Motorized Gliders of Iowa Teratorn

The Teratorn was a single-seat single-engined high-wing monoplane with hybrid control. Wing has unswept leading and trailing edges, and constant chord; cruciform tail. Pitch control by weight-shift; yaw control by fully flying rudder; roll control by one-third-span spollerons; control inputs through weight-shift for pitch/yaw/roll. Wing braced from above by kingpost and cables, from below by cables; wing profile; 33% double-surface. Undercarriage has three wheels in tail-dragger formation; suspension on tailwheel and bungee suspension on main wheels. No ground steering. No brakes. Aluminium-tube framework, without pod. Engine mounted above wing driving pusher propeller. Leading edges stiffened with Mylar.

The Teratorn which we are concerned with is itself a venerable design, having appeared at the birth of microlight aviation around the same time as the first powered version of the famous Quicksilver, with which it has a certain similarity. The Teratorn was powered, up till 1982, by the single cylinder Yamaha KT100S giving 15 hp through a reduction drive of 5/1, with initially the option and later the standard replacement by a twin-cylinder Rotax of 28 hp with a 2.5/1 reduction drive.

On an original note, the company chose black anodising for the tubes on this hybrid control machine and the wires too were covered in black vinyl. The Teratorn is delivered as a kit requiring 20 to 25 h assembly according to the maker, and costs $3895 with the Rotax motor in 1983. Options include an instrument panel, skis, Kevlar floats and the choice of the Yamaha KT100S, which drops the price by $400. The machine is trailer transportable or on a roof rack and folds to around 16 x 5 x 1 ft (4.9 x 1.5 x 0.3 m). A kit allowing the Teratorn to be converted to the Teratorn TA with three-axis control is also available.

The Teratorn TA was a single-seat single-engined high-wing monoplane with conventional three-axis control. Wing has unswept leading and trailing edges, and constant chord; cruciform tall. Pitch control by elevator on tail; yaw control by fully flying rudder; roll control by one-third-span spoilerons; control inputs through stick for pitch/roll and pedals for yaw. Wing braced from above by kingpost and cables, from below by cables; wing profile; 33% double-surface. Undercarriage has three wheels in taildragger formation; steel-spring suspension on tailwheel and bungee suspen-sion on main wheels. No ground steering. No brakes. Aluminium-tube framework, without pod. Engine mounted below wing driving pusher propeller.

This is the three-axis version of the hybrid-control Teratorn. The TA appeared in 1982 with the Yamaha KT100S 15 hp engine, though today that has become just an option, the machine being fitted in standard form with the Rotax 300 of 28 hp or the Rotax 377 with 34 hp. Rigging time for the earlier model is 25 min, while this model requires 25 min to rig with two people. The Teratorn TA is sold so that it requires only 20h to complete, according to the maker, and for a price of $4295 with Rotax 300 or $4595 with Rotax 377. The options include the Yamaha engine for a reduction of $300, floats of Kevlar, skis and instrument panel.
Production was phased out in favour of the more advanced Tierra.

Teratorn
Engine: Rotax 300, 28hp at 6200rpm
Propeller diameter and pitch 60 x 24 inch, 1.52 x 0.61 m
Reduction ratio 2.5/1
Power per unit area 0.18 hp/sq.ft, 1.9 hp/sq.m
Fuel capacity 3.3 US gal, 2.8 Imp gal, 12.5 litre
Length overall 18.0 ft, 5.49 m
Height overall 9.0 ft, 2.74m
Wing span 32.0ft, 9.75m
Constant chord 5.0 ft, 1.52 m
Sweepback 0 deg
Total wing area 160 sq.ft, 14.9 sq.m
Wing aspect ratio 6.4/1
Tailwheel diameter overall 3 inch, 7 cm
Main wheels diameter overall 16 inch, 41 cm
Empty weight 212 lb, 96 kg
Max take-off weight 474 lb, 215kg
Payload 262 lb, 119kg
Max wing loading 2.96 lb/sq.ft, 14.4 kg/sq.m
Max power loading 16.9 lb/hp, 7.7kg/hp
Load factors; +3.0, -3.0 ultimate
Max level speed 50 mph, 80 kph
Never exceed speed 55 mph, 88 kph
Economic cruising speed 35 mph, 56 kph
Stalling speed 15 mph, 24 kph
Max climb rate at sea level 600 ft/min, 3.1 m/s
Min sink rate 250 ft/min at 25 mph, 1.3 m/s at 40 kph
Best glide ratio with power off 8/1 at 25 mph, 40 kph
Take-off distance 50 ft, 15 m
Landing distance 75 ft, 23 m
Service ceiling 10,000 ft, 3050 m
Range at average cruising speed 70 mile, 113 km

Teratorn TA
Engine: Rotax 300, 28 hp at 6200 rpm
Propeller diameter and pitch 60x24 inch, 1.52x0.61m
Reduction ratio 2.5/1
Power per unit area 0.18hp/sq.ft, 1.9 hp/sq.m
Fuel capacity 3.3 US gal, 2.8 Imp gal, 12.5 litre
Length overall 18.0 ft, 5.49 m
Height overall 9.0ft, 2.74m
Wing span 32.0ft, 9.75m
Constant chord 5.0 ft, 1.52 m
Sweepback 0 deg
Total wing area 160 sq.ft, 14.9 sq.m
Wing aspect ratio 6.4/1
Tailwheel diameter overall 3 inch, 7 cm
Main wheels diameter overall 16 inch, 41 cm
Empty weight 227 lb, 103kg
Max take-off weight 489 lb, 222kg
Payload 262 lb, 119 kg
Max wing loading 3.06 lb/sq.ft, 14.9kg/sq.m
Max power loading 17.5 lb/hp, 7.9 kg/hp
Load factors; +4.0, -3.0 ultimate
Max level speed 50 mph, 80 kph
Never exceed speed 55 mph, 88 kph
Max cruising speed 45 mph, 72 kph
Economic cruising speed 35 mph, 56 kph
Stalling speed 17 mph, 27 kph
Max climb rate at sea level 600 ft/min, 3.1 m/s
Min sink rate 270 ft/min at 28 mph, 45 m/s at 45 kph
Best glide ratio with power off 8/1 at 28mph, 45kph
Take-off distance 50ft, 15m
Landing distance 75ft, 23m
Service ceiling 10,000ft, 3050 m
Range at average cruising speed 70 mile, 113km

Engine: Rotax 377, 34 hp at 6400 rpm
Propeller diameter and pitch 60x36 inch, 1.52x0.91m
Toothed-belt reduction, ratio 2.6/1
Max static thrust 240 lb, 109kg
Power per unit area 0.21hp/sq.ft, 2.3 hp/sq.m
Fuel capacity 4.4 US gal, 3.7 Imp gal, 16.7 litre
Length overall 18.0 ft, 5.49 m
Height overall 9.0ft, 2.74m
Wing span 32.0ft, 9.75m
Constant chord 5.0 ft, 1.52 m
Sweepback 0 deg
Total wing area 160 sq.ft, 14.9 sq.m
Wing aspect ratio 6.4/1
Tailwheel diameter overall 3 inch, 7 cm
Main wheels diameter overall 16 inch, 41 cm
Empty weight 237 lb, 108kg
Max take-off weight 499 lb, 226kg
Payload 262 lb, 119 kg
Max wing loading 3.12 lb/sq.ft, 15.2kg/sq.m
Max power loading 14.7 lb/hp, 6.6 kg/hp
Load factors; +4.0, -3.0 ultimate
Max level speed 55 mph, 88 kph
Never exceed speed 63 mph, 101 kph
Stalling speed 23 mph, 37 kph
Max climb rate at sea level 900 ft/min, 4.6 m/s