AAIB report extract
Synopsis
Whilst attempting to take off from his home strip, the pilot and owner became aware that the aircraft was not gaining height. He was therefore forced to attempt a landing straight ahead, in a tall crop.
History of Flight
The pilot reported that he took off into a light wind which was blowing approximately along runway 21 of his landing strip. The upslope on this runway is approximately 2%. The take-off initially appeared normal. Although the engine appeared to the pilot to be functioning correctly and maintaining the correct RPM, he was unable to climb without losing airspeed once he was beyond the end of the strip and had left ground effect. Consequently it became necessary to land ahead. The presence of the tall crop in which he was forced to land led to severe damage to the aircraft.
Background
The SD-1 Minisport is an ultralight single seat aircraft of tail-wheel layout and it is of East European design. The aircraft features are such that it falls into the single-seat deregulated category when operated in the UK.
The type is available with a choice of engines. In the case of G-CIMA, the geometry of the CH750 engine installation results in the crankshaft axis and the directly driven propeller being positioned lower on the fuselage than in the case of some other engine types available. Additionally, the propeller diameter is smaller than that on some other installations. Consequently, the slipstream has only limited effect on the high mounted stabilator. The owner /pilot has confirmed that the ability to raise the tail to put the aircraft axis in the low-drag horizontal position during take-off is almost entirely dependent on airspeed rather than being largely affected by applied engine power. In addition, the low wing and short landing-gear enables the aircraft to fly horizontally in ground effect at speeds well below that required for level flight in free air.
Although limited performance figures have been stated by the manufacturer, being an unregulated design, these have not been independently verified.
The pilot began operating the aircraft from his home base during January 2015, and had carried out approximately 50 flights totalling approximately 14 hours on the machine at the time of the accident. The machine had accumulated 201 airframe hours since new, having previously served as a demonstrator by the designer and manufacturer of the type in the Czech republic. The pilot also operates another fixed wing microlight aircraft type from the strip; the other aircraft has superior airfield performance and is of high wing configuration.
The pilot now considers that G-CIMA had marginal performance from the strip, having on a few earlier occasions noted that he had difficulty in establishing a positive climb rate once the aircraft was beyond the end of the runway and necessarily no longer operating in ground effect. Consequently, a combination of adverse factors on the day of the accident probably resulted in the achieved airspeed being inadequate for a successful climb-out.
Some of the possible contributory factors are as follows;
(1)The steady increase in ambient temperature between when he began operating the aircraft in January and that at the time of the accident in May. This would have resulted in a progressive but not very noticeable reduction in performance which may have seemed more than adequate when he first flew the machine.
(2)The problem of the wind direction on the day favouring a take-off direction conflicting with the opportunity to use the otherwise favourable downhill direction.
(3)A lower wind speed at the strip than that quoted in TAF and METAR for nearby Cambridge as used for flight planning.
(4)Delay in transitioning from a high drag tail-down position to a low drag fuselage level position early in the take-off roll.
Since reliable take-off performance data, taking account of wind speed and direction, surface slope and condition, ambient temperature and pressure, pilot technique and loaded weight is not available for the type, accurately estimating the required take off distance is not possible. In addition, frequently flying a type with superior take-off performance and having little difference in behaviour between that in ground effect and that in free air may have caused the pilot to have been less alert to the marginal take off performance for his home strip of the SD-1 equipped with the CH 750 engine.