RE: RE: Re: Formula for percentage arcs anyone?

From: N. A. Monllor <nmonllor_at_tampabay.rr.com>
Date: Fri, 1 Nov 2013 05:13:30 -0400

Here is the formula I got from somewhere and when checked against the online calculator, seems to work out quite well.

 

R=((25*C) / (2*P)) + ((C * P) / 200)

 

Ren

 

From: Indoor_Construction_at_yahoogroups.com [mailto:Indoor_Construction_at_yahoogroups.com] On Behalf Of leop_at_lyradev.com
Sent: Thursday, October 31, 2013 11:48 PM
To: Indoor_Construction_at_yahoogroups.com
Subject: [Indoor_Construction] RE: Re: Formula for percentage arcs anyone?

 

  

Mike,

 

John Barker's formula for the radius of an arc from the chord and camber height is correct:

 

r = 0.5(c^2/(4h) + h)

 

Another way of stating the formula is:

 

r = c^2/(8h) + h/2

 

I like to use h/c, or the "percentage arc" times 100 to get:

 

r = (c/2)( 1/(4(h/c)) + (h/c) = 0.5c(.25/(h/c) + (h/c))

 

If anyone wants to see the simple derivation, let me know (off list or whatever) and I will send it out.

 

LeoP

 

 



---In Indoor_Construction_at_yahoogroups.com, <indoor_construction_at_yahoogroups.com> wrote:

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_at_...> 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 Fri Nov 01 2013 - 02:13:59 CET