L13AC Blanik

Baer Selen, two-time world Champion from the Netherlands flies the L13AC Blanik

Another L13AC is taking off at the facory airport in Kunovice, Czech Republic

L13AC Blanik ready to be loaded in the enclosed TV2 trailer for transport to its next destination

Flight Testing Report

During the second half of 1997 the L13AC Blaník was flight-tested by the LET factory chief test pilot S. Sklenár, and by the Czech government Civil Aviation Authority (CAA) test pilots V. Príhoda, F. Barton, S. Vlcek, and M. Tošovský. This is what the various pilots have said about their experience with the L13AC Blaník:

• LET factory chief test pilot S. Sklenár: "Already during the first flights with the glider L13AC Blanik it became obvious that the goal to improve aerobatic handling has been successfully reached. The roll rate is particularly remarkable, the stall characteristics have improved, and the falls are symmetrical. The air brakes are more effective and without side effects. Other good properties of the L13 and L23 were retained."
• CAA test pilot V. Príhoda: "The Civil Aviation Authority has started type certification testing with the L13AC Blanik ballasted to forwardmost center of gravity position for the inverted flight tests . . . Take-off and control during aerotow were normal and with the exception of the aileron effectiveness did not differ from the L13 . . . During solo flights, inverted flight was initiated by a half roll at an entry speed of 140 to 160 km/h (75 to 86 kts). I recommend 150 km/h (81 kts). Inverted stalls were tested up to the speed of 180 km/h (97 kts). The stall warning speed was ascertained at 108 to 112 km/h (58 to 61 kts). The warning became noticeable by shaking of the glider including one or two oscillations of the control stick in the aft-forward position. The stall occurred at around 100 to 98 km/h (54 to 53 kts). Immediately after the fall the controllability of inverted flight could be resumed by pulling the stick slightly aft. The speed after recovery from the stall was not exceeding 160 km/h (86 kts), while no uncontrollable banking or turning developed. The rudder as well as ailerons displayed an acceptable effectiveness even during the fall. The ailerons cause, due to their differentiated deflection, a turning tendency if not checked. Until the moment of fall (while decelerating at the rate of about 2 km/h/s [1 kt/s]) there is sufficient reserve in the movement of the control stick in the forward direction. The dynamics of the elevator control were sufficient and the responses to the control inputs were pleasant, slightly better than those of the glider variants L13 and L13A. . . .The flights [with two persons] at maximum full-up weight and at maximum forward center of gravity (23 % MAC) were initiated by an inverted roll with an entry speed of 160 to 165 km/h (86 to 89 kts). The recommended speed should not drop below 160 km/h (86 kts). Straight inverted flight and turns up to 20° bank were tested. During the straight inverted flights, speed was allowed to build up to 160 km/h (86 kts). The dynamics of the elevator control were still acceptable, and the reserve of the control stick movement remains sufficient up to the stalling speed of about 105 km/h (57 kts). The glider warns of the impending stall by shaking, possibly from the vertical tail surface when the airspeed drops below 125 km/h (68 kts). The recommended airspeed in inverted flight solo is 130 km/h, in dual 140 km/h (70 and 76 kts). The forces in the controls are in harmony, and their effectiveness is good. The airbrakes effectiveness is sufficient and higher than at the L13, and the unpleasant force required for their closing has disappeared. The slipping maneuver is effective, and the fuselage deviation is subjectively higher than at the L13. The transitions between the fuselage deviations [from left to right slip and reverse] between speeds of 80 and 100 km/h (43 to 54 kts) are safe and without any transition tendency to a spin. The landing is easy and the touchdown speed is about 5 km/h (3 kts) higher than at the L13 with the same crew. . . . The glider is recommended to be approved for the type certificate including inverted and roll maneuvers with dual crew up to the maximum gross weight. Other maneuvers such as loop, wingover, spin and falls are the same as with the L13 or L13A and are without problems. . ."
• CAA test pilot F. Barton: "During the two days of testing I flew this glider 8 times concentrating on advanced aerobatic maneuvers, including kick rolls. Further we tested the glider in group acrobatic flight and mirror flight [one glider inverted and one glider below in a normal position]. The pilotage of the "shortie" [L13AC] does not differ practically from the pilotage of the gliders L13 or L13A. The L13AC, however, rolls quicker around the longitudinal axis, and the stick aileron control forces during higher speeds are slightly lower. The glider picks up airspeed quicker and also slows down quicker. All aerobatic maneuvers performed according to the Flight Manual may be executed without a problem. Inverted flights including inverted turns are quite pleasant and more stable than with the L13 or L13A. Various airspeeds were tested including stalling speeds. The force needed to push the stick to slow down was favorable, and the 'supply' of stick forward travel was sufficient. Basic inverted gliding flights were executed at the airspeed of 140 km/h (76 kts). For the kicked and pulled maneuvers, such as the flick roll, the optimal entry speed is 130 km/h (70 kts). After the glider is introduced into the flick roll the first half is faster than the second one. The rounding out is without problems. The glider is introduced into kicked maneuvers in level or slightly-climbing flight. The airbrakes are very effective and what's more important, the force needed to actuate them during higher speeds has disappeared, and their actuating handle does not interfere with the knees when full aileron deflection is needed. Mirror flight, including oncoming fly-by, was without problems (judged from the viewpoint of the pilot flying the plane inverted). During group aerobatic flight with the L13 and L13A, the L13AC was faster and outdistanced the "normal" Blanik, which of course is logical. The glider L13AC will be a suitable plane for elementary and advanced aerobatic training."

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Last modified: August 26, 1999