RE: Nitro models pusher Bobcat?
Knowcrash, it all depends on what you want this pusher jet to do. Seeing as you are familiar with grass, and know that it typ. takes larger wheels then on pavement then you have the first part down.
If you are wanting top speed, then you will want your k&b to rev higher then it will with a 10x8 prop. If you are not looking for speed, but want great verticle I would think a 10x6 pusher would suit you good. It will have a lot more thrust then the 10x8 (which you will prob. want for grass) and it will have very good verticle push to it. I also fly a shrike (similar to this but about 1.5lbs lighter) and with a 10x6, it keeps the speed down a little (still hauls butt) but it has unlimited verticle. If you are looking for speed, I would look for a 10x7 pusher. the ultimate would prob. be a 9x8, but good luck finding one. The k&b 7.5 likes to turn and I assume it would turn the 10x6 great, give you good speed and lots of thrust. this is just my opinion from flying these type of airplanes and the k&b 7.5.
Hope this helps some.