ORIGINAL: RapTaz
Thanks to all for these great responses. This group's unselfish willingness to help out a newbie is a wonderful thing!<div>
</div><div>The trainer I have is the Tower branded ARF Trainer 60 MKII from Tower Hobbies. The wing is flat bottomed 12 1/2'' from leading to trailing edge and 69'' span (I just ran out and measured). I powered it with a Magnum .61 2 cycle, the size recommended. This engine is actually one of the lightest available in this size (for entry level engines). The plane is NOSE heavy. Using 1 oz mixing cups and BBs I balanced to the recommended 3 3/4'' from leading edge CG. It took about 1 1/3 of these cups on the tail to balance, and about 1/3 cup on the left wingtip. I tried moving the battery pack aft of the servos, but the most readily method of securing the battery was to attach it to the pushrod tubes, something that just didn't feel right to me so I'm not willing to do. I'm going out of town this weekend so I'll look at it when I get back and perhaps think if something different. Even with the battery moved to this position it still is nose heavy.</div><div>
</div><div>I think I'll go with the external method since this is my first plane and not worry too much about the cosmetics. It is, after all, likely to have some battle scars and war wounds before long anyway...</div>
Good, the Tower Trainer is frequently mixed-up with the Great Planes look alike but which has far too much dihedral. You say 3&3/4 ". That gives the 30% that I stated as a max. in my above post. I still prefer the magical 25% MAC. On your machine that would be 3.13 inches back vice the 3.75" It's good in all cases.
My 101" Eindecker plans showed CG at 35%. I knew it was bad. I did it anyway. Almost lost it. Now at 25%, 15 oz. LEAD on the firewall and the engine mounts. Flies well. Take-Offs and landings are very nice. About 4 years old, and makes all the local War Bird events. Last event had over 40 pilots. In a big discussion, all those involved agreed that war Birds should forget any kit instructions and set up 23-26% MAC CGs. At that event there were 3 accidents but none were because of aft CGs.
I forget if the Tower Trainer series uses rubber bands or bolts. I have built several of the 40s for instructing with, and I always use a bolt system. They don't slide! Once they get overly messed up (the covering starts getting bad rather soon, but patchable and I could do better cleaning. [&o] ) I trash and put another together.
There is always some wood, cardboard, sponge rubber (black insulation rolls are very good) that can be used to place and secure batteries, tank, etc. and hold things fairly well where they should be. I use a bit of such scraps, and can remove any item and replace within 20 minutes to several hours, depending on how badly I need to get it done.
One other good point of a slightly nose heavy airplane is that you will have to learn the real landing technique of holding the proper ever increasing back-pressure on the elevator stick as the airspeed slows and the engine comes to idle which loses the accelerated airflow over the Stabilizer/Elevator, thus you have to keep the nose up for touchdown as the aircraft slows rapidly. Nose gear airplanes don't accept 3 point landings very well. Tail draggers just the oposite.
In addition do demonstrate your professional abilities by taxing out with the ailerons held INTO the wind, and the elevator
slightly down to stear better if on grass, on hard surface, you may have to do opposite with the elevator slightly up. Taildraggers, hold "UP".
"Airplane Drivers do what the book says." PILOTS KNOW the book yet do as they need for the situation, when the book doesn't work! BTDT!
So Tower now recommends 30% CG. They used to show close to 35% or more. Glad they can learn.