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-   -   CG stands (https://www.wattflyer.com/forums/showthread.php?t=80325)

zoltron55 08-28-2019 10:31 PM

CG stands
I have been looking for a cg stand . HK stand looks cheap , great planes looks ok or do I go youtube & build my own. I like how both ready made stands let you set how far from the LE the cg is what is your opinions ?

Wildflyer 08-28-2019 11:59 PM

I made a CG stand out of a few boards and a couple of shelf brackets.
Bottom is a wide board able to handle the weight of the plane without tipping over. You don't want a 5lb plane on a 1x2.

Vertical supports are 1x4 boards fastened to the shelf brackets but not screwed to the bottom unless you want. I can move the shelf brackets around for small or big airplanes.

Cross boards centered at top of the verticals are about 12" long flat. there is a 1/2" high triangle shaped piece in the center of the cross board, with dimensions running forward measured from the peak of the triangle which is rounded so no damage.

I did it this way so that I can set the plane on the triangle points with the correct distance back from the leading edge, and it won't fall off the whole thing if it is out of balance. The plane just tips a little until the trailing edge or leading edge is touching the cross board.
I have one of the fancy units but the plane can fall off while you are working on it. I don't use it any more.

solentlife 08-29-2019 07:58 AM

I have the Hobby King CoG stand and its CRAP !

Its fine for small stuff ... but anything more than a Parkflyer light machine is not so easy to sort.

The horizontal arms 'float' on top of ball joints loose ... if they were clicked onto the ball joints sintaed of the grub screws - it would be much better. The screws when wound in to stop arms falling of - then restrict pivoting motion.
As Wildflyer says - plane falls off if not correct CoG.

Much better to just ditch the arms and put hard foam balls or eraser rubbers onto the ball joints ..

I have it there on the bench ... but my preferred way now is the old two fingers job ...

solentlife 08-29-2019 10:01 AM

At times I look at the Hobby King CoG set-up and try to figure out how to improve on it.

The HK page shows this :


Which as most people know - the Stinger in the frame should be inverted. That photo must be 'rigged' by fixing the arms rigid to hold it.

This is the problem :


That metal round section is a cup that sits on a ball joint on top of the leg. It is prevented from falling of the ball by a set screw threaded in under the ball. If you use that screw, then the balance arm is restricted in its movement, as the screw binds with the underside of the ball. Slacking off to working solution - the balance arm then can fall off !


As I said earlier - its OK for small to moderate sized models of say 1kg max .. but as long as they are not large such as sailplanes !

I have toyed with the idea of making an axle based pivot system instead of the ball joints. With as Wildflyer describes - long arms extending to catch the model if it tips when out of balance.

solentlife 08-29-2019 12:29 PM

The Hobby King CoG stand - after carefully thinking about it - it dawned on me how to cure the design fault in it.

The grub screw that stops the balance assembly from falling of the pivot ball - restricts the movement of the balance arm as it hits the pin its sitting on. The grub screw is threaded in the pitch moment part of the support :


The movement is such :

Opposite to the screw and plenty movement ...


But in same as the screw - the movement is substantially less ...


The solution was simple ! Drill and tap into the side so that the screw never interferes with movement :


Now the balance arm is secure - but free to give all movement both fore and aft.

zoltron55 08-29-2019 09:33 PM

I like that idea that was 1 of the bigger complaints about that stand

solentlife 08-30-2019 09:01 AM

Its funny that your question about stands made me drag mine out and dust it off .. then I sat looking at it to figure out how to improve it !!

Will I now use it ? Maybe ... but the two fingers are far easier !!

zoltron55 08-30-2019 10:09 PM

thanks guys I am going to build 1 out of 1/2 " pvc pipe (13mm to you metric guys ) I'll show pics when done if I see the HK one at a swap meet I might give it a shot

solentlife 08-31-2019 08:05 AM

The price of the Hobby King unit is peanuts really ... the wood part with the ability to vary the distance between to accommodate different fuselages is worth it on its own.

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