The Flying Plank was developed in 1954 by Al Backstrom, assisted by Phil Easley and Jack Powell. The prototype EPB-1 was used for drag reduction tests at the Mississippi State College, using a modified Abrial reflex airfoil.
Plans for the -1A development were sold and a number built, most with twin wingtip rudders, but some were completed with a central fin and rudder at the end of a lengthened fuselage (EPB1-C) to improve performance and control. Span have varied up to 9.30 m / 30.5 ft. A self-launching model was developed later.
Except for the fiberglass nose cap for the fuselage, standard wood structure was used throughout, and construction time for an experience woodworker was in the neighborhood of 600 hours. More than 150 sets of plans were sold.
Construction of the powered Plank was begun in 1972, most of the work being done by Van White, a director of the EAA (Experimental Aircraft Association). It was intended originally to fit a Sachs Wanzel or OMC snowmobile Wankel engine, but as neither became available, a fan-cooled single-ignition Kiekhaefer Aeromarine 440 was installed, driving a two-bladed pusher propeller via belts.
The original tandem-wheel/outrigger undercarriage was replaced by a more robust tricycle unit in 1976.
An improved version, the “Super Plank”, was under development in 1973. At least two of them were built, including N20WB, by Larry Linville and Dennis Harmon. Backstrom also built a motor glider light aircraft called WPB-1 Powered Plank in early 1970s.
The Backstrom WPB-1 is on display at the Airpower Museum in Blakesburg, IA. And the Vintage Sailplane Association has plans.
EPB-1A
Wing Span: 7.62m / 25ft
Wing Area: 9.29sq.m / 100sq.ft
Empty Weight: 68kg / 150lb
Payload: 91kg / 200lb
Gross Weight: 159kg / 350lb
Wing Load: 17.11kg/sq.m / 3.5lb/sq.ft
L/DMax: 20@ 97 kph / 52 kt / 60 mph
Seats: 1
MinSink: 1.07 m/s / 3.5 fps / 1.88 kt
Aspect ratio: 6.25
Airfoil: Abrial 15%
Structure: wood / fabric
WPB-1 N20WB
1975
Engine: 40hp Kiekhafer Aeromarine 440
Wingspan: 21’0″
Length: 11’0″
Useful load: 220 lb
Max speed: 106 mph
Stall: 55 mph
Seats: 1
All Aero 