ORIGINAL: tommythecat
I am fairly new to modelling and have a COG question.
I built and am flying a GWS A-10.
The COG on my plane is a bit behind the recommended location, meaning my model is tail heavy.
Honest, about all that means is that your model has it's CG behind where the mfg suggests you have it. The mfg's suggested CG is sometimes recommended for amazingly different reasons than those based on sensible design practices. One of my recent ARF manuals used the CG location and surface throws descriptions from an earlier manual..... of a different model..... that wasn't even the same proportions....... no lie
How your model flies is a much better indication of whether or not it's tail heavy.
i would have expected this to cause the plane to porpoise upward to a stall, but in flying I have found it has quite the opposite affect of what I was expecting.
The way the plane responds is very often a result of where things like the elevator are when you launch the sucker. Or how correctly they're tuned to that model. And the one thing we have to do, is take what the airplane did as being "true" compared to what we thought would be "true". If it doesn't act the way we think it should, then we're either wrong about why it's acting that way, or we're wrong about how things that're that way act.
the plane wants to nose in with the elevator centered. I actually have to apply a good bit of up elevator to achieve level flight. Is this normal?
Having the elevator centered isn't a dependable indicator of anything lots of times. Where it winds up after you've trimmed it so the airplane flies level can be a good indicator, but until you've sorted out your particular model, where stuff points can be the luck of the draw. How the workers glued stuff together and where they put it and how much it weighed versus what it was supposed to have weighed are just a few things that can make your particular model act "funny".
Are my initial thoughts on the affect of being tailheavy 180 degrees off?
Maybe so, maybe not.
If you're not sure of a CG location and wish to verify it, an excellent way to do that is with the very easy to use geistware.com application. It's easy to use and the computations it does (all you gotta' do is measure some things like spans and chords) have been proven over and over by the airplane industry that designs the planes, and the industry that uses them.
http://www.geistware.com/rcmodeling/cg_super_calc.htm
If the CG checks out then look at the airframe to see if the wing is seated completely, the horizontal tail is straight and square and seated completely, the engines pods are aligned, the motors are square within them, the surfaces move the right amount and direction.
Our models don't have really any magic in them that hasn't been found and measured and documented. We do have to find what's wrong when they don't fly right, and sometimes our first guess isn't the reason. But it's a good place to start looking, and looking the right way is the best way to start.
This is a kewl hobby that's fun when things go right, and when they don't, it's kewl that we have a chance to learn. And sometimes things aren't like we thought. This also isn't a soundbyte simple hobby. But there are good tools that help to understand it.