Center of gravity
 

On my 33% yak it needs 1 or 2 degrees of up trim to fly level. Inverted at this setting it climbs slightly. Does this mean that I should add some nose weight?

RE: Center of gravity
 

G'day Mate,
Yes.

RE: Center of gravity
 

If you need up elevator to fly level then the nose is heavy. Speed is also a factor. Your wing / tail incidence could also be the culpret.

RE: Center of gravity
 

Hi whitedog4491
Sometimes I get mixed up in my thinking, or understanding. I see a possible problem in communicating, and it usually is my problem, so please bear with me. When you trim the elevator to 2 degrees of UP TRIM, does the trailing edge of the elevator move Up or Down? I believe the correct answer is Up. I have seen others call this Down because they are holding the transmitter oriented vertically in their hand and are moving the elevator trim Down. Please let me know.

RE: Center of gravity
 

The trailing edge move up. I did check the wind and horizontal with a digital meter and they were at 0 degrees but I will check them again. I was doing these checks at about 1/2 throttle. Going level it seemed to want to climb while inverted. while going up at approximately a 45 degree angle it seemed like it would hold there better if that makes any sense.

RE: Center of gravity
 

I should also say that I only have 4 flights on the airplane. On the first 3 flights I needed about 4 degrees of up trim ( elev trailing edge up) to hold level while upright. At this setting it would dive when inverted. I moved my batteries aft and did one more flight and now have what I state above. I suppose I should do some more flights and feel it out some more as it was much better on the last flight. This is my first large gasser and I am still not real comfortable with it yet. Other than the balance/ele trim issue it flies great.

RE: Center of gravity
 

Sounds like it's slightly nose heavy with too much down thrust to me.... The nose heavy requires some up elevator to hold level, but when inverted the downthrust becomes up thrust, pulling the nose up.

Just one theory...

J

RE: Center of gravity
 

That is kinda what I was thinking also. At what throttle setting should I be checking this? I read someplace that when upright I should have to pull up ele. just a little and when inverted I should have to push down ele. a little bit. Does that sound correct or do I want to be able to fly upright and inverted with no ele. input. If this is the case then at what throttle setting. If I do need to ajust the down thrust is there some way to calculate this and are there shims available. Thanks for the help.

RE: Center of gravity
 

What you read sounds right........a plane, any plane, needs a positive angle-of-attack to produce lift, which means the elevator has to be pushing down a little (either via a tiny bit of up elevator, or incidence). This is the ideal situation in most cases. OTOH, a finely balanced model with near-perfect CG will reduce the elevator-downforce requirement to almost nil, but will be kinda tricky to fly (which may be just fine for whatever sort of flying you're doing, like aerobatics). Some race planes have even used slight aft CG to offload some of the lifting requirement to the elevator/horizontal stabilizer, which purportedly helps reduce drag on some designs. Makes a sure 'nuff unstable airplane though.

With that said, I'd go with Jburry's advice and guesstimate that you have a little too much down-thrust. Try shimming some of it out. Then I'd go from there with CG (in other words, just move CG back a little at a time and see how you like it).