The design goals of the CA-2 described a plans-built aircraft for the US FAR 103 Ultralight Vehicles category, including a maximum 254 lb (115 kg) empty weight.

The CA-2 was also intended to be one of the lowest cost ways of obtaining an ultralight aircraft. These goals were met and the resulting aircraft has an empty weight of 250 lb (113 kg), when equipped with a 28 hp (21 kW) Rotax 277 engine.

The CA-2 requires about 600 hours to build. The airframe is of all-metal construction using 2024-T3 aluminum sheet, extruded angles and tubing, fastened primarily with stainless steel pop rivets. Construction requires normal hand tools, plus a small bending brake and a tube bender.

The fuselage and wings are of monocoque stressed skin construction. The wings include plain flaps and differential ailerons and are stressed to +4.4 and -2.2 g. The wings are removable by withdrawing three bolts. The control surfaces are made from aluminum tubing, are fabric covered and actuated by pushrods.

The landing gear is of conventional configuration with a steerable tailwheel linked to the rudder.

The prototype was powered by a Rotax 277. Heavier engines can be installed, although the aircraft will not then meet the US FAR 103 weight requirements as an ultralight aircraft. Other engines used include the 40 hp (30 kW) Rotax 447, 35 hp (26 kW) Rotax 377, 30 hp (22 kW) 1/2 VW and the 22 hp (16 kW) Hirth F-33.

General characteristics:

Crew: one
Capacity: no passengers
Length: 16 ft 6 in (5.03 m)
Wingspan: 26 ft 0 in (7.93 m)
Height: ()
Wing area: 117 ft² (10.9 m²)
Empty weight: 250 lbs (113 kg)
Useful load: 270 lbs (122 kg)
Max. takeoff weight: 520 lbs (235 kg)
Powerplant: 1 × Rotax 277, 28 hp (21 kW)


Never exceed speed: 80 mph (130 km/h)
Maximum speed: 63 mph (102 km/h)
Cruise speed: 50 mph (81 km/h)
Stall speed: 26 mph (42 km/h)
Range: 125 sm (203 km)
Service ceiling: 10,000 ft (3050 m)
Rate of climb: 600 fpm (3.05 m/s)
Wing loading: 4.4 lb/ft² (21.6 kg/m²)
Power/mass: 18.6 lb/hp (0.09 kW/kg)

Ultralight aviation was inspired by grass roots aviators! You can’t get more grass roots than the Hummel CA-2 a little 250 lbs single seat all metal craft that you build from plans.

At the show I came across a little CA-2 that was recently completed by Delmar Preston.

According the Delmar “the plans come in 17 x 11 sheets, are very clear and easy to follow, and include a step by step builders manual which also gives you a complete parts list and materials list.”

Delmar says the plane can be built with regular tools but he purchased “a small 30 inch shear and an air riveter to help install the over 4,000 rivets.” Delmar built his CA 2 in his basement which required cutting a hole in the wall to get it out.

His shop area was 14 x 10 feet. He started construction on the tail first to get the feel of building his “first plane” and then moved on to the wings and then the fuselage.
In total he put in about 400 hours on the airframe and another 200 hours on engine installation, paint and rigging. He indicated that there was no welding required in the whole plane, “just a lot of pop rivets and bolts.”

His little CA-2 is powered by a half Volkswagen engine, with 94 mm jugs and a 69 mm stroke. He also built the engine from plans and installed a secondary motorcycle ignition. The engine is direct drive and spins a 54 x 22 Tennessee wood prop. This engine and prop configuration gives him a take off distance of about 200 feet a climb of around 300 feet per minute and a cruise of 55 mph on 1.5 gallons of fuel per hour!