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Author Topic: Min maneuver speed change-over at 20000 ft  (Read 2145 times)

simonijs

  • Join date: Oct 2014
  • Location: Amsterdam
  • Posts: 149
Re: Min maneuver speed change-over at 20000 ft
« Reply #20 on: Thu, 28 Jan 2021 10:33 »
When you're flying at very low airspeeds, I think such a jump of the amber band is acceptable, but a similar jump on the red band would be rather shocking, in my opinion.

Well, yes: that makes sense! I was thinking that the aircraft - at 20.000 ft - already would be climbing at ± 330 KIAS, with the red band no longer visible.

Your numbers at 20220 ft are very close to mine. Thank you.

Regards,
Simon

Darksidedriver

  • Join date: Mar 2018
  • Location: Dark Side of the Aviation World.
  • Posts: 41
  • You sleep - we fly.
Re: Min maneuver speed change-over at 20000 ft
« Reply #21 on: Thu, 28 Jan 2021 11:28 »
A very interesting read associated with this topic concerns the in-flight upset involving a Qantas
Boeing 747-438, VH-OJU. It is an Australian Transport Safety Bureau report and is available with a short web search.

Hardy Heinlin

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    • Aerowinx
Re: Min maneuver speed change-over at 20000 ft
« Reply #22 on: Fri, 5 Feb 2021 19:50 »
Slightly off-topic, but related:

I've seen an LCD PFD with the flap UP bug in view although the aircraft was above 20200.
I've seen many CRT PFDs where the flap UP bug was removed when above 20200.

Question: Does the LCD version keep the UP bug on the tape forever, or does it remove the UP bug just a bit later?

By "remove" I mean "blank" while the speed tape is fixed (not "scroll off" due to the speed tape moving down).


|-|ardy

Hardy Heinlin

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Re: Min maneuver speed change-over at 20000 ft
« Reply #23 on: Sat, 6 Feb 2021 09:54 »
OK, so, thanks to this discussion I learned the amber band will never be higher than the UP bug when the aircraft is below 20000 with flaps up.

What if I select flaps 1 at 19000 ft and 400 tons? According to the flap-up rule discussed, the 1.3 factor will then be applied. Is that correct? That would place the flap 1 bug inside the amber band. Or will the amber band now be limited to the flap 1 bug?

As the amber band logic has an "UP" bug limit below 20000, does it also have a "1" bug limit when flaps 1 are set?

I couldn't find any details in the manuals.


Regards,

|-|ardy

simonijs

  • Join date: Oct 2014
  • Location: Amsterdam
  • Posts: 149
Re: Min maneuver speed change-over at 20000 ft
« Reply #24 on: Sat, 6 Feb 2021 15:59 »
Hi,

From the FTCM - "Note: During normal conditions, the flap maneuver speed for the current flap detent should always be equal to or faster than the minimum maneuver speed."

Is this what you were looking for, or did I misunderstand the question?

Regards,
S.

Hardy Heinlin

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Re: Min maneuver speed change-over at 20000 ft
« Reply #25 on: Sat, 6 Feb 2021 16:41 »
Hi, yes, thanks, but does the word "should" address the pilot or the software designer? Should the pilot set the command speed accordingly, or should the computer place the amber band accordingly?

If this "should" refers to the machine, the machine doesn't always do what it should do :-)


Regards,

|-|ardy
« Last edit: Sat, 6 Feb 2021 16:57 by Hardy Heinlin »

dhob

  • Join date: Sep 2019
  • Posts: 67
Re: Min maneuver speed change-over at 20000 ft
« Reply #26 on: Sat, 6 Feb 2021 21:25 »
As stated earlier, when flaps are not up, the minimum maneuver speed is always 1.3g to Vss. When Flaps 1 is selected, Vs1g, Vss and Minimum maneuver speed all decrease. Referencing the FCTM charts for flaps extended maneuver margins, at flaps 1 maneuver speed (Vref 30 + 60), there is approximately 1.5g to stick shaker available. As such, the top of the amber band (minimum maneuver speed), is 1.3g, which is less than (below) the flaps 1 maneuver speed at 1.5g.
Haven't extended flaps at 19000 before, but I'll try it in the sim when I have an opportunity.

Hardy Heinlin

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Re: Min maneuver speed change-over at 20000 ft
« Reply #27 on: Sun, 7 Feb 2021 06:19 »
Is this the same chart that shows a 1.42 margin for flaps UP? Are we on the same page?

As we know, at high weights at high altitudes, the 1.3 amber band is above the UP marker. This couldn't be the case if the UP bug were to sit on the 1.42 margin all the time. Therefore I assume this chart is only valid for low altitudes or low weights.

I have now modified my model so that it very much agrees with real-world observations. I now see the jump in my model when the amber band comes off the UP marker limit. When I extend the flaps at 400 tons at 19000 ft, all my flap speed markers (1 thru 20)* are lower than the 1.3 amber band. I have already reduced my stick shaker speed data at high altitudes. To get the flap speeds out of the 1.3 margin, I'd have to reduce the stick shaker speed even more (more than 10 kt) and that wouldn't look plausible, in my opinion.

Perhaps this chart refers to max landing weight and below 10000 ft?

If it were valid in all flight situations, there would be no jump at 20200. Or maybe I'm confused again :-)


Regards,

|-|ardy


* Of course, flap 30 isn't applicable at 400 tons, not even at low altitudes. So that chart must be limited somewhere.


P.S.: I see two variants of that chart; one for flap retraction and another one for flap extension. The latter shows that 1.5 margin for flaps 1. On the flap retraction chart, the flaps 1 margin is even higher, at 1.7. Very confusing. I would assume, the retraction chart refers to departure (high weights) and the extension chart to arrivals (low weights). -- I've never seen the green flap speed schedule jumping up and down when flaps are moved up and down and up ... e.g. when starting a go-around. So if something really changes, then it must be the stick shaker speed: When retracting the flaps, the stick shaker speed decreases; when extending the flaps, the stick shaker speed increases. Bizarre.

Well, here's a quote of the intro text:
"These charts are generalized to show relative trends of maneuver capability during flap retraction and extension and are not meant to be representative of any one takeoff or landing condition."
« Last edit: Sun, 7 Feb 2021 06:58 by Hardy Heinlin »

Hardy Heinlin

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Re: Min maneuver speed change-over at 20000 ft
« Reply #28 on: Sun, 14 Feb 2021 01:02 »
The effects discussed above are now implemented in PSX update 10.130. See item 130.08:

https://aerowinx.com/board/index.php?topic=4191.0


|-|ardy