I obtain data (DOW and DOI) from Loadsheet gaetan
Question is whether the different loadsheets have the same design equation for IU. Keep in mind that the IU equation can vary from trimsheet to trimsheet .. ie I could design 10 A320 trimsheets which might look generally similar but have incompatible IU equations. So far as the pilot is concerned, the only obvious difference would be the IU value to start the trimsheet calculation.
Hence the need for us to know just which trimsheets you are using .. you may end up needing to post a scan of them so that we can reverse engineer the IU equation to check out just why you are getting apparently incompatible answers.
when I take paper trim sheet A320 from company alpha I can't use it for all A320, in fact for the first plane (DOI 27,1) le LITOW is out.
Exactly .. you MUST NOT use a trimsheet for another operator unless you have established that the document is compatible both for configuration and IU equation.
there must be an generic equation which give %Mac for all Airbus or aircraft.
No, not at all when it comes to trimsheets as you are plotting %MAC as a set of values of W by IU so, if the IU equation is different, then you need to take that into account when comparing things ... you MUST compare apples with apples for the numbers to make much sense.
The relationships are OK for basic calculations such as we have been using above. However, the IU equation is variable according to the views of the trimsheet designer ... so two different sheets may .. or may not ... be compatible when it comes to playing with the numbers.
It would be reasonable to presume that any trimsheet designed by Airbus will be as they describe in their document. Indeed, I would imagine that most airline Airbus operators would follow the Airbus model for convenience.
However, if I, or some other designer, were to design an Airbus trimsheet that trimsheet might be quite different in the detail when compared to the Airbus trimsheet. As I suggested earlier, just because Airbus chooses to design a trimsheet one way doesn't mean that that is the only way. Same thing applies with Boeing or any other OEM.
I have a doubt about this equation % Mac =100*C*(I-K)/Weigth*Length of RC + 25 and I have a doubt about 25,
You appear to have left out some brackets above. Just to clarify, the Airbus equation from p124 becomes -
%MAC = 25 + 100*C*(I-K)/(W*MAC)
(I've rearranged it a bit to emphasis what the brackets are doing .. RC is the same as MAC)
Nothing wrong with the Airbus equation. What do you see as the difficulty and we can discuss it to remove the concern ?
The "25" simply relates to the Airbus choice of trim datum to be 25%MAC and is 25%.
I'm sure that a few more exchanges and we will have your concerns put to rest.
Looking forward to your reply.