davidgp

I'm building a CMP 72" Katana using a G26 engine. The engine needed 7/8" standoffs to put the prop backplate right outside of the cowl. With this heavy engine I expected the plane to be very nose heavy. It's very tail heavy instead!!! The COG is so far back that I think I must have something set up wrong. The only weight in the tail are the three Hitec 65MG servos. The COG is supposed to be 100-120mm from the leading edge. It's more like 145 instead. I really don't want to add more weight to the nose if I can help it. The radio gear is not installed yet but it's not heavy enough to balance the plane. Any ideas?

Thanks,

David

nitro wing

My Feedback: (1)

sounds weird.I had a 1.20 4 stroke and it balanced with ease..Are you balancing inverted?Put your wing servos and linkages in before you recheck CG

Rocketman_

My instruction manual says the CG should be 110mm - 130mm, measured on the wing at 150mm from the side of the fuselage.
By the way, isn't the Hitec HS-65MG a micro servo?

Jetdesign

My Feedback: (8)

where's the battery mounted?

davidgp

Oops, you are right. The HS65's went in a PA Extra 260, and the Katana got HS625's I think (not at home now) . The Hitec Hi torque metal gear version. The battery is not in until I figure out the CG thing. The instructions say the CG is 100-120mm back measured at 242mm from the centerline.

I'll try it upside down ... and at 150 from the fuse.

David

Jetdesign

My Feedback: (8)

the battery will make a huge difference, and so will balancing upside down. if you put the battery in the fuel compartment you might even be nose heavy. Also the idea of a 5 cell battery to help a little.

Rocketman_

davidgp,
Follow the suggestions made by nitro wing and gaRCfield and install ALL of your equipment before checking the CG. Install everything that the plane is going to be flown with except fuel. To get an accurate reading of your CG location install the servo extension leads, tail wheel, prop, spinner, wheel pants, wing retaining springs, bottom hatch, fuel tank assembly, etc. Everything.

I'm wondering if we're talking about the same model. If your model looks like my two Katanas in the picture below then it is the same. Mine were purchased back in 2003 and I believe they've made changes to it since then. Both of mine are powered by OS 1.60's with Bisson Pitts style mufflers and Perry VP-30 pumps and they balanced within the range specified in the manual.
Maybe your servo weight accounts for some of the difference between our models. Your Hitec's weigh 2.11oz each and my Futaba's weigh 1.4oz each. With three servos in the tail you have 2.13oz more weight back there than I do.