S-9 Chaos

The RANS S-9 Chaos is a single-seat mid-wing aircraft that Randy Schlitter designed in 1986 as an affordable aerobatic mount for homebuilders. It is the basis of the two-seat S-10 Sakota and was built from 1986 to 2006 and again from 2009. The number built is uncertain: Wikipedia quotes 215 examples completed and flown by December 2011, but gives the same figure for the two-seat S-10 Sakota, so it probably covers both types together. Either way the Chaos is genuinely rare in Europe, and every listing is an individual case.

The airframe follows the RANS pattern: a welded 4130 steel-tube cockpit cage, a bolted aluminium-tube rear fuselage and fabric-covered surfaces. With a 6.71 m span, 4.78 m length and 8.50 m² of wing area the Chaos is a compact sport aircraft; the 26-inch cockpit is unapologetically single-seat but offers 38 inches of headroom and 45.5 inches of legroom. The documented engines are the Rotax 503 (50 hp) as standard plus the Rotax 582 (64 hp) and the 100 hp Hirth 3701 as options, each with a wooden propeller and 1:2.58 reduction; the published performance figures refer to the two-stroke 503 and 582. Kit build time is quoted at roughly 500 working hours.

In the air the Chaos lives up to its name: +6/-3 g limits, a 100 degree per second roll rate, a 53 km/h stall and roughly 137 to 161 km/h cruise on the two-strokes – the factory data sheet quotes 85 to 100 mph depending on engine, with a Vne of 130 mph (209 km/h). Climb rate is 800 to 1,000 ft/min and service ceiling 13,500 to 15,500 ft depending on the source. The 34-litre standard tank gives around 340 km of range without reserve, the optional 68-litre tank considerably more.

Strengths are the roll response, a low mass of roughly 154 to 170 kg, low running costs and an airframe that can be inspected and repaired with simple tools. The weaknesses are equally clear: one seat, no baggage space, two-stroke engines with their maintenance demands and short TBO, and virtually no support infrastructure in Europe. No verifiable source exists for German ultralight certification of the S-9. One important buying check: if an advert quotes a Rotax 912 or a takeoff weight of 472.5 or 475 kg, that does not fit the single-seat S-9 at 304 to 322 kg – it is very likely a data-entry error or a mix-up with the two-seat S-10 Sakota.

The S-9 Chaos suits experienced pilots with aerobatic ambitions who want a cheap, light solo sport aircraft and are happy to handle maintenance and re-covering themselves. Anyone wanting to fly two-up or travel cross-country should look at the S-10 Sakota or the S-6 Coyote II.