Rigger Balance

[Simon.O.]

Yes I know I research myself to insanity most of of the time and I love it.
I am now after rigger balance points.

Call it Cg, CofG, CB, CofB or what ever you want. There are 2 numbers I need for this survey or 1 if you already have the answer.

Dim#1 Afterplane length, from rear of sponson wet rear to prop dog.

Dim#2 Balance point aft of sponson wet rear

If you already have the % fig at hand then please post that up.

I am asking all of this again as I know a lot of things have changed over the years and I want to see where most riggers run the point of balance.

I run a very tight oval so slow turn and wot passes. Solo only for those who don't know me well.

[martin]

Ive seen figures of 60% of the model weight when you sit the sponsons running edge on the scales & 40% with the prop on the scales. Martin.

[Fluid]

It all depends on the model and its speed. The most common CG% value is 15-20% of the afterplane length behind the sponsons. The 60/40 weight values are really more relevant, but few use them. Even still they are guidelines, not absolutes.


.

[m4a1usr]

Since you are running an oval configuration I would say to stay focused on COB approx to the turn fin. But Jay is right about speed and weight. I can add this too. Also depends on if your running a lifting prop. One of my rules is to increase lift the further back the COB ends up. Seems to work for me as long as the strut is adjusted as well.

I am one of those who probably confuses the normal term reference. I use COB only because I worked in the rigging world for a few years. Never confuse COG with COB in that arena. They are totally different creatures. And when I state COB that means a hulls balance in both the front/back (Pitch) and left to right (Roll) axis. I normally dont care about Yaw since the assumption is a hull is true and will not pull to one side or direction excessively. Most hobbyists tend to describe COG as just the Pitch effect.

John

Here is some of the very basics for those curious; http://www.modelpowerboat.com/conten...-hull-attitude

[pda75]

Hi,

I have done some research on that topic and would be more than happy to get a feed back from your survey.

What is key is the lift of the prop, which must be balanced by the weight on the strut.

The lift depends on rpm and prop feature (size, shape, ...). I have an excel spreadsheet which estimates that lift for standard octura props.

For SAW riggers, the ratio you're looking for can go up to 33% because they have fast rotating prop which provides high lift. On the other hand, for oval racing rigger, it's more likely to be in the 15 to 20% range.

As it really depends on the prop and it's rotation speed, I never use this ratio in order to build a rigger : I start with an estimates of the lift, which provides a range of magnitude for the weight on the strut. The rest of the weight must be on the front sponsoms : you've got your CofG very easily !

For my last rigger (10S2P, 33 000rpm), the total RTR weight is 7.5 kg and the weight on the strut is 1.4 kg eg the ratio you're looking for is 18%.

The length between the rear of the sponsom and the wet part of the strut is 75 cm
The length between the rear of the sponsom and the CoG is 18cm.

Regards

Pierre