Water Ballast Malfunctions
Water ballast systems are relatively simple and major failures are not very common. Nevertheless, ballast system failures can threaten the safety of flight. One example of ballast failure is asymmetrical tank draining (one wing tank drains properly but the other wing tank does not). The result is a wing-heavy glider that may be very difficult to control during slow flight and during the latter portion of the landing rollout. Another example is leakage. Some water ballast systems drain into a central pipe that empties through the landing gear wheel well. If the drain connections from either wing leak significantly, water from the tanks can collect in the fuselage. If the water flows far forward or far aft in the fuselage, pitch control of the glider may be severely degraded. Pitch control can be augmented by flying at mid to high airspeeds, giving the elevator more control authority to correct for the out-ofbalance situation, and affording time to determine whether the water can be evacuated from the fuselage. If pitch control is dangerously degraded, abandoning the glider may be the safest choice. The best prevention for water ballast problems is regular maintenance and inspection combined with periodic tests of the system and its components.
Retractable Landing Gear Malfunctions
Landing gear difficulties can arise from several causes. Landing gear failures arising from mechanical malfunction of the gear extension mechanism generally cannot be resolved during flight. Fly the approach at normal airspeed. If the landing gear is not extended, the total drag of the glider is less than it is normally during an approach with the landing gear extended. It may be necessary to use more spoiler/dive brake than normal during the approach. Try to land on the smoothest surface available, preferably an area that has good turf to help reduce the damage to the glider. The landing must be under control and as soft as possible. Slightly above stall speed soft touchdowns are preferable to full stall landings resulting in hard landings. This helps avoid a tailwheel first landing, and a hard touchdown of the glider onto the runway. Avoiding the hard touchdown helps to avoid injury and lessen damage to the glider components.
The glider makes considerable noise as it slides along the runway, and wingtip clearance above the ground is reduced. Keep the wings level for as long as possible. Try to keep the glider going as straight as possible using the rudder to guide the glider. The primary goal is to avoid collision with objects on the ground or along the runway border, including runway lighting and signage. Accept the fact that minor skin damage to the glider is inevitable if the gear cannot be extended and locked. Concentrate on personal safety during the approach and landing. Any damage to the glider can be repaired after an injury-free landing.
Primary Flight Control Systems
Failure of any primary flight control system presents a serious threat to safety. The most frequent cause of control system failure is incomplete assembly of the glider in preparation for flight. To avoid this, use a written checklist to guide each assembly operation and inspect every connection and safety pin thoroughly. Do not allow interruptions during assembly. If interruption is unavoidable, start the checklist again from the very beginning. Perform a positive control check with the help of a knowledgeable assistant. Do not assume that any flight surface and flight control is properly installed and connected during the post-assembly inspection. Instead, assume that every connection is suspect. Inspect and test until certain that every component is ready for flight.
The most serious control system malfunction is a failure of the elevator flight control. Causes of elevator flight control failure include the following:
- An improper connection of the elevator control circuit during assembly.
- An elevator control lock that was not removed before flight.
- Separation of the elevator gap seal tape.
- Interference of a foreign object with free and full travel of the control stick or elevator circuit.
- A lap belt or shoulder harness in the back seat that was used to secure the control stick and not removed prior to flight.
- A structural failure of the glider due to overstressing or flutter.
To avoid a failure, ensure that control locks are removed prior to flight, that all flight control connections have been completed properly and inspected, and that all safety pins have been installed and latched properly. Ensure that a positive control check against applied resistance has been performed.
If the elevator irregularity or failure is detected early in the takeoff roll, release the towline (or reduce power to idle), maneuver the glider to avoid obstacles, and use the brakes firmly to stop the glider as soon as possible. If the elevator control irregularity or failure is not noticed until after takeoff, a series of complicated decisions must be made quickly. If the glider is close to the ground and has a flat or slightly nose-low pitch attitude, releasing the towline (or reducing power to zero) is the best choice. If this is an aerotow launch, consider the effect the glider has on the safety of the tow pilot. If there is sufficient elevator control during climb, then it is probably best to stay with the launch and achieve as high an altitude as possible. High altitude gives more time to abandon the glider and deploy a parachute, if worn.
If the decision is to stay with the glider and continue the climb, experiment with the effect of other flight controls on the pitch attitude of the glider. These include the effects of various wing flap settings, spoilers/dive brakes, elevator trim system, and raising or lowering the landing gear. If flying a self-launching glider, experiment with the effect of power settings on pitch attitude.
If aileron control is functioning, bank the glider and use the rudder to moderate the attitude of the nose relative to the horizon. When the desired pitch attitude is approached, adjust the bank angle to maintain the desired pitch attitude. Forward slips may have a predictable effect on pitch attitude and can be used to moderate it. Usually, a combination of these techniques is necessary to regain some control of pitch attitude. While these techniques may be a poor substitute for the glider elevator itself, they are better than nothing. If an altitude sufficient to permit bailing out and using a parachute is achieved, chances of survival are good because parachute failures are exceedingly rare.
Elevator gap seal tape, if in poor condition, can degrade elevator responsiveness. If the adhesive that bonds the gap seal leading edge to the horizontal stabilizer begins to fail, the leading edge of the gap seal may be lifted up by the relative wind. This provides, in effect, a small spoiler that disturbs the airflow over the elevator just aft of the lifted seal. Elevator blanking that occurs across a substantial portion of the span of the elevator seriously degrades pitch attitude control. In extreme cases, elevator authority may be compromised so drastically that the glider elevator is useless.
The pilot may be forced to resort to alternate methods to control pitch attitude as described above. Bailing out may be the safest alternative. Inspection of the gap seal bonds for all flight control surfaces prior to flight is the best prevention.