The Harmon Der Donnerschlag (English: Thunderclap) is an American homebuilt aircraft that was designed and produced by Harmon Engineering of Howe, Texas. The aircraft was intended for amateur construction.^[1]

Design and development

Der Donnerschlag features a wire-braced shoulder-wing, a single-seat open cockpit, fixed landing gear and a single engine in tractor configuration.^[1]

The aircraft's 19.5 ft (5.9 m) span wing has two beam-type spars and employs a 16% airfoil at the wing root, tapering to a 12% airfoil at the wingtip. The standard engine used is the 75 hp (56 kW) Volkswagen air-cooled engine automotive conversion, driving a two-bladed wooden propeller.^[1][2]

The aircraft has an empty weight of 350 lb (160 kg) and a gross weight of 600 lb (270 kg), giving a useful load of 250 lb (110 kg). With full fuel of 10 U.S. gallons (38 L; 8.3 imp gal) the payload is 190 lb (86 kg).^[1]

The aircraft was later developed into the Harmon Mister America.^[1]

Operational history

By October 2013 there were no examples registered in the United States with the Federal Aviation Administration and none may exist anymore.^[3]

Specifications (Der Donnerschlag)

Data from Plane and Pilot^[1]

General characteristics

• Crew: one
• Length: 14 ft 6 in (4.42 m)
• Wingspan: 19 ft 6 in (5.94 m)
• Empty weight: 350 lb (159 kg)
• Gross weight: 600 lb (272 kg)
• Fuel capacity: 10 U.S. gallons (38 L; 8.3 imp gal)
• Powerplant: 1 × Volkswagen air-cooled engine four cylinder, air-cooled, four stroke automotive-conversion engine, 75 hp (56 kW)
• Propellers: 2-bladed wooden

Performance

• Maximum speed: 120 mph (190 km/h, 100 kn)
• Cruise speed: 110 mph (180 km/h, 96 kn)
• Stall speed: 55 mph (89 km/h, 48 kn)
• Range: 500 mi (800 km, 430 nmi)
• Service ceiling: 10,000 ft (3,000 m)
• Rate of climb: 800 ft/min (4.1 m/s)