What is the offset in a seaplane's hull?












15












$begingroup$


I noticed there is a little offset in a seaplane's hull (highlighted in the following picture). I suppose this is useful as it exists in all the seaplanes I know. It seems it does not help hydrodynamics neither aerodynamics. I could not find any clue by myself as I don't know this feature's name.



My question, what is its name and purpose?



Catalina (original image from https://upload.wikimedia.org/wikipedia/commons/2/20/PBY_Catalina.jpg)

(wikimedia.org)






aircraft-design feature-identification fuselage seaplane







share|improve this question











$endgroup$

















    15












    $begingroup$


    I noticed there is a little offset in a seaplane's hull (highlighted in the following picture). I suppose this is useful as it exists in all the seaplanes I know. It seems it does not help hydrodynamics neither aerodynamics. I could not find any clue by myself as I don't know this feature's name.



    My question, what is its name and purpose?



    Catalina (original image from https://upload.wikimedia.org/wikipedia/commons/2/20/PBY_Catalina.jpg)

    (wikimedia.org)






    aircraft-design feature-identification fuselage seaplane







    share|improve this question











    $endgroup$















      15












      15








      15





      $begingroup$


      I noticed there is a little offset in a seaplane's hull (highlighted in the following picture). I suppose this is useful as it exists in all the seaplanes I know. It seems it does not help hydrodynamics neither aerodynamics. I could not find any clue by myself as I don't know this feature's name.



      My question, what is its name and purpose?



      Catalina (original image from https://upload.wikimedia.org/wikipedia/commons/2/20/PBY_Catalina.jpg)

      (wikimedia.org)






      aircraft-design feature-identification fuselage seaplane







      share|improve this question











      $endgroup$




      I noticed there is a little offset in a seaplane's hull (highlighted in the following picture). I suppose this is useful as it exists in all the seaplanes I know. It seems it does not help hydrodynamics neither aerodynamics. I could not find any clue by myself as I don't know this feature's name.



      My question, what is its name and purpose?



      Catalina (original image from https://upload.wikimedia.org/wikipedia/commons/2/20/PBY_Catalina.jpg)

      (wikimedia.org)






      aircraft-design feature-identification fuselage seaplane




      aircraft-design feature-identification fuselage seaplane






      share|improve this question















      share|improve this question













      share|improve this question




      share|improve this question








      edited 16 hours ago









      ymb1

      69.8k7222371




      69.8k7222371










      asked 16 hours ago









      Manu HManu H

      5,5701058137




      5,5701058137






















          2 Answers
          2






          active

          oldest

          votes


















          18












          $begingroup$

          That's called the step. Without it, you'd have to fight against the buoyancy of the rear end of the hull when you rotate for takeoff.




          However, a seaplane float or hull must be designed to permit the seaplane to be rotated or pitched up to increase the wing's angle of attack and gain the most lift for takeoffs and landings. Thus, the underside of the float or hull has a sudden break in its longitudinal lines at the approximate point around which the seaplane rotates into the lift off attitude. This break, called a "step," also provides a means of interrupting the capillary or adhesive properties of the water.



          The water can then flow freely behind the step, resulting in minimum surface friction so the seaplane can lift out of the water. The steps are located slightly behind the airplane's centre of gravity, approximately at the point where the main wheels of a landplane are located. If the steps were located to far aft or forward of this point, it would be difficult, if not impossible, to rotate the airplane into a pitch-up attitude prior to planing (rising partly out of the water while moving at high speed) or lift off. Although steps are necessary, the sharp break along the float's or hull's underside causes structural stress concentration, and in flight produces considerable drag because of the eddying turbulence it creates in the airflow.







          share|improve this answer









          $endgroup$









          • 3




            $begingroup$
            Re the drag in flight, an obvious question would be whether anyone had a retractable fairing behind the step to solve that problem? I hit Google and found a few places speculating about that (including US patent US6042052A in 1998), but no evidence of designers actually using one.
            $endgroup$
            – Graham
            5 hours ago



















          9












          $begingroup$

          enter image description here



          It's called a hull step. Below is with and without:




          enter image description here



          It reduces water drag. As the plane gains speed and the aft body is lifted, only the forward hull will be in contact with the water.




          Source: Laté 631 Replica - Chapter 3 - Hydrodynamics






          share|improve this answer









          $endgroup$














            Your Answer





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            2 Answers
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            active

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            2 Answers
            2






            active

            oldest

            votes









            active

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            active

            oldest

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            18












            $begingroup$

            That's called the step. Without it, you'd have to fight against the buoyancy of the rear end of the hull when you rotate for takeoff.




            However, a seaplane float or hull must be designed to permit the seaplane to be rotated or pitched up to increase the wing's angle of attack and gain the most lift for takeoffs and landings. Thus, the underside of the float or hull has a sudden break in its longitudinal lines at the approximate point around which the seaplane rotates into the lift off attitude. This break, called a "step," also provides a means of interrupting the capillary or adhesive properties of the water.



            The water can then flow freely behind the step, resulting in minimum surface friction so the seaplane can lift out of the water. The steps are located slightly behind the airplane's centre of gravity, approximately at the point where the main wheels of a landplane are located. If the steps were located to far aft or forward of this point, it would be difficult, if not impossible, to rotate the airplane into a pitch-up attitude prior to planing (rising partly out of the water while moving at high speed) or lift off. Although steps are necessary, the sharp break along the float's or hull's underside causes structural stress concentration, and in flight produces considerable drag because of the eddying turbulence it creates in the airflow.







            share|improve this answer









            $endgroup$









            • 3




              $begingroup$
              Re the drag in flight, an obvious question would be whether anyone had a retractable fairing behind the step to solve that problem? I hit Google and found a few places speculating about that (including US patent US6042052A in 1998), but no evidence of designers actually using one.
              $endgroup$
              – Graham
              5 hours ago
















            18












            $begingroup$

            That's called the step. Without it, you'd have to fight against the buoyancy of the rear end of the hull when you rotate for takeoff.




            However, a seaplane float or hull must be designed to permit the seaplane to be rotated or pitched up to increase the wing's angle of attack and gain the most lift for takeoffs and landings. Thus, the underside of the float or hull has a sudden break in its longitudinal lines at the approximate point around which the seaplane rotates into the lift off attitude. This break, called a "step," also provides a means of interrupting the capillary or adhesive properties of the water.



            The water can then flow freely behind the step, resulting in minimum surface friction so the seaplane can lift out of the water. The steps are located slightly behind the airplane's centre of gravity, approximately at the point where the main wheels of a landplane are located. If the steps were located to far aft or forward of this point, it would be difficult, if not impossible, to rotate the airplane into a pitch-up attitude prior to planing (rising partly out of the water while moving at high speed) or lift off. Although steps are necessary, the sharp break along the float's or hull's underside causes structural stress concentration, and in flight produces considerable drag because of the eddying turbulence it creates in the airflow.







            share|improve this answer









            $endgroup$









            • 3




              $begingroup$
              Re the drag in flight, an obvious question would be whether anyone had a retractable fairing behind the step to solve that problem? I hit Google and found a few places speculating about that (including US patent US6042052A in 1998), but no evidence of designers actually using one.
              $endgroup$
              – Graham
              5 hours ago














            18












            18








            18





            $begingroup$

            That's called the step. Without it, you'd have to fight against the buoyancy of the rear end of the hull when you rotate for takeoff.




            However, a seaplane float or hull must be designed to permit the seaplane to be rotated or pitched up to increase the wing's angle of attack and gain the most lift for takeoffs and landings. Thus, the underside of the float or hull has a sudden break in its longitudinal lines at the approximate point around which the seaplane rotates into the lift off attitude. This break, called a "step," also provides a means of interrupting the capillary or adhesive properties of the water.



            The water can then flow freely behind the step, resulting in minimum surface friction so the seaplane can lift out of the water. The steps are located slightly behind the airplane's centre of gravity, approximately at the point where the main wheels of a landplane are located. If the steps were located to far aft or forward of this point, it would be difficult, if not impossible, to rotate the airplane into a pitch-up attitude prior to planing (rising partly out of the water while moving at high speed) or lift off. Although steps are necessary, the sharp break along the float's or hull's underside causes structural stress concentration, and in flight produces considerable drag because of the eddying turbulence it creates in the airflow.







            share|improve this answer









            $endgroup$



            That's called the step. Without it, you'd have to fight against the buoyancy of the rear end of the hull when you rotate for takeoff.




            However, a seaplane float or hull must be designed to permit the seaplane to be rotated or pitched up to increase the wing's angle of attack and gain the most lift for takeoffs and landings. Thus, the underside of the float or hull has a sudden break in its longitudinal lines at the approximate point around which the seaplane rotates into the lift off attitude. This break, called a "step," also provides a means of interrupting the capillary or adhesive properties of the water.



            The water can then flow freely behind the step, resulting in minimum surface friction so the seaplane can lift out of the water. The steps are located slightly behind the airplane's centre of gravity, approximately at the point where the main wheels of a landplane are located. If the steps were located to far aft or forward of this point, it would be difficult, if not impossible, to rotate the airplane into a pitch-up attitude prior to planing (rising partly out of the water while moving at high speed) or lift off. Although steps are necessary, the sharp break along the float's or hull's underside causes structural stress concentration, and in flight produces considerable drag because of the eddying turbulence it creates in the airflow.








            share|improve this answer












            share|improve this answer



            share|improve this answer










            answered 16 hours ago









            HobbesHobbes

            4,0421017




            4,0421017








            • 3




              $begingroup$
              Re the drag in flight, an obvious question would be whether anyone had a retractable fairing behind the step to solve that problem? I hit Google and found a few places speculating about that (including US patent US6042052A in 1998), but no evidence of designers actually using one.
              $endgroup$
              – Graham
              5 hours ago














            • 3




              $begingroup$
              Re the drag in flight, an obvious question would be whether anyone had a retractable fairing behind the step to solve that problem? I hit Google and found a few places speculating about that (including US patent US6042052A in 1998), but no evidence of designers actually using one.
              $endgroup$
              – Graham
              5 hours ago








            3




            3




            $begingroup$
            Re the drag in flight, an obvious question would be whether anyone had a retractable fairing behind the step to solve that problem? I hit Google and found a few places speculating about that (including US patent US6042052A in 1998), but no evidence of designers actually using one.
            $endgroup$
            – Graham
            5 hours ago




            $begingroup$
            Re the drag in flight, an obvious question would be whether anyone had a retractable fairing behind the step to solve that problem? I hit Google and found a few places speculating about that (including US patent US6042052A in 1998), but no evidence of designers actually using one.
            $endgroup$
            – Graham
            5 hours ago











            9












            $begingroup$

            enter image description here



            It's called a hull step. Below is with and without:




            enter image description here



            It reduces water drag. As the plane gains speed and the aft body is lifted, only the forward hull will be in contact with the water.




            Source: Laté 631 Replica - Chapter 3 - Hydrodynamics






            share|improve this answer









            $endgroup$


















              9












              $begingroup$

              enter image description here



              It's called a hull step. Below is with and without:




              enter image description here



              It reduces water drag. As the plane gains speed and the aft body is lifted, only the forward hull will be in contact with the water.




              Source: Laté 631 Replica - Chapter 3 - Hydrodynamics






              share|improve this answer









              $endgroup$
















                9












                9








                9





                $begingroup$

                enter image description here



                It's called a hull step. Below is with and without:




                enter image description here



                It reduces water drag. As the plane gains speed and the aft body is lifted, only the forward hull will be in contact with the water.




                Source: Laté 631 Replica - Chapter 3 - Hydrodynamics






                share|improve this answer









                $endgroup$



                enter image description here



                It's called a hull step. Below is with and without:




                enter image description here



                It reduces water drag. As the plane gains speed and the aft body is lifted, only the forward hull will be in contact with the water.




                Source: Laté 631 Replica - Chapter 3 - Hydrodynamics







                share|improve this answer












                share|improve this answer



                share|improve this answer










                answered 16 hours ago









                ymb1ymb1

                69.8k7222371




                69.8k7222371






























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