Environmental Envelope

[frankice]

Hi guys,

I was reviewing the environmental envelope limitation, from the attached presentation (with participation of Airbus), page 9, it looks like the low temperature limitation near sea level it's mainly due to the 'Landing Gear Structure'. I just can't figure out how the landing gear 'structure' can impose a temperature limitation, any help?

Thanks

[Eric Janson]

Metals become brittle at extremely cold temperatures so the chance of failure will increase.
Also your seals will harden allowing things like Nitrogen and Hydraulic fluid to escape.

I don't know whether the above is the reason behind this.

[underfire]

Fluid viscosity at low temp. Gear up at extreme low temperatures can take a long time. The nose gear is especially an issue, with the low viscosity, the system may not be able to overcome the resisting aerodynamic load on the gear.
Gear down is not usually an issue, as the aerodynamic load actually helps bring the gear down.

[washoutt]

The manufacturer chooses the desired environment enveloppe., and designs the aircraft for those paprameters, mainly temperature effects. As Underfire states, if the u/g cannot cope as a design for the chosen low temparatures, then the certified minimum temp for raising the gear becomes the left border of the enveloppe and that could be substntial warmer than siberian temperatures. In that case, the aircraft will have a limitation in the AFM for not operating in Siberia, so to speak.

[underfire]

Just to give you an idea of the viscosity differences with temperature, the is AeroShell 4 Fluid:

Kinematic viscosity mm²/s

@ 100°C 4.0 min 5.30
@ 40°C 13 min 14.1
@ –40°C 500 max 491
@ –54°C 3000 max 2300

[frankice]

Well thank you very much guys, very interesting.