[popeyepete]

Rebuilding my Island Hopper after breaking the wing in half, and now adding some better finished mods to the plane. Given I've learnt flying this plane comfortably. i want to continue to refine the skill of "not breaking things & keeping it in the air".
One thing I'm not sure of is how to find the COG of a plane if your plans/manual doesn't tell you where it is. There loads of stuff on the net but its all in inches and in the old speak of imperial.
One thread i read tells you to measure 4" from the fuselage along the thickest part of each wing
Any advice???

Some of the rebuild pics of the Hopper below.
   

   

   

   

[robair]

Gday Peter

There is a "right" way and a "close enough" way to approach this issue.
The method also changes if you are are calculating for a straight wing aircraft as opposed to a swept wing. I find the "close enough way" is generally adequate for the straight wing.

For simplicities sake at this point, to calculate a straight wing merely mark a point 1/3 into the chord of the wing each side next to the fuselage. Balance the aircraft with your fingers on the points, if the wings are parallel to the ground and/ or the aircraft does not slide off your fingers you are in the ballpark. Add or remove weight as applicable to achieve the finger balance.
You would be surprised how well this works.

If you like I can go into more detail re the right way which is to calculate the mean aerodynamic chord, weigh your aircraft and go from there. There will be some omissions here but I know John J and Steve M like myself have all used the MAC method above. This is a much better method for swept wing aircraft.
I am sure you will get a lot more comments from other club members to help you with this.



Cheers
Rob B

[smuzz]

Yes Pete, Rob is summing it up perfectly - swept wings need a bit more geometry to approximate the aerodynamic centre and centre of lift, but for a model like the Hopper which has a pretty-much rectangular wing planform ...

1. Measure the chord at the wing-root and get it to balance somewhere between 25% and 30% of the chord behind the leading edge.
2. For more docile behaviour have it nearer to 25% of the way back from the leading edge
3. A couple of flights later you can move the battery or whatever so that the CoG moves further back, closer to 30% of the chord behind the leading edge where it is less stable and potentially more interesting/responsive/touchy to fly.

Cheers,
Stevem

[paulj]

Just another point, If the aircraft has a high wing(ie. above the cockpit) you test the balance
with the plane upright.
If it has a low wing ( Mustangs,Spitfires etc) you test the balance with the plane inverted.
As both Rob and Steve say the just try to get within a ball park figure and then refine after a test flight.

[Cessna]

Hey, I have approximately 30grams of weight to add to the tail of my Cessna 310, whats the best way to add weight, I didn't want to tape 50c pieces to the tail :-/ (as I did to my Cessna 182) how can I add weight neatly to a specific area of the plane?

[robair]

Gday Danial

Nooooooo.
Adding weight in my eyes should be avoided if possible.
Are you able to hack some weight out of the nose area or shift, change your battery?

Cheers
Rob B

[kizza42]

Sticky tape works well for me, but as rob said, You shouldn't need to add weight, especially on your cessna thing

[Cessna]

Oh good! I was really hoping not to add weight, I guess it depends who is flying it, several people with that particular plane have added 30-40grams of wait to the plane... I might just take it up myself and see if it actually needs it. And yes I have since moved RX and a bunch of wires as far back as possible and Batt will also go as far back. Was just confused as to why people were adding so much weight to their plane, weird.

[kizza42]

The question you have to ask yourself is if you are noticing it being too nose heavy for your flying?

[Cessna]

I know when when its held it is nose heavy, but will be taking out today to try it out.