Packs Off Takeoff
Joined: Oct 2004
Posts: 911
Likes: 43
From: Bournemouth UK
Packs off allows more engine thrust to be used for the take off. The maximum weight you can take off with is determined by the runway length, obstacle clearance and climb gradient which are all affected by the temperature and pressure (aircraft also have max structural take off weights). If a "Packs On" take off gives you a climb obstacle clearance limit of 55t, you will find that with Packs Off you can take off at 56t because you have a little bit extra thrust.
So the conditions when you will use it is when the aircraft weight, the field limits, or the climb limits mean that you need the extra thrust.
SW
So the conditions when you will use it is when the aircraft weight, the field limits, or the climb limits mean that you need the extra thrust.
SW
Joined: Jun 2004
Posts: 1,843
Likes: 0
From: Australia
As others have said, Packs OFF provides additional engine thrust, thus the RTOW may be increased.
Yes, it does save fuel, at any time that the fuel burned is providing for OTHER than engine thrust (e.g. Bleed Air, Generators, Hydraulics) the overall fuel use increases. Of course, turning any of the generators or hydraulic pumps off is unthinkable, but the example is there. At low altitude of course, pressurisation is not an issue, but perhaps a comfort issue in hot climates, which, coincidently, is when you'll most likely need to do a Packs Off Takeoff.
Reducing bleed air for pressurisation / air conditioning is a current trend for fuel saving, e.g. the now-common use of recirculation fans to reduce bleed air requirement.
Regards,
Old Smokey
Yes, it does save fuel, at any time that the fuel burned is providing for OTHER than engine thrust (e.g. Bleed Air, Generators, Hydraulics) the overall fuel use increases. Of course, turning any of the generators or hydraulic pumps off is unthinkable, but the example is there. At low altitude of course, pressurisation is not an issue, but perhaps a comfort issue in hot climates, which, coincidently, is when you'll most likely need to do a Packs Off Takeoff.
Reducing bleed air for pressurisation / air conditioning is a current trend for fuel saving, e.g. the now-common use of recirculation fans to reduce bleed air requirement.
Regards,
Old Smokey
Joined: Oct 2003
Posts: 577
Likes: 0
From: Gweriniaeth Cymru
Interstingly RR requires operators of the Trent 700 powered A330 operators to do a periodic packs-on take-off to encourage surge. This is due to a HPC wear issue that can be brought on during a packs on take-off.
So if the operator has an engine go bang during this periodic take-off, they can then apply to AIB to fly-on for about 10 flights with packs-off take-offs before engine replacement.
Brgd's
So if the operator has an engine go bang during this periodic take-off, they can then apply to AIB to fly-on for about 10 flights with packs-off take-offs before engine replacement.
Brgd's
Joined: Feb 2005
Posts: 4,581
Likes: 0
From: flyover country USA
Another approach is to use perf data for PACKS ON (assuming you're not TOGW limited), but select PACKS OFF to reduce EGT/TIT a few degrees. In the long run it's good for engine life.
I'm interested in the RR periodic PACKS ON TO check for stall. Other engines (CF6-50 comes to mind) used to have an "off-idle hangup" (actually a low-energy stall) if packs were off at throttle advance from ground idle. It could be cleared by turning packs on, then off again at half-throttle.
I'm interested in the RR periodic PACKS ON TO check for stall. Other engines (CF6-50 comes to mind) used to have an "off-idle hangup" (actually a low-energy stall) if packs were off at throttle advance from ground idle. It could be cleared by turning packs on, then off again at half-throttle.
