Death Spiral

A common technique in pairs figure skating:

From "Skating: elegance on ice", by Howard Bass.

The death spiral is characterized by the girl spiralling on one skate in circular motion round her partner, who acts as pivot, retaining virtually the same pose while holding her with one or both hands.

More aptly, the state of a doomed computing project. There is a famous Dilbert comic strip where Dilbert recounts to DogBert how his new project has just gone through many meetings just to choose a name; Dogbert suggests "Project DeathSpiral".

In sailplanes (aka gliders), there is a fascinating DeathSpiral maneuver called a "spiral dive." Incorrect recovery results in the wings separating from the aircraft, followed by severe deceleration trauma to the pilot as the remaining parts of the aircraft impact the ground. The maneuver starts with a pilot circling in a thermal (a rising column of hot air). If the pilot banks too steeply, the nose will drop and airspeed will increase. If the pilot pulls back on the stick to get the nose back up but does not correct the bank angle, the bank will increase, the G-load will increase, airspeed will increase, and the nose will again drop. Repeat until the wings come off. The whole process, from the first indication of trouble until the wings come off, can happen very quickly. This is different from a spin, in that the wings are never stalled, but recovery is the same: relax back pressure, use opposite rudder to level the wings, and recover from the dive. Recovery from the dive must be more aggressive than with spin recovery, because airspeed is higher.

The spiral dive happens because sailplanes have long, skinny wings. That causes the outside wing to generate more lift than the inside wing during a turn, because the outside wing is going faster. The same effect happens in powered aircraft, but the long wings of a sailplane accentuate the effect, making it much more noticeable at a given bank angle than in a powered plane. The additional lift of the outside wing causes it to raise up, steepening the bank angle. The pilot applies opposite aileron to counter the effect; this means that the sailplane is cross-controlled (ailerons applied opposite to rudder) in turns. This tendency of the bank to steepen if left uncontrolled gives a sailplane its tendency towards the spiral dive.

The differences between SpiralModel and the DeathSpiral are small. With each iteration of the spiral, is there progress? Yes, then you are practicing SpiralModel. No, then you are in the DeathSpiral. - RandyCharlesMorin

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