The hallmark of a successful airplane builder is the ability to evolve its designs. Starting from scratch to create an all-new airplane must be a rare event. Real success comes through finding ways to stretch, enlarge and enhance airplanes already in production. And no company, at least in the personal and business aviation sector, has been better at that then Beech.
In 1947 Beech introduced the revolutionary Bonanza that is the foundation of a host of models including the A36 Bonanza and Baron 58 still in production today, more than 70 years later. Then came the Twin Bonanza in 1952. Despite the name, the Twin Bonanza borrowed little from the original other than the wing planform. But the “Twin Bone,” though not a huge success in its own right, was the foundation of the Queen Air, which with turboprop engines added in 1964, became the King Air, and the rest, as they say is history.
Given its string of success in evolutionary model design it was natural for people at Beech to continue to look for more ways to evolve their airplanes in new directions. In the early 1980s somebody, or perhaps a small group of people, realized they had the basis for a very good single-engine turboprop. That airplane was the pressurized Baron 58.
I don’t know how long it took, but probably months, not years, to remove the piston engines from the wings of a Baron 58P and install a single turboprop in the nose. The prototype was an elegant looking airplane with the classic lines of the Bonanza/Baron, and by all accounts, the same excellent flying qualities those airplanes have always been admired for. Beech named the new airplane the Lightning. I remember thinking at the time the name was a perfect match for the way the airplane looked, and the performance it promised.
The reason the Lightning looked so good, and came together so smoothly, was selection of the Garrett TPE331 turboprop engine. The 331 is a compact engine measuring just over three feet long. And it’s light. At under 400 pounds it weighs less than a big-bore Continental piston engine. The 331 also has the best fuel efficiency of the small turboprop engines, and its throttle response is quick, very much like a piston engine responds so pilots transitioning from piston to turboprop would need to adjust their flying techniques very little.
I hung around Beech and Cessna and the other manufacturers a lot in those days, and both Richard Collins and I heard good reports about the Lightning development. The prototype was flying frequently and performing well. There were said to be no “show stoppers.”
That was dead wrong. There was a show stopper. A big one. And it was in the nose of the Lightning. When word got around that Beech was using the Garrett engine, the Beech dealers went crazy. Not only no, but hell no. They wouldn’t sell an airplane with a Garrett engine, no matter how well it flew or attractive its capabilities.
As the firestorm from the dealers built, Beech management relented and sawed up the Lightning prototype to put a Pratt & Whitney PT6 turboprop engine in the nose. The graceful and elegant Lightning grew a schnoz that an army of plastic surgeons couldn’t fix. I don’t know how something grows a pot belly on its nose, but that’s what the PT6 powered Lightning looked like to me.
The problem is the PT6 engine draws intake air at the rear and exhausts its hot gases out the front of the engine. The Garrett 331 takes air in through a classic “smile” inlet in the front and exhausts out the rear.
With a Garrett in the nose, the Lightning nacelle was sleek and compact. And the propeller plane was right where you want it. When a cowling was created that could take air in the front and turn it 90 degrees to enter the rear of the PT6, the girth of the cowling grew enormously. And the much longer PT6 engine shoved the propeller plane far forward, which is very destabilizing to flying qualities and would have almost certainly required a larger horizontal tail, or other significant design changes.
Compared to the PT6, the Garrett 331 is lighter, more fuel efficient, and more durable with thousands of hours longer interval between overhauls.
Because the 331 is a fixed-shaft engine it has one major drawback compared to the PT6 and that’s starting. To start a 331, everything in the engine, including the propeller, must be rotated fast enough to move air through the engine when you lite the fire. That requires lots of battery power, or better yet, a ground power cart.
To keep the propeller pitch flat during start, the Garrett requires “start locks,” a complexity the PT6 doesn’t require, And the compressor and turbine sections of the 331 rotate very fast, somewhere around 40,000 rpm, so the engine emits a banshee howl on the ramp that is loathed by line crew and other pilots everywhere.
In contrast, the PT6 is a free turbine engine, meaning there is no mechanical linkage between the gas generating section and the power section that rotates the propeller. To start a PT6, you need only rotate the gas generator section which takes comparatively little effort. You can even start a PT6 with the propeller feathered. The engine doesn’t care. Because everything is turning so much slower in a PT6, the noise level is far lower and not remotely as annoying as the Garrett engine.
But it wasn’t the starting challenges or ground noise level of the Garrett that put the Beech dealers into a rage. It was the history of turboprop market competition. For decades Beech people had been selling against the Turbo Commander, Mitsubishi MU2, Cessna 441 Conquest and the Swearingen Merlin, all Garrett powered. The King Air is a great airplane, the PT6 is a great engine, and, well, Garrett engines and the airplanes they power aren’t as popular. Beech sales people simply weren’t going to change their pitch for the Lightning.
Beech flew the PT6-powered Lightning some, but I didn’t hear much positive about the testing. When the extra weight, complexity and cost of switching to the PT6 were added up, the Lightning no longer made sense as a derivative of the P Baron so the project was shelved.
Would a Garrett-powered Lightning have succeeded in the market? I don’t know. It would have had a few years head start on the TBM, Pilatus PC12 and Piper Meridian that are so popular and successful in the market. And the PT6 reputation for being bullet proof still makes pilots feel comfortable flying behind that single engine.
The TBM, PC12 and Meridian prove that a nice looking and efficient cowling can be designed for a PT6 engine. And the PT6 is probably the most revered turbine engine ever, at least the most admired turboprop in terms of reliability and simplicity. But creating a PT6 cowling that looks and fits naturally on the nose of a Baron may not be possible, or at least not simple and easy.
So if you want to know what doomed the Lightning, it was the people who would have sold it. With a Garrett in the nose, they could no more do that than a Red Sox fan can say anything good about the Yankees. One thing is certain: airplane development programs seldom proceed in a straight line, and technical issues are only one consideration, and often not the first.