Abstract: A method of analysing blade tip displacements (dijk) derived from a rotor having an array of blades that rotate at a rotational speed (?). The blades are monitored by an array of stationary timing probes for at least two revolutions (j) of the rotor. Define asynchronous displacement (dijk_A) as a sum of a sinusoidal term (Va) and an offset per probe term (Oo). Define synchronous displacement (dijk_S) as a sum of a sinusoidal term (Vs) and a common offset term (Cc). Solve the asynchronous displacements (dijk_A) using the blade tip displacements (dijk) to give asynchronous amplitude (|a|), offset per probe (ok) and asynchronous residuals (rijk_A). Solve the synchronous displacements (dijk_S) using the blade tip displacements (dijk) to give synchronous amplitude (|s|), common offset (cj) and synchronous residuals (rijk_S).

Abstract: A method of analyzing blade tip timing data obtained from an array (Pk) of stationary timing probes (3) that are spaced at integer multiples of a base angle. Replace one of the probes (3) with a virtual probe (Pv) to give a virtual probe set (42). Set an initial probe angle (?v) and an initial engine order (EOv) for the virtual probe (Pv). Calculate the condition number (CN) for the virtual probe set (42). If the condition number (CN) at least meets a threshold criterion, solve the virtual probe set (42) for blade tip displacement amplitude. Else increment the virtual probe angle (?v) and/or the virtual engine order and iterate from calculating the condition number. Else reinstate the replaced probe (3) and replace a different probe (3) from the array of probes (Pk) with the virtual probe (Pv); then iterate from setting the initial virtual probe angle and engine order.

Abstract: A method of determining rotor blade axial displacement (bij). The rotor blade tip (34) comprises first and second measurement features (36, 38) arranged to make an acute angle therebetween. Measure time of arrival (tijk) of the once per revolution feature (1), first and second edges (40, 42) of the first measurement feature (36), and first and second edges (44, 46) of the second measurement feature (38), for at least two revolutions of the rotor (2). Convert these to circumferential distances (dijk) for each revolution. Calculate a feature angle (?ijk) between each measurement feature (36, 38) and the once per revolution feature (1) for each revolution. Calculate blade untwist angle (?ij) from the change in feature angle (?ijk) between measured revolutions. Calculate the rotor blade axial displacement (bij) from the blade untwist angle (?ij) and the circumferential distance (dijk) of the point from one of the measurement features (36, 38).

Abstract: A method of analysing blade tip displacements (dijk) derived from a rotor having an array of blades that rotate at a rotational speed (?). The blades are monitored by an array of stationary timing probes for at least two revolutions (j) of the rotor. Define asynchronous displacement (dijk_A) as a sum of a sinusoidal term (Va) and an offset per probe term (Oo). Define synchronous displacement (dijk_S) as a sum of a sinusoidal term (Vs) and a common offset term (Cc). Solve the asynchronous displacements (dijk_A) using the blade tip displacements (dijk) to give asynchronous amplitude (|a|), offset per probe (ok) and asynchronous residuals (rijk_A). Solve the synchronous displacements (dijk_S) using the blade tip displacements (dijk) to give synchronous amplitude (|s|), common offset (cj) and synchronous residuals (rijk_S).

Abstract: A method of analysing blade tip timing data obtained from an array (Pk) of stationary timing probes (3) that are spaced at integer multiples of a base angle. Replace one of the probes (3) with a virtual probe (Pv) to give a virtual probe set (42). Set an initial probe angle (?v) and an initial engine order (EOv) for the virtual probe (Pv). Calculate the condition number (CN) for the virtual probe set (42). If the condition number (CN) at least meets a threshold criterion, solve the virtual probe set (42) for blade tip displacement amplitude. Else increment the virtual probe angle (?v) and/or the virtual engine order and iterate from calculating the condition number. Else reinstate the replaced probe (3) and replace a different probe (3) from the array of probes (Pk) with the virtual probe (Pv); then iterate from setting the initial virtual probe angle and engine order.

Abstract: A method of determining rotor blade axial displacement (bij). The rotor blade tip (34) comprises first and second measurement features (36, 38) arranged to make an acute angle therebetween. Measure time of arrival (tijk) of the once per revolution feature (1), first and second edges (40, 42) of the first measurement feature (36), and first and second edges (44, 46) of the second measurement feature (38), for at least two revolutions of the rotor (2). Convert these to circumferential distances (dijk) for each revolution. Calculate a feature angle (?ijk) between each measurement feature (36, 38) and the once per revolution feature (1) for each revolution. Calculate blade untwist angle (?ij) from the change in feature angle (?ijk) between measured revolutions. Calculate the rotor blade axial displacement (bij) from the blade untwist angle (?ij) and the circumferential distance (dijk) of the point from one of the measurement features (36, 38).