tHANX FOR RECOGNIZING THAT FHUBER! I did man o.s.engines. However, The reason I ask this question is because I have a trainer that i would like to attach a camera to. The engine i have on there is in fact an old 40 Max FP. If I were to keep this on here with the added weight, I belive the plane would fly but at much lower speeds. I am just unsure that i would be wisely spending the 80 bux for another .06 cu in of power in a tower bb 46 engine.

Which trainer you putting the camera on/in? (in is better, if there's room... less drag.)

You will probably find that you can add 1 to 2 lb of lead on the CG of the trainer and it will still take off OK and fly around. Landing speed will increase, top speed will decrease, aerobatics will be out of the question. (as Montey pythion would say... "WAY out.")

If you are using a 10X6... shift to a 11X4. (12X3 if you can find it... made em in the 1970's.) Better pull at low flight speed, better accelleration for take-off.

Probably don't really need to change engines. I've loaded many trainers up with bomb bays and parachute drops.

At the same time, don't be fooled by displacement numbers alone --

The 40fp is optimized for reliability, lots of focus on smooth idle rather than on max power. My recollection is that it was rated at about 1.1hp. A 46fx is focussed much more on power and is rated at about 1.6hp -- so the .06 cu.in. increase in displacement doesn't sound like much, but combined with the different design approach, you get 45% more horsepower out of it.

Note -- don't mistake this as meaning that I think you ought to buy the .46... it's neat that it has so much more power, but the more important issue is still whaether or not you need more power.