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.