Heckie

11-14-2000, 05:36 AM

All over the Internet I find links to the article of Paul Zander, “Design and construction of centerboards and rudders”(march 1996). Having a heavily restricted design class boat, I tried to work out the formula for the parallel sided foils. Unfortunately I have to conclude they are not perfect. The original formula for the leading edge reads:

y = (t/2) * ((8*sqr(x) / 3sqr(Xle)) - (2*X / Xle) + ((x^2) / (3*Xle^2)))

where x is the position along the chord from 0 to 1

y is the thickness at a given value of x

t is the maximum thickness as a fraction of the chord and

sqr is the square root function.

The above taken from the earlier mentioned NACA-formulation, and

Xle is the distance that the leading edge is faired.

Using these variables will not give proper figures!

My calculations show that the formula for the leading edge should be:

y = (t/2)*((8*SQRT(x) / (3*SQRT(Xle)))-(2*x/ Xle)+((x^2)/(3*(Xle^2))))

where

t = total thickness of the profile (mm).

x = the position along the chord of the fairing (mm).

Xle is the distance that the leading edge is faired (mm).

Also, the formula for the trailing edge doesn’t seem to give proper results:

y = (t/2) * ( (1- 3x^2) / 2*Xtl + x^3 / 2*Xtl^3 )

where x is the distance from the start of fairing.

Xtl is the distance the trailing edge is faired.

Or in Excel-language:

=(t/2)*((8*SQRT(B44)/(3*SQRT(fairing)))-(2*B44/fairing)+(POWER(B44,2)/(3*POWER(fairing,2))))

Having learnt from the leading edge I presume all distances should be in real length (mm). But that still doesn’t get me the right results. And also I feel the formula should be something like:

=(t/2)*(1-(((3*X^2))/(2*Xtl))+(((X^3)/(2*(Xtl^3))))))

Or, in Excel-language:

=( t/2)*(1-(((3*POWER(D44,2))/(2*fairing))+((POWER(D44,3)/(2*POWER(fairing,3))))))

This at least gives me a starting point at the thickness of the foil. But I still can’t get it right; I need a correction-factor. But then I’m not shure I have the right profile...

Is there anybody who can help me with this one?

Thanks,

Eric

y = (t/2) * ((8*sqr(x) / 3sqr(Xle)) - (2*X / Xle) + ((x^2) / (3*Xle^2)))

where x is the position along the chord from 0 to 1

y is the thickness at a given value of x

t is the maximum thickness as a fraction of the chord and

sqr is the square root function.

The above taken from the earlier mentioned NACA-formulation, and

Xle is the distance that the leading edge is faired.

Using these variables will not give proper figures!

My calculations show that the formula for the leading edge should be:

y = (t/2)*((8*SQRT(x) / (3*SQRT(Xle)))-(2*x/ Xle)+((x^2)/(3*(Xle^2))))

where

t = total thickness of the profile (mm).

x = the position along the chord of the fairing (mm).

Xle is the distance that the leading edge is faired (mm).

Also, the formula for the trailing edge doesn’t seem to give proper results:

y = (t/2) * ( (1- 3x^2) / 2*Xtl + x^3 / 2*Xtl^3 )

where x is the distance from the start of fairing.

Xtl is the distance the trailing edge is faired.

Or in Excel-language:

=(t/2)*((8*SQRT(B44)/(3*SQRT(fairing)))-(2*B44/fairing)+(POWER(B44,2)/(3*POWER(fairing,2))))

Having learnt from the leading edge I presume all distances should be in real length (mm). But that still doesn’t get me the right results. And also I feel the formula should be something like:

=(t/2)*(1-(((3*X^2))/(2*Xtl))+(((X^3)/(2*(Xtl^3))))))

Or, in Excel-language:

=( t/2)*(1-(((3*POWER(D44,2))/(2*fairing))+((POWER(D44,3)/(2*POWER(fairing,3))))))

This at least gives me a starting point at the thickness of the foil. But I still can’t get it right; I need a correction-factor. But then I’m not shure I have the right profile...

Is there anybody who can help me with this one?

Thanks,

Eric