Go Back  RCU Forums > RC Airplanes > Kit Building
Reload this Page >

How to balance properly

Notices
Kit Building If you're building a kit and have questions or want to discuss kit building post it here.

How to balance properly

Old 07-25-2009, 08:25 AM
  #1  
outdoorhunting
Senior Member
Thread Starter
 
Join Date: Sep 2006
Location: Bradenton, FL
Posts: 2,057
Likes: 0
Received 0 Likes on 0 Posts
Default How to balance properly

OK. I'm stupid,I admit it. Now that's over with. I know you balance a "high wing" right side up. A "low wing" inverted,& that's worked great for me ! However, I've been getting into "midwings" & the only way I seem to be able to balance them is "right side up". If I try to balance them "inverted" it's impossible!! If I "flip " it over, it'll balance quickly. I use the Great Planes balance machine. I can spend all day trying to get a midwing to balance inverted & NOT get anywhere. It seems that the "midwings" are a tad "squirrely" or a maybe a better description would be "touchy to the controls". Is that because of balancing or the "nature of the midwings? When flying, the planes doesn't fly "tailheavy" or anything. Can somebody explain ?? Thanks for any response
Old 07-25-2009, 10:59 AM
  #2  
andrew66
Senior Member
 
andrew66's Avatar
 
Join Date: Jan 2006
Location: Brandon, MB, CANADA
Posts: 1,057
Likes: 0
Received 0 Likes on 0 Posts
Default RE: How to balance properly

What type of plane is it? When i balanced my SSE i just balanced it right side up. If it is touchy, you could add a bit of expo into the radio (assuming you have a computer radio) When i set up my plane, on the first flight, i could only use very slight controll inputs, or the plane was "all over the sky" I think i put as much as 50% in the ailerons, and 70% in the elevator
Old 07-25-2009, 01:11 PM
  #3  
outdoorhunting
Senior Member
Thread Starter
 
Join Date: Sep 2006
Location: Bradenton, FL
Posts: 2,057
Likes: 0
Received 0 Likes on 0 Posts
Default RE: How to balance properly

GP Extra 300S (60) kit.I put a "90" Super Tigre in it ( notice the statement at bottom of post). I worked 1/2 a day trying to balance it inverted. It wouldn't balance right. I could get it almost perfect (14oz. lead in the nose) & it would either slowly start drifting down or up on the balance machine. I finally turned it upright to try it & it took 3/4 oz. to get slightly nose heavy. I flew it & it seemed to be a little "tail heavy" It's all for naught as about 2 mins into maiden it "tip stalled" & augered. The plane was totaled. Although, I hate it that I wrecked it, it would be nice to know for future reference.
Attached Thumbnails Click image for larger version

Name:	Jh15154.jpg
Views:	9
Size:	74.5 KB
ID:	1243312   Click image for larger version

Name:	Pk30837.jpg
Views:	14
Size:	82.8 KB
ID:	1243313  
Old 07-25-2009, 03:53 PM
  #4  
GAP-RCU
Senior Member
 
Join Date: Nov 2002
Location: Round Rock, TX
Posts: 417
Likes: 0
Received 0 Likes on 0 Posts
Default RE: How to balance properly

Use whichever way, upright or inverted, that is stable on your balancing machine.

For either upright or inverted, the plane is stable if... the plane is on the balancer and is balanced level, and you push the nose or tail down a slight amount, it should return to level. If you push the nose or tail down, and the plane continues to fall over, then flip the plane over. Once you've figured out which way is stable, then proceed with adding weight to balance at a specific location. Use the same approach if you just balancing with your fingers.

As for locating the forward-aft position of the cg, the plane doesn't care if it's upright or inverted. We just choose either so it's stable on the machine (or fingers).

Hope this helps, and I didn't misunderstand your question.
Old 07-25-2009, 05:41 PM
  #5  
Campgems
Senior Member
 
Join Date: Feb 2006
Location: Arroyo Grande, CA
Posts: 4,465
Likes: 0
Received 0 Likes on 0 Posts
Default RE: How to balance properly

I've got to pass on the tip I picked up at the field the other day. Tie a string to each wheel axle and the tie them to gether and hange the plane from the center of the three strings. Drop a plumb bob from the same place you are hanging the plane from. Let it settle down. The plumb bob will be poiinting at the CGof the plane. You can then add weights to get the CG where you want. The plane suspended by three strings from a common point will always setttle with the CG directly under that point. I expect you could do the same with a string tied to the outboard aileron hinge on each wing and one tied to the prop shaft. or a string on each elevator outboard hinge and the third on the engine. As long as the three attachment points such that the actual and desired CG are between them, it will work, right side up or upside down.

This will not work outside or in front of an open window, it has to be in dead air so the only thing affecting where it settles down is gravity.

Don.
Old 07-25-2009, 06:38 PM
  #6  
GAP-RCU
Senior Member
 
Join Date: Nov 2002
Location: Round Rock, TX
Posts: 417
Likes: 0
Received 0 Likes on 0 Posts
Default RE: How to balance properly

Campgems' method is the thing to do when a plane is unstable on a balancing machine in both the upright and inverted positions. This may happen occasionally when the vertical position of the cg is just right - usually right in line with the cordline of the wing.
Old 07-25-2009, 07:07 PM
  #7  
smithcreek
My Feedback: (25)
 
smithcreek's Avatar
 
Join Date: Jun 2008
Location: Westerly, RI
Posts: 1,064
Likes: 0
Received 0 Likes on 0 Posts
Default RE: How to balance properly

That sucks, looked like you did a nice job. I finished that kit a couple months ago. I could be wrong, but I considered it a low wing plane and balanced it inverted. I didn't run into the same problem as you, balancing was pretty straightforward.
Old 07-25-2009, 07:28 PM
  #8  
Campgems
Senior Member
 
Join Date: Feb 2006
Location: Arroyo Grande, CA
Posts: 4,465
Likes: 0
Received 0 Likes on 0 Posts
Default RE: How to balance properly


ORIGINAL: outdoorhunting

GP Extra 300S (60) kit.I put a "90" Super Tigre in it ( notice the statement at bottom of post). I worked 1/2 a day trying to balance it inverted. It wouldn't balance right. I could get it almost perfect (14oz. lead in the nose) & it would either slowly start drifting down or up on the balance machine. I finally turned it upright to try it & it took 3/4 oz. to get slightly nose heavy. I flew it & it seemed to be a little "tail heavy" It's all for naught as about 2 mins into maiden it "tip stalled" & augered. The plane was totaled. Although, I hate it that I wrecked it, it would be nice to know for future reference.
I put a repaired plane back in the air about two weeks back. White knuckles and I was astonded that I got it down in one piece. It was tail heavy to th extreem. I re-caculated the CG and found I needed 9 oz up front to balance it you. Ifabercated a huge weight and bolted it under the engnine. Well It flew OK, none of the wild pitching from the first flight, but it took about 3/4 down to hold it level when Inverted. Obviously 9 oz was to much. I drilled out an ounce when I got home and the next fly day, things were better, but still a tad nose heavy. More drilling, better but not quite there yet. I then pulled the remainder of and moved the engine ahead the length of th mounting lugs. Better but still not there. I moved the engine back and fabed up some lead sheet and by now, I was down to 2oz. I could now pull off weight at the field with little effort and today, It was just about as good as you could get. Very slight down to hold it level when inverted, actually almonst none. Inow am right back to the balance I initally started with that was "way tail heavy". I think I was just letting the adrenillan take over and was over sticking the plane on the first flight. If flys very well now. Nothing moved nothing added, and nothing taken away.

After all the ribbing about the boat anchor I put on for weight, I was a little red faced telling the guys what I found.

Just a work of advise, first flight should be noticably nose heavey. It may not fly the best, but you will get it back down and can work your way down to the correct banlance.

Don
Old 07-25-2009, 08:41 PM
  #9  
gboulton
My Feedback: (15)
 
gboulton's Avatar
 
Join Date: May 2005
Location: La Vergne, TN
Posts: 3,743
Likes: 0
Received 0 Likes on 0 Posts
Default RE: How to balance properly

The following will come as a huge shock to those who know me, I'm sure.

=======

[link=http://home.mindspring.com/~the-plumber/Vanessa%20CG%20Machine.htm]Vanessa CG Machine[/link]

Elegant, simple, inexpensive (can probably be made from parts you have around), and will locate AND help you adjust the Cg of anything from a 4 oz foamy to a 33% Pitts S2S Biplane and beyond.

Not to mention, it's a darn handy instructional tool as well!
Old 07-26-2009, 06:17 AM
  #10  
sgillmore
My Feedback: (50)
 
sgillmore's Avatar
 
Join Date: Jul 2003
Location: Jefferson City, MO
Posts: 294
Likes: 0
Received 0 Likes on 0 Posts
Default RE: How to balance properly

I can vouch for the Venessa CG Machine. I've been using this method for years with everything from high-wing trainers to bi-planes. It works great. One real advantage to the Venessa is that you can balance a large plane by yourself. I used it to balance my 50cc Yak (18lbs/87" WS) a couple weeks ago with no help. I've attached a couple pics of my setup if it helps to visualize the system. I used a arrow head for the plumb bob (just don't screw up and drop it into the covering!
Attached Thumbnails Click image for larger version

Name:	Db86172.jpg
Views:	15
Size:	81.2 KB
ID:	1243675   Click image for larger version

Name:	Sn40310.jpg
Views:	14
Size:	101.5 KB
ID:	1243676   Click image for larger version

Name:	Fk16725.jpg
Views:	12
Size:	104.8 KB
ID:	1243677  
Old 07-26-2009, 12:31 PM
  #11  
Gray Beard
My Feedback: (-1)
 
Join Date: Apr 2003
Location: Hemderson, NV
Posts: 14,394
Likes: 0
Received 6 Likes on 6 Posts
Default RE: How to balance properly

I have always done what Gap and Don are doing. In my old shop in Calif. I had both my CG machine and I had a pully set up for the old plumb bob system.
I have a question about the Vanessa CG Machine though. I plan on putting one in my new shop.
When using Vanessa don't you still have to know the Datum Line and have a level on it to get the CG?? I have read the instructions and it seems like something is missing?? Or is it just that the dowel rolls so the plane tilts.
Never mind, I got it!! The fog from the brain fart disapated and I can now see the light!! Takes me a while but I usually get it!!!
Old 07-26-2009, 06:07 PM
  #12  
gboulton
My Feedback: (15)
 
gboulton's Avatar
 
Join Date: May 2005
Location: La Vergne, TN
Posts: 3,743
Likes: 0
Received 0 Likes on 0 Posts
Default RE: How to balance properly

LOL Gray Beard! I have that problem myself!

The question you asked, though, probably does bear some discussion.

it's worth noting...the Vanessa does NOT tell you where the CG should be. That information is up to the modeler to determine, by any one of the numerous methods available. (Manual, experience, forumlas, whatever)

What the machine does tell you is where the CG is. Rotate the dowel to bring the aircraft level (again...knowing where the datum line is is the modeler's responsibility, though NEARLY every airplane has a 0 degree incidence surface SOMEwhere *heh*), and when the plumb bob stops moving, it IS pointing at the CG.

Another recent thread on this topic brought up a GREAT modification that I've made to my own...forgive me, i do not remember who the user was that came up with it.

He used a laser pointer instead of a plumb bob...nice red dot right on the CG. It's a FANTASTIC upgrade. I'm currently working on trying to come up with a method that will lock the "laser pointer" in place, relative to the airplane's yaw axis, so i can substitute a laser LEVEL, and project a line across the entire wingspan.
Old 07-26-2009, 07:04 PM
  #13  
Rcpilot
My Feedback: (78)
 
Rcpilot's Avatar
 
Join Date: Mar 2002
Posts: 7,793
Received 9 Likes on 8 Posts
Default RE: How to balance properly

I've yet to balance a plane and have it fly perfectly on the maiden. Every plane needs CG adjustments to get it trimmed in. There is no point in trying to get it balanced EXACTLY in the middle or on the front of the recommended range.

So set it somewhere close to the manufacturers recommendation and go fly it. Adjust for the type of flying you want.
Old 07-27-2009, 08:04 AM
  #14  
MinnFlyer
Senior Member
My Feedback: (4)
 
MinnFlyer's Avatar
 
Join Date: Apr 2002
Location: Willmar, MN
Posts: 28,519
Likes: 0
Received 7 Likes on 7 Posts
Default RE: How to balance properly

outdoorhunting, Here is a very short article that explains why some planes balance right-side-up and others upside-down.

It doesn't cover mid-wings, but once you read it, you will understand which way is better for you:

http://www.rcuniverse.com/magazine/a...article_id=601
Old 07-27-2009, 11:46 AM
  #15  
Gray Beard
My Feedback: (-1)
 
Join Date: Apr 2003
Location: Hemderson, NV
Posts: 14,394
Likes: 0
Received 6 Likes on 6 Posts
Default RE: How to balance properly


ORIGINAL: Rcpilot

I've yet to balance a plane and have it fly perfectly on the maiden. Every plane needs CG adjustments to get it trimmed in. There is no point in trying to get it balanced EXACTLY in the middle or on the front of the recommended range.

So set it somewhere close to the manufacturers recommendation and go fly it. Adjust for the type of flying you want.
You poor dear!! Don't worry, maybe some day it will happen!! Just stick with it and keep trying!!!
Old 07-27-2009, 12:00 PM
  #16  
MinnFlyer
Senior Member
My Feedback: (4)
 
MinnFlyer's Avatar
 
Join Date: Apr 2002
Location: Willmar, MN
Posts: 28,519
Likes: 0
Received 7 Likes on 7 Posts
Default RE: How to balance properly

Rcpilot is correct. What is perfect for one person is too sensitive for another (or vice-versa)

Get it close, keep it toward the nose-heavy side and fly it. Then adjust as necessary.

For me, I rarely even bother to balance it again. I'll just add a few ounces of lead, or shift the battery around and try it again. If it's still not right, repeat as necessary.

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell or Share My Personal Information -

Copyright © 2023 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.