Aircraft Stability

[Driver170 42]

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?

 

Thanks.

[jcomm 5,920]

Good source here:

 

http://www.flightlab.net/Flightlab.net/Home.html

 

under

 

http://www.flightlab.net/Flightlab.net/Download_Course_Notes.html

 

and this one, which is a Classic already :-):  http://www.av8n.com/how/

 

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 )....

[Driver170 42]

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?

[jcomm 5,920]

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 :-)

[Driver170 42]

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

[jcomm 5,920]

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.

[Driver170 42]

Positive static stability

Neutral * *

Negative * *

 

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

[jcomm 5,920]

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 

[Dave Morgan 68]

Hi.

 

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:

 

http://www.boldmethod.com/learn-to-fly/aerodynamics/3-types-of-static-and-dynamic-stability-in-aircraft/

 

http://www.flybetter.com.au/sitebuildercontent/sitebuilderfiles/bookone3rdedition.pdf

 

 

*** ***

 

I couldn't see a download link in the flybetter homepage but googling 'flybetter.com.au' turns up the direct download links.

 

Best regards,

Dave