I built mine to the TT spec with an OS91fs , i did reinforce the undercarriage and carry out a few of the suggested mods. I originally reduced the downthrust as per the suggestions here but found I needed to add a little back, it flies just fine, no problems with the stab so far. I feel too many people just stuck oversize engines in, added all sorts of extras and put the wieght up and then had problems. Not trying to defend TT but i think if one sticks to the recommended powerplants it is less likely to be a problem