Hi,
I'm still in the early stage of learning to 3D. Could anyone give me some idea as to whether the tank should be full or half-full when adjusting CG while flying inverted? Or, is that really critical?

Thanks,
Richard

i run all of my tanks in the middle of the CG so they say you can tell a difference. I do this on glow planes to by running a VP-20 or 30 pump or running a YZ motor.

Tank should be empty when you set the CG. When you fill it up, it will be a tad nose heavy if the tank is in the nose. If you can, set the tank on the CG, however unless you have motors with pumps or install a pump (weight) this will not work. On most planes the tank is designed to be in the nose, so for the first half of your flight the CG will be towards the nose, however towards the end, it will be just right. Don't run out of fuel in a low hover!

If your brave, set the CG half full, however when the fuel gets low, it may make the plane twitchy. Or, just fly pattern stuff until half tank then cut loose when the CG shifts.

Or go to YS or gas motors with pumps.

I think richng is talking about adjusting the CG by trying to get it to fly straight and level, hands off, in both upright and inverted flight. I don't think he's talking about static balancing on the bench. I'd be interested in seeing some responses from folks with experience at this method of achieving final CG.

==Mike==

Set up your plane with the tank empty. If when you fly the plane needs a significant amount of down to maintain level flight while inverted, then move the cg back in small increments. I like mine to need no more then 1 or 2 clicksworth of trim for hands off inverted flight, but I trim it for upright level flight. Any further back & Extras, Edges, Yaks & the like become a handfull.

Hi krayzc-RCU,
Since I'm flying my cap232 .46R most of the time with tank near the nose, I'm not sure about glow plane and what is meant by running a VP-20 or 30 pump or running a YZ motor. Sorry about that. Just a guess, does this mean that the tank is located at the center of the CG? I also have the katana50 and just bought the katanafreestyle40. Thanks.

Hi YNOT,
Since my plane's tank is up front, I think what you mentioned is intuitive about just flying pattern stuff until half tank then cut loose. This could be another likely reason why I'm having more difficulties practising hovering high up at the beginning of the flight then towards landing times - not just due to warming-up. Of course, I'm still very much an early learner too. Thanks.

Hi GoMike,
You are right, I'm trying to understand about CG adjustment while flying inverted, and whether it should be done on full or half tank, and also whether is that all that important for especially new 3D learner like myself. Thanks.

Hi cstevec,
So, is the cg based on full or half tank while making adjustment on the fly? Thanks.

There is another thing, which I also like to understand....
I'm presenting using FMS simulator and really appreciate the value in it. I'm also thinking of buying the REFLEX sim, so, could anyone also give me some idea as to whether this sim is able to simulate the auto changing of the model's CG when the tank is full and when half-full? I'm very interested to know. Thanks.

Richard
I'm still a learner, please be patient with me.

richng

you are correct that i mean the tank is in the center range of the CG. YS or glow motors that are able to pull glow fuel from a distance. A vp-20 or Vp-30 is a pump used on glow motor 2 or 4 Strokes so that you can acheive the pump action with the glow fuel. This enable me to run all of my planes tank on the CG and not worring about starvation issues. here are a few pics of a pump and such.

Here is a link to read up on the vp pumps for now pumped glow motors:

http://www.perrypumps.com/prod02.htm


this pump is not requried for a gas engine or YS glow engine

The addition of fuel has a big effect on the cg on most model planes. A typical profile 40 size 3d plane weighs 50 ozs, has the center of the tank about 10" fwd of the cg and carries 8 ozs of fuel. For this example, when the tank is full the cg is about 1.5" fwd of the position when the tank is empty. There is nothing you can do about it short of moving the tank closer to the cg. I am surprized the planes fly as well as they do both full and empty. We set the cg so that the plane is not uncontrollable empty.

Hi krayzc-RCU,
Thanks for your info, pictures and link. It certainly helps me to understand alot better what it really takes to virtually stop the CG from unintentional changes on the fly. The only thing is, it'll require times to modify the fuse in order to move the tank - quite a fair bit of work. Thanks again.

Hi Jack Hyde,
If I understand correctly, if the model is balanced with empty tank initially on the ground, then towards landing period with almost an empty tank, the model should still be flying very nicely. When the tank is full during take off and subsequent flying around nose heavy, the model will be stable. It is only when things like hovering are done, that the CG is likely to become sensitive.

When you get a new plane there is usually a recommended cg to be used as a starting point for the first flight. It is hopefully based on what test flights of the plane have shown. It is largely a matter of opinion - what I say is nearly unstable you may think is way too stable. It is usually very conservative. For convenience the recommended cg is almost always for an empty tank. Otherwise you would have to fool around with a tank full of fuel while setting up for the desired cg before the 1st flight.
If the tank is located near the cg, the cg will not change much from full to empty. Most proifle planes have the tank located in front of the wing, about 10" ahead of the cg. When you balance the plane empty, the cg moves forward an inch or 2 when 10 or so ozs of fuel are added. The plane is bound to fly somewhat nose heavy at first if it is going to be stable at the end of the flight when the 10 ozs of fuel are gone. I fly this type of planes and it is surprising how little the fuel load seems to change the way they fly as the fuel is used up.
The idea is to set the cg such that at no time during the flight the plane becomes more dificult to handle than you are happy with. If you set it at your limit at take off the cg may move back so far as fuel is depleted that is will become more pitch sensitive than you are happy with (or can control) at the end of the flight. The good news is these planes are very easy to land and can work pretty well with an aft cg.
You don't set the cg to make it easy to hover, you set it as far aft as you like and that may make it easier to hover.

Hi Jack Hyde,
Thanks for your explanation.... Richard

Richard, you could also balance it with full tank, so near the end of the flight you could surprise everyone with some spectacular manouvers thanks to the more aft CG

there are also a few planes that the wing tube is in the way for putting the tank directly over the CG like the Funtana 90. in this case the tank will be behind the CG. balence it with a full tank for 3D then by the time its ready to land it is nose heavy and lands very easy compared to the other way around

wow drumbum
u may be on something with that bird[8D]