C of G calculations

[mike ryan]

Hi folks,
I'm planning on building a Vulcan as my next model, and was thinking of doing it from scratch as I can't find any plans that are exactly what I am wanting. It will be a bit off yet but thinking ahead I was wondering how you go about calculating center of gravity. I have found some calculations for conventional type wing and tail models, but not really sure about a flying wing like the Vulcan.

[cymaz]

 

Here

Here

Here

There are any number on google- but that will keep you going for a bit.

Edited By cymaz on 02/08/2014 10:05:36

Edited By cymaz on 02/08/2014 10:06:42

Edited By cymaz on 02/08/2014 10:07:57

[PeterF]

I have recently completed a B2 Stealth and looked into this. There are a few links to some sites with CoG calculators for simple single panel flying wings below.

**LINK**

**LINK**

For more complex shapes such as the B2 with multiple panels and the Vulcan to some extent you can use the link below to download a program that will do this for you to calculate the centre of pressure or to input the CoG position as a %age of the mean aerodynamic chord. I wrote something similar to do the calculation in Excel before I found the program.

**LINK**

There is a large thread on RC Groups covering this which is where I found the info from when building the B2.

**LINK**

[DelRay]

PeterF,

Could you please PM me, I have some questions about the B-2 stealth you built ?

I built one last year, and I don't want to clog this C.G. thread with my B-2 questions.

Many thanks,

Jim

[Mark Kettle 1]

Mike I us the web link a lot, and had lots of success using it. However there is another way to find the balance for flying wings.

I give you a few pictures to explain : below is the kit needed to do it....

It Involves a 'Plumb Bob'. Basically set up some kit, as in photo - then hang up by the wing tip and put the plumb bob from the same point of the hang, with masking tape on the wing centre line mark where the cotton used crosses the centre line. The trick is to check it by doing the same from the other wing tip. This is the balance point.

The funny thing is at any point that you check either along the LE or TE of the wing this method confirms the balance point, once the plumb bob stops swinging it always passes through the original mark.

Vulcan shape wing below Mike.

You will see this on my build thread, black epp foam Vulcan 44" span.

The balance using the 'plumb bob' method confirms 40% of wing chord, with the radio gear in a practical position in the middle part of the body, the is for my model 228 mm from TE = 40 % I feel this will the best place. However you could do and fly with a set up with the balance more forward Mike.

And I could find that the when I fly it that the centre of pressure may move forward and I'm ready for a change with my set up. Pre calculated 25% of chord which is for my model 286 mm from TE. Done a little test and the battery needs to be under the cockpit area and have 3 oz of lead along side, so balancing is well within scope of the model fuselage space and not to much weigh involved.

Mike what span is your Vulcan ideas, and what materials are you using?

Edited By Mark Kettle 1 on 02/08/2014 11:58:12

[mike ryan]

Hi, thanks for your replies, all very useful. I was thinking around about a metre and a half, maybe slightly bigger. As far as materials go I quite fancy having a go building with foam covered with glass cloth. Certainly for the fuselage and centre section of the wings, housing the fan units. It's just in my head at the moment, I need to finish the model I am currently building first, but the more I think about it the more it is wanting me to build it. I have the free plan from November last year for a small avro 707a built using foam. I think I will build this first to get a feel for this type of construction. Again thanks for your replies, and I will post on here if it makes it from idea to the drawing board and beyond. Hopefully in the not too distant future!
Thanks,
Mike.

[Mark Kettle 1]

No problem Mike.