Home made adjustable CofG frame/cradle thingy

[Tony Kenny]

OK, so trying to balance 3.5kg of delta wing on my finger tips, putting it down, adjusting, picking up again, taking an eye out, bump on the head... there had to be a better way, without spending any more money!

A few scraps and bits of things I just refused to throw away over the year managed to come together into am adjustable stand that I can use for all my planes and means I can tweak without having to constantly pick up and put down!

It's maybe not all that special but thought it worth sharing just in case anybody had a similar thought.

 

Edited By Chris Bott - Moderator on 03/06/2019 19:58:20

[Tony Kenny]

By the way, see the first image... if anybody can think of a better use of the handles on a treadmill, please do let me know!

[Mark Kettle 1]

Very good Tony, its always a more consistent method to balance a model.

Here's Tim Mackey's balancer being used to balance my epp Spitfire glider in its development stage.

Made from wood, two frames with arms that are kept separated by threaded rod and some thin steel finger pieces that contact the wing.

[Tony Kenny]

That's a great one and also very precise

Because I've got models of various different fuz widths, the arms can be altered by loosening the screws at each end and sliding the arms sideways. To enable that, I've used screws from an old flat pack and some very wide washers under the centre boards. Best I could come up with at short notice and the bits I had to hand.

[eflightray]

There is also the 'Vanessa CG Rig' -- **LINK** -- but it does require having a 'sky hook'.

But then a measured CG is often just a starting point, flight testing will then determine where you like it to be, the 'sweet spot'.

[Martin Harris - Moderator]

Just a tip boom boom!

...you've done very well to balance your models - especially the first one - to take the photos but low wing models are normally much easier to balance inverted so that the 3 dimensional C of G is below the pivot point.

[Erfolg]

The first is much the same as my own, hewn from tree trucks.

A slightly more sophisticated version, does not have radiused tops, which risk damaging a model, especially when they are heavy, is to have the point as a pivoted hinge. I have seen this done several ways. One has horizontal bar either side of the pivot or hinge. The other is to use the same radiused end with a bar, where a central conical or semi spherical hole has been produced, The intention in both cases is spread the load, and provide a clear reference point for the pivot (works well only when the location point is near the upper surface, other than that hilarious.

[cymaz]

A Vanessa rig is good. Not forgetting that it tells you where the CG is not where it should be.

[Geoff S]

You did extremely well to balance those low wing models the right way up. They usual practice, as Martin Harris says, is to balance inverted.

Of course, like every CoG jig I've seen so far, it doesn't work on biplanes Then it's fingers.

Geoff

[PatMc]

Knocked this balance weight measurer [is there such a word] up in 15 mins from bits that were around my garage/workshop :

Drilled 2 x 8mm holes at fuselage width + a bit apart in scrap of 60mm sq wood, plugged in pencils, placed assembly on digital scales.

Desired balance point is marked as chordwise lines on each wing. Model is placed on pencils to balance level on it's wings at wherever it happens to balance, in similar manner as the OP photos. Digital scales are now switched on & should give a zero reading.
With the scales still switched on the model is now removed & replaced with the pencils this time on the balance lines.
Assuming it's tail heavy, the model is held steady at the tail with one hand then pressed down at the nose with a finger of the other hand on the point any weight would be added to achieve balance until level. The steadying hand is removed, leaving only the finger on the nose to hold the model level. Now read the weight indicated on the scales. That gives the amount of weight & the point to fit it to achieve balance.

Easier done than written.

 

 

Edited By PatMc on 16/09/2017 19:56:08

[john stones 1 - Moderator]

Copy cat.

[Stevo]

I know it's not home made, but got one of these years ago. You can set the CoG measurement on the top then balance the model.

Just a hint for your DIY balancers!

Edited By Stevo on 16/09/2017 20:24:32

[Erfolg]

Yes, Stevo, that is what I was trying to describe.

Oh, er, is that my balancer, Patmac? Although I have Never thought to use the kitchen scales in that manner. In my case i put the mixing bowl that came with it on top, then the model.

Edited By Erfolg on 17/09/2017 15:02:39

[PatMc]

Posted by Erfolg on 17/09/2017 15:02:20:

Oh, er, is that my balancer, Patmac? Although I have Never thought to use the kitchen scales in that manner. In my case i put the mixing bowl that came with it on top, then the model.

My method tells you the weight required & where it needs to be fitted to achieve the correct balance point [AKA "CG"].

[Erfolg]

I take on board the brilliance of the scale usage.

As my electric models have increased in size, more importantly weight, which puts quite a force onto the balance points. I have increasingly considered improving my CG balancer, by adding arms as per the Stevo concept, this also almost makes the use of the horizontal legs to provide stability a must have. In principal is sounds good, other than i always have storage issues, for what is used a few times a year. Are there any designs out there which incorporate the functionality of the Stevo balancer, and the feature of breaking down into a small set of units for storage.

[Gordon Tarling]

Erfolg - the balancer which Stevo shows is this one - it breaks down easily for storage and should be available from your local Multiplex dealer.

[Eagle 899]

Posted by Stevo on 16/09/2017 20:24:05:

I know it's not home made, but got one of these years ago. You can set the CoG measurement on the top then balance the model.

Just a hint for your DIY balancers!

Edited By Stevo on 16/09/2017 20:24:32

I use the HK one which works the same as Stevo's but cost less than a tenner

Edited By Eagle 899 on 18/09/2017 14:19:00

 

Edited By Eagle 899 on 18/09/2017 14:24:07

[Stevo]

I think I bought mine 20 years ago!!