Center of Gravity Issue ???
 

I have an old Ultimate, GreatPlanes I think
little 24 or so inch span. Running on Brushless. 2 and 3 cell lipo's, gotta beefy stick plane power system set-up in it.
Bought it off a friend.
I read somewhere the CG needed to be roughly 3.5-4inches behind the leading edge of the top wing.
there is a little hook, does the plane need to be centered from it?

If so, does the plane need to rest with the gear horizontal?
or does the fuseloge need to be level ?

any help, thanks

-Josh

p.s. sorry for the hellish spelling

RE: Center of Gravity Issue ???
 

An airplane will be balanced at whatever point you support it or suspend it at when the fuselage sits level.

John

RE: Center of Gravity Issue ???
 

Or to put it another way, the C.G. is where ever that point is, as John says.

Your intent is to make that point occur at the recommended distance.

Biplanes are normally balanced using the top wing centerline.

-

Now what is this "little hook"?

There should not be anything protruding from the center of the top wing that is unattached.

RE: Center of Gravity Issue ???
 

Fixed tail surfaces should be horizontal - not the "landing gear"

RE: Center of Gravity Issue ???
 

The best starting point for CG on a biplane is as follows......27 to 30 % back from the leading edge of both wings.....make a little mark.......now draw an imaginary line between the two marks....the CG will be on that line at the middle point between both wings.....

Thats a starting point, as with all airplanes the true measure of CG will be in flight.....to test CG fly the airplane....go into a 45 deg climb and roll inverted.....let go of the sticks.....if she climbs she is tail heavy.....if she dives she is nose heavy......bare in mind your fuel load, as you set CG with an empty fuel tank so that when you fly you burn fuel off to CG....

Usually you don't notice fuel load too much.....what you will notice is that a tail heavy airplane is very difficult to fly....sensitive to pitch inputs, dragging her but around the sky if she can be controlled at all...a nose heavy airplane is a little more sneaky to detect.....you'll find that she doesn't want to slow down on final....and that you'll think you aren't flairing soon enough.

bottom line if you set CG and you like the way she handles your good to go....

RE: Center of Gravity Issue ???
 

Having flown and crashed many bi-planes, my first being a Andrews Aeromaster back in 1973, I tend to make the CG a little forward of the recommended point on its maiden flight. Jetmech05 recommended 27 to 30 percent and that is a good starting point, I'd start at 27. Most bi-planes have a very short tail movement and planes like the Pitts Special and Christen Eagle don't like being tail heavy at all. Being tail heavy can easily lead to a crash. A little nose heavy plane tend to be sluggish but you can land it in one piece and take off a little weight and rebalance it.

RE: Center of Gravity Issue ???
 

Actually, on a biplane, the easiest way is to block up the tail so that the bottom wing incidence is at zero. Then use a framing square, placing it so that one leg meets the leading edge of the top wing, and placing a mark where the bottom angle of the square meets the surface that the plane is resting on. Then move the square so that it meets the trailing edge of the lower wing, and place another mark on the surface. Measure the distance between these two marks. This is your Mean Aerodynamic Chord distance. Compute 26-28% of the Mean Aerodynamic Chord, and that is where you should place your Center of Balance. The Center of Gravity is about 12,500 miles below your feet.

Bill, Waco Brother #1