Oxford Aviation books
 

Hi all!

I'm coming back to aviation after quiting my comercial pilot course 20 years ago. I got some books in order to revise theoretical knowledge. Among those is the Oxford Aviation "Principles of Flight", which I was really liking until reached the chapter covering longitudinal stability.

As far as I know, few airplanes had the cg behind the cp and most modern airplanes horizontal stabilizers are set in a way to contrapose a nose down tendency. Yet, in the above referred book, the stability analysis is made with the cg back of the ac, compensated by an up vector component of the horizontal tail.

I would like to know if someone here could comment on this book and the way this concept is treated by it, since I really don't know if I should go on reading or try something else. I take this opportunity to ask about a good and comprehensive book on this subject.

I don't have the Oxford book on hand, but I have the Bristol book which is using the same syllabus. In the Bristol book, there is one picture depicting the CG behind the CP with an up vector on the horizontal stabilizer, but it clearly states that this is an unstable configuration in a traditional airplane. Does that help at all?

"Now consider a wing together with a tailplane. The tailplane is positioned to generate a stabilising moment about the aircraft CG. The same vertical gust will increase the angle of attack of the tailplane and increase lift, which, when multiplied by arm 'y', will generate a negative (nose down) pitching moment about the aircraft CG.

If the tail moment is greater than the wing moment the sum of the moments will not be zero and the resultant nose down moment will give an angular acceleration about the CG. The nose down angular acceleration about the CG will return the aircraft towards its original position of equilibrium. The greater the tail moment relative to the wing moment, the greater the rate of acceleration towards the original equilibrium position. (Too much angular acceleration is no good).

[picture]

There are two moments to consider; the wing moment and the tail moment. The wing moment is a function of the change in wing lift multiplitd by arm 'y'. The lenght of both arms is dependent upon CG position. If the CG is considered in a more forward position, the tail arm is larger and the wing arm is smaller. A more forward CG position increases static longitudinal stability.

If the nose down (negative) tail moment is greater than the nose up (positive) wing moment, the aircraft will have static longitudinal stability."

I have transcribed one segment. Is there a corresponding segment in your book?