Bill Gates is betting some of his considerable fortune on a new plan: energy-efficient aviation.

Speaking at Flight School, an offshoot of the PC Forum here run by News.com publisher CNET Networks, Eclipse CEO Vern Raburn acknowledged that the world's richest man--and his former boss at Microsoft--is one of the many equity investors in the company. Gates holds the second-largest stake, behind another Fortune 500 individual, he said. To date, Eclipse has not formally disclosed its investors. The Albuquerque, N.M.-based company is working on the Eclipse 500, a six-seater that can fly at a maximum speed of 375 knots. Designed for flights of about 300 miles to 600 miles, the plane, which will sell for $1.3 million, will likely be used by companies promoting on-demand flight services. Raburn said he expects the company to get Federal Aviation Administration approval to use the planes in a commercial setting in about a year. Raising money is a serious issue for the company and others with new ideas for transportation. Eclipse has designed the plane and said it will remain the manufacturer when it goes into commercial production. Production facilities cost money. So far, the 450-employee company has raised $400 million in debt and equity, and most of that total is equity, Raburn said. About $175 million alone was spent on nonrecurring engineering costs.