Here we present the new installation of the Brechtel Manufacturing Inc. Counterflow Virtual Impactor (CVI) inlet on the FAAM BAe146 large research aircraft. Previous computational fluid dynamics calculations informed extensive structural design changes, which were required so that the inlet was outside of the aircraft boundary layer and particle shadow zones, as the BAE146 has a wider fuselage than those of previous installations.
We designed and manufactured a bespoke 7-port turbulence probe that was retrofitted to the CVI inlet and flown during two test flights. Results from a series of runs across a range of Indicated AirSpeed (IAS) and aircraft pitch angle show that the local airflow Angle of Attack (AoA) at the CVI inlet is within the ± 1° tolerance for satisfactory CVI performance (Shingler 2014). Furthermore we present the first in situ scientific observations from this CVI during research flights that show good comparison between CVI residual number concentrations and calibrated wing mounted cloud microphysics probes when collection efficiency and CVI cut size are considered.
During a standard BAe146 research sortie the pitch of the aircraft flies at a science speed of IAS = 105 ms-1, resulting in True Airspeed values of the operating envelope of between 100 and 170 ms-1. This results in a range of aircraft pitch angles as a function of altitude. During a flight, as fuel load decreases, the range of pitch angles reduces, as the lift required to keep the aircraft airborne for a given IAS decreases. At the CVI inlet, the local airflow AoA is nearly double the aircraft pitch angle. By modulating IAS throughout a flight, to account for changes in lift due to fuel burn, it is shown that it will be possible to fine tune the local airflow AoA at the CVI inlet. This has important consequences for other CVI installations, on aircraft where pitch changes as a function of fuel burn. The same applies to other instruments and inlets that do not maintain a constant angle of attack during a flight, on both this aircraft, and others with similar flight parameters.
Shingler et al, Characterisation and airborne deployment of a new counterflow virtual impactor inlet. AMT 2012.