Ok thanks people.

My fault, we can forget about zero. I’ll explain it a bit clearer this time with some images. The numbers refer to kilograms of force as shown in the example graph:

My software records the thrust of solid fuel model rocket motors, then calculates the results. The hardware device and load cell are mounted similar to a standard set of electronic kitchen scales and the test motor is mounted on top vertically with the nozzle pointed upwards then tared to zero. The motor is mounted into the vertical ‘V’ shaped holder as shown (ex-motor):

The problem is that after the motor is fired, naturally the fuel has been consumed and therefore we end up with a ‘negative’ weight at the end of the graph (not shown in the example). This is useful because then we know what the fuel weight was for other calculations.

What I need to do is to adjust the graph to account for the loss of fuel, and do it over the whole time period. This is a two step process.

Step one was to divide the amount of samples by the weight lost, then distribute that number (n) in a linear fashion over the time period. ie. sample one+(1 x n), sample two+(2 x n), sample 100+(100 x n), etc. and so on. This worked well and the graph is adjusted so that the end of the graph now shows at zero (as shown in the graph).

I could leave it at that, but it’s not entirely correct. Although the mean/average would be correct, the peak force is not or any of the other readings across the time line. It’s important to note that there are two main types of model rockets motors. There are ‘end burners’ where the solid fuel burns in a linear way (like a cigarette) and maintains an even amount of thrust, then there are ‘core burners’ where the fuel has an internal hollow core and burns from the inside out, with ever increasing thrust (as in the graph).

If there were only ‘end burners’ then Step one is only required. For example, you would see a graph that showed a straight line going across the time line but at an angle dipping down to the right. I want my software to work with both. The whole problem would not exist if the recording device was mounted sideways - but that is much more complicated and not very portable.

This graph shows the thrust curve of an off the shelf Estes D-12:

You’ll notice an initial peak thrust at the beginning - this is a combination of end and internal burner. There will be various thrust curves that the software needs to evaluate. If I just used the process described in step one, then it would unfairly assign less at the beginning than the end.

Therefore we need step two.

Looking at both graphs you’ll see the peak force. It’s fair to say that the amount of fuel consumed is directly proportional to the thrust produced. Therefore I want to redistribute the lost fuel weight correctly. I’ve already added it back in step one, so now what?

In other words, some of the areas of least thrust got more and visa-versa. I could remove that initial weight. Lets say it was 120grams of fuel, but this time remove the same amount from each sample, then redistribute it to each sample but this time where there is more force it gets more etc. Sorry, but I don’t know if the distribution is “linear, polynomial, logarithmic, exponential”??

I hope this makes more sense than my first post. It’s been very difficult to describe. I’ve probably left something out so please ask. It’s also possible that there only needs to be one single process but I can’t work it out.

Cheers.