2 tools from skyrc for plane guys. looks awesome.

[kallend]

So, what I was trying to ascertain was, by using these “weigh scales” under each wheel, does it tell me exactly where the CG of a plane is, which may not necessarily be the same as what the book recommends?

That is a whole different question. Being able to precisely locate the CG in a position that might not be correct is clearly a concern. I know of several models where the manual gave a totally wrong value and had to have corrections made (The HK Lancaster V1 is an example I remember without even having to look it up). I shall continue to use my fingers.

If I really needed to do it by weighing on a heavy model, I'd use digital kitchen scales (much cheaper and just as accurate) and do the math myself. The math is no harder than balancing a teeter-totter or see-saw)

And I still intend to use a ruler to measure control surface deflections.

[Twowingtj]

The typical CG stand works great until you try to balance a biplane or something with the gear or struts that hit the stand posts. They are also limited to weight capacity.

I used a Vanessa rig for quite a while. Even that is a challenge when trying to heft a 30+lb plane and try to keep it from spinning around.

This setup takes care of the above challenges. You do have to ensure that the plane is perfectly level and ensure that your measurements are accurate. Using a cross style laser level helps make this easier.

[xviper]

When I first started flying nicer (read: more expensive) planes, I got one of those balancers that you prop the plane up under each wing. There was a gauge that you use to dial in the recommended CG to show exactly where to prop the plane up. Then you move the battery around till the plane balanced level. This, of course depended on what the manual said to use for the CG, which may or may not be the best place for the best flying characteristics. This method proved to be very cumbersome so I stopped using it and just used my fingers and continue to do so to this day.
So, what I was trying to ascertain was, by using these “weigh scales” under each wheel, does it tell me exactly where the CG of a plane is, which may not necessarily be the same as what the book recommends? Am I correct to say that kallend’s answer gave this result? That being the case, using these scales, there is really no need to even look at the book CG, since like the book CG, it’s still a starting point and the final CG will be determined by “trial and error” during actual flight testing, yes?

[mongo]

it is the bling, baby, gotta have the bling...

[kallend]

Can someone explain how these work? Do they figure out where the best CG should be, regardless of what the recommended CG is? Or do they tell you exactly where the recommended CG is?

They measure the weight on each of the wheels, and knowing the position of the wheels you can calculate the moments (force x distance) from any given location. Since all moments have to sum to zero at the CG, you can calculate where the CG is.

It's how it's done on full size aircraft where you can't balance them on your finger tips (or a simple balance stand, $30 on eBay, less if you make your own).

May be worthwhile for a really heavy model (say 20kg or more). Anything lighter a balance stand works fine, and can give you the CG within a mm or so. How much more accuracy do you need?

I certainly don't know why an electronic instrument is needed to measure elevator or aileron deflection. What's wrong with a ruler?

[bob_nj]

Do they figure out where the best CG should be

Not exactly.
It will tell you where it is, COMPARED to the recommended CG.
We use a similar method for our unmanned systems.
Granted, it's meant for larger aircraft, but the theory stays the same for RC.
It is a bit overkill, but like I said, I'm a tool junkie.
Things like this are one of my ways of keeping up.
As we age, things are different.

Cool tool...

[xviper]

Can someone explain how these work? Do they figure out where the best CG should be, regardless of what the recommended CG is? Or do they tell you exactly where the recommended CG is?

[serpentracer]

I'm a tool junkie, and like these a lot, but it doesn't show a price, or how to get them.
Have you ordered from there before?

Thanks, and take care
Bob

looks like helidirect has them as a set https://www.helidirect.com/collectio...-wing-airplane

[Twowingtj]

I've got the Xicoy setup. Definitely worth every penny. No more guess work or "that looks about right".

[kallend]

Pass.

I find my fingers work very well for CG, and a cheap ruler works nicely for control surface deflections.

[bob_nj]

I'm a tool junkie, and like these a lot, but it doesn't show a price, or how to get them.
Have you ordered from there before?

Thanks, and take care
Bob

[serpentracer]

these look like a huge leap in technology for setting up airplanes. I searched but didn't see any posts about these.

the electronic CG gauge https://www.skyrc.com/Accessory/cgg-020
the electronic angle gauge https://www.skyrc.com/sam-020?from=nav