Q-136: Years ago I enjoyed flying a variety of ducted-fan units in semi-scale RC models. These fans were all powered by high-performance, glow-fueled engines and manufactured at the time by a company known as Kress Jets. Having recently become involved with electric-powered flight, I wondered about the possibility of using some of the new outrunner-type brushless motors along with Li-Poly battery packs to power ducted-fan units. Do you have any ideas or suggestions?
A-136: Yes I do, and you are going to be surprised. Kress Jets was started years ago by Bob Kress who was one of the principal designers of the Grumman F-14 TOMCAT and now a retired Grumman VP of Advanced Systems. Bob was my “Big Boss” while at Grumman and a close friend. We still talk all the time.
As you might imagine, I’ve been giving Bob an earful recently on brushless motors and Li-Poly batteries. Several months ago, Bob and his son John developed a prototype electric-powered fan that uses an AXI 2212/20 outrunner brushless motor installed in a Kress Jets RK-709E ducted-fan assembly. Total weight of this fan/motor combination is only 5.8 ounces! The efficiency of a brushless motor, combined with higher-capacity/lower-weight Li-Poly batteries, have made it possible to greatly improve the performance of electric-powered, ducted-fan aircraft. Toward that end, Bob and John have developed a new F-4 Phantom semiscale aircraft kit to accept the new brushless motor/fan unit. Kits will soon be available for this aircraft.
The wing span is 24 inches, wing area 219 square inches, with a total flying weight of 22.5 ounces. Space doesn’t permit more details at this time, but I can refer you to the Kress Jets ducted-fan Web site at: http://kress-jets.com/outrunner.htm. The F-4 Phantom kit information can be found at this specific Web site: http://kress-jets.com/Fantom-RK-709E-AXI-Fan.htm. For who are those interested in serious electric ducted-fan performance, I suggest you look up both of these Web sites just referenced.