Re: Titanium Foil
Posted: Sat Nov 23, 2013 5:36 pm
I'm sorry.
Did your rig last any longer than the video?
Any projections for the future?
-bill
Did your rig last any longer than the video?
Any projections for the future?
-bill
It lasted a couple more minutes after the gopro self shut off.zfennell wrote:I'm sorry.
Did your rig last any longer than the video?
Any projections for the future?
-bill
Hawaiis wrote:It lasted a couple more minutes after the gopro self shut off.zfennell wrote:I'm sorry.
Did your rig last any longer than the video?
Any projections for the future?
-bill
I will rebuild with wood, so it will not sink.
Any recommendation on bidirectional twin tip foil shapes?ronnie wrote:Hawaiis wrote:It lasted a couple more minutes after the gopro self shut off.zfennell wrote:I'm sorry.
Did your rig last any longer than the video?
Any projections for the future?
-bill
I will rebuild with wood, so it will not sink.
From fiddling around with that Foilsim program using an ellipse with camber/bend in it as the cross-section (for a twintip).
It seems that the 10 to 1 ratio for chord length to thickness seems to come out optimum for angles of attack around 3 degrees. Fatter foils seem to require higher angles of attack and have lower lift/drag ratios.
The angle of attack seems to decide how much bend to have in the ellipse and whether the bend makes the ellipse more convex on the top (which seems to be when the angle of attack is below 2 degrees) or more convex on the bottom [-0.2% camber seems to be the most effective figure](from 2 degrees and up). You can get lift/drag ratios just under 14 to 1.
That assumes the Foilsim program is accurate of course.
I can't find a program that draws the ellipse, but I guess producing an ellipse with a 10 to 1 length to thickness ratio would be easy enough and then draw an arc with the major axis curved down 0.2% at the centre. Then at each point along the major axis, you move the top and bottom surfaces down by the distance the arc is below the major axis and you get your foil shape.
Its a bit counter-intuitive to use a shape that seems like it should be the other way up, with a more convex top surface, but that's what the Foilsim program says about the ellipse. The camber figures do seem to be very small for the large changes in L/D that the program says result from small changes in the camber.
The good news is that a flat plate is quoted as a 13.85 lift/drag ratio at a 2.32 degrees angle of attack, so the ellipse doesn't seem to have any notable advantages based on that. But it doesn't change the figure if you vary the thickness of the plate, so its more of a theoretical figure I think. The other odd thing is that if you use a curved plate, that -0.2% camber figure is quoted as optimum again, so that seems a bit strange.
There is a lot of change you can input to the ellipse shape and the results do vary in accordance whereas with the flat plate all you can seemingly change is the angle of attack.
Any recommendation on bidirectional twin tip foil shapes?[/quote][/quote]Hawaiis wrote:[quote="Ronnie]
From fiddling around with that Foilsim program using an ellipse with camber/bend in it as the cross-section (for a twintip).
It seems that the 10 to 1 ratio for chord length to thickness seems to come out optimum for angles of attack around 3 degrees. Fatter foils seem to require higher angles of attack and have lower lift/drag ratios.
The angle of attack seems to decide how much bend to have in the ellipse and whether the bend makes the ellipse more convex on the top (which seems to be when the angle of attack is below 2 degrees) or more convex on the bottom [-0.2% camber seems to be the most effective figure](from 2 degrees and up). You can get lift/drag ratios just under 14 to 1.
That assumes the Foilsim program is accurate of course.
I can't find a program that draws the ellipse, but I guess producing an ellipse with a 10 to 1 length to thickness ratio would be easy enough and then draw an arc with the major axis curved down 0.2% at the centre. Then at each point along the major axis, you move the top and bottom surfaces down by the distance the arc is below the major axis and you get your foil shape.
Its a bit counter-intuitive to use a shape that seems like it should be the other way up, with a more convex top surface, but that's what the Foilsim program says about the ellipse. The camber figures do seem to be very small for the large changes in L/D that the program says result from small changes in the camber.
The good news is that a flat plate is quoted as a 13.85 lift/drag ratio at a 2.32 degrees angle of attack, so the ellipse doesn't seem to have any notable advantages based on that. But it doesn't change the figure if you vary the thickness of the plate, so its more of a theoretical figure I think. The other odd thing is that if you use a curved plate, that -0.2% camber figure is quoted as optimum again, so that seems a bit strange.
There is a lot of change you can input to the ellipse shape and the results do vary in accordance whereas with the flat plate all you can seemingly change is the angle of attack.
_____________________________________________Hawaiis wrote:Ronnie:
Thanks,
Since the front is also the rear when bidirectional, I think you are right the sharp edges will be have less resistance at a cost of more drag at higher angle of attack. Can you show a simple drawing on drilling a channels? I have a hard time visualizing.
Mahalo
Yes.Hawaiis wrote:Someone found my Titanium bidirectional Foil, It was up current of where I lost it, guess the current at the bottom is opposite of what's on the surface. Thanks everyone.
It look like the wood and Chinese Made screws failed.
Ronnie:
Are you saying to drill parallel holes into the foil?