Taped to the wall of Gerry Merrill's office in Phoenix, Arizona, is a three-view engineering blueprint of a sleek, two-seat personal jet. Finely curved, it sports a V-tail and a single fat engine nacelle atop the rear fuselage. Merrill, a wiry 73-year-old, tells me that, compared to current propeller-driven light airplanes (which he dismisses as "archaic crap"), the airplane on his wall will fly twice as fast, get better fuel mileage, and be 30 times quieter. His proposed family of jet-powered light airplanes, he says, will revolutionize private aviation, if only he can raise the $120 million it would take to get them certified by the Federal Aviation Administration and into production.
The good news: "This is potentially a multi-billion-dollar business," he says. The bad: He can't break into the market.
Since the 1940s, jet engines have revolutionized military, airline, and corporate flying. But somehow, the jet revolution never trickled down to personal flying. A practical, affordable, jet-powered light airplane for private pilots—a Cessna Skyhawk, say, without the propeller—has for decades been only a dream. Five- or six-seat, $1.5 million to $3 million very light jets (VLJs) are just now on the market, but the vision of a single- or double-seat jet with the price tag of a propeller aircraft—one-eighth the cost of a VLJ—has never become more real than three-view drawings taped to the office walls of dreamers everywhere.
But Merrill stands apart from the rest; he probably knows more than anyone about small jet engines. A propulsion industry lifer who has worked on everything from torpedoes to funny-car dragsters, he's had a hand in the design of some 80 jet engines, ranging from the General Electric J79, used in U.S. fighters and bombers in the 1950s and 1960s, to the Teledyne CAE J402, used in today's air-to-surface and cruise missiles. But for more than 40 years, his abiding passion has been the idea of a small jet engine for light aircraft. He has spent most of that time bouncing back and forth between manufacturers, who weren't willing to bet the store on an engine that was not certified, and investors, who wouldn't put up the money for certification because the light-airplane market was too unpredictable.
Conventional wisdom holds that jet engines burn too much fuel at low altitudes to be suitable for light aircraft. Jets, it's said, are efficient only above 30,000 feet or so, where light airplanes fear to tread. "That's bullshit," says Merrill flatly. Sure, every jet flying today gulps prodigious amounts of fuel when going low and slow. But that's because they were all designed to run high and fast. The secret, Merrill says, is to simply optimize the configuration of an engine's turbines, compressors, and fan for, say, 250 mph at 15,000 feet instead of 500 mph at 40,000 feet. "It's not rocket science," he says. "My engine technology and materials are basically 1960s. The breakthrough is conceptual."
The results of optimizing a turbofan engine for low and slow are breathtaking—on paper, at least. According to Merrill's numbers, his theoretical 490-pound-thrust turbofan would, at 10,000 feet, push along his theoretical two-seat Cloudster airplane at 270 mph while burning 12 gallons of fuel per hour. That's 22 miles per gallon—about the same fuel efficiency that Cessna claims for its two-seat, propeller-driven 152, which flies not even half as fast. Climb to 23,000 feet, and the Cloudster will do 220 mph while burning seven gallons per hour. That's 31 miles per gallon. So much for the notion that jets at low altitude suck too much fuel, Merrill says.
Two primary factors account for the amazing low-and-slow fuel efficiency of Merrill's turbofans. All have extremely high bypass ratios and very low fan pressure ratios. (The bypass ratio is the amount of the air that passes through the fan—known as "cold thrust"—compared with the amount that passes through the core, or combustion chamber —"hot thrust." Typically, the higher an engine's bypass ratio, the better its fuel efficiency.) Merrill's engine for the Cloudster on his wall has a bypass ratio of 19, which is five or six times that of the current crop of VLJ engines, and double that of the most advanced jetliner turbofans. Merrill calculates a specific fuel consumption of around 0.30 pound per hour per pound of thrust—an extraordinarily low number, and one that is 50 percent better than the current VLJ mainstay engines, the Williams FJ33 and the Pratt & Whitney PW600 series.
But the real breakthrough in Merrill's engines is in their low fan pressure ratios. The ratio of pressures across the fan stage is a rough indicator of how much kinetic energy is wasted as air passes through the fan. "You've got to match the fan pressure ratio to the airspeed," says Merrill. "The lower the speed, the lower the FPR." Merrill is cagey about disclosing his engines' precise fan pressure ratio, but claims it is much lower than that on the VLJ engines.


Comments
Seems like a few dollars from each member of the EAA could get this off the ground.
Posted by Robert Graham on March 20,2008 | 04:24PM
Warren Buffett bought net jets after he looked at it.Like Donald Douglas Jr. he got it immediately.Berkshire-Hathaway's stock value has increased 10,000 % since it went public in 1960's.Maybe he would see the opportunity and benefits to aviation and his stock holders to come up with the 120M Gerry needs to make it happen.I saw the article in air and space. Respectfully submitted Pat Simmons
Posted by patrick simmons on March 20,2008 | 09:20PM
How about teaming up with James Dyson, of vacuum cleaner fame? Lesser known, Dyson's firm has also developed the Airblade, an equally revolutionary hand dryer. He certainly seems to know his way around the motion of air. Industries have been built on more obscure alliances.
Posted by Tracy Kreckman on April 9,2008 | 12:09PM
It's difficult to understand why someone would not either put up the money, or at least spearhead the drive to get the design proven
Posted by Ted M Sharpe on April 9,2008 | 02:59PM
I, have had the idea that by replacing the conventional fuel control of a gas turban engine with a computer controlled fuel injection system it would cut the cost substantially for a small engine.
Posted by G. Phillips on April 13,2008 | 04:46AM
What will be the cost of a six seated flight.Pl mail models with photograph and price.Needs for a resort project. Sangram
Posted by SANGRAM on April 23,2008 | 10:22PM
I realize I am late to the discussion, but it seems to me the problem here is Mr. Merrill is not radical enough. The market for inexpensive turbine power lies in power generation, not propulsion. The idea being to provide low-cost home and industrial power generation using proven turbine technology, which by it's very nature is "flex-fuel." That market is immense, world-wide and ripe for new products. A similar small low cost power generating turbine could be used to power a turbo-prop which would replace the common, antiquated piston power in small private aircraft. This eliminates the need for new airframes. The engine is simply adapted to current ones. What is most shocking is the conservatism of the aircraft industry and the market. As much as 20 years ago, automobile manufacturer Porsche tried to market a "Flugmotor" based on it's very well proven aircooled flat six. It had numerous advantages to the then current Lycoming, was essentially a bolt-in and yet, the project sunk without a trace. One can only imagine the uphill climb a new turbine engine would have if Porsche couldn't sell their superior piston engine to the same market.
Posted by Oski Eno on May 13,2008 | 10:30AM
For much less than $120 million, Mr. Merrill could build prototypes of his engine. If a picture is worth a thousand words, then a functioning prototype is priceless. In the article Mr. Merrill is quoted as saying “My engine technology and materials are basically 1960s.” A quality modern machine shop could easily fabricate the parts. After ground testing, the engine could be installed in a modified Rutan Long EZ for flight testing. Good luck Mr. Merrill.
Posted by David Zehender on June 2,2008 | 04:22PM
I saw a forum presentation by Gerry Merrill at Oshkosh a few years ago and was just mesmerized ! The possibilities ! I remember thinking "Here is a guy with the imagination of a Burt Rutan or a Roy LoPresti." Ah, but for money....
Posted by Craig Lamison on August 10,2008 | 09:16PM
Does anyone know how to get in touch with Gerry? I may have some investors in Asia that would be interested in producing his engine.
Posted by Jim Ryan on September 8,2008 | 01:27AM
Mr. Ryan, I'm his son. It's easy to map search on the web. But here it is anyway. Advanced Propulsion Inc. 254 W Baseline Rd # 105 Tempe, AZ (480) 829-1099 Mike
Posted by Michael Merrill on October 31,2008 | 02:01PM
for $150 grand to have a jet for that price would be awesome
Posted by carmine.p on January 3,2009 | 09:47AM
Like Tucker with the Torpedo or Custer with the Channelwing, or Northrop with the Flying Wing, or (I forgot the name) with the flying horseshoe designs, the big industry doesn't want new technology that could threaten their position in the market, so they lock up funding, buy politicians, etc. Even if Mr. Merrill can get an engine built and business started, the FAA requires a type rating for all jets, with expensive training. As a result, there would be fewer pilots able to buy an aircraft of this type. Next in line of obstacles would be insurance companies. Most require an enormous hour and experience requirement before they will insure a pilot of a jet. Even a low and slow jet would be subjected to ridiculous restrictions by these companies until it can be proven to be a low risk product. I applaud the efforts and wish the circumstance were different, but don't really see a hole in the glass ceiling.
Posted by Danny Bilyeu on January 29,2009 | 08:30AM
30/05/09 Dear Mr. Merrill, greetings from Belfast ,N.Ireland,just a thought for you to muse on, instead of a gas guzzling jet why not build a "DUCTED FAN"aircraft with the engine & 4 stage fan enclosed within the fuselage, there is no reason why it could not work perfectly, the radio controlled models are a dream to fly & provided you used a high performance high revving engine like the Mooney aircraft engines you could make it work, the Fan units could add as much as 25-30%to the speed, & the overall speed could be the equivelant or faster than a jet& a lot more economical & easier to insure, i know this has been tried a few times before but the reason it did not work was because the wrong engines were used the fans need to be high revving to produce the thrust so you need a high revving sport type engine to do this , this is just a thought , let me know what you think, Regards ....Tom
Posted by tom pritchard on May 30,2009 | 03:38AM