1. © Crown copyright Met Office Wind and turbulence measurements on the BAe146 Phil Brown, OBR Conference, Dec 2012

2. © Crown copyright Met Office Table of Contents Wind measurements from an aircraft – how do they do that? The BAe146 turbulence probe system Components Calibration Performance The AIMMS-20

3. © Crown copyright Met Office Wind measurement from an aircraft 1.Measure the velocity of the aircraft relative to the ground GIN velocity components GIN pitch, roll and yaw angles … and rates of change 2.Measure the velocity of the air relative to the aircraft True airspeed Attack and sideslip angles 3.Wind vector is the vector difference between the two 4.Simples!

4. © Crown copyright Met Office Aircraft velocity and attitude Older inertial navigation systems suffer from “Schuler” errors – oscillatory errors in position and velocity with ~84 min period Removed by reference to a stable position reference – GPS Now done by means of real-time Kalman filtering with the Applanix GIN system Vn, Ve accuracy in level flight ~0.1 ms -1

5. © Crown copyright Met Office Issues Attitude offsets between the GIN system and aircraft axes Pitch and roll offsets can be measured with GIN data on the ground and measurements of the floor angles Yaw offset can be estimated using the technique of runs along the runway centreline (a known track angle) Best done at the end of a flight as full heading accuracy in the GIN system is only achieved after some manoeuvring

6. © Crown copyright Met Office Radome flow angle measurement Check transducers to detect possible icing of attack / sideslip ports Vertical flow measurement, AoA Lateral flow measurement, AoSS Reference dynamic pressure Static source S10  Pairs of ports in the vertical and horizontal planes measure differential pressures  These are scaled by the dynamic pressure and calibrated to derive angles of attack and sideslip

7. © Crown copyright Met Office Inside the radome....  Pipe installations and water traps designed to avoid acoustic resonances within the measurement frequency range (<32Hz).  External icing protection currently by means of ICEX silicone coating applied prior to flight  Centre port heating

8. © Crown copyright Met Office Angle of attack calibration Differential pressure scaled by dynamic pressure INU Pitch angle is a proxy for AoA in straight/level flight in still air Sensitivity to Mach Number is consistent with similar installations on other aircraft Data points are from flight segments of between 2-5 minutes duration at a range of different heights and speeds. Angle of Sideslip is calibrated similarly using scaled differential pressure measurements during yawing oscillation manouevres. INU drift angle provides proxy sideslip data

9. © Crown copyright Met Office AoA calibration by acceleration Data are 1-sec averages taken from accelerating / decelerating straight-level runs, filtered to include only points that have 9.75 < dVz/dt < 9.87 ms -2. AoA < 2 deg was obtained with flaps down. This calibration is of necessity Mach-independent B263 26/01/07 runs at 8000, 11000, 15000, 20000 and 30000ft

10. © Crown copyright Met Office Angle of sideslip calibration Data points are 1Hz values during yaw oscillation manoeuvres. Each manoeuvre is typically 2min duration with ~10 cycles of oscillation. De-trended INU drift angle provides proxy sideslip data. Differential pressure scaled by dynamic pressure groundspeed airspeed wind vector Drift angle

11. © Crown copyright Met Office Iteration of TAS, α, β Centre-port sensitivity to α, β obtained from BAES flight tests pre-delivery

12. © Crown copyright Met Office Systematic errors: along heading True airspeed error gives error in along- heading wind component Airspeed correction factor Typically ~ 0.985 – 0.995 True airspeed wind True airspeed wind Groundspeed

13. © Crown copyright Met Office Systematic errors: “Rodi” manoeuvres Orbits to left and right with simultaneous yawing oscillation In this condition, measured vertical wind is sensitive to roll, pitch, AoSS and AoAA Derive optimal set of corrections to these parameters such that variance of w during the manoeuvres is minimized

14. © Crown copyright Met Office Systematic errors: “Rodi” manoeuvres w u,v

15. © Crown copyright Met Office B412 / RF07 intercomparison 31/10/2008 Above cloud C-130BAe146 GPS Altitude m 1819.51838.1 Temperat ure C 14.65 De-ice non-deice 15.05 15.65 Dew point C -25.49-22.47 U-1.18-1.37 V1.941.75 W-0.130.08 Below cloud C-130BAe146 GPS Altitude m 189.8181.6 Temperat ure C 15.40 De-ice non-deice 15.05 15.65 Dew point C 7.64 U-3.43-3.60 V7.717.42 W-0.200.06

16. © Crown copyright Met Office B412 / RF07 intercomparison 31/10/2008 Δ(C130-146) Above cloud Δ(C130-146) In cloud Δ(C130-146) Below cloud De-iced temp C0.400.950.35 Non-deiced C-0.17-0.05-0.25 Dew point C-3.02 U0.190.150.17 V0.190.560.29 Conclusions: Temperature – additional wetting of 146 Rosemount in cloud? - reduced wetting impact on 146 non-deiced Rosemount? U,V – consistent offsets at all levels

17. © Crown copyright Met Office B412 / RF07 intercomparison 31/10/2008 Std.devtn of w C-130BAe146 Above cloud 0.0150.008 In cloud0.2310.191 Below cloud 0.2120.175

18. © Crown copyright Met Office B412 / RF07 intercomparison 31/10/2008 Horizontal wind Std. devtn. (u’ 2 + v’ 2 ) 0.5 C-130BAe146 Above cloud0.220.19 In cloud2.852.29 Below cloud1.531.37 Conclusions: Vertical and horizontal wind variances for 146 appear to be systematically lower.

19. © Crown copyright Met Office AIMMS-20: Airborne Integrated Meteorological Measurement System Incorporating: -Temperature and RH - GPS/Inertial position/velocity - 5-hole probe (TAS, α, β) - static pressure - de-ice heating with purging of water ingress - 40Hz measurement (?)

20. © Crown copyright Met Office AIMMS data from SAMBBA, B732 R1-6 Core FAAM values in black, AIMMS in red Temperature comparison is with FAAM non- deiced These runs are not necessarily all straight/level Runs 1/2 are FL240 – higher offsets in some parameters at this altitude

21. © Crown copyright Met Office Vertical wind, w

22. © Crown copyright Met Office Easterly wind, u

23. © Crown copyright Met Office Northerly wind, v

24. © Crown copyright Met Office Temperature, C FAAM = non-deiced

25. © Crown copyright Met Office Static pressure

26. © Crown copyright Met Office TAS

27. © Crown copyright Met Office AIMMS – current issues De-ice heating power – return to Aventech for adaptation of 115 Vac supplies to 28 Vdc heaters High frequency performance Static pressure / TAS errors at higher altitude?

28. © Crown copyright Met Office Questions and answers