I am looking at a question I found in the internet: why can a paraglider fly without a tail rudder and elevator assembly whereas a normal fixed wing aircraft can't?

One part of the answer is , the elevator helps to control pitch whereas the rudder controls yaw for a fixed wing aircraft.

A paraglider has flexible wings that can be deformed to control both the axis.

The other part that is vexing me : the tailplane also provides stability, not just axis control. So why is such (lack of) stability providing equipment not detrimental to a paraglider?

Even birds and there flexible-ish wings need a tail.

How do I even approach this question? Is it because the bird wings are not that flexible, and so the large tail feathers are necessary for fine control?

What about the fixed wing aircraft? Is it because the tubular shape causes the centre of lift and centre of gravity to be far away and so a tailplane is mandatory?

I would like a full mathematical answer please- thank you?

  • $\begingroup$ Paragliders and hang gliders have a pilot at the bottom. The center of mass is well below the wing. They are not very maneuverable. Certainly nothing like a bird. I once saw a small bird fly through a chain link fence. $\endgroup$
    – mmesser314
    Nov 24, 2022 at 3:17
  • $\begingroup$ What you are looking for is termed "longitudinal stability analysis". Here you can find a very good overview. $\endgroup$
    – sophit
    Dec 28, 2022 at 0:09
  • $\begingroup$ Because of the "pendulum effect". The center of mass is way below the wing. $\endgroup$ Dec 28, 2022 at 12:28
  • $\begingroup$ @quietflyer True, and the pendulum effect is enhanced by a HUGE anhedral wing. $\endgroup$ Dec 28, 2022 at 14:34

1 Answer 1


An aerofoil is unstable in airflow; if it pitches down slightly then the centre of lift will move rearwards, amplifying the downward pitch. In early hang gliders this could result in a ‘luffing dive’ which was typically unrecoverable. This was resolved by adding luff lines that pull the sail into a reflex form. In paragliders, pitch stability is provided by placing the pilot far below the wing. This is somewhat contentious because ‘pendulum stability’ is typically negligible in rigid aircraft where the c of g is not far from the centre of lift. Yaw stability is inherent because of the large side area presented by the curved wing.


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