wsherif1
21st Jul 2003, 06:56
I was in a Boeing 707 at 37,000 feet, in the clear above thunderstorm activity. First updraft, I knocked off the auto-pilot. Second updraft, aircraft pitched up 25 to 35 degrees. Resultant relative wind from strong updraft and aircraft's velocity increased the angle of attack and the lift, moving the center of lift forward on the swept wing, pulling the nose up. Because of the relative wind direction little or no increase in aircraft load factor, therefore little loss of kinetic energy! Aircraft continued on projected flight path, in this attitude, with no iminent stall threat. Both pilots' looking out the windows at a visual horizon were not affected by flight instrument readings. Eased the nose back down to the visual horizon and continued on course.
NWA 705 pitchup. Boeing 720B (8 feet shorter than a 707, thus more susceptible to a pitchup (shorter moment arm). Aircraft pitched up to about 35 degrees. Pilot applied forward pitch control with little effect, (strong updraft). Trimmed the horizontal stabilizer full nose down. When the aircraft exited the updraft and returned to normal relative wind conditions, the aircraft pitched over into a vertical dive. The aircraft came apart in the air.
Subsequent examination of the gyros showed severe impact damage to the nose down stops, from the rapid rotation of the aircraft about its center of gravity. (lateral axis.)
NWA 705 pitchup. Boeing 720B (8 feet shorter than a 707, thus more susceptible to a pitchup (shorter moment arm). Aircraft pitched up to about 35 degrees. Pilot applied forward pitch control with little effect, (strong updraft). Trimmed the horizontal stabilizer full nose down. When the aircraft exited the updraft and returned to normal relative wind conditions, the aircraft pitched over into a vertical dive. The aircraft came apart in the air.
Subsequent examination of the gyros showed severe impact damage to the nose down stops, from the rapid rotation of the aircraft about its center of gravity. (lateral axis.)