Keel effect: Difference between revisions
Mark viking (talk | contribs) added reflist template |
Mark viking (talk | contribs) →top: clarify, add alt name and ref |
||
| Line 1: | Line 1: | ||
In [[aeronautics]], the '''keel effect''' (also known as the '''pendulum effect''') is the result of the sideforce-generating surfaces being above (or below) the [[center of mass]] (which coincides with the [[center of gravity (aircraft)|center of gravity]]) in ''any'' aircraft. Examples of such surfaces are the vertical stabilizer, rudder, and parts of the fuselage. When an aircraft is in a [[Angle of sideslip|sideslip]], these surfaces generate sidewards [[Lift (force)|lift]] forces. If the surface is above or below the [[center of gravity (aircraft)|center of gravity]], the sidewards lift forces generate a rolling moment. This "rolling moment caused by sideslip" is "[[Dihedral (aircraft)|dihedral effect]]". Keel effect is the contribution of these side forces to rolling moment (as sideslip increases), i.e. keel effect is the contribution of the side forces to [[Dihedral (aircraft)|dihedral effect]]. Sideforce producing surfaces ''above'' the center of gravity will ''increase'' dihedral effect, while sideforce producing surfaces below the center of gravity will decrease dihedral effect. |
In [[aeronautics]], the '''keel effect''' (also known as the '''pendulum effect''' or '''pendulum stability'''<ref name="Hitchens2015">{{cite book|last1=Hitchens|first1=Frank|title=The Encyclopedia of Aerodynamics|date=2015|publisher=Andrews UK Limited|isbn=9781785383250|url=https://books.google.co.uk/books?id=Zjv0CgAAQBAJ&pg=PT369&lpg=PT369&dq=keel+effect&source=bl&ots=oXtgenPd6b&sig=328Et4PZkGArGtEjXonZ4H-3iPs&hl=en&sa=X&ved=0ahUKEwih35fKyJLWAhWnLcAKHZiED1w4ChDoAQg9MAU#v=onepage&q=keel%20effect&f=false|accessdate=13 September 2017|language=en}}</ref>) is the result of the sideforce-generating surfaces being above (or below) the [[center of mass]] (which coincides with the [[center of gravity (aircraft)|center of gravity]]) in ''any'' aircraft. Examples of such surfaces are the vertical stabilizer, rudder, and parts of the fuselage. When an aircraft is in a [[Angle of sideslip|sideslip]], these surfaces generate sidewards [[Lift (force)|lift]] forces. If the surface is above or below the [[center of gravity (aircraft)|center of gravity]], the sidewards lift forces generate a rolling moment. This "rolling moment caused by sideslip" is "[[Dihedral (aircraft)|dihedral effect]]". Keel effect is the contribution of these side forces to rolling moment (as sideslip increases), i.e. keel effect is the contribution of the side forces to [[Dihedral (aircraft)|dihedral effect]]. Sideforce producing surfaces ''above'' the center of gravity will ''increase'' dihedral effect, while sideforce producing surfaces below the center of gravity will decrease dihedral effect. |
||
Increased dihedral effect (helped or hindered by keel effect) results in a greater tendency for the aircraft to return to level flight when the aircraft is put into a bank. Or, reduces the tendency to diverge to a greater bank angle when the aircraft starts wings-level. |
Increased dihedral effect (helped or hindered by keel effect) results in a greater tendency for the aircraft to return to level flight when the aircraft is put into a bank. Or, reduces the tendency to diverge to a greater bank angle when the aircraft starts wings-level. |
||
| Line 5: | Line 5: | ||
Keel effect is also called "Pendulum Effect" because a lower [[center of gravity (aircraft)|center of gravity]] increases the effect of sideways forces (above the center of gravity) in producing a rolling moment. This is because the ''moment arm is longer'', ''not'' because of gravitational forces. A low center of gravity is like a pendulum (which has a ''very'' low center of gravity). |
Keel effect is also called "Pendulum Effect" because a lower [[center of gravity (aircraft)|center of gravity]] increases the effect of sideways forces (above the center of gravity) in producing a rolling moment. This is because the ''moment arm is longer'', ''not'' because of gravitational forces. A low center of gravity is like a pendulum (which has a ''very'' low center of gravity). |
||
The effect is is an important consideration in [[seaplane]] design, where pontoon floats generate strong sideforces.<ref name="Flying1945">{{cite book|title=Flying Magazine|date=December 1945|pages=82|url=https://books.google.co.uk/books?id=7Uq_TImQyQYC&pg=PA82&lpg=PA82&dq=keel+effect&source=bl&ots=91mdj_aYTF&sig=3pVdVYxFoKm0Bd2BMTcMsAftIbE&hl=en&sa=X&ved=0ahUKEwih35fKyJLWAhWnLcAKHZiED1w4ChDoAQhAMAY#v=onepage&q=keel%20effect&f=false|accessdate=13 September 2017|language=en}}</ref> |
The effect is is an important consideration in [[seaplane]] design, where pontoon floats generate strong sideforces with a long moment arm.<ref name="Flying1945">{{cite book|title=Flying Magazine|date=December 1945|pages=82|url=https://books.google.co.uk/books?id=7Uq_TImQyQYC&pg=PA82&lpg=PA82&dq=keel+effect&source=bl&ots=91mdj_aYTF&sig=3pVdVYxFoKm0Bd2BMTcMsAftIbE&hl=en&sa=X&ved=0ahUKEwih35fKyJLWAhWnLcAKHZiED1w4ChDoAQhAMAY#v=onepage&q=keel%20effect&f=false|accessdate=13 September 2017|language=en}}</ref> |
||
==References== |
==References== |
||
Revision as of 17:43, 13 September 2017
In aeronautics, the keel effect (also known as the pendulum effect or pendulum stability[1]) is the result of the sideforce-generating surfaces being above (or below) the center of mass (which coincides with the center of gravity) in any aircraft. Examples of such surfaces are the vertical stabilizer, rudder, and parts of the fuselage. When an aircraft is in a sideslip, these surfaces generate sidewards lift forces. If the surface is above or below the center of gravity, the sidewards lift forces generate a rolling moment. This "rolling moment caused by sideslip" is "dihedral effect". Keel effect is the contribution of these side forces to rolling moment (as sideslip increases), i.e. keel effect is the contribution of the side forces to dihedral effect. Sideforce producing surfaces above the center of gravity will increase dihedral effect, while sideforce producing surfaces below the center of gravity will decrease dihedral effect.
Increased dihedral effect (helped or hindered by keel effect) results in a greater tendency for the aircraft to return to level flight when the aircraft is put into a bank. Or, reduces the tendency to diverge to a greater bank angle when the aircraft starts wings-level.
Keel effect is also called "Pendulum Effect" because a lower center of gravity increases the effect of sideways forces (above the center of gravity) in producing a rolling moment. This is because the moment arm is longer, not because of gravitational forces. A low center of gravity is like a pendulum (which has a very low center of gravity).
The effect is is an important consideration in seaplane design, where pontoon floats generate strong sideforces with a long moment arm.[2]
References
- ^ Hitchens, Frank (2015). The Encyclopedia of Aerodynamics. Andrews UK Limited. ISBN 9781785383250. Retrieved 13 September 2017.
- ^ Flying Magazine. December 1945. p. 82. Retrieved 13 September 2017.
- Illman, Paul; The Pilot's Handbook of Aeronautical Knowledge; Fig 2.34