Airbus A320 Climb Thrust EPR

[Guest bbain]

Hey Everybody,I'm new to the PSS A320 and I think it is a great product, I just have a quick question. The Takeoff Flex Temp is what determines the power for a reduced thrust takeoff, and that works fine, but how come the Climb thrust is always the same? It seems to me that conditions that require a reduced-thrust takeoff should also have a reduced-thrust climb. It doesn't make sense to me why the power actually INCREASES when I bring it down to climb thrust in some cases. It always starts around 94-96% N1, which in some cases makes me climb at over 3500 fpm, which I know is too much (shouldn't it be 2500?). I tried messing with the cost index and that didn't do anything. Is there any way to fix this besides manually controlling the vertical speed, or is this the way it's supposed to be? Any help will be greatly appreciated.Ben Bain

[Guest speight]

Try entering -42 flex temp in fmgs instead of the default +42

[Bob Scott 7,721]

If you're flexing down below Climb EPR you're flexing too far.Don't have the tech data here with me, but there's a limit on how far down you can flex. The PSS panel doesn't check that, and in fact has the logic more or less backwards. But...you don't just put -42 in...more than likely that's way, way too far.In reality flex temp is above actual temp...you're telling the MCDU to schedule thrust on the engine as if the temp were higher (which will result in a lower thrust setting). Flex temps are usually no more than around 20-30 deg C higher than actual, because more than that will exceed the allowable flex reduction. But in the PSS panel, you have to flex down rather than up due to faulty MCDU logic, meaning that flex temp should be no more than 20 to 30 deg C below actual temp. So if the actual temp is 20 deg C, entering a flex temp lower than -10 deg is likely to reduce the power too much. As a rule of thumb, I use 20 deg below actual in the PSS panel. It's all something of a wag anyway, because the power curves on the PSS panels are notional to begin with.So, bottom line, if you're seeing a thrust increase when selecting Climb Power after a flex takeoff, you've probably flexed the power back too far.For PSS--I've explained this phenomonon numerous times here in the forum...understand that it's not going to be fixed, but would really appreciate it if you could pin this topic or place this info on flexing in a FAQ so that it remains in the known universe of PSS knowledge...RegardsBob ScottATP IMEL Gulfstream II-III-IV-V L-300Santiago de Chile

[Guest vrandar]

I too have had to explain the programing error many times. I hope this helps: the approximate N1% figures you will get for each negative flex temp is shown below. Don't forget that an N1% figure of lower than 75% of maximum thrust (105%) is not permitted by Airbus.FLEX N1% -1 97.5-2 97.4-3 97.2-4 97.1-5 96.9-6 96.7-7 96.6-8 96.4-9 96.3-10 96.1-11 96.0-12 95.8-13 95.6-14 95.5-15 95.3-16 95.2-17 95.0-18 94.9-19 94.7-20 94.5-21 94.4-22 94.2-23 94.1-24 93.9-25 93.8-26 93.6-27 93.5-28 93.3-29 93.1-30 93.0 -31 92.8-32 92.7-33 92.5-34 92.4-35 92.2-36 92.1-37 91.9-38 91.7-39 91.6-40 91.4-41 91.3-42 91.1-43 91.0-44 90.8-45 90.7-46 90.5-47 90.3-48 90.2-49 90.0-50 89.9-51 89.7-52 89.6-53 89.4-54 89.3-55 89.1-56 88.9-57 88.8-58 88.6-59 88.5-60 88.3Rob Elliott, EGPE InvernessPSS Airbus Support andAirbus Fleet Training Captain, British Airways Virtual airbus@speedbirdonline.co.ukhttp://www.speedbirdonline.co.uk/airbus.htmlhttp://www.bavirtual.co.uk

[Bob Scott 7,721]

Went back and dug up some of the old discussions we had a few years ago about this. Turns out that a flex temp of up to +60 deg is common in the real-world bird, which represents a typical +30-40 deg delta. At a flex temp of +60, the takeoff thrust and climb thrust will be about equal.It should also be noted that a max reduction of 25% in thrust as Rob noted does *not* equate to a 25% reduction in N1 RPM...the relation between N1% and thrust produced is not linear. I ran a test suite (AFSD) on the bus with Pedro Oliveira's FDE (which I use), and 75% of max rated thrust (105%) was measured at 87.7% N1 on a standard day. This checks with the accepted real-world rule of thumb that a takeoff N1% less than 90% is generally suspect...something that would have saved the Air Florida guys that hit the 14th St Bridge in DC when they tried taking off with iced-up EPR probes that caused the EPR gauges to indicate falsely high readings...had they been trained to look, the N1 gauges would have told them otherwise.All that said, if you flex more than minus 20-25 deg in the PSS bus, you're going to see the aforementioned increase in power when you select climb power. That could probably be fixed with some careful and time-consuming reworking of the low-mach end of the thrust curves...as for me, I'll just limit myself to 20 deg or accept the "sim-ism" of the power increase....and that's the rest of the story...CheersBob ScottATP IMEL Gulfstream II-III-IV-V L-300Santiago de Chile

[Guest bbain]

Thanks everyone for the great replies. It would be real nice if they released a patch or something for it, but it's a great product nonetheless and I can live with it.