Honda's Powerplant For Aircraft
General Electric, which has partnered with Honda to squire the engine through the FAA certification maze, says Honda did things differently when it developed its engines. In GE's large fanjets, such as the giant GE90-115B found in the Boeing 777, TBOs of 20,000 to 30,000 hours are common, with 5000 hours "on wing" not unusual. In Honda's 400-pound package, the 2000-pound thrust HF118, Honda and GE are aiming for a 5000-hour TBO, with no interim hot section overhaul, something that's predicted to reduce operating costs and downtime. Like the Pratt 600-series used on the Eclipse and Cessna Mustang, the HF118s have drastically reduced parts counts compared to small jet engines of even a decade ago. Fuel specifics in small engines are difficult because critical internal tolerances represent a larger percentage of overall size than they do in a high-thrust engine and the small aircraft these tiny engines power have less room to carry fuel. GE told us the HF118s will burn about 40 gallons per hour at typical high-altitude cruise speeds, making for a specific fuel consumption of .7 pounds per hour per pound of thrust and a thrust-to-engine-weight ratio of five to one. Compared to a large, high-bypass ratio turbofan, those numbers aren't especially impressive. But given the difficulty of scaling jet engines down to VLJ-suitable size and weight, says GE, they're an incremental leap forward.
Among all the would-be suitors to the very light jet market, only one proposes to make both the engine and the airframe: Honda. Despite having little direct-to-the-customer aviation experience, Honda plans to do it all, with the possible exception of avionics, an arena in which Garmin seems to have an inside track, since the test article is G1000 equipped. But, as always, it's the engines that are the predominant driver of how a design evolves and Honda tells us the HF118s on the prototype are the fruit of a 20-year development effort that few people in the industry knew about. Small size and low cost were the most important considerations, but durability is critical, too.