Convert Trim Sheet to excel

[iPahlot]

I currently have a paper based trim sheet for weight and balance and want to convert it to excel to make a quick load calculator.
Has anyone got any experience on how to convert a trim sheet to excel accurately?

Any help would be greatly appreciated. :sad:

[john_tullamarine]

Straightforward once you see how a trimsheet is designed.

How about you link to a graphic of the trimsheet so we know what you are starting with .. and we can work you through the exercise.

This sort of question arises from time to time .. so there are those about who might like to play with the same thing in the future.

So far as accuracy goes, if the trimsheet has been designed sensibly, and we have the TCDS/AFM/POH etc. it will be fine. Indeed, for a well designed trimsheet, the accuracy is of practical equivalence to a manual calculation.

[iPahlot]

Thanks John

I have scanned the trim sheet and just blurred out some of the info that may be seen as sensitive by some...

http://i1306.photobucket.com/albums/s561/pahlot/Screenshot2012-10-03at103006AM_zps92acfea2.png

[john_tullamarine]

Good man.

By the style, I'm presuming the sheet is one of Bruce C's examples and it will reverse engineer quite easily.

What I suggest is that we give you (and any other folk who are interested) a series of pointers as to what needs to be done. That way you can work your way progressively through the exercise and, by the end, have a pretty good idea of how to design a trimsheet off your own bat.

First up read off a number of chart values -

(a) for each trim line, count the number of division intervals along the line and note the IU unit delta for that distance. As the background vertical scale for the whole sheet is IU, you can extend the IU scale at the top to maximise the number of divisions counted.

Dividing the delta IU/divisions will give a pretty accurate value for the IU per division. This will allow us to figure the loading arm for the particular trim line station.

(b) the shape of the CG envelope tells us that the envelope is the normal light aircraft shape - constant forward limit at low weights, straight line sloping forward limit at higher weights (above about 1810 kg - exact weight we can get from the AFM/POH/TCDS) and constant aft limit.

Note that, when the upper forward limit is a sloping straight line on the CGxWT graph, that converts to a simple curve on the IUxWT version.

Read off the IU x WT co-ordinates for the following points -

(i) a lowish forward weight
(ii) the forward intersection at approx 1810 kg
(iii) the forward intersection at 2495 kg
(iv) the aft intersection at 2495 kg
(v) a lowish aft weight

Trim sheet datum position

One of the usual traps for young players is that the trimsheet designer generally doesn't use the usual POH longitudinal datum. Reason for this is that it usually sits well out forward of the envelope and does dreadful things to the trimsheet accuracy. Usual practice is to put a revised datum for the trimsheet somewhere in the rear end of the envelope.

From the trimsheet, we can detect the trimsheet datum pretty easily -

(a) with this style of sheet, where the IU entry line is unshifted, the zero IU point equivalent CG IS the datum point for the sheet

(b) the nil delta IU for the forward fuel load suggests that the datum is at or near to the forward fuel loading arm

(c) a vertical line on the envelope graph will give the datum away - usually picked up most easily if the designer has included an MAC overlay on the envelope. The other option is that some designers use the most aft CG limit as the datum and, in this case, the aft most CG line will be vertical. Not going to work for us on this sheet but just as well for you to be aware of the consideration.

Suggest you run up the numbers requested and post them for comment.