New Products Flash Sale
Thread Tools
Old Sep 21, 2015, 09:55 AM
Bellke is offline
Find More Posts by Bellke
Registered User
Bellke's Avatar
United States, AZ, Gilbert
Joined Oct 2014
40 Posts
Discussion
Finding the CG on a Large Plane

How do you find the CG on a larger plane? With a small foamy you can set it on a balance stand. On a larger plane I'm sure you could make a larger stand, but then it would punch through the covering on the bottom of the wing. I guess my question is what contraption is used to determine where the CG is located at on a plane with a 72" or 108" wingspan that may weigh 10-15 lbs? Pictures would be great.

Thanks
Bellke is offline Find More Posts by Bellke
Reply With Quote
Sign up now
to remove ads between posts
Old Sep 21, 2015, 12:04 PM
grosbeak is offline
Find More Posts by grosbeak
Illegitimi non carborundum
grosbeak's Avatar
Canada, ON, Ottawa
Joined Mar 2011
2,244 Posts
Hey Bellke,

Check this out - it's my go-to method for larger planes.

http://testorcc.webs.com/TopCap/2008/topcap2008-feb.pdf
grosbeak is offline Find More Posts by grosbeak
Reply With Quote
Old Sep 21, 2015, 07:52 PM
bhady is offline
Find More Posts by bhady
Registered User
Fairmont MN
Joined Jun 2006
95 Posts
I use a "Vanessa" rig, simple to use and set up. Works very well on any size plane. Search the forms here on RCG and RCU
bhady is offline Find More Posts by bhady
Reply With Quote
Old Sep 22, 2015, 06:11 AM
ARUP is offline
Find More Posts by ARUP
Registered User
Joined Mar 2010
2,608 Posts
http://scalesoaring.com/forum/forum/...-balance-stand
ARUP is offline Find More Posts by ARUP
Reply With Quote
Old Sep 22, 2015, 07:52 AM
tacx is offline
Find More Posts by tacx
Registered User
tacx's Avatar
United States, MI, Washington
Joined Apr 2009
3,481 Posts
Use a "Vanessa" rig, as bhady suggests. Easy to make and easy to use.

But, you should also be able to cobble together a cheap stand. If you build the stand so the "resting feet" are right next to the fuse there should be some solid sheeting in that area to prevent damage to the wing.
tacx is offline Find More Posts by tacx
Reply With Quote
Old Sep 22, 2015, 10:38 AM
grosbeak is offline
Find More Posts by grosbeak
Illegitimi non carborundum
grosbeak's Avatar
Canada, ON, Ottawa
Joined Mar 2011
2,244 Posts
Quote:
Originally Posted by tacx View Post
...you should also be able to cobble together a cheap stand. If you build the stand so the "resting feet" are right next to the fuse there should be some solid sheeting in that area to prevent damage to the wing.
I made one of those for my smaller airplanes. Adjustable base and a strip of rubber on the tips to ease the pressure.



grosbeak is offline Find More Posts by grosbeak
Reply With Quote
Old Sep 23, 2015, 08:10 AM
solentlife is offline
Find More Posts by solentlife
222 km/hr Parkjet flyer
solentlife's Avatar
Latvia, Ventspils pilsēta, Ventspils
Joined Jan 2010
14,052 Posts
I use the Hobby King CoG tester ... and that's supported my 1.6m Zlin machine with no problem and no marks.

Nigel
solentlife is offline Find More Posts by solentlife
Reply With Quote
Old Sep 23, 2015, 12:34 PM
bogbeagle is offline
Find More Posts by bogbeagle
Registered User
Joined Mar 2007
1,969 Posts
Big planes ... take moments.
bogbeagle is offline Find More Posts by bogbeagle
Reply With Quote
Old Sep 23, 2015, 12:44 PM
exf3bguy is online now
Find More Posts by exf3bguy
Registered User
exf3bguy's Avatar
United States, CA, Sacramento
Joined Oct 2011
2,625 Posts
Get it close enough to safely fly then adjust according to how the airplane is flying. Setting CG is like setting engine mixture. It needs to be fine tuned after a couple initial flights. IMO spending a lot of time setting your CG to an arbitrary location is a waste.
exf3bguy is online now Find More Posts by exf3bguy
Reply With Quote
Old Sep 23, 2015, 01:01 PM
ARUP is offline
Find More Posts by ARUP
Registered User
Joined Mar 2010
2,608 Posts
I really like the stand recently purchased in my above post. The model can be trimmed for best c.g. then measurements can be saved for future reference, say, if another flier wants to duplicate your model or compnentry is changed. This stand very accurately measures any balance point via a scale. It's really a well thought out instrument!
ARUP is offline Find More Posts by ARUP
Reply With Quote
Old Sep 23, 2015, 03:12 PM
solentlife is offline
Find More Posts by solentlife
222 km/hr Parkjet flyer
solentlife's Avatar
Latvia, Ventspils pilsēta, Ventspils
Joined Jan 2010
14,052 Posts
Quote:
Originally Posted by ARUP View Post
I really like the stand recently purchased in my above post. The model can be trimmed for best c.g. then measurements can be saved for future reference, say, if another flier wants to duplicate your model or compnentry is changed. This stand very accurately measures any balance point via a scale. It's really a well thought out instrument!
Similar concept to HK's that I use.

Nigel
solentlife is offline Find More Posts by solentlife
Reply With Quote
Old Oct 22, 2015, 12:18 PM
E-Challenged is offline
Find More Posts by E-Challenged
Registered User
E-Challenged's Avatar
United States, CA, Garden Grove
Joined Oct 2000
13,964 Posts
However you do it, have model a little nose-heavy and adjust as needed removing nose weight and using elevator trim after maiden flight. A little down and right engine thrust is good too.
E-Challenged is offline Find More Posts by E-Challenged
Reply With Quote
Old Oct 30, 2015, 07:29 AM
SrTelemaster is offline
Find More Posts by SrTelemaster
I HATE GLOW PLUGS!
SrTelemaster's Avatar
United States, NY, St Lawrence
Joined Feb 2012
1,703 Posts
Quote:
Originally Posted by Bellke View Post
How do you find the CG on a larger plane? With a small foamy you can set it on a balance stand. On a larger plane I'm sure you could make a larger stand, but then it would punch through the covering on the bottom of the wing. I guess my question is what contraption is used to determine where the CG is located at on a plane with a 72" or 108" wingspan that may weigh 10-15 lbs? Pictures would be great.

Thanks
Here's a 110" WS 13# aircraft on a balance stand.


It's rated for 2-40# & has enough wing chord capacity for much larger planes than this one.
SrTelemaster is offline Find More Posts by SrTelemaster
Last edited by SrTelemaster; Oct 30, 2015 at 07:48 AM.
Reply With Quote
Old Oct 30, 2015, 08:01 AM
bogbeagle is offline
Find More Posts by bogbeagle
Registered User
Joined Mar 2007
1,969 Posts
Nowadays, I build-in some means of supporting the model at its CG, whenever I can.

This might be a hole drilled through the fuselage, at the balance point. A thick wire can then be passed through and used as a pivot point from which to suspend the model.

It might be a hard-point in the wing, such that a hook can be screwed in, and the airframe thus supported.

One of my models has a pylon which supports landing wires. I designed this so that its apex coincides with the desirable CG position.

Obviously, these things are more tricky if you are building serious scale models. Scale modellers will just have to do it the hard way, I guess.

.
bogbeagle is offline Find More Posts by bogbeagle
Reply With Quote
Old Oct 30, 2015, 01:14 PM
600Bob is online now
Find More Posts by 600Bob
Registered User
United States, OR, Canby
Joined Aug 2011
3,276 Posts
I have a 1/4 scale Cub and an 88" WS Tiger Moth, both weigh about 17 lbs. I just balance them on my finger tips, I don't have any kind of balance rig.
600Bob is online now Find More Posts by 600Bob
Reply With Quote


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Advice on best way to find CG on f550 with landing gear? Troiano27 Multirotor Electronics 1 Sep 04, 2015 06:18 AM
Discussion *Finding CG On A Hexacopter* olezippi Multirotor Talk 0 Jul 10, 2015 06:52 AM
Discussion Finding the CG on a plane with on a lifting body flyonline Slope 1 May 06, 2008 03:04 AM