Interpolation?
 

Ok I'm having Saturday morning brain strain!

Could someone put me out of my misery and explain how I interpolate data?

Question: If 2,000ft = 1% fuel penalty what would the fuel penalty be at 2,100ft?

I know the answer is quite straight forward, but I just can't remember how you work this out (and it's not in my maths book) so could someone please help?

Thanks....

The way that I read this is:

100 is 1/20th of 2000.

2000ft = 1%. Therefore 100ft = 1/20th of 1% or .05%

Add the percentage for that extra 100ft onto the percentage for 2000ft.

1 + 0.05 = 1.05%

This looks too easy for my liking so it is probably wrong. I will be corrected. What is this for. Is it for those ATPL writtens?

Bill

That works for me - thanks!

Yes - it's for Flight Planning...

JetMouse

My thoughts on this are as follows:

Interpolation is based on two known factors to find a third.

WIRELESS is correct in his working but I am not sure you could call it interpolation. We were given 2000ft and 1% as the only data and asked to find a third value by interpolation. This is not possible with the given data so we must make some assumptions.

I will assume 2000ft and 1% are the LOWER values. I will also assume that the interpolation is linnier so I can assume the UPPER values to be 4000ft and 2%. NOW I have enough data to Interpolate any value between 2000ft and 4000ft.

Given 2100ft I came up with 1.05% which is correct. 2350ft is 1.18% (2dp)

I made a very handy Interpolation formula in excel that I would be happy to email to you...

I guess the easiest way to describe interpolation is to use a data table (provided you have one) to plot a graph and simply read off the required value. I would use the Paramac method but it assumes a linear progression...does the question include any other data?

P.S. I'd like to compliment JetMouse on his use of the "From" field in personal details :D

If the relationship is linear, or near so, then one can use a simple linear proportion, either mentally, or with the prayer wheel CD scales or, if you really can't function without batteries ... your calculator/nav computer. This sort of stuff is covered at PPL theory level in a number of areas ...

If the relationship is not sufficiently linear then there are any number of statistical procedures to interpolate using calculators or simple PC programs.