My purpose in contributing questions to this thread was to encourage readers to think about the subject matter, rather than simply reciting things that they had previously read or been told.
As an ATPL Theoretical Knowledge Instructor I have found that far too many students devote very little effort to actually trying to understand anything remotely complicated. This approach may be OK if we accept the idea that modern pilots are intended to simply be button pushers, but I am not at all comfortable with this idea.
Some of the responses to my questions show quite clearly that readers are perfectly capable of giving references to textbooks, or mathematical explanations, but have not previously given any thought to fundamentals such as the direction of the force acting on the propelling nozzle.
Some of those who have contributed and the much greater number who have viewed this thread since my first post, have probably now realised that their initial “conventional wisdom” was wrong. Hopefully this will encourage them to give a little bit more thought to other subjects.
In that sense Mr Optimistic is correct in suggesting that “this is a wind up”.
My suggestion that contributors should avoid the use of “heavy maths” was not driven by any personal dislike for the subject. It has always been one of my favourite subjects, and I recognise the fact that the use of complex maths is absolutely essential in gaining a detailed understanding of the world in which we live. But the sad fact is that less than 1 in 20 of current JAR ATPL students in the UK are able to use maths in any meaningful way. A depressingly large number would have great difficulty in rearranging something like, Lift = CL 1/2Rho Vsquared S, to get the value of CL. These students represent the next generation of airline pilots.
Because of this lack of mathematical skill, the vast majority of students will instinctively turn away from any explanation that involves mathematics. The bottom line here is that if you want the majority of PPRUNE readers to understand your posts, then you must avoid any use of mathematics. If you are a scientist or a design engineer and you wish to be understood only by your peers, then by all means use as much maths as you wish.
BryceM has advised readers that
“there are books (I mentioned a couple earlier in the thread….”.
The simple fact is that most modern ATPL students will never consult such books. If a subject cannot be explained in simple terms then they will simply turn away from it.
He has also made reference to “
pointless, wrongheaded Gedanken experiments”
The vast majority or PPRUNE members will never have access to facilities to carry out any practical experiments. This means that thought experiments are the only type that are available to them.
Having been away from internet access for several days I have just read through the posts that have been made since 3rd July. It is good to see that some contributors have been asking themselves some probing questions.
An example of this is the discussion of the divergent section of a supersonic air inlet. Here we appear to have two conflicting effects.
A. The increasing static pressure caused by the deceleration of the air produces a net forward force on the intake.
B. But the incoming air is being decelerated, so the intake must be applying a forward acting force upon it. The Newton3 reaction to this should be a rearward acting force on the intake.
So
Does the intake produce thrust or drag?
And
If it is producing thrust, then how does it overcome the rearward acting Newton3 force in item B?
I personally do not know the answer to these questions.