×
Welcome to the CPL Aerodynamics 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.
Hi, I'm not a pilot and have recently started working my way through Bobs Recreational Aircraft BAK book. Pg54 Aircraft Motion refers to the Yaw axis being called the Normal Axis. It goes on to say that Vertical axis is an old term.
I have searched the site for 'normal axis' and can't find any discussion about it. I was hoping somebody could inform me how the normal axis terminology came about and why it has superseded vertical axis.
John.Heddles replied the topic: Normal Axis Terminology
Alan,
Full marks to you for asking the question. A lot of folks would just roll their eyes up, shake their head a bit in shell shock ..... and keep on reading .... It's far better to find out what a word means when you come across it in a context which is important to you.
The tech term "normal" confuses a lot of non-techo folk.
The dictionary meaning for the geometric application is along the lines of -
(Of a line, ray, or other linear feature) - "intersecting a given line or surface at right angles"
So, for this example, we are talking about an axis (ie the line, or direction, about which rotation is occurring) "normal" (ie at right angles) to the (inferred) nose to tail/wingtip to wingtip plane of symmetry. Rotation about this axis is referred to as a yawing motion which, for the flying side of things, creates a sideslip angle where the wind comes on to the nose of the aircraft somewhat displaced to the side, rather than from straight ahead.
Vertical axis would make a lot more sense but that's the world of techo stuff for you. I don't think that anyone is going to get upset if you use "vertical axis" so long as you are aware of the general usage. Just be aware that we can use "normal" generically. For instance, I can say that the lateral axis is normal to the vertical plane so we need to be a little bit careful sometimes. Basically "normal" just means that a line is at right angles to another line or a 2D surface.
One of the traps for techo folks (like Bob and me) is that, despite our best efforts not to fall into the trap, we tend to assume knowledge on the part of students when we ought not to do so.
I'm not a pilot
Ah, but you are working towards that goal so welcome aboard the merry (sometimes, mad) world of aviation.
Engineering specialist in aircraft performance and weight control.
Thank you for your in-depth reply, John.. It will take me some time to get my head around your explanation, and I appreciate you taking the time... Cheers, Alan
