Spiral divergence or spiral instability is a condition where an aircraft is directionally very stable, but laterally very unstable. … This tendency explains why an aircraft cannot be flown “hands off” indefinitely. A spiral divergence is not a type of spin because neither wing is stalled.
What is spiral divergence?
What causes spiral divergence?
Spiral divergence is characterized by an airplane that is very stable directionally but not very stable laterally; for example, a large finned airplane with no dihedral. In this case when the airplane is in a bank and sideslipping, the side force tends to turn the plane into the relative wind.
What causes spiral instability?
One of the primary causes of spiral instability is the fact that once a turn begins, the outboard wingtip is moving along a larger circumference and therefore moving faster, and tending to produce more lift, than the inboard wingtip. So the bank angle tends to increase.
What is spiral mode aircraft?
Spiral mode development. The spiral mode is usually excited by a disturbance in sideslip, which typically follows a disturbance in roll and causes a wing to drop. Assume that the aircraft is initially in trimmed wings level flight and that a disturbance causes a small positive roll angle ϕ to develop.
How does Dutch Roll happen?
Answer: Dutch roll is a natural aerodynamic phenomenon in swept-wing aircraft. It is caused by the design having slightly weaker directional stability than lateral stability. The result is the tail of the airplane seeming to “wag” or move left and right with slight up and down motion.
What is sideslip angle aircraft?
The sideslip angle, also called angle of sideslip (AOS, AoS, , Greek letter beta), is a term used in fluid dynamics and aerodynamics and aviation. It relates to the rotation of the aircraft centerline from the relative wind.
What is roll subsidence?
Roll subsidence mode is simply the damping of rolling motion. There is no direct aerodynamic moment created tending to directly restore wings-level, i.e. there is no returning "spring force/moment" proportional to roll angle.
What is Phugoid motion?
A phugoid or fugoid /ˈfjuːɡɔɪd/ is an aircraft motion in which the vehicle pitches up and climbs, and then pitches down and descends, accompanied by speeding up and slowing down as it goes "downhill" and "uphill".
What is spiral model in SDLC?
The spiral model is a systems development lifecycle (SDLC) method used for risk management that combines the iterative development process model with elements of the Waterfall model. The spiral model is used by software engineers and is favored for large, expensive and complicated projects.