Aerofoil floats !

[Santiago]

The foil being curvy just increases drag so becomes more efficient at causing lift.

[Paul D]

Since these floats are not powered surely they can only work by the force of drag??? In which case the 'foil' is probably superfluous...???


I put wires on mine so that I might fiddle with the angle of water flow....I really should at least try them out......daft not to have.....

A glider isn't powered either. The flow of water over the foil creates the lifting force. Incidentally the section shown at the beginning of this topic is called a reflex section and is a high lift low speed section.

[Nobby]

Hmmm.... Isn't a glider powered by gravity continuing the movement provided by the initial tow-plane or catapult? obviously it is able to soar, but not forever.....


Not being pedantic, but the airfield I used to work at had some powered gliders.....one owner was always trying to get me to graft a Kawasaki engine into his...I doubt the CAA would have allowed it....This thing could allegedly already make the Alps from Denham!

[SeanM]

Sorry Paul, but I'm not confusing drag with lift at all. I'll keep it brief:

The common explanation of how an aerofoil generates lift by "sucking" the wing upwards due to a negative pressure (supposedly explained by the Bernoulli equation) is what is known as "the equal transit time fallacy". Its a gross oversimplification. There is always a positive pressure on the upper surface of the wing or foil. The pressure is higher on the underside of the wing and it pushes the wing upwards.

From memory the most complete nonmathematical explanation is that lift comes from a combination of mass deflection (the air under wing is deflected downwards) causing and equal and opposite reaction on the wing. This is the first cause of lift. Then when the wing is moving faster the fluid above the wing is deflected upwards causing a low pressure region. The fluid over the wing is accelerated by this region and contributes to the lift.

A flat wing will generate lift purely from its angle of attack and an aerofoil will generate lift from a combination it's shape and its angle of attack. Both however must be constrained at an angle to the fluid medium or they won't generate lift.

I would suggest that these aerofoil floats are pretty unreliable as they depend on their form to hold the float at an angle to the flow. Small differences in shape will make a big difference to the stability of the set up and the sideways force generated. I seem to remember Nobby using a wire to try to hold the float at a better angle. The side planers use a wire harness to hold a flat vane at an angle to the flow. The line is held in a clip and, when a fish takes, the line pulls out of the clip and the vane collapses.

Sorry!

[Santiago]

Depending on the flow, one day they'll work really well, the next day if the flow rate is different they will fail or be less effective.