3D and CG

[Bartman]

Guys,



I mentioned to someone in another thread to move the CG back to make their sim 3D better. In thinking about it though, how much do you have to move it and can a regular sport plane 3D? Is it just having monster throws and power or does CG have to be moved a lot?



A while back I bought a used .40 OMP profile Edge and didn't check the CG before I took it out to fly it. The CG was so far back I could barely fly it and was lucky to make it back on the ground. I'll be getting it going again in the next couple of weeks but.....what's the trick? Way back? A little bit? or a lot?



Bart

 

[Ant]

Personally, I try to make the sim planes feel as close to my real planes as possible. I fly all my planes just forward of neutral cg . The only real purpose to being tail heavy is maybe the plane will hang in a hover a tad easier, maybe. I hate landing a tail heavy plane and having to push the nose down to get the plane on the ground. Just me.

 

[Bunky.F.Knuckle]

Different airplanes needs different CG's. What I may like for CG, you wouldn't.



Aim for neutral CG. Then go from there.

 

[Bartman]

ok so it isn't impossible to take a sport plane that has the power and throws and get it to 3D without moving the CG way back? in other words, i suck as much as i think i suck?

 

[Ant]

What plane? LOl I'm no 3d expert, more of a hack than anything.

 

[ericb]

Bartman;7778 wrote: ok so it isn't impossible to take a sport plane that has the power and throws and get it to 3D without moving the CG way back? in other words, i suck as much as i think i suck?

Most planes will fly best with a neutral CG. Some pilots prefer it a little tail heavy. I used to think I had to go tail heavy to 3D, but if you have a good airframe, i.e. EF or PAU, you will be able to 3D with a neutral cg. There are people who will say "it's a plane and they all fly the same". They are wrong imho. The top airframes are easier to fly and fly better than others.

 

[Terryscustom]

Bartman;7778 wrote: ok so it isn't impossible to take a sport plane that has the power and throws and get it to 3D without moving the CG way back? in other words, i suck as much as i think i suck?

CG is nowhere near as important as proper setup of the rest of the plane. You can 3D the snot out of a nose heavy plane, no problems. You need the right size plane, the right power to weight ratio, the right wing loading, the right control surface size, throw and servos. Take out any one or multiples of those and you chances of success goes down. As an example, the maiden I did the other day turned outto be a CG about 1.5"+ ahead of where it needed to be......yup, 3D's because that was the only factor missing: https://www.youtube.com/watch?v=5tXgGsjG4uc&list=UUmN3am68lG1nMdT8ujT6GyQ#t=271



Basic setup as Bunky says....shoot for neutral. Tail heavy sucks for everything except straight nose up flying, and nose heavy flies cleaner lines and is easier to land but suffers only slightly for 3D. If you want to torque roll for 10 minutes go tail heavy, otherwise no.



What is neutral? Neutral is when you trim out your plane and fly a flat and level line at half throttle or slightly more, roll inverted and your plane DOES NOT climb and the nose fall off just barely. If it climbs, you are too tail heavy.....if it pulls the nose to the ground you are slightly or way nose heavy depending on how bad. You can do the 45 degree upline thing but that is less accurate because a fully symmetrical wing needs AOT to generate lift so at a 45* upline your wing is lifting and will not show nose heavy as accurately.



As for your .40 slab, your kinda on your own there but I imagine similar principals apply.



As for simulator planes, what I do is modify the heck out of them. Scale them up slightly to see better for one, add about 30% to the weight to make them less floaty, modify the travel on the surfaces and engine power to be more realistic or as realistic as possible. Then fly the crap out of them while the ground is white outside!

 

[Bhughes]

I think tail heavy comes in handy for high alpha harrier and rollers. And tail heavy planes seem to hold a hover better IMHO. But yes you can 3d a neutral or nose heavy plane but I would think it requires more input on the sticks when preforming these manoeuvres. I'm no expert either still haven't figured out rolling harries lol.

 

[Bunky.F.Knuckle]

I had a 35% Carden 330S, and it was set up stupid nose heavy! Even with the canister mufflers I had in it at 1 time, it was nose heavy then. But when I took the cans off at XFC '05, I was still nose heavy. I was at a fly in, and I tried a QQ with it, torque roll it no handed. It did it for several revolutions. My buddy couldn't believe it. He asked me if it was tail heavy? I said, hell no! Took it up and showed him! It pulled hard to the nose, inverted.

 

[3D-Joy]

Yeah I don't quite understand why I keep hearing tail heavy is better (easier) for 3D.

Yes the elevator and to some extend rudder authority increase with a more tail heavy plane but it never makes it that much easier to fly. This is my opinion here : all you do by flying tail heavy planes is screwing the clean lines your plane was capable of.....not a good compromise.

As Bunky said aim for neutral first and then adjust to your liking but what I'd like to add is do yourself a favor and really try your plane more than a couple of flights with a neutral CG. This way you'll really see what you are loosing by shifting the CG back and then you decide for yourself if the compromise is good for you.