Interpolation Formula

[pilot_jimuk]

Hello,

I may have bitten off more than i can chew here.

I'm trying to create a document that colleagues can use to interpolate takeoff masses from tables such as the picture attached based on wind and temperature

IMG_0037.jpg

So for instance a pilot would enter the 4 figures highlighted in Red (Mass) and the figures in Green (Temp & Wind)

We would then enter the current conditions and the document would interpolate the values to give an exact take off mass

There are 100's of these tables which get updated regularly so entering all the data behind the scenes wouldn't be practical.

The document would look something like this but im struggling with the formulas to interpolate
Screenshot 2024-03-19 221937.png

Any help would be much appreciated

Thanks

[6StringJazzer]

Welcome to the Forum pilot_jimuk !

The arithmetic of doing interpolations is not hard. What's hard is knowing how to model your data to get an accurate interpolation.

The numbers you have here are not linear, although we could use linear interpolation anyway--how much accuracy do you need? I would imagine that for takeoff mass you want that to be accurate.

I looked at the numbers you have around the red-boxed figures. The decrease in mass as the wind speed goes up is less and less as the wind speed gets higher. Going from -10kt to 0kt, the mass drops by 1077. But going from 0 to 10 it drops by only about 350. Then oddly going from 10 to 20 it is still a drop of about 350. The affect of temperature drop is also nonlinear (and in some cases makes no sense).

Do you have that first table available in a form that can be loaded into Excel? I see it's your first post--it's always better to attach an Excel file vs. a screen shot.

Here is just a sliver of data plotted so you can see what I mean:

windspeed.jpg

(P.S. Title should say Takeoff Mass vs. Wind Speed)