Gemini Engine Moving Toward Production

Designing, testing, certifying, and producing a new aircraft engine is never an easy process. A sour economy that sends investors into hiding just makes the process that more challenging. But the three-cylinder, six piston diesel/Jet A  Gemini 100 (see Gemini Diesel Engine Attracts Industry’s Eye) is gaining on that goal, says Tim Archer, president of Powerplant Development USA.

Being developed in Britain, the company just received the UK equivalent of a small business loan that will put the Gemini 100 into limited production in April 2009. The first engines will be going to Tecnam, which will use its Eaglet to evaluate both the 100 and, at a later date, the turbocharged Gemini 125. “I don’t think we’ll make Sun ‘n Fun,” Archer says, but the Gemini Tecnam should be ready for AERO Friedrichshafen 2009, Europe’s leading GA trade show, and EAA AirVenture Oshkosh.

Fuel is, perhaps, first among the reasons why aviation needs a production piston powerplant that efficiently drinks a turbine’s favorite liquid.  Compared to diesel/Jet A, 100 LL avgas is a drop in the refiner’s bucket, and environmental agencies and groups have it in their sights as the work to rid the world of the last leaded fuel. 

Before Gemini 100 production begins, it must complete its test stand program in Hastings UK, which is now focusing on mapping the fuel system. With its unique opposed-piston design (two pistons in one cylinder), Powerplant Developments had to design its own fuel system, says Archer. Being unique, there were no data points to compare it to and more quickly determine the optimum fuel quantity and spray pattern for each engine rpm and horsepower setting.

Creating this map is time consuming and involves a lot of minute changes to the high pressure fuel nozzles, Archer says. The good news is that the mapping effort is nearly complete. “We’re at 90 percent engine rpm and approximately 80 percent power.” To determine the final spray patterns and injection timing, PPD is testing the system on a separate test rig. When this testing is complete, the system returns to the engine to complete the fuel mapping process.

The only other engineering challenge is designing the new supercharger mounting interface. For initial testing PPD modified an off-the-shelf belt-driven unit to accept a drive shaft. The production unit should be ready by the time the fuel mapping is done. Once the Gemini 100 is in limited production, PPD will turn its attention to the Gemini 125, basically the same engine with a turbocharger. It should follow the 100 by three or four months. —Scott Spangler