measuring CG

[nuevo]

In various threads in this forum, I read about people setting their CG at 107mm, 112mm, etc. What machine measures CG to a repeatable resolution of 1mm?



I did find this cute jig somewhere on rcgroups. Don't want to use it on my planes. ;)

[KurtMc]

This is the single best $14.00 I've spent on tools for the hobby. Makes setting CG and adjusting it simple and accurate. My planes went from wobbly rolls to axial rolls when the CG was set dead on. Great tool!

http://www.mountainmodels.com/product_info.php?cPath=47_51&products_id=172
Kurt
http://www.laserarts.com/images/cgl.jpg

[Lite2bolt]

Greqt planes balancer has both inches and mm on the measuring sticks for each side. It also has littile rods that stick up and touches leading edge. That way it measures from leading edge back real easy. i have had no problems using it.

[Jurgen]

This Great Planes CG balancer is not precise, lost many time with the bugger ending in frustration:
http://www.greatplanes.com/accys/gpmr2400.jpg

This one from multiplex did very good (#693054):
http://www.hobbydirekt.de/images/product_images/info_images/069305402.jpg
Cheers, Jurgen.

[tewatson]

I'll second that. Very precise and easy to use.

Tom

This is the single best $14.00 I've spent on tools for the hobby. http://www.mountainmodels.com/product_info.php?cPath=47_51&products_id=172

[markdrela]

In various threads in this forum, I read about people setting their CG at 107mm, 112mm, etc. What machine measures CG to a repeatable resolution of 1mm? I turn the glider upside down, and balance it on a wood-pencil eraser.

[Lance Prior]

I like this one.

http://www.supertrc.com/details.asp?ProdID=62&category=12

[mr_editor]

I agree about the Multiplex being better than the Great Planes. Both do work but the MPX seems easier and more consistent.

[Avaldes]

Pencil eraser here, same as Mark.

[target]

I have a MPX balance stand. It was a gift. I had almost bought one during a group buy, and was bummed I didn't.

I was totally happy when a friend of mine that I cut some wing cores for told me he "Was going to send me a little something extra" with the check for the foam cores.
In to my hand came the MPX balance stand, and I WONT loan it out, EVER!

I LOVE it.

Target

[PDX Slope Pilot]

I love my MPX stand too. Tried all the rest and will never go back.

PDX

[Lance Prior]

Do you guys have a link to more info about MPX?

[mr_editor]

Multiplex (http://www.multiplex-rc.de/)

[Tuomo]

I love my MPX stand too. Tried all the rest and will never go back.


I think this is quite universial opinion among glider pilots. Great Planes stand may work in your living room, but I regard it more or less as a toy. Try using GP stand in the field while trimming or ballasting your glider :mad:

[nuevo]

what characteristic of the G.P. stand that earns such a bad reputation among some of you? Same question for the Multiplex stand. What makes it so good? Difficult to tell from a very few photos.

[Lance Prior]

I have used each of the balancing stand listed here except for the MXP and the one in my previous post works the best. The GP one is to fragile and spindly to work well, broke one of the little plastic rulers the first time I tried to use it. The other one kind of looks like a better solution but was wobbly and sort of tough to get it lined up correctly.

I should say that I don’t recommend using any of them to measure the CG position that is best done as recommended earlier by Mark. Instead what I do is set the arms to the cg measurement I want and tighten the little screws so they don’t move. Then place the model on the stand and bring it forward till the leading edge touches the arms then add or remove nose weight until it balances. Trying to do things the other way around by balancing the plane on the stand and then moving the arms to the leading edge to measure the cg doesn’t work very well on any of them.

[tewatson]

Just from a construction viewpoint, my guess is the GP stand suffers from flexing, particularly with planes heavier than your average woody. It looks to be made with fairly thin metal rod. The MPX appears to be made of larger cross-section square rod, and assuming a good fit between the legs and base sockets, would not have the same problem.

Tom

[atjurhs]

nuevo,

I have the Great Planes CG Balancer. It seams to work ok. I'd be willing to try others, and see how well they work. You can borrow mine anytime you want to.

[PDX Slope Pilot]

After using the MPX stand, the GP stand became junk for me. For F3X planes, the MPX stand is sturdier and supports the plane better. Measurement of the CG is also easier to read. The CG point on the MPX is on a pin rather than an unstable ball link.

[atjurhs]

I'd like to see a useable link for a US distributor where can one order an MPX stand?

[Neil Walker]

I have the GP stand and while I haven't tried any thing else, I have to think there's something better.

The pads that support the plane are over ball joints (nice idea) and big soft pads that support the wing (again nice idea) but they stick too much and it's very difficult to shift the model slightly to make small adjustments, and often a challenge to even get both pads at precisely the same spot on each wing.

The measuring arms that stick out from the support pads can move around too much. As a result it's very easy to get them at a slight angle (either vertically or horizontally), making the measurement longer than it should be. Combine this with the fussiness of getting the pads lined up evenly on the wings, and you've got a recipe for +/- a few mm.

Also as others point out it's a little flimsy.

[wakumann]

I have a CG stand, but always use my 2 FINGERS.

With a tiny F5D ship this may not work, but with F3X planes it's good enough.
Fishing line taped on both side works also well (proven for up to 16 lbs glider)

m2c
Thomas

[atjurhs]

Fishing line taped on both side works also well (proven for up to 16 lbs glider)

m2c
Thomas

I like that idea! You could even tie a loop in the fishing line and slide it over the wing tips down to the roots. Then suspend the plane from the loops attached to your wife's favorite chandelier :D

[bobthenuke]

The measurment arms on the GP balancer are not balanced themselves and add a bias to the CG. I had a heck of a time with DLG balance until it occurred to me that everytime I checked the CGs with it, they were way off - biased by the weight of the measurement arms. I guess the GP balancer is OK for larger planes in which this bit of offset is negligable.

I have now reverted back to the old standby from years gone by - a block of wood with two dowel pegs with wedgie pencil erasors at the ends. Another plus for the KISS principal.

-bob

[target]

MPX unit has sliding weights to compensate for longer/shorter cg measurements from the LE....

T