Calculating Cross Sectional Area

Place to add formulas. If you post a formula please make sure your abbreviations are spelled out so it avoids a lot of follow-up postings. I know a lot of abbreviations are common or taken to be common knowledge. Please be sure to checkout the new FAQ of common abbreviations.

Please post formulas in separate topics, do not add formulas to someone else's post unless it relates to the original post. Also in the topic line make a note of what your posted formula is about . Thanks
coulterracn
Posts: 450
Joined: Wed Feb 24, 2010 5:44 am
Location: Mississippi Gulf Coast
Contact:

Calculating Cross Sectional Area

Post by coulterracn »

When calculating a rectangular port with radius corners, how do you subtract the area of the radius?

Example: intake port opening 2.57"h x 1.91"w with 5/8" corner radius

Formula for calculating throat cross sectional area?

Ray
My Flowbench is better than their's
tweaks
Posts: 22
Joined: Wed Mar 03, 2010 11:12 pm
Location: New Zealand

Re: Calculating Cross Sectional Area

Post by tweaks »

area of 5/8 dia = 3.142 x .3125 x .3125 = 0.3095 sq inch

area of 5/8 square = .625 x .625 = 0.5840

0.5840 minus 0.3095 = 0.2745 sq inch

subtract that from the large port area 2.57 x 1.91 = 4.9087

4.9087 - 0.2745 = 4.6342 square inches

hope you understood all this ..lol

Cheers

Lynds
jfholm
Posts: 1628
Joined: Fri Feb 19, 2010 7:36 pm
Location: Grantsville, Utah 45 min west of Salt Lake City

Re: Calculating Cross Sectional Area

Post by jfholm »

Lynds,
First of all nice hearing from you again! I appreciate your formula and it helped a bunch. I did it, but my math came out a little different.
area of a 5/8" circle that I did was Pi X R^ or 3.1416X(.3125X.3125)= .306796875
area of a 5/8" square is .625X.625 = .390625
so the difference I get is .083828125 and subtracted from 4.9087 gives me 4.824871875 square inches. Am I missing something or doing it wrong? Or did I get the correct answer?

John
coulterracn
Posts: 450
Joined: Wed Feb 24, 2010 5:44 am
Location: Mississippi Gulf Coast
Contact:

Re: Calculating Cross Sectional Area

Post by coulterracn »

Thanks Lynds and John.

I was confused with the formulas for Area of a circle and circumference of a circle.

Ray
My Flowbench is better than their's
Flash
Posts: 778
Joined: Thu Feb 25, 2010 3:39 pm

Re: Calculating Cross Sectional Area

Post by Flash »

this is some good math, and i have added it to my notes.

One question though, how do you decide what size the corner radius is?
Is it as simple as measuring from were the bend starts to were it ends????
Gordon
coulterracn
Posts: 450
Joined: Wed Feb 24, 2010 5:44 am
Location: Mississippi Gulf Coast
Contact:

Re: Calculating Cross Sectional Area

Post by coulterracn »

Flash wrote:One question though, how do you decide what size the corner radius is?
Is it as simple as measuring from were the bend starts to were it ends????
You can use radius gages or make some using a hole template available from most office supply stores or drafting supplies.

Ray
My Flowbench is better than their's
SWAirflowServices
Posts: 143
Joined: Tue Jun 15, 2010 7:51 pm
Location: So Cal
Contact:

Re: Calculating Cross Sectional Area

Post by SWAirflowServices »

Flash wrote: One question though, how do you decide what size the corner radius is?
Is it as simple as measuring from were the bend starts to were it ends????
I also find using the unsharpened end of a drill bill useful sometimes.
http://www.facebook.com/SWAirFlowServices You know you want to "Like" it!
Flash
Posts: 778
Joined: Thu Feb 25, 2010 3:39 pm

Re: Calculating Cross Sectional Area

Post by Flash »

Sooo lets say i take a 1/4" drill bit and it fit perfection in the corner.......is that a 1/4 radius or 1/8 radius or...........................

And then do i times that # by 4 aka 4 corners? Before i subtract from to total?
Gordon
coulterracn
Posts: 450
Joined: Wed Feb 24, 2010 5:44 am
Location: Mississippi Gulf Coast
Contact:

Re: Calculating Cross Sectional Area

Post by coulterracn »

Devide 1/4" by 2 equals 1/8" or .250/2 = .125" radius

Or you could use this calculator Stan Weiss posted on Larry Meaux's forum to do the math:
http://users.erols.com/srweiss/index.html#jcalc

Ray
My Flowbench is better than their's
Flash
Posts: 778
Joined: Thu Feb 25, 2010 3:39 pm

Re: Calculating Cross Sectional Area

Post by Flash »

Input Arc Radius o
Input Arc Diameter o


Yaah i seen that but was confused about my options

so if a 1/4" fit in each corner, i would enter .125 in each corner and then select Radius, not diameter...Right?
Gordon
Post Reply