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1.3 pitch attitude and GD speed in cruise


cmbaviator

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Hi guys,

 

thnaks for the update :)

I did notice that the pitch attitude seems quite hight during cruise, was wondering if its normal or due maybe to "experimental FM" ?

Also why is the GD speed below Vls ? Almost 5° in the screen below

Both screen ZFWCG was 14.9

 

GW: 51.5

image.thumb.png.be760adebbef465cffa84623fafa7e49.png

 

 

here is a bit less (around 3°) and seems a bit more realistic

GW 48.5

image.thumb.png.e05059075d8daf9d2c976afbf4d99737.png

 

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18 minutes ago, Litjan said:

Can´t really comment unless I know (and see) all relevant parameters. Most important weight (please output to screen like the framerate).

Cheers, Jan

 

I put the current GW when the screen was taken +- 0.2tons, what other parameters are needed ?

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Ah, ok - I see the weights.

.72 is slow for a 737 in cruise - the pitch seems appropriate. Not sure what cost index you used. Note that the optimum altitude indicated is purely a function of weight, not of speed (which means you probably fly too high for the slow speed calculated by the FMS).

The "green dot" denotes the optimum L/D speed with engines running, the top of the yellow bar will include a MACH buffet margin, so at high altitudes it will be "higher" than the green dot.

And - as Morten pointed out - if you have a "far forward" center of gravity, the tail has to push down hard to keep the plane level. This extra "push down" needs to be balanced by the wings, so they need more "nose up" to create the necessary lift. The saying is "As a rule - aft trim saves fuel" ;)

Cheers, Jan

 

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21 minutes ago, Litjan said:

Ah, ok - I see the weights.

.72 is slow for a 737 in cruise - the pitch seems appropriate. Not sure what cost index you used. Note that the optimum altitude indicated is purely a function of weight, not of speed (which means you probably fly too high for the slow speed calculated by the FMS).

The "green dot" denotes the optimum L/D speed with engines running, the top of the yellow bar will include a MACH buffet margin, so at high altitudes it will be "higher" than the green dot.

And - as Morten pointed out - if you have a "far forward" center of gravity, the tail has to push down hard to keep the plane level. This extra "push down" needs to be balanced by the wings, so they need more "nose up" to create the necessary lift. The saying is "As a rule - aft trim saves fuel" ;)

Cheers, Jan

 

thanks for the input :)

 

i'm using CI35, would you mind telling me what CI LH used back in the day for the 733 ?? :P

 

L/D ? I've flying the A320 (fslabs) the last couples of years haha, the green dot will always been put above the Vls even if the calculated one initially was lower than VLs I think.

this is what confirmed it for me.

 

The image below shiws the PFD of the A321 at FL370 with a GW of 67t prior to TOD

67.0 is quite light for an A321 so having a GD speed close to 250 kts at 67tons is very odd but I was explained that because the VLS was so high that the GD speed was just recalculated to be above Vls (margin) because normally at 67t, the GD speed in an A321 in cruise should be around 230kt ( in the fslabs at least).

Even though he must have been cruising near the rec max, i still don't understand how it's possible to have a Vls that high unless the aicraft is actually heavier than the data inserted in the MCDU

 

image.png.a32709ac8990d6add833067f7be88656.png

 

 

I've tried to reproduce that with the fslabs with the A321 at GW 70ish and being just 500ft below REC MAX and I couldn't the VLS being that high 

image.thumb.png.8b93f0a32e023a991705d5af71fac320.png

 

sorry for the slight off topic haha

Edited by cmbaviator
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