Nosewheel Glider Oscillations During Launches and Landings

Introduction to Glider Flying > Abnormal and Emergency Procedures > Nosewheel Glider Oscillations During Launches and Landings

Many tandem two-seat fiberglass gliders, and some single-seat fiberglass gliders as well, feature a threewheel landing gear configuration. The main wheel is equipped with a traditional large pneumatic tire; the tailwheel and the nosewheel are equipped with smaller pneumatic tires. During taxi operations, if the pneumatic nosewheel remains in contact with the ground, any bump will compress the nosewheel tire. When the pneumatic nosewheel tire rebounds, an uncommanded pitch-up occurs. If the pitch-up is sufficient, as is likely to be the case after hitting a bump at fast taxi speeds, the tailwheel will contact the runway, compress, and rebound. This can result in porpoising, as the nosewheel and tailwheel alternate in hitting the runway, compressing, and rebounding. In extreme cases, the fuselage of the glider may be heavily damaged.

Figure 8-5. Pitch attitude power setting relationships for self-launch glider with engine pod.

During takeoff roll, the best way to avoid porpoising in a nosewheel-equipped glider is to use the elevator to lift the nosewheel off the runway as soon as practicable, then set the pitch attitude so the glider’s main wheel is the only wheel in contact with the ground. To avoid porpoising during landing, hold the glider off during the flare until the mainwheel and tailwheel touch simultaneously. During rollout, use the elevator to keep the nosewheel off the ground for as long as possible.