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Author Topic: Looking for Memo on Setting Manual Takeoff Thrust  (Read 443 times)

emerydc8

  • Join date: Jun 2015
  • Location: Tucson, AZ USA
  • Posts: 1954
Looking for Memo on Setting Manual Takeoff Thrust
« on: Thu, 21 May 2020 07:04 »
I'm looking for the memo for the CF6 engine that discusses the ram-rise effect when setting thrust manually for takeoff. I remember reading it at some point but can't seem to find it now. This is the memo that discusses setting the N1 slightly less than thrust ref in anticipation of the N1 increasing as speed increases. Anyone remember where this is located? Thanks.

Jon

DougSnow

  • Join date: Jun 2009
  • Location: KMEM
  • Posts: 205
Re: Looking for Memo on Setting Manual Takeoff Thrust
« Reply #1 on: Fri, 22 May 2020 00:09 »
I looked in MyBoeingFleet and didn't find anything...

Hardy Heinlin

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Re: Looking for Memo on Setting Manual Takeoff Thrust
« Reply #2 on: Fri, 22 May 2020 00:15 »
Isn't this something that only RB211 users take into consideration? I know that the effect occurs on all engine types (it's also modeled in PSX), but, as we know, the RR uses the "integrated EPR" method for the primary thrust control.

dhob

  • Join date: Sep 2019
  • Posts: 35
Re: Looking for Memo on Setting Manual Takeoff Thrust
« Reply #3 on: Fri, 22 May 2020 05:39 »
CF6 is a broad brush as there are many different versions. The initial 767-200/300s were powered by CF6-80A engines. These were non-FADEC engines. You could over speed or overtemp the engines manually. At times during takeoff in hot weather with TO thrust, the EGT would overtemp during takeoff. This happened on several flights I made, especially leaving LAS in the summer. The 747-400 is powered by the CF6-80C2 series, which are FADEC. As such, FADEC will manage thrust to include N1, EGT etc., and prevent exceeding engine limits. The EECs prevent any overboost or overspeed. There is no such recommendation regarding setting takeoff thrust for the 747-400.

emerydc8

  • Join date: Jun 2015
  • Location: Tucson, AZ USA
  • Posts: 1954
Re: Looking for Memo on Setting Manual Takeoff Thrust
« Reply #4 on: Fri, 22 May 2020 06:47 »
CF6 is a broad brush as there are many different versions. The initial 767-200/300s were powered by CF6-80A engines. These were non-FADEC engines. You could over speed or overtemp the engines manually. At times during takeoff in hot weather with TO thrust, the EGT would overtemp during takeoff. This happened on several flights I made, especially leaving LAS in the summer. The 747-400 is powered by the CF6-80C2 series, which are FADEC. As such, FADEC will manage thrust to include N1, EGT etc., and prevent exceeding engine limits. The EECs prevent any overboost or overspeed. There is no such recommendation regarding setting takeoff thrust for the 747-400.

It has nothing to do with overboosting or overtemping. All our 767-300s use the CF6-80C2 engines. We have the B6, B6F and B7F engines. The B6 (no F) are non-FADEC (PMC). There was a memo published about manually setting takeoff thrust prior to 80 knots, but I'm not sure if it came from GE or Boeing. In any case, I don't think it was specific to PMC or FADEC engines.

DougSnow

  • Join date: Jun 2009
  • Location: KMEM
  • Posts: 205
Re: Looking for Memo on Setting Manual Takeoff Thrust
« Reply #5 on: Sat, 23 May 2020 15:11 »
There was an FCOM Bulletin in MBF for PW4000 engines (probably due to fan blade leading edge erosion)... looking in our Boeing FCOM for our 67s, and we have the -B7F and I see no bulletins about setting thrust.

emerydc8

  • Join date: Jun 2015
  • Location: Tucson, AZ USA
  • Posts: 1954
Re: Looking for Memo on Setting Manual Takeoff Thrust
« Reply #6 on: Sat, 23 May 2020 18:50 »
Thanks for looking. I'll post it here if/when I find it.

IefCooreman

  • Join date: May 2011
  • Posts: 229
Re: Looking for Memo on Setting Manual Takeoff Thrust
« Reply #7 on: Sat, 23 May 2020 21:55 »
I'm a bit confused as to the "situation". Do you refer to the manual "finetuning" of N1 if the autothrottle was too slow, or no use of the autothrottle at all for takeoff?

It does sound like the standard procedure for a PMC off takeoff to be honest. The PMC is the part of the engine that stops that N1 increase from happening. Whatever you set manually, the PMC will keep the N1 constant (as N1 is the engine regulating parameter). PMC off, and the N1 will rise with airspeed and then the procedure calls for no N1 changes during the takeoff.

Can't find any reference for a takeoff with the EEC's in hard alternate mode, if the same procedure applies. Have done this with GE90 and CFM56, but my memory... can't find anything in the books though.

emerydc8

  • Join date: Jun 2015
  • Location: Tucson, AZ USA
  • Posts: 1954
Re: Looking for Memo on Setting Manual Takeoff Thrust
« Reply #8 on: Sat, 23 May 2020 23:52 »
It's for setting manual takeoff thrust when the A/T is DMId. If I recall correctly, there was a memo about setting the N1 slightly below the takeoff N1 in anticipation that the ram rise would cause the N1 to increase as you passed into the high-speed regime. This may have been for the 767 only. Usually the reason the A/T is DMId on our 767s is due to an inoperative thrust management computer, so you have two things going on here.

IefCooreman

  • Join date: May 2011
  • Posts: 229
Re: Looking for Memo on Setting Manual Takeoff Thrust
« Reply #9 on: Sun, 24 May 2020 10:36 »
Yes, but in high speed regime the A/T is "hands off" anyway, even with A/T on for takeoff? So it would happen every takeoff? Or is the CF6-80 N2 regulated which would be odd...

emerydc8

  • Join date: Jun 2015
  • Location: Tucson, AZ USA
  • Posts: 1954
Re: Looking for Memo on Setting Manual Takeoff Thrust
« Reply #10 on: Sun, 24 May 2020 20:08 »
I'll have to find the memo.

dhob

  • Join date: Sep 2019
  • Posts: 35
Re: Looking for Memo on Setting Manual Takeoff Thrust
« Reply #11 on: Tue, 26 May 2020 01:40 »
The 747-400/-8 cannot be dispatched with both FMC's inoperative. The left or right must be operative to include the FMCS thrust management function. As such, the thrust can never be set above the TO thrust limit.