I just started building my TT Trainer .60 and have come across a dilemma. I'm new to building and so I'm very unsure of what types of modifications can be made without weakening the model structurally. In this case, I have 4 Futaba S3151 servo's that came with my new 7C transmitter that I am trying to use with this trainer. I've looked into the S3004 Standard BB servos that Futaba makes and the dimensions seem the same. The servo area that I have cut out of the wings is a tad too small for the servo I am trying to place in there. Being that this servo slot is cut out of the inside of each wing half (where I will be epoxying them together) I was wondering if I go beyond the precut bulsa area to accomidate the servo, will i be weakening the structure too much? It is a bit frustrating since the only part of the servo that is having difficulty fitting is the small rubber grommet on the bottom that goes around the servo wires. I don't want to pinch the wire either. My other consideration is that there is a small wooden frame that fits over the hole that I have cut to actually mount the servo to, I don't want to cut away its support underneath by making the hole too long. If you have built this model or have any ideas I'd love to hear them. Thanks!

I built the 40 size TT trainer and had a similar issue. You sould be fine by enlarging the hole. I did, and never had any issue.
I actually made a little cavity for the wires to come out of the servo, and out of the wing, so they won't get pinched. Then I just cut a little slot out of the servo mounting plate for the wires to come out.

Thank you very much for that info. I've done what you said, just need to sand the hole out a bit so that I don't get vibrations from the wing frame. I'm looking forward to flying this soon.

Note... you can always enlarge that hole to the rear... but toward the front you might runinto the main spar. DON'T cut the main spar to make room for the servo!

Oh yeah, I would never cut the main spar. It only took about 1/4" extra to make the servo fit well. I plan on smoothing out the surfaces of the epoxied sides with a dremel just to make sure my servo only contacts the mount. Mosty that includes sanding down the excess epoxy. Thank you though.