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Meyerflyer

Takeoff thrust with higher Flex temp is lower than climb thrust

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Hello,

 

after updating to latest experimental update I just noticed that the thrust for takeoff was lower than the climb thrust. So I took off with the A319 IAE with a flex temp of 74 and about 58t, so quite light.

 

The thrust was felt and audible very low, the take off run was waaay longer than expected and before the update. Climb performance was absolutely bad. When I retarded the thrust levers to CL/CLB the engines spooled up instead of down and the climb performance improved.

 

Is this as expected? Since now, I only knew that the climb thrust of an engine of the 777 could be higher than flex. I think there is something wrong in the new update.

 

What's going on here?

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I noticed and something similar happens in the descent and approximation phase, after the last update, the speed is always in the lower limit, never in the correct and assigned, I did not notice the ascent phase, but if I noticed something different when passing power of takeoff to CL , today I will look.

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74 is an extremely high flex temp. IRL I almost never use a flex temp of more than 60, even on a completely empty aircraft.  If you have a flex temp of around 55 or lower it either be a thrust reduction or sometimes little to no reduction in the higher temps after climb power is selected. Many aircraft using a highly derated takeoff see a thrust increase when climb power is selected. What you describe sounds like normal systems operation to me. 

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Okay but this cannot be a normal behaviour as the recommended flex temp was 67 so I only added 7 for economic reasons due to using a 3300m long runway with the A319. I'm pretty sure, the takeoff performance would have been been with the flex temp of 67.

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Just tested in ESSA / 01L, A320 IAE vs CFM and the CFM takes off just fine with a flex of +60 and 60.1T TOW where as the IAE was only giving ~1.25-.35 on the EPR and couldn't even accelerate at 0 ftp after rotation.

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There are so many reports of a bug with the IAE busses right now. Someone should seriously have a close look at this now. Something went wrong with one of the latest updates.

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A319 IAE (1.2.1.3). T/O run is about 500 ft longer as with CFM engines (67° at 55t). V2+10 feels a lot sticky, but the ECAM indications look normal.

If i set the CL detend the engines run smoothly without any glitches, but in V/S mode, the needles are dancing up and down, the donout stays there he should.

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28 minutes ago, Meyerflyer said:

There are so many reports of a bug with the IAE busses right now. Someone should seriously have a close look at this now. Something went wrong with one of the latest updates.

 

Yep. FLEX temp is not working anymore as it should on IAE. Applying FLEX thrust means taking off with the horsepower of my Seat Ibiza. The same FLEX temps (not the same but relative) works fine on CFM though. Using http://www.wabpro.cz/A320/ I had no problems until 1.2.1.1.

So now I'm using latest update with the exception of ECAM_D2D.dll, which is from 1.2.1.0. Until this gets fixed.

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Hi, for flex with IAE there are some rules. A flex of 76 is not allowed. TFLEXMAX at sea level is 70degree. Less if you are higher. I also have FCOM that state as max 57 and 60, depending on engine.

There are more rules. I’m not sure if wabpro is calculating all correct. These calculations are very Engine depending. Also how old is an engine. An official departure tool should be reference and not an online tool. You should use the built in flex temp calc.

 

28F6F648-6D4C-45C6-A0FA-0BE760812B64.jpeg

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8 minutes ago, masterhawk said:

I’m not sure if wabpro is calculating all correct. An official departure tool should be reference and not an online tool.

 

Nice joke. You can't expect us to have access to that kind of information. The best we can do is use tools like wabpro or topcat (which doesn't have IAE profiles). The Aerobus doesn't calculate FLEX for intersection departures for example.

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I can ask the dev if there was something modified for IAE in regard of flex calc. Only thing that was modified is the CLB perf of the 320IAE.

 

I will look into the intersection calculation. Maybe it can be added.

 

 

 

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Keep in mind that there are other limitations in play; check the FCOM for these

 

  • Thrust must not be reduced by more than 25 % of the full rated takeoff thrust.
  • The flexible takeoff N1 cannot be lower than the Max climb N1 at the same flight conditions. \

The FADEC takes the above two constraints into account to determine flexible N1.

  • The flexible takeoff thrust cannot be lower than the Max Continuous thrust used for the final takeoff flight path computation (at ISA +40).
  • This constraint limits the maximum flexible temperature at ISA + 43 (58 °C at sea level).

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17 hours ago, Mathijs Kok said:

Keep in mind that there are other limitations in play; check the FCOM for these

 

  • Thrust must not be reduced by more than 25 % of the full rated takeoff thrust.
  • The flexible takeoff N1 cannot be lower than the Max climb N1 at the same flight conditions. \

The FADEC takes the above two constraints into account to determine flexible N1.

  • The flexible takeoff thrust cannot be lower than the Max Continuous thrust used for the final takeoff flight path computation (at ISA +40).
  • This constraint limits the maximum flexible temperature at ISA + 43 (58 °C at sea level).

 

Well it obviously doesn't take these constraints into account as it gives EPR of just 1.25-.35 with FLEX given by a takeoff performance calculator.

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Let me say that this problem we have encountered in the latest updates is not a subtle feeling that the IAE is underpowered with some FLEX temp. It's clearly not an error of calculation within the calc tool we may use.

It's a clear and noticeable lack of power whatever the FLEX temp you use. But it used to work until 1.2.1.1. with the same tools.

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There's definitely something wrong with the current IAE FLEX settings. I tried again a takeoff in ESSA with numbers put into wabpro, which gave me a FLEX of 67. I lowered it down to FLEX 54C (OAT -1) and after rotation and following the FD the speed kept slowing down and I ended up in alpha floor. Same airport, runway, weather and weight the CFM climbs out just fine with FLEX 79.

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I may be having the same issue with the IAE model.

I set up everything according to correct procedures and had a FLEX of 67 in the MCDU. Take off commenced and I rotated at the calculated speed and correct rate. Within seconds of lift off speed started to decay rapidly and I was forced to firewall the throttles and drop the nose to maintain level flight until speed was sufficient to recommence climbout. When speed was sufficient and positive rate was achieved I retracted the undercarriage and set the Autopilot. The aircraft accelerated to 250knts and continued to climb at a satisfactory rate.

This not the first time I have had this problem and I can't be certain (and I certainly could be wrong)  but it may have started when the IAE taxi rate was altered to slow taxi speed down under idle throttle conditions.

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Just had the same things happen to me taking of from LHBP. This was only using a FLEX of  52 for the A320 IAE. I had to advance throttles to the TOGA detent to get enough power for TO.  The RWYS at LHBP are more than long enough and my aircraft was more than light enough for a derated TO. 

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14 hours ago, chumley said:

......

This not the first time I have had this problem and I can't be certain (and I certainly could be wrong)  but it may have started when the IAE taxi rate was altered to slow taxi speed down under idle throttle conditions.

This comment related to the CFM engine variant so is not relevant.

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