[Harri Pihl]

Originally Posted by Crumpp

You are about to be ignored. I know very well what the formula's are for as I am degreed in Aeronautical Science.

I see that your knowledge has improved somewhat since the days you were posting to the AH board. However, you seem to still have serious problems to deal with basic performance calculations, this case being a good example.

Originally Posted by Crumpp

Now go back and find where I said anything about there not being a relatively small top level speed reduction due to weight affects. No one has ever claimed anything but that. Graham is the only one who has tried to narrow the issue to that one subject.

The thread is about the performance on deck and Graham (and I) have pointed out that the effect of the fuel state to the top speed at deck is small. And we did that by using the correct method which accounts the change of the Cl/AoA.

However, you posted a formula:

V2/V1 = SQRT(W2/W1)

Which is valid only for the constant Cl/AoA and therefore wrong for this particular case. And this is exactly what Graham responded to you in the first page of this thread.

Note that the polar approach used by Graham and me works for any given flying condition while your approach works at one exact Cl/AoA.

All considered it’s a healthy concept to keep in mind: the flying weight of your aircraft directly affects its performance. Each time. Every time. No exceptions.

That is true and no one denies that. However, Graham was correct when he noted that at these particular conditions the effect of the fuel state is not that important, just few km/h.