ok, when I'm trimming my plane out for the correct setting centre of gravity, should I do it with a full tank, an empty tank , half full or what?
Thanks in advance[8D]

no fuel in tank. DRY.

I'm not sure what you mean by trimming if your asking about setting the cg correctly it's with an empty tank. you see it's better to be a tad nose heavy than tail heavy. if you set cg with a full tank, as you burn the fuel the cg would move aft. not good. but with an empty tank you take off a tad nose heavy and as you burn fuel cg still moves aft but to the desired cg range.
hope that makes sense to ya good luck

Both answers are correct

When you check your CG for the maiden flight its with an EMPTY tank.

If skycom means checking CG by flying inverted then its different. If that were the case, that is how I set my CG ... again it would depend on wha makes you feel comfy and how you like to fly. Safest is to use a full tank and the plane flies inverted with a little DOWN elevator. As the fuel runs out the CG will as what ashley says will start to move aft but not that far back.

In my F90 I set the CG with hands off inverted with a full tank ... then when I come in for landing she is obviously tail heavy and needs some DOWN trim to land. That I do for 3D as I want my CG as far back as possible.

This comes to the the point where a lot of flyers move the tank back as close as possible to the CG. So when the fuel runs out your CG change is not prominent.

Set CG with EMPTY tank. As said above, if you set CG with full tank, the plane will be tail heavy when the fuel is gone. Not good. Ideally, the best place for your fuel tank is as close as possible, and just forward, of the CG. But this is usually not practical.

Thanks for your replies guys. I'll set it with an empty tank then see how it flys and adjust if necessary. Thanks again

Wasn't the first answer (from NJAirstrike) adequate?

While the answer has already been given above (balance with the tank empty), I do want to make a comment about something that has been said. Several places above suggest that the best place for the fuel tank is on the CG of the plane. This is 100% correct in that it is the best place to put the tank as far as balancing the plane goes, but I would like to add that in most cases it is difficult to put the tank there. Why? Because most standard glow engines simply can't push/pull the fuel from a tank that far away from the engine. Most glow engine use muffler pressure to help feed fuel to the engine, but the further away from the engine that the tank is moved the more pressure that will be required to push that fuel from the tank. In most cases with the fuel tank that far away there will not be enough pressure to feed fuel to the engine. This is why most plane have the tank mounted directly behind the firewall, keeping the tank as close to the muffler/engine as possible. If you want to place the tank further back so it's on the CG you need to have a different method of delivering the fuel to the engine. YS motors have a pump that actually pressurizing the tank which make them ideal for situations like this, or you can use an add on pump such as those made by Perry. While it's not impossible to mount a tank on the CG, these things that I've mentioned do need to be taken into account.

Just adding my 2ΒΆ worth

Ken

Also the dry adjustment is best for most beginners and sport flyers. The wet/inverted method sound OK for a more advanced pilot who like a more challenging or competitive flight envelope. For most flyers, especially beginners, the dry method will yield an easier plane to fly, and might help it last longer.
I'd suggest learn to fly properly first, phase into aerobatic and/or 3D, then see if the wet method fits your subsequent flying style. Centering the tank on the CG is most practical on largwe planes or on ducted fans or turbo jets.

That was a lot more than 2ΒΆ worth We had to take a wizz break while reading it. [&:]

As simple as the answer to this question is, now someone has gone and got me confused, again! What in da heck is the wet/inverted method?