IS-4 Jastrząb

The IS-4 Jastrząb (Instytut Szybownictwa – gliding institute) was a single-seat aerobatic glider designed and built in Poland from 1949.

IS-4 Jastrząb
Role	Glider
National origin	Poland
Manufacturer	Instytut Szybownictwa
Designer	J Niespał
First flight	21 Dec 1949[1]
Introduction	1950
Number built	37[1]

Development

The IS-4 was built for aerobatics with a high structural strength and a very high maximum speed which could not be achieved in a vertical dive. Due to the pilot's sitting position and the arrangements of the controls, it was difficult for pilots to exceed the 8g loading limit. During high speed flight it was possible for the air-brakes to be sucked out violently, so most pilots ensured that they remained closed by holding the airbrake control.^[1]

Variants

• IS-4 Jastrząb – two prototypes built in 1949.^[1]
• IS-4 Jastrząb bis – Thirty-five production aircraft, three of which were exported.^[1]

Specifications (IS-4 Jastrząb bis)

Data from The World's Sailplanes:Die Segelflugzeuge der Welt:Les Planeurs du Monde Volume II^[1][2]

General characteristics

• Crew: 1
• Length: 6.25 m (20 ft 6 in)
• Wingspan: 12 m (39 ft 4 in)
• Height: 1.3 m (4 ft 3 in) at cockpit
• Wing area: 12 m² (130 sq ft)
• Aspect ratio: 12
• Airfoil: Root – NACA 2418, Tip – NACA 2412, Mid – NACA 0012
• Empty weight: 240 kg (529 lb)
• Gross weight: 357 kg (787 lb)

Performance

• Stall speed: 67 km/h (42 mph, 36 kn)
• Never exceed speed: 450 km/h (280 mph, 240 kn)
  
• Rough air speed max: 200 km/h (120 mph; 110 kn)
• Aerotow speed: 200 km/h (120 mph; 110 kn)
• Winch launch speed: 150 km/h (93 mph; 81 kn)
• g limits: +7 -4 at 200 km/h (120 mph; 110 kn)
• Maximum glide ratio: 20.2 at 87 km/h (54 mph; 47 kn)
• Rate of sink: 1.04 m/s (205 ft/min) at 70 km/h (43 mph; 38 kn)
• Wing loading: 29.7 kg/m² (6.1 lb/sq ft)

See also

Aircraft of comparable role, configuration, and era

• Vogt Lo 100