Waypoints

The return of the V-tail

September 1, 2007

Editor in Chief Thomas B. Haines owns a Beechcraft Bonanza A36 — with a straight tail.

One could almost feel the group's collective eyebrow go up as it studied the Cirrus personal jet mock-up. A V-tail? The members of the aviation media murmured to each other comments such as "Don't they remember the Bonanza?" "What about Dutch roll tendencies?" "Lateral stability. How are they going to solve that?" "Do they know how a V-tail will handle at high speed, high altitude flight?"

The naysayers were alive and well, once again questioning the wisdom of the Klapmeier brothers who have turned Duluth, Minnesota, into one of the leading aircraft manufacturing cities in the world. The doubters were some of the same ones I remember in the 1990s saying that no one could ever certify or mass-produce an all-composite airplane.

It seems as if some have built entire careers around doubting the Klapmeiers — and losing. The company that some said would never survive has become the producer of the most popular airplane in the United States, the SR22. Cirrus has made "glass cockpit" a household phrase in the aviation community. Thanks to Cirrus, whole-airplane parachutes have gone from a curiosity to a mainstream feature on many models beyond their own.

A source who had seen the Cirrus V-tail jet concept a few weeks before the unveiling had given me a heads-up, so I was free to watch the reaction of the other media representatives when we were given a first look at the mock-up at the Cirrus Owners and Pilots Association Migration Five event at the Duluth factory in late June. Undoubtedly anticipating the questions about the V-tail, Dale and Alan Klapmeier were well prepared, backstopped by their vice president of advanced development, Mike Van Staagen.

The Klapmeiers see their jet with the single engine nestled on the top of the aft fuselage as a logical step-up airplane for their SR22 customers. It has been conceived and designed to resemble the piston-powered airplanes in many ways, especially in low-speed handling — an important point for pilots not used to flying jets. As Alan Klapmeier pointed out, the notion of a "personal jet," another variation on the highly undefined "very light jet" category of airplanes, dates back to the 1950s. But engines were always the problem. Engines necessary to provide the required thrust for a light jet were too big and fuel inefficient. Cirrus was a major partner in the federally funded General Aviation Propulsion program in the 1990s. That program encouraged manufacturers to develop alternative engine programs aimed at the GA market.

One result was the Williams EJ22 engine that was originally destined for the Eclipse 500 VLJ. That engine was ultimately determined to be not powerful enough for the twin-jet Eclipse, which is now powered by Pratt & Whitney PW610F engines. However, it was the EJ22 program that helped Williams refine its FJ33 and FJ44 family of engines, making them even lighter and more efficient — and good choices for Cirrus, Diamond, and Piper for their single-engine VLJs.

The Klapmeiers have been talking with Sam Williams, founder of Williams International, for years about ways to build their vision of a personal jet. One of the big issues in a single-engine jet is engine placement — and you can see a variety of schemes at work today. For its D-Jet, Diamond embeds the engine under the aft fuselage, ducting the combustion and bypass air from side inlets. Piper is installing the single engine in its PiperJet in the vertical fin, somewhat like the third engine in the McDonnell Douglas DC-10. As noted, Cirrus chose the top of the fuselage, using the V-tail arrangement to allow the thrust a clear path aft.

As with everything else aerodynamic, each arrangement has its own plusses and minuses. Any ducting of combustion and bypass air or thrust complicates manufacturing and decreases engine efficiency. The seemingly straightforward approach by Piper maximizes efficiency but opens the door for center-of-gravity and pitch issues with power changes and demands an extremely strong structure high up on the tail.

Studying these and other concepts, Van Staagen ultimately decided that for Cirrus, the best choice was to put the engine in a pod on the top of the fuselage, angling the engine slightly downward and then vectoring the thrust to straighten it out as it passes between the tail surfaces. The positioning eliminates concerns about foreign object damage, allows the construction of a simple engine nacelle, reduces cabin noise because the engine is behind the cabin area, and also reduces rotor burst concerns.

The V-tail reputation

It is the reputation of early Beechcraft Bonanzas and their V-tails that causes some to wonder about the tail arrangement. The Bonanza V-tail, designed in the 1940s, was discovered to be a weak point in the design when pilots allowed the slippery airplane to stray outside the normal flight envelope. When attempting to recover, the pilots would overstress the tail structure, causing it to fail. Beechcraft created an effective fix in the 1980s that consisted of a simple strengthening bracket at the base of each ruddervator. But the damage was done. The V-tail's reputation was set and the company shortly thereafter stopped making the V-tail models.

To those who cling to the Bonanza's V-tail reputation, Van Staagen points out that engineers have learned a thing or two about aerodynamics and structures in the past 60 years. He holds up the Global Hawk and F-18 as examples of high-performance, modern airplanes that successfully deploy V-tail designs.

Not that the Cirrus decision necessarily needed any additional validation, but it didn't hurt when another new-think manufacturer surprised the media crowd at EAA AirVenture in July — some of the same ones murmuring at Duluth a few weeks earlier — with the unveiling of not just a mock-up of a single-engine V-tail jet, but an actual flying concept airplane. The crowd was stunned when Eclipse Aviation founder Vern Raburn taxied up to the media event in the concept jet. As it turns out, Eclipse contractors had built the single-engine jet in secret at the NASA Wallops Island facility in Virginia and flown it nearly 30 hours by the time it landed at Oshkosh — including at speeds up to 250 knots and up to 25,000 feet.

Not that a 30-hour flight test program of a concept airplane in any way resembles a real FAA certification program, but it should go a long way in quieting those who believe there is nothing new to learn about designing and building airplanes. Stay tuned as we watch these single-engine jet programs mature over the next three years. My guess is that more than one old wives' tale will be skewered before the first of the new models rolls out the door.

E-mail the author at thomas.haines@aopa.org.