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GA Thrust Setting

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GA Thrust Setting

Old 20th Feb 2023, 04:15
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fdr
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GA Thrust Setting

Questions to Boeing, Airbus and EMB drivers, engineers, perf engineering.

1. What is the reference that the GA thrust rating applies?
2. For your Thales/Smiths(GEAvn)/Honerywell FMC, what company policy is amendable in the FMC?
3. For Airbus electrojets, do all now have a reduced GA thrust and a full GA thrust level, similar in concept to the single or double tap TOGA for Boeing?

Once upon a time the GA ref was predicated on the TO THR page on Boeing FMCs... Its been a while and I am not sure that remains the case. Airbus amended their GA after I last played with those too, so am after some current status.
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Old 20th Feb 2023, 13:13
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What is an electrojet???
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Old 20th Feb 2023, 13:30
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fdr:

The single-aisle AB new 'soft GA' feature.
a) advance TLs all the way to TO/GA detent (thrust supplied to rating limits and all the AFDS g.a. modes engage)
b) bring TLs back one step to MCT/FLEX detent. Previously this would supply MCT (CON) but now is the smart, soft-GA power.
c) reduce to CL detent when ready to resume i) CL limit, ii) ATHR control.

All modes: Max Rated (toga notch) and AST+ soft-ga + CON (flex/mct notch) are fixed thrust, ATHR cannot reach the engine in those and remains armed only.

Not able to provide the rules of calculation behind each n1/epr setting for those. Comes from the box, not displayed on the box. Visible on the EIS when the modes are active. Top-right corner of the upper central display.

The only available pilot-user modification is to overwrite the pre-pinned FMS values for
(AEO) thr-red & acc alt
(OEI) acc alt
that may or may not provide some advisories on the PFD as the aeroplane gains altitude. No effect on the active thrust.





Last edited by FlightDetent; 20th Feb 2023 at 13:42.
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Old 29th Mar 2023, 11:58
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fdr
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Many thanks guys.

check out www.delta-burn.com, the video is of one of my jets... it is pretty neat.
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Old 29th Mar 2023, 19:34
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On most Boeing aircraft, Max Go-Around is the same as Max Takeoff - and if you advance the thrust levers full forward, that's what you'll get (assuming you're in the TO altitude envelop). But there are a couple exceptions I know of.
On the 747 (-400 and -8), the FMC commanded Max Go-Around is less than TO (memory says it's Max Climb but I wouldn't swear to that). This is due to a specific case of doing a go-around with two engines out on the same side - Max Takeoff can cause you to run out of rudder. However if you advance the thrust lever full forward, Max TO is still available.
787 has some unusual logic that not only limits Max Go-Around, it can also limit Max Takeoff even with the lever full forward. I don't know details of the implementation, but apparently there are situations where if you're light and doing a big derate, if you lose an engine after V1, advancing the other throttle to Max TO can cause you to run out of rudder - and the same can happen during an engine out go-around. So the FMC and the FADEC work together to limit the max amount of thrust available in those situations.
When I heard about that 787 logic, it made me glad I didn't work that program - that sort of thing scares the crap out of me due to the potential failure modes... On all other Boeing installations - if you put the thrust levers full forward, you'll get (at least) the max rated thrust for those conditions - regardless of anything that might be wrong on the aircraft side (aside from fuel feed and thrust lever position of course).
Us propulsion types took grim satisfaction in the fact that the FADEC engines on Aero Peru worked perfectly as they floundered around with garbage air-data right up to point where they hit the water.
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Old 30th Mar 2023, 05:48
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fdr
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Originally Posted by tdracer
On most Boeing aircraft, Max Go-Around is the same as Max Takeoff - and if you advance the thrust levers full forward, that's what you'll get (assuming you're in the TO altitude envelop). But there are a couple exceptions I know of.
On the 747 (-400 and -8), the FMC commanded Max Go-Around is less than TO (memory says it's Max Climb but I wouldn't swear to that). This is due to a specific case of doing a go-around with two engines out on the same side - Max Takeoff can cause you to run out of rudder. However if you advance the thrust lever full forward, Max TO is still available.
787 has some unusual logic that not only limits Max Go-Around, it can also limit Max Takeoff even with the lever full forward. I don't know details of the implementation, but apparently there are situations where if you're light and doing a big derate, if you lose an engine after V1, advancing the other throttle to Max TO can cause you to run out of rudder - and the same can happen during an engine out go-around. So the FMC and the FADEC work together to limit the max amount of thrust available in those situations.
When I heard about that 787 logic, it made me glad I didn't work that program - that sort of thing scares the crap out of me due to the potential failure modes... On all other Boeing installations - if you put the thrust levers full forward, you'll get (at least) the max rated thrust for those conditions - regardless of anything that might be wrong on the aircraft side (aside from fuel feed and thrust lever position of course).
Us propulsion types took grim satisfaction in the fact that the FADEC engines on Aero Peru worked perfectly as they floundered around with garbage air-data right up to point where they hit the water.

Yikes.

The thrust set for the takeoff gives the relevant V speeds, the rationale of increasing the thrust after an engine failure would raise some eyebrows.

In the case we have at present, the mod reduces the RPM for a given FN, and the normal engine parameters follow the RPM, so N1/N2/(N3)/EGT/FF remain the same relation, the engine just puts out a higher thrust, so for a given thrust, the N1 (and everything else) is lower. Not magic, but magical to watch occur.

Works fine for a manual thrust setting, like my own jet, works find for the FMC in my jet too, where there is no performance data base, the fuel predictions are purely instantaneous rate/speed/distance(time)....

Works fine for an A320 with V2500's the FMC can take the correction factor of more than /-9.9%.... and the V2500 uses EPR so that is simple. A B737, Smiths FMC is masked to limit +/-9.9% change, and the real pain, while TO is no factor, you are just always in a derated condition, but the G/A is much more interesting. The PMC/EEC is governing to N2 or N1 (on other engines) and so the engine not knowing any better, can go directly to the N1 that is called for on the FMC, and that gives, a bit more than 30% greater thrust than standard... which is around the same as zone 2 burner. That occurs at the normal EGT, N1/N2m and fuel flow of the standard engine. As much fun as that is, with a rear engine, its like driving a lightweight F5, or a Lear 24B on min fuel and empty, but with underwing engines, I am trying to sort out the N1 target, as right now, we are concentrating on the EPR, non Boeing products for the STC's.

The video in the following, link, www.delta-burn.com .... the guy in the RHS is the fuel efficiency expert for Honeywell. The charts showing the N1/N2, N1/EGT, FN/EGT, Wf/FN (TSFC) are in the videos and in the charts. We were just given a CF34 for testing, am after a test cell for that. The other engines we have now are a RR Trent to enter test, and a CFM56, working on the agreement for the V2500.












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