integrated electronics unit (AIEU) with dual FADEC channels, dual 3-axis autopilot and autothrottles."
The level of integration in Eclipse’s approach is getting into the territory more common to advanced fighter avionics design than people-haulers.
It is no secret that aircraft companies tend to obscure or highlight their performance data to put on their best face for potential customers. This is not necessarily deviousness on the part of manufacturers, but it is at least partially due to the fungible nature of aircraft performance. That is to say, unless two aircraft were designed to meet exactly the same specifications, one really can’t compare the two and state objectively if one is better than the other. Each is different with different strengths. Combine this fact with the reality that the customer rarely knows exactly what they need or what would be best for their operation and you get statements of performance data couched in vague enough terms and in various different ways, as to make most direct comparisons impossible. For example, aircraft range will be specified without all-important supporting information, such as with how many ‘people on board’ or what the total payload weight was or without the “fuel consumed” data. Unreal planning factors such as an average passenger weight of 150 lbs, accompanied by a trivial amount of baggage, or something equally un-“real world” may be given in the marketing pitches.
Eclipse is a remarkable exception to the rule in that not only has it been famously transparent in their development progress, but also in characterizing their claimed and forecasted performance data. Adam Aircraft I would gauge as the second most transparent: they present some data; probably a reasonable amount, given the ambiguities they still have to resolve in their final design and test stages. I would assess Cessna the least transparent of all, as they require interested parties to contact their staff if they are doing some comparison shopping.
Since all of the jets use latest generation technology optimized to some degree for the same flight regimes, some basic assumptions about performance can be made with relatively low risk of significant error. In their respective and equivalent design-optimized cruise altitudes, the lighter jet will generally have the lowest fuel consumption and highest cruise speeds. This would seem to give an edge to the Eclipse, and indeed, the cruise speed at altitude for the Eclipse is significantly higher (375Kts) versus approximately 340Kts for the other two aircraft.
In the Eclipse’s payload ‘sweetspot’ (pilot plus three passengers) it appears the Eclipse also has longer range and better fuel economy than the others. Economically, the Adam 700 may have some significant advantage at shorter ranges with higher passenger load factors.
This is an easy topic, because one thing aircraft manufacturers will usually tell you eventually is the price. [The hard part to figure out later is: what is the ‘Life-Cycle Cost’ vs. Utility that yields the ‘Value’ – the real bottom line.]
Straight out of the box, the Eclipse is the least expensive plane to acquire. in ‘June 2006’ dollars, the Cessna is projected to cost $2.623M, the Adam 700: $2.284M, and the Eclipse: $1.495M.
If the Eclipse 500 meets a buyer’s overall needs, it would take a lot of comparative savings in recurring costs for the other two aircraft to overtake the Eclipse’s substantial edge in acquisistion costs, to be competitive in a total life cycle cost comparison. But that is another post for another time.