Center of gravity
 

Hi everybody, I need help with my homemade plane.
Is there any mathematical formula to find the best place for center of gravity on the plane???

Thanks!

RE: Center of gravity
 

There are a few but it there are different ones for different wings but I tried one of them on my cap 232 and it was way out I needed 500g on the front but if it’s a straight wing it will be very, very close to it some more info on your wing would help.

RE: Center of gravity
 

Follow the link and fill in all the appropriate boxes. These calculators will get you to a safe cg for your first flight, After that you will need to adjust the cg to suit your style

oops forgot to post the link, bobmac has posted the link that I was going to recommend.

RE: Center of gravity
 

I think this one is pretty good, and works for all types of wing shapes...

http://www.geistware.com/rcmodeling/cg_super_calc.htm

Bob

RE: Center of gravity
 

or if u can accurately describe the wing ( a pic plus dimensions would be good ) I will happily do it for you......

RE: Center of gravity
 

I will post a picture with dimension, just need 20 minutes...

RE: Center of gravity
 

Better yet, just take a yardstick and measure the following:

Wingspan
wing root chord
wing tip chord
leading edge sweep back at tip

stabilizer span
stab root chord
stab tip chord
leading edge sweep back at tip

distance from LE of wing to LE of stab along fuselage.
Easy to do and takes a couple of minutes, not 20, and no great skills required.
Then plug those 9 measurements into the geistware application that has already been suggested twice above. Click on the button and you got your answer. And you'll be able to do it for yourself next model, and the next after.

RE: Center of gravity
 

ok, so here we go, this is my very first home made plane:)...
The measure are in milimeters
And here is my results... It's that I just don't know what's what:D

RE: Center of gravity
 

For that type of plain vanilla untapered wing, with the tail the size relative to the wing and where it is, the c.g is just a percentage of the root chord (including the aileron chord).
Your 25% location would be considered conservative, making for a very stable airplane.
For more activity, going back to 30% would increase the manuverability, if you would care to do that.

RE: Center of gravity
 

an You please show me exsactly on my plane (picture) where is the CG.

25% from where???

...sorry, I'm just an absolute beginer...[8D]

RE: Center of gravity
 

Hi neuroza
The front of the wing is called the leading edge (LE). The back of the wing, including the ailerons, is called the trailing edge (TE). Your wing cord is 300MM. 25% of that is 75MM. Measure that from the wing LE toward the wing TE. That is the location of the CG. After you fly the plane you may want to move the CG a little to make the plane do what you want.

RE: Center of gravity
 

RE: Center of gravity
 

Hey Neuroza,

Please try and find some local help before you fly that plane. There are other things besides C.G. that need to be checked to insure a sucessful flight. Call a local hobby shop and ask where you can find a flying field to get some help. When you get to the field, just ask "Is there anyone here that does not mind helping a student pilot". Many of us are glad to help!

Brett

RE: Center of gravity
 

Thanks, this is just what I was looking for...

Again, thanks...

RE: Center of gravity
 

Here in my town or close there are no club or hobby center where I can go to learn, so the only way was this way... "do it yourself"...

The closest place to buy or learn to fly RC is in Zagreb, that is 250km from my place...

RE: Center of gravity
 

The red circle shows you input a Static Margin of 10%. It shows in the green circle that the CG for that SM would be 7.26 back from the LE of the wing.

The CG range is usually from a SM of 10% to 15% for just flying around safely. If you reinput the measurements into that geistware and ask for 15%, you'll see the other location for the range where the CG will be safe.

It will be safe to fly an airplane with the measurements you input with the CG somewhere from 7.26 to wherever the 15% input gives for that input.

RE: Center of gravity
 

I would get really good on a simulator or the life expectancy of your plane will be measured in seconds after rotation.

Edit - Since da Rock ran the actual #'s I would start off just in front of the line I drew.

RE: Center of gravity
 

Thanks guys!

I have another question, my plane now has 2600 grams with full fuel tank. Did this will be to heavy??? The engine is 0.40 magnum GP...

By the way I did a lot of simulator flying...;)

RE: Center of gravity
 

Your weight, wing area and power should be fine. I have seen lighter and heavier fly well.

RE: Center of gravity
 

Don't forget to balance it laterally (side to side) also. Suspend the plane from just behind the prop and the top of the vertical stablizer (I use 15lb fishing line) add weight to whichever wing tip goes up. [8D]

RE: Center of gravity
 

Hey Neuroza

One of the most important things to consider is the direction and throw of your control surfaces. If you get the aileron throws backwards, you won't get past the first turn.

If you are standing behind the plane, push the aileron stick to the right. The right aileron should go up and the left aileron should go down.

The throws of each control surface should be maybe a little less than half of the total. To much throw and you will over control right into the ground.

Maybe some others on the board could expand on begining throws for the plane you have Pictured.

By the way, where did you get the plans, I might like to build one to bump around with

Brett

RE: Center of gravity
 

GUIDE TO CUT THE ANGLE OF WINGS SHAPES

RE: Center of gravity
 

That may sound silly but it actually happens.

RE: Center of gravity
 

If you are stuck with teaching yourself then I very, very strongly suggest you just hang this one on the wall and use it as your third or fourth model.

You need to build and fly something that is far more gentle and slow for self teaching. Something more like a glider or a cabin style rudder-elevator model that has the same stability and layout as a free flight model.

Even with simulator time you will not be ready for the realities of actual flying. I've tried most of the better simulators and none of them fully handle all the factors that the real thing throws at you.

RE: Center of gravity
 

One of those realities is pucker factor. Pucker factor = (Money x time) ^3
Bruce gives good advice. The very few people that are successful at teaching themselves on this type of plane had someone else at least maiden to check trim and balance.