[Citation Ultra] Irregular CG curve in custom W&B config — any ideas?

[Konstantin Fedchenko]

Hi, guys! I try to do the manual mass and balance for the Cessna Ctitation V (Ultra) and i am getting this strange curve on M&B, only if the fuel us between 3100 take off and landing 800lbs, may be other settings, the curve disappeares if i add full fuel. I did cross check the fuel weight-arm with the standard M&B offered by ForeFlight and it is IDENTICAL what i did, except the pax loading config - we have special configuration (seats removed), thats why i am actually doing my own M&B. Any clue? Thanks!

 

[Let'sgoflying!]

seems out of place

 

[MauleSkinner]

Have you checked that the fuel moment table is correct at 900 lbs?

 

[GeorgeC]

Interesting. Maybe they're doing some kind of piecewise interpolation and something is getting dorked up when they go to make a pretty plot?

I would try a simpler table without the fractions and see what ForeFlight does, e.g.

100lb - 30000 in-lb
200lb - 60000 in-lb
...
5800lb - 1700000 in-lb

 

[nauga]

European data? It looks like the comma in the moment value at 900lb and 5814lb is maybe a decimal representation but the plotter is not interpreting it that way. I'd bet the moment at 900lb fuel is 269949.594 in-lb and the moment at 5814lb fuel is 1764316.5 in-lb. If you consider the fuel arm as ~300in and check moment calcs yourself you can see the discrepancy a little easier.

Nauga,
armed

 

[MauleSkinner]

European data? It looks like the comma in the moment value at 900lb and 5814lb is maybe a decimal representation but the plotter is not interpreting it that way. I'd bet the moment at 900lb fuel is 269949.594 in-lb and the moment at 5814lb fuel is 1764316.5 in-lb. If you consider the fuel arm as ~300in and check moment calcs yourself you can see the discrepancy a little easier.

Nauga,
armed

And who decided that those two numbers were the only ones that needed that level of accuracy?

 

[nauga]

And who decided that those two numbers were the only ones that needed that level of accuracy?

My money would be on a human transcription error or a format change (or similar) that caused a parser to miss the conversion and subsequent rounding or truncation on those two values.

Nauga,
and the reason we do unit-level testing

 

[MauleSkinner]

My money would be on a human transcription error or a format change (or similar) that caused a parser to miss the conversion and subsequent rounding or truncation on those two values.

Nauga,
and the reason we do unit-level testing

Can you translate that for those of us who are excessively monosyllabic?

 

[nauga]

Can you translate that for those of us who are excessively monosyllabic?

[human]If the comma is the decimal marker in the source data I think that whoever was transcribing the data for the plotting tool in the OP may have missed those two and copied them verbatim, or if, say, a script was used to convert the data for the plot tool, that a difference in the way those two values were formatted, like maybe an extra space or a hidden character or even an extra comma, caused the script to skip them when rounding or truncating the data.[/human]

Nauga,
and his data validation/verification

 

[dtuuri]

Somebody must've borrowed a PEMDAS calculator when their PEJMDAS calculator batteries wore out.