Rob,

I would stick with the Norvel .061 for the Pathfinder.

The Jr. Lightning Streak was created before Brodak got the rights to the Flite Streak series. It was set-up to accommodate older baffle piston engines in the engine sizing. A modern .10 is about ideal IMHO. It will accept a .15 if you like fast flying and will probably fly on an .061 if you build very light and use shorter lines, although you may have to add weight in front for balance. An older .09 could be used successfully.

Don't just go by wingspan or area to determine size, also check the structure. The Pathfinder structure is set up for 1/2A. It has a large wing that is lightly loaded to provide good stunt capabilities. The Jr. Lightning Streak is structured for a larger engine and general flying. Both airframes are designed to balance using the engines recommended.

I'm guessing that you wanted to buy one engine and use it for both planes. I would not reccommend it.

George