Re: Formula for percentage arcs anyone?

From: <mkirda_at_sbcglobal.net>
Date: Fri, 01 Nov 2013 03:08:17 -0000

Hi John.

Are you sure this formula is correct?

I used this to convert Bill Gowen's A6 plan ribs to arcs.
They convert very closely to 6% and 3% for wing/stab.

I had misplaced my 6% template and made one up after printing it out in Profili. Immediately afterwards I found the template I had lasercut using this formula. I compared them and they do not match - My lasercut one is far taller.

Then to make matters worse, I drew a 5" radius arc and it is even taller than the lasercut template at the referenced 2.25" chord for the Gowen A6.

Regards.
Mike Kirda
P.S. Taking down the arcs spreadsheet until I can verify this formula.



--- In Indoor_Construction_at_yahoogroups.com, "John Barker" <john.barker783@...> wrote:
>
> Mike,
>
> Don has shown how to do the arc in Autocad but if you want a formula to
> solve the problem then one can be written from the geometry of intersecting
> chords and I give it below.
>
>
>
> Radius of Arc = 0.5(C^2/4h + h) where C is the chord of the arc and h is
> the height at the centre of the camber.
>
> Example: A 6" chord with a 5% camber height at the centre.
>
> Then camber height, h = 0.05 x 6 = 0.3".
>
> Radius = 0.5(6^2/(4 x 0.3) + 0.3) = 15.15".
>
>
>
> John Barker - England
>
>
>
>
>
> From: Indoor_Construction_at_yahoogroups.com
> [mailto:Indoor_Construction_at_yahoogroups.com] On Behalf Of
> mkirda_at_...
> Sent: 04 September 2013 05:04
> To: Indoor_Construction_at_yahoogroups.com
> Subject: [Indoor_Construction] Formula for percentage arcs anyone?
>
>
>
>
>
> Greetings.
>
> I am trying to reproduce a 5% airfoil in AutoCAD and I'm not having a lot of
> luck. Everything seems to default to degree arcs, which isn't a problem,
> however I cannot find a formula to convert between the two.
>
> Anyone have the formula handy?
>
> Regards.
> Mike Kirda
>
Received on Thu Oct 31 2013 - 20:08:19 CET