1.8 Simulated Altitude Test Cells
21
1.8 Simulated Altitude Test Cells
1.8.1 Impact of Altitude
Wind tunnels are useful to study aerodynamic phenomena under atmospheric pressure that is to say at ground level. However the difference in atmospheric conditions at varying altitude may have significant effects, especially on the operation of
air-breathing engines and on the risk of ice accretion.
The category of air-breathing engines for both manned and Unmanned Aerial
Vehicle (UAV) includes turbojets and turboprops, helicopter turboshafts and missile
turbojets (see Fig. 1.16). They are subject to atmospheric conditions at varying altitude during flight: the higher the altitude, the lower the ambient static pressure and
temperature. This has an impact on the working of gas turbine engines. For instance,
if the mass flow rate of the engine is lower at altitude due to lower pressure, in-flight
re-lighting is more difficult and so on.
Altitude has a significant influence on ice accretion as well. When an aircraft
is flying through clouds ice may accrete on probes (Pitot probes for example), the
leading edge of wings and/or at the engine intakes. Such ice accretion leads to an
increased risk of system failures or severe consequences. Indeed ice accretion on a
Fig. 1.16 Icing test on a helicopter intake at simulated altitude conditions—Test cell R6 (© DGA
Aero-engine Testing)
21
1.8 Simulated Altitude Test Cells
1.8.1 Impact of Altitude
Wind tunnels are useful to study aerodynamic phenomena under atmospheric pressure that is to say at ground level. However the difference in atmospheric conditions at varying altitude may have significant effects, especially on the operation of
air-breathing engines and on the risk of ice accretion.
The category of air-breathing engines for both manned and Unmanned Aerial
Vehicle (UAV) includes turbojets and turboprops, helicopter turboshafts and missile
turbojets (see Fig. 1.16). They are subject to atmospheric conditions at varying altitude during flight: the higher the altitude, the lower the ambient static pressure and
temperature. This has an impact on the working of gas turbine engines. For instance,
if the mass flow rate of the engine is lower at altitude due to lower pressure, in-flight
re-lighting is more difficult and so on.
Altitude has a significant influence on ice accretion as well. When an aircraft
is flying through clouds ice may accrete on probes (Pitot probes for example), the
leading edge of wings and/or at the engine intakes. Such ice accretion leads to an
increased risk of system failures or severe consequences. Indeed ice accretion on a
Fig. 1.16 Icing test on a helicopter intake at simulated altitude conditions—Test cell R6 (© DGA
Aero-engine Testing)