Last nights speedbird out of JFK

[dc8driver@night]

getting it right

Originally Posted by euroflyer

Interesting post but you do not need to increase power(burn more fuel) to increase rate of climb. By climbing at a lower speed you can climb quicker and with a higher pitch attitude. This would therefore not affect your fuel burn.
Regards

Euroflyer: You are partially right. Since the advent of Turbofan engines and the demise of Turbojet engines, there is only one “Climb Power” setting and true “Cruse Climbs” are a thing of the past. You are correct in stating that your merely increase pitch and thus rate of climb. Your are wrong in your statement about this does not cost fuel. As there is only one “Climb Power” setting, there is also only one “Best Rate of Climb Speed” and this is determined based on the aircraft weight on that day. As you slow down from that speed, you are increasing drag and thus using more fuel to travel the same distance. If you have to continue increasing the rate of climb, you will find the loss of airspeed and increase in drag may become critical. I have been asked to slow to 210 knots* in the climb until out of FL 250 by Center and found that at FL 250 it was impossible to accelerate to normal climbs speed without leveling off depending on our weight on that day. (*This was done by increasing pitch and thus rate of climb, never touching the thrust levers except to maintain “Climb Thrust” as we climbed to higher levels.) Both the pilot and ATC can help in saving fuel, but it requires proper procedures and knowledge as well as effective communication.

[Tight Slot]

all depends on the day

Some turbofaned a/c still have a few climb thrust settings, eg the RR engined 757's. Its a balancing game between getting to opt. cruise level quickly, and fuel burn getting there. Using full climb thrust will get you into the nice thin air quicker, and some would say, save fuel - esp in if there are strong head winds down low. On other days, using a de rated climb all the way up can lead to a lower overall trip burn.

If theres other a/c fighting to get the opt. cruise levels then I'd tend to use full climb to get the best level before my chums on the same track can - makes quite a big diff over fuel burn in the trip.

[dc8driver@night]

Derate Thrust

Tight Slot: Your right about there still being a few de-rate thrust settings out there such as the 757 and 767. Both the PW & RR powered 757 have "De-rate Thrust Setting". This is NOT a fuel savings measure or approved by either engine manufacturer. It was a sales pitch by Boeing (dare I call it a gimmick?/ I am not bad mouthing them as I dearly love both of these aircraft!) to help sell the aircraft. Their claim was that it would reduce operating cost by reducing; engine wear, vibration, and noise. If you run the numbers or have the charts in your AOM, you will see less fuel burned in climb at Max Climb Thrust. If you will note, only UPS and Delta used De-rated Thrust on the PW 757, and both of them have had turbine blade failures related to harmonics in the hot section at de-rated climb settings. UPS at least no longer uses a de-rated climb setting on PW 757s. They may use a Reduced Take Off Thrust setting, but then go to Max Climb Thrust after cleaning up. Further, the RR 757 on De-rate 2, has a deep power reduction built in until you are cleaned up and climbing. I can’t remember if this is based on flap setting or Radio Altimeter as I have been off of the 757 for almost 4 years. This feature is for noise abatement, not fuel savings. The 757 requires the pilot to select a higher power setting as your climb degrades, but at least our 767s (GE) do this automatically as you climb based on FL instead of performance.

[Slimbitz]

In addition to the climb performance, hold/approach speeds, and post-flight wing icing, associated with tankering fuel into LHR, some more considerations spring to mind. Landing distance increases for higher landing weight, and the runway exit needs to be planned. Some company SOPs use only reverse idle for landing (+ autobrake) - if at higher weight more reverse should be considered. Turnround times may be tight, in which longer brake cooling time may become a factor.