Sign in to follow this  

Aircraft Stability

Recommended Posts

I'm self teaching myself all 7 books of the PPL before going onto the ATPL stuff at oxford. Having a little difficuilty understanding how each axes - Longitudinal, lateral and vertical correspondes to a type of stability!?


For example, take the lateral axis how can that be longitudinal stability? Is there an easy way to picture all the axis and there stability type?



Share this post

Link to post
Help AVSIM continue to serve you!
Please donate today!

Good source here:




and this one, which is a Classic already :-):


But, regarding the axis, the lateral one is the imaginary line that crosses the aircraft from wing tip to wing tip going through the center of rotation, in pitch - the aircraft pitches up or down rotating around that axis, with positive values up, negative down ( by convention )


Then, the longitudinal axis is the symmetry axis along the aircraft fuselage, and the aircraft banks around it, left or right, right being positive ( by convention )


Finally, the vertical axis is orthogonal ( 90º) to the other two and crosses the fuselage through the Center of rotation upside-down, and the aircraft yaws around it, left or right, right being positive ( again by convention )....

Share this post

Link to post

Thanks for the great links ;)


Just got that light bulb lol so you could say to help you imagine it, is, putting a stick through the longitudinal axis and twisting it at both ends and obseving the plane rotating at its axis?

Share this post

Link to post

Nope, the stick would be the axis of rotation ( in bank in that case... )...


The texts and images in the links will certainly make it even more evident :-)

Share this post

Link to post

Thats what i mean't, its the planes axis and in this case its lateral stibility (roll)

Share this post

Link to post

Vernon, the axis give you only the rotation part of the "math"... Stability ( static and dynamic ) that's the next step you'll have to learn.

Share this post

Link to post

Positive static stability

Neutral * *

Negative * *


Currently on that chapter now. Can you only get positive static with dynamic stability

Share this post

Link to post

In general you have three types of static and dynamic stability:


Static: Stable, Indifferent or Unstable

Dynamic: heavily damped, damped, indifferent...


You usually have positive static stability associated with (positive) damped dynamic stability, but other combinations are possible.


But to be more precise, there are actually 6 types of dynamics response in stability:


- aperiodic stable

- aperiodic neutral

- aperiodic unstable

- periodic stable

- periodc neutral

- periodic unstable 

Share this post

Link to post



Put simply...
Static stability is concerned with an aircraft's tendency to return to its former state after a brief disturbance like a strong gust.
Dynamic stability is concerned with the oscillations the plane will make after such a disturbance.
Positive, neutral and negative just mean 'returns to its previous state', 'stays in its new state' or 'gets worse'.
*** ***
The first of these sites shows the six combinations clearly without graphs or maths. The second is one part of an easily readable work on handling aircraft:
*** ***
I couldn't see a download link in the flybetter homepage but googling '' turns up the direct download links.
Best regards,

Share this post

Link to post

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this