lørdag, marts 26, 2011

NACA profil til stiksværd

Har via det internationale Minitransat forum http://www.minitransat650.com/ fået et par forslag til både NACA profil for stiksværd samt et par navne på beregningsprogrammer for profilerne.
Det ser ud til at det sikre konservative valg er NACA 0012 alternativt NACA 0009.

Her link til forslagene:

Og her et par forslag til beregningsprogrammer:



2 kommentarer:

  1. Hi Jesper,

    For a dagger-board your main concern is not the breaking strength because there is no keel bulb at the end of it so the load is similar to a rudder and far less than a keel. The worst that can happen is that it breaks, and you need to make a new one.

    I would go for the NACA-0010 and not more (width is 10% of cord length, so if your cord length is 300mm then the width is 30mm). The thicker NACA profiles perform better at wider angles of attack (like a rudder), but a dagger-board has a low angle of attack. Obviously a thicker profile has much higher breaking strength but you don't need that here.

    The 0010 is what we use for the Scandinavian Cruiser 20 keel strut, and the lift is great as soon as you reach a couple of knots of speed, the resistance is low, and it is strong enough to hold the keel bulb.

    In very light air you would not use the dagger-board anyway as you would keep the keel down. Keel and dagger-board combined gives a lot of wetted-area surface resistance so you need to experiment with different combinations in different conditions. This is a very complicated boat to sail, particularly in a short race.

    I would build the dagger-board the same way the surfboard guys make their surfboards (shape a high-density foam core, and apply carbon fiber skin). I would guess that 600g/m2 woven carbon fabric in the skin is enough. It is easy to find building instructions for this on the Internet.

    Best regards

    Nis Peter Lorentzen
    Scandinavian Cruisers

  2. Hi Nis,

    Thanks for the info.
    I was planing on using a NACA0009 or NACA0012 build as stripplanking in cedar and with two 400g glass rowing with epoxy.
    Alternatively make a simple one-use-only mould of thin plywood painted a couple of times with warnis before casting. Then afterwards gluing the two half pieces together. but it seems as a lot of work for only one casting.