ORIGINAL: mike109

Once upon a time, many years ago I had a PT40. I built it for my son to learn to fly. One thing I seem to remember is that the wing is rather thin and the wing joining arrangement is therefore not very wide. I eventually took out the original Magnum GP40 which was fine for training and put in a SuperTigre 45. In level flight it was quite a bit quicker and also in level flight the wing joiner failed. Your 61 is going to be stronger than my ST45 so I would be a little worried that you may manage to overstress the wing. If you are sure it is nice and strong in the middle then go ahead, but if not, then either strengthen the centre section or as suggested earlier, add some glass fibre reinforcement on the outside of the wing centre section. A bloke where I learned to fly had a Thunder Tiger Eagle 40 size trainer with a piped Rossi 60 in it. It was built with the Rossi in mind and was a truely awesome beast, especially when he flew over the strip inverted at about 1 foot. Kadet Seniors I have had have had engines from 40 four strokes up. My current one has a 72 Saito which is total overkill. It still flies the same and is not really any faster but its acceleration is impressive and I was able to remove all the weight from the front. I also have a Saito 100 in a Four Star 60 which is a bit over the top but rather nice to fly.