If the answers which we give to questions in these threads are to be of any value to the questioners, it is essential that we consider the context of the question. If we ignore this need we will be wasting our time and theirs.
The original post was
Recently I had to answer the following exercise:
"An aeroplane maintains straight and level flight while the IAS is doubled. The change in lift coefficient will be: ..."
In my opinion the true answer would be x 0.5. Explained with the lift formula which is: L = 0.5 x rho x V^2 x CL x S.
IAS is the same as dynamic pressure, isn't it?
If this is true, then IAS would be 0.5 x rho x V^2. And if this whole term is doubled, then CL must be half the previous value to maintain same lift force.
This my thoughts. But they are wrong. It was stated, that the correct answer would be x 0.25.
Has someone an explanation for this problem?
The following facts can be deduced from the post:
a. The author of the post is on some kind of course.
b. The author understands very little about the basic relationships
between airspeed, dynamic pressure and lift.
c. The author's grasp of fairly basic maths is not very good.
What may be less clear to some readers is the fact that the question has been taken from the Principles Of Flight section of the JAR/EASA ATPL question bank.
Any useful response to the OP must be pitched at a level that is appropriate for both the level of the JAR/EASA ATPL syllabus and also the level of knowledge of the author.
gfunc
Yes we could of course launch into a debate about poor quality of the question. But this would serve no useful purpose. We could argue about whether or not the syllabus has been dumbed down to an unacceptable level. But again this would serve no useful purpose. Any useful response must concentrate on the thought processes employed by the examiner in constructing the exam question and how these led to the required answer.
selfin
Yes, we could construct an explanation dealing with every apsect of the subjects that you have raised. We could, if we wished, go to even higher levels of detail and complexity. But given the apparent state of knowledge of the original poster, he/she is unlikely to gain anything useful from reading it. His/her response is far more likely to be "Oh sod it, this is far too complicated, I'll just rememeber the answer". You may be surprised at how many ATPL students do exactly that.