cg dilemma  
View related threads: (in this forum | in all forums)

Tower Hobbies
Enter up to 4 keywords or Tower stock numbers
Logged in as Guest



Users viewing this topic: none
  Printable Version
       


HPI Racing E10 Lamborghini Touring RTR 4WD Car
Seller:  Erick Royer
Details:   $150.00   |  7/29/2008   |  Classified Ad
We will rotate YOUR AD in this spot if you select "Forum Featured" when placing or editing your ad!

All Forums >> RC Airplanes >> Questions and Answers >> cg dilemma
Page: [1]

Login
Message << Older Topic   Newer Topic >>
cg dilemma - 5/14/2008 1:22:45 PM   
tazzzz


 

Posts: 276
Joined: 3/12/2007
From: wilmington, NC, USA
Status: offline 		I purchased a Carl Goldberg Tiger 2. It was built from a kit. I checked on line for the CG, from CG themselves. It states the cg should be from 3 1/2 to 4 3/8" from leading edge of wing at the fuselage ( im assuming that mean with the plane upside down seeing how it is a low wing symmetrical wing. Well I went back 3 3/4". I got it to balance fine,,but when I turn it over (right side up) it seems to go tail heavy,,but if I push down a little on the nose itll go nose heavy. This happens only on the upright position. Shouldnt it balance the same either way, or should I stick with the up side down balance and go with it?

Thanks Guys-TAZZZZ
       Post #: 1

RE: cg dilemma - 5/14/2008 1:29:24 PM   
Ed Smith


 

Posts: 2820
Joined: 12/29/2001
From: Brantford, ON, CANADA
Status: offline 		Balance it the right way up with the supports at the extreme win tips, at the correct position chordwise of course. If balanced it will not tip backwards or forwards.

Ed S

(in reply to tazzzz)
       Post #: 2

RE: cg dilemma - 5/14/2008 1:47:42 PM   
alan0899


 

Posts: 2015
Joined: 4/17/2006
From: Cundletown, NSW, AUSTRALIA
Status: offline 		G'day Mate,
It's a low wing plane, so balance it upside down, because if you try to balance it upright it will be unstable, as you have noticed.

_____________________________

Good Flyin Mate. Keep Thyne Airspeed up, lest the ground arise & smite thee, Allan.

(in reply to tazzzz)
       Post #: 3

RE: cg dilemma - 5/14/2008 2:07:26 PM   
JohnBuckner



Posts: 3826
Joined: 12/23/2001
From: Kingman, AZ, USA
Status: offline 		First yes the airplane should balance the same either way. The problem arises and what you experiancing when you turned it back up is there is not enought stability to be able to balance it. In other words the vertical center of gravity needs to be sufficiently lower than the balance supports to be able to balance the airplane. Trying to balance many low wings upright is next to impossible to do accurately, Just like trying to balance a pencil on its point.

If the low wing has considerable dihedral then it may be possible to balance upright if the supports are fairly wide apart. However most commercial balancing devices won,t spread that far.

If the airplane is perfectly level upside down at the point you are looking for then that is the balance point.

John

< Message edited by JohnBuckner -- 5/14/2008 2:09:31 PM >

_____________________________

"Keep your controllines tight"

(in reply to Ed Smith)
       Post #: 4

RE: cg dilemma - 5/14/2008 2:22:15 PM   
Jim Dines


 

Posts: 1344
Joined: 2/27/2002
From: Keller, TX, USA
Status: offline 		Balance it heavy side down (that's inverted for a low wing, upright for a high wing).

(in reply to tazzzz)
       Post #: 5

RE: cg dilemma - 5/14/2008 2:29:23 PM   
SoCalSal


 

Posts: 913
Joined: 3/5/2005
From: spring valley , CA, USA
Status: offline
quote:

ORIGINAL: tazzzz

I purchased a Carl Goldberg Tiger 2. It was built from a kit. I checked on line for the CG, from CG themselves. It states the cg should be from 3 1/2 to 4 3/8" from leading edge of wing at the fuselage ( im assuming that mean with the plane upside down seeing how it is a low wing symmetrical wing. Well I went back 3 3/4". I got it to balance fine,,but when I turn it over (right side up) it seems to go tail heavy,,but if I push down a little on the nose itll go nose heavy. This happens only on the upright position. Shouldnt it balance the same either way, or should I stick with the up side down balance and go with it?

Thanks Guys-TAZZZZ


Question? Is this a taildragger???????????? If so I have the solution for you. I have a Excel spread sheet set up to show you the correct balance at the CG point. All you will need is a small postal scale and a tape measure. This spread sheet will work on any size aircraft from our smallest models to full scale.
If you would like a copy just PM me with your e-mail address and I will send it along to you.

_____________________________

Let''s be open minded.... But not so open that your brain falls out

(in reply to tazzzz)
       Post #: 6

RE: cg dilemma - 5/14/2008 2:52:57 PM   
spiral_72



Posts: 496
Joined: 3/7/2007
From: Chesnee, SC, USA
Status: offline 		I noticed the same thing when I bought my first low wing. Theoretically the plane should balance the same upright and inverted, but as another has pointed out, the plane is unstable and unpredictable right side up.

Right side up the plane's center of mass is just too high (normally you would say CG, but that'd be a little misleading in this case) to be repeatable. You'd have to balance the plane on two pins and add lead a gram at a time. A bit too tedious(SP?) for my taste.

I've balanced my low wing inverted since I've bought it. Err on the nose heavy side to make sure. You can always remove lead after you fly it.

I have a PVC rig for checking CG. I measure from the tip of the spinner to the table and that gives me a definite(SP?) measurement to adjust from once I fly the plane.

_____________________________

Wasn't that cool? I meant to do it.

(in reply to tazzzz)
       Post #: 7

RE: cg dilemma - 5/14/2008 3:28:13 PM   
tazzzz


 

Posts: 276
Joined: 3/12/2007
From: wilmington, NC, USA
Status: offline 		Yea,,,Sounds interesting,, Its not a taildragger,,,although some day it might be. I bought this plane at a smokin' deal I just couldnt pass up


My e- mail is-eaglelite@aol.comThanks...TAZZZZ

(in reply to SoCalSal)
       Post #: 8

RE: cg dilemma - 5/16/2008 12:59:01 AM   
Ed Smith


 

Posts: 2820
Joined: 12/29/2001
From: Brantford, ON, CANADA
Status: offline
quote:

Balance it the right way up with the supports at the extreme win tips, at the correct position chordwise of course. If balanced it will not tip backwards or forwards.


I stand by what I said. balance the airplane in the attitude it flies.

Ed S

(in reply to tazzzz)
       Post #: 9

RE: cg dilemma - 5/16/2008 1:48:45 AM   
da Rock



Posts: 6370
Joined: 10/11/2005
From: western, NC, USA
Status: online 		You know why the Pyramids sit with the wide side on the desert floor? CG problems.

The CG of the Pyramids don't change when they're pointy side down or pointy side up. But they were easier to keep level when they have most of their weight below the CG. Same with our models.

Balance however it's easiest to keep the model from tipping. You've just seen that it's almost impossible one way. Don't worry that you won't be able to find the CG because you will. It's not more accurate either way, just nearly impossible one way.

(in reply to Ed Smith)
       Post #: 10

RE: cg dilemma - 5/16/2008 4:57:00 PM   
jetmech05


 

Posts: 1555
Joined: 7/12/2005
From: Jacksonville, FL, USA
Status: offline 		balance a low wing plane upside down...high wing plane right side up...balance your fuel tank empty because the tank is forward of the CG point.....remember xx amount of inches from the leading edge means draw a line up from the leading edge and measure from there...don't measure along the wing from the leading edge,,,,

(in reply to da Rock)
       Post #: 11

RE: cg dilemma - 5/16/2008 5:15:32 PM   
Deadeye



Posts: 3641
Joined: 7/16/2002
From: Conrad, MT, USA
Status: offline 		Here's how I balance my planes. Low wing, high wing, doesn't matter, always right side up. I feel for the spar with my fingertips, if I am within a half an inch or so of the spar (usually to the tail side of the spar), I go fly it. I then go inverted in a 45 degree upline and feel how much pressure I have to put on the elvator to keep it at 45 degrees. I adjust accordingly. I will also fine tune my CG by doing flat spins. The flatter the spin, the closer I am to it's sweet spot.

_____________________________

The USA is not a free country anymore

(in reply to jetmech05)
       Post #: 12

RE: cg dilemma - 5/16/2008 7:15:47 PM   
scratchonly


 

Posts: 945
Joined: 6/3/2006
From: winnipeg, MB, CANADA
Status: offline 		Be sure to start with your plane level; if it is sitting tail down or up this will influence the balance.

_____________________________

Real planes have two wings and round engines

(in reply to tazzzz)
       Post #: 13

RE: cg dilemma - 5/16/2008 8:21:44 PM   
RCPAUL


 

Posts: 619
Joined: 12/15/2001
From: Gahanna, OH, USA
Status: offline 		tazzzz


I have not had a Tiger 60 for quite a while but I remember that it will do as you say. If you push the tail down, it will stay that way even if it is balanced properly. Move the main gear back a little.

Paul

_____________________________

Gosh, model airplanes are not a matter of life and death --- they're more important than that!

(in reply to scratchonly)
       Post #: 14

Page:   [1]
All Forums >> RC Airplanes >> Questions and Answers >> cg dilemma
Page: [1]





Jump to: