A320 performance

  • 1. way too high idle N1 in flight. E.g. at low altitude and at 220kts N1 should be around 23%
    Once the flaps are out of 0, idle N1 increases (due to the IRL horrible slow acceleration out of idle) to approx 31%
    With flaps up on the Aerofly A320 idle RPM at 250kias is 39%

    2. engine acceleration way too fast
    IRL the CFM56 is very slow to accelerate out idle. Even at the 30% approach idle it needs almost the full 8sec.
    But this is not uniform at all. It takes 5sec to achieve any noticeble but still very low thrust. Once it's above 60-70% is accelerates and decelerates very fast.
    On the Aerofly it's reversed. Good acceleration at low RPM and the higher the RPM gets the more the acceleration slows down.

    3. basic drag too high. But even at this high idle N1 in clean config the ROD at green dot is noticable higher than it is IRL (should be 1200-1300ft/min)

    4. flap drag too high. Until conf 3 everything is still in acceptable range but in config full with gear down at idle at 150kias the ROD should be 1500ft/min and 1° nose down attitude while the Aerofly drops like a stone with -8° and 2400ft/min.
    ROD and pitch attitude at conf 3 would be close to the real A320 at conf full.

    Despite this (and when using conf 3 for approach) the A320 is very nice to fly and e.g. climb performance is spot on at MCT and CLB thrust.

  • Hi bbrz,

    thanks for the numbers, I'll try to tweek it into the right direction.
    Yes the high inertia of the engines when accelerating from idle to 50% or so should be a lot higher.
    The drag with flaps and gear extended can be changes easily. From where do you take the numbers for the descent rates?
    When I set the clean configuration drag I used a video of a real world a320 and compared its rate of descent, throttle setting and airspeed. For the light grossweight of our current A320, what would be the sinkrate that you expect at, say 210kts?


  • I've taken the numbers from actual Airbus LPC-NG calculations I made when I verified the Aerosoft A320 performance.
    Here are the actual numbers for 62t

    idle descent 300kias 28% N1 -3.0° pitch, -2400fpm conf 0
    idle descent 250kias 26% N1 -0.5° pitch, -1600fpm conf 0
    idle descent 210kias 23% N1 +2.0° pitch, -1300fpm conf 0
    idle descent 210kias 32% N1 +3.0° pitch, -1150fpm conf 1

    hope that helps

  • Thank you very much! Any real world data is much appreciated!

    I also have data for the pitch trim from a RL A320 captain:

    A320-200 GW 64.5t - CG 35.5%

    230kias, trim 0.5 up, pitch 3.0deg, clean config
    195kias, trim 1.1 up, pitch 5.5deg, conf 1
    170kias, trim 0.2 dn, pitch 2.5deg, conf 2, speedbrakes extended
    170kias, trim 1.5 up, pitch 2.0deg, conf 2
    155kias, trim 1.7 up, pitch 2.0deg, conf 3, gear down
    140kias, trim 1.8 up, pitch 2.0deg, conf 4, gear down

    In couple of cockpit videos I have seen pitch trim values as high as 3.5up on final approach with a more forward center of gravity. I guess 5.0up would be ok if its very nose heavy...

    Do you remember the CG for your data by any chance?


  • pitch 3.0deg etc is the actual pitch attitude, not pitch trim. However CG for the calculations was 25% and I didn't record the trim setting.

  • To bbrz:

    Can you comment on the take off speeds and rotation behaviour at V1,2,R (as currently implemented in the sim) for me?
    Would appreciate your experience (how realistic is it currently?)

    use variants of flaps, trim sets, and weight to lift off-ratios as you like.
    Thanks for your help.

  • Unfortunately not as I never calculated the take off speeds simply because the variations are way too many and differences too large to be able to provide 'typical' speeds.
    Rotation force required / unstick attitude in conf 1+F at approx 140kts seems to be correct. With conf 3 the unstick attitude is noticable lower.
    Trim setting depends only on CG, regardless of the flap setting: 1 up at 24% 0 at 28% 1 dn at 33%

    IRL rotation is quite difficult with the A320 due to the unfortunately quite commen loading/loadsheet errors.
    I did have take offs where I immediately had to push the stick briskly forward again after the rotation started because CG was apparently further aft than written on the loadsheet and of course the opposite as well where you are pulling back on the side stick and absolutely nothing happens.

    The only noticable difference is the too high acceleration rate during take off due to the present noticable drag/thrust mismatch.

    Airbus A320 gdot 209kias 5°/55% N1___250kias 3°/62% N1
    Aerofly A320 gdot 209kias 5°/55% N1___250kias 3°/56% N1

  • feels akward flying a no payload airbus as it currently is.

    ??? The Aerofly version weighs approx 62t.
    IRL the DOW is approx 43t and the MLW is 64.5t which means the Aerofly A320 is only 2.5t below the landing weight limit.

  • No, the Aerofly Airbus currently weighs 52.9t... The grossweight in the lower ecam should yield the correct value at initialization. (Since fuel mass doesn't decrease yet its only correct in the first moment :D ) The value in the description text might be wrong. Max landing weight is 61.something I think...

  • Well in that case the aerodynamics and performance are way off. e.g. gdot in the Aerofly version is around 210kts but at 53t it should be 20kts lower!
    MLW is normally 64.5t and the higher grossweight option allows 66.0t

  • Well in that case the aerodynamics and performance are way off. e.g. gdot in the Aerofly version is around 210kts but at 53t it should be 20kts lower!
    MLW is normally 64.5t and the higher grossweight option allows 66.0t

    Well the current green dot speed is just a static value, we can just set it to a different speed :p:)
    So the green dot in the A320 doesn't really come from bad aerodynamics...
    I'll fine-tune the A320 when I have time for it :)

  • The point is that the Aerofly version weighs 53t but the pitch attitude, thrust setting and gdot speed is correct for 62t.
    Same goes for the climb performance.