Boeing-Airbus Static Margins

Tue Mar 13, 2001 9:07 am

In the dedision not to use the variable swept-wing design in aircraft like the 777 and the A3XX as well as the proposed SST successor, these companies said that, in addition to other problems such as weight, that the variable swept-wing has large shift in center of pressure with corresponding increase in static margin. And that the increase in the static margin leads to higher trim drag and reduced maneuverability at high sweep angles of the wing.

Can someone tell me more about what static margins are? Thank you in advance.
aaron atp
Posts: 517
Joined: Sun Mar 19, 2000 1:17 pm

Static Margins

Tue Mar 13, 2001 10:50 am

The margin of static stability is simply the difference between neutral static stability and the positive value possessed by that aircraft.

  • Too much stability is detrimental to maneuverability.
  • Not enough stability is detrimental to controllability.

    The Center of Pressure is always behind the Center of Gravity. The further the two are apart, the greater the pitch stability. Thus if the CP moves aft at high angles of attack, the stab and elevator trims have to compensate for changing moments. The CP moving aft have would have the same affect on the taildown force required as if the CG were moved forward -a greater TDF- which induces more drag.

    Further explanation of the effects here would be redundant for most readers, but let me know if you would like to read my definitions et al...


    RE: Static Margins

    Tue Mar 13, 2001 11:34 am

    I've found descriptions of static margin difficult to find. It's great to get the info you've already presented. Yes, please add to this further explanation and effects... as you see fit.

    Many thanks.

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