Center of gravity

Center of gravity
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Center of gravity - 1/17/2008 5:21:30 PM

neuroza

Posts: 118
Joined: 11/17/2007
From: Porec, CROATIA (HRVATSKA)
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Hi everybody, I need help with my homemade plane.
Is there any mathematical formula to find the best place for center of gravity on the plane???

Thanks!

Post #: 1

RE: Center of gravity - 1/17/2008 6:24:18 PM

speed lover

Posts: 129
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From: , UNITED KINGDOM
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There are a few but it there are different ones for different wings but I tried one of them on my cap 232 and it was way out I needed 500g on the front but if it’s a straight wing it will be very, very close to it some more info on your wing would help.

(in reply to neuroza)

Post #: 2

RE: Center of gravity - 1/17/2008 7:59:25 PM

danny03

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From: Muskogee, OK, USA
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Follow the link and fill in all the appropriate boxes. These calculators will get you to a safe cg for your first flight, After that you will need to adjust the cg to suit your style

oops forgot to post the link, bobmac has posted the link that I was going to recommend.

< Message edited by danny03 -- 1/17/2008 9:52:39 PM >

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(in reply to neuroza)

Post #: 3

RE: Center of gravity - 1/17/2008 8:12:58 PM

bobmac010

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I think this one is pretty good, and works for all types of wing shapes...

http://www.geistware.com/rcmodeling/cg_super_calc.htm

Bob

(in reply to danny03)

Post #: 4

RE: Center of gravity - 1/17/2008 8:16:48 PM

highhorse

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From: Memphis, TN, USA
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or if u can accurately describe the wing ( a pic plus dimensions would be good ) I will happily do it for you......

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Post #: 5

RE: Center of gravity - 1/17/2008 8:57:11 PM

neuroza

Posts: 118
Joined: 11/17/2007
From: Porec, CROATIA (HRVATSKA)
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I will post a picture with dimension, just need 20 minutes...

(in reply to highhorse)

Post #: 6

RE: Center of gravity - 1/17/2008 9:41:10 PM

da Rock

Posts: 6694
Joined: 10/11/2005
From: western, NC, USA
Status: online

quote:

ORIGINAL: neuroza

I will post a picture with dimension, just need 20 minutes...

Better yet, just take a yardstick and measure the following:

Wingspan
wing root chord
wing tip chord
leading edge sweep back at tip

stabilizer span
stab root chord
stab tip chord
leading edge sweep back at tip

distance from LE of wing to LE of stab along fuselage.
Easy to do and takes a couple of minutes, not 20, and no great skills required.
Then plug those 9 measurements into the geistware application that has already been suggested twice above. Click on the button and you got your answer. And you'll be able to do it for yourself next model, and the next after.

(in reply to neuroza)

Post #: 7

RE: Center of gravity - 1/17/2008 9:58:18 PM

neuroza

Posts: 118
Joined: 11/17/2007
From: Porec, CROATIA (HRVATSKA)
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ok, so here we go, this is my very first home made plane

...
The measure are in milimeters
And here is my results... It's that I just don't know what's what

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< Message edited by neuroza -- 1/17/2008 10:30:06 PM >

(in reply to neuroza)

Post #: 8

RE: Center of gravity - 1/17/2008 11:06:54 PM

Tall Paul

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From: Palmdale, CA, USA
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For that type of plain vanilla untapered wing, with the tail the size relative to the wing and where it is, the c.g is just a percentage of the root chord (including the aileron chord).
Your 25% location would be considered conservative, making for a very stable airplane.
For more activity, going back to 30% would increase the manuverability, if you would care to do that.

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(in reply to neuroza)

Post #: 9

RE: Center of gravity - 1/17/2008 11:21:41 PM

neuroza

Posts: 118
Joined: 11/17/2007
From: Porec, CROATIA (HRVATSKA)
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an You please show me exsactly on my plane (picture) where is the CG.

25% from where???

...sorry, I'm just an absolute beginer...

< Message edited by neuroza -- 1/17/2008 11:30:25 PM >

(in reply to Tall Paul)

Post #: 10

RE: Center of gravity - 1/18/2008 12:40:43 AM

Villa

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From: Wilson, NC,
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Hi neuroza
The front of the wing is called the leading edge (LE). The back of the wing, including the ailerons, is called the trailing edge (TE). Your wing cord is 300MM. 25% of that is 75MM. Measure that from the wing LE toward the wing TE. That is the location of the CG. After you fly the plane you may want to move the CG a little to make the plane do what you want.

(in reply to neuroza)

Post #: 11

RE: Center of gravity - 1/18/2008 12:43:31 AM

Mike Connor

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From: Tulsa, OK, USA
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quote:

ORIGINAL: neuroza

an You please show me exsactly on my plane (picture) where is the CG.

25% from where???

...sorry, I'm just an absolute beginer...

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http://www.mikesrc.us/

(in reply to neuroza)

Post #: 12

RE: Center of gravity - 1/18/2008 2:39:47 AM

bwgoodnow

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From: Las Vegas, NV, USA
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Hey Neuroza,

Please try and find some local help before you fly that plane. There are other things besides C.G. that need to be checked to insure a sucessful flight. Call a local hobby shop and ask where you can find a flying field to get some help. When you get to the field, just ask "Is there anyone here that does not mind helping a student pilot". Many of us are glad to help!

Brett

(in reply to Mike Connor)

Post #: 13

RE: Center of gravity - 1/18/2008 12:36:37 PM

neuroza

Posts: 118
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From: Porec, CROATIA (HRVATSKA)
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Thanks, this is just what I was looking for...

Again, thanks...

(in reply to Mike Connor)

Post #: 14

RE: Center of gravity - 1/18/2008 12:44:05 PM

neuroza

Posts: 118
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From: Porec, CROATIA (HRVATSKA)
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Here in my town or close there are no club or hobby center where I can go to learn, so the only way was this way... "do it yourself"...

The closest place to buy or learn to fly RC is in Zagreb, that is 250km from my place...

(in reply to bwgoodnow)

Post #: 15

RE: Center of gravity - 1/18/2008 1:13:47 PM

da Rock

Posts: 6694
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From: western, NC, USA
Status: online

quote:

ORIGINAL: neuroza

ok, so here we go, this is my very first home made plane ...
The measure are in milimeters
And here is my results... It's that I just don't know what's what

The red circle shows you input a Static Margin of 10%. It shows in the green circle that the CG for that SM would be 7.26 back from the LE of the wing.

The CG range is usually from a SM of 10% to 15% for just flying around safely. If you reinput the measurements into that geistware and ask for 15%, you'll see the other location for the range where the CG will be safe.

It will be safe to fly an airplane with the measurements you input with the CG somewhere from 7.26 to wherever the 15% input gives for that input.

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