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Welcome to the CPL Performance question and answer forum. Please feel free to post your questions but more importantly also suggest answers for your forum colleagues. Bob himself or one of the other tutors will get to your question as soon as we can.
In the same vein as a comment offered for another thread, one really needs to be careful when using the (2 x TAS) approximation for (G/S out + GS home) if you have much drift. Generally, we consider the case where wind speed is a high fraction of the TAS to be the situation which raises concern and for which the person running the sums needs to be on his/her toes. My philosophy is not to set yourself up to fail but, rather, always use the groundspeed values - a bit like the approximation for ETAS on the Jepp for small drift angles where cos(drift) gets closer to 1.0. Why bother straining your brain with extra stuff to remember and figure on the fly ?
It is illustrative to rework the calculations for this example (where drift is significant - up around 16 degrees) using the calculated groundspeed values just to see the sort of errors which can creep in using the approximation. Sure, the approximation is fine if the drift angle is small but this is not always the case.
I work in minutes because our instructor always use minutes that's why I'm confuse
That's not really a problem. You pick whichever you prefer of hours or minutes and run with that unit. Really no difference which you might prefer - it is only a matter of choice. Keep in mind that, if you run the calculations on your whizz wheel, rather than that dreadful electronic calculator gadget, it is much easier as you have all these calculations set up as easy proportions - one of the reasons I prefer to run my calculations on the slide rule. (Then again, I was weaned onto slide rules at a very young age when we didn't have PCs and electronic calculators were big, bulky things which cost a mint so it's pretty easy for me to say that ..)
Engineering specialist in aircraft performance and weight control.