It say's it fly's on a 60, but what is the biggest engine someones used and results. I'm going to build one for a large glider tow plane and need some input. I'd like to go to gas for the sake of economy.

i wouldn't use a 60 on it. i had a 60 on mine, she broke ground got to about 6 ft and dropped like a rock. busted the wing up pretty good. after i rebuilt the wing and almost mortgaged the house to cover it, i put an Irvine 150 in the nose. the 150 flies it real nice. of course i reinforced the firewall and fiberglassed the entire nose so the 150 doesn't rip it off.
i also converted mine to a tail dragger as the nose gear would bend all the time, even just taxiing around. i also had to beef up the main gear after the conversion as that was now bending. i used B&B landing gear support bolts with a 7/32 music wire. no problems with ground handling now.
she need alot of rudder as the ailerons do not seem to be too effective. she wants to crab to the left all the time, i am currently working on trying to figure that one out.
it is alot of fun to fly and she lands like a dream (nice and easy)but takeoffs can be an experience. seems she wants to drop the right wing after breaking ground. if you are ready for it and use alot of rudder you can deal with it.
i didn't build mine but if i did i would drill a lot of lightening holes in the fuse. with the 150 on it mine weighs 16 lbs. didn't think that was too bad considering the size but then again i din't have a manual to know what the finished weight should be.
i included a picture of bg bertha after the repairs and tail conversion, but the beefing of the main gear came after the picture was taken. good luck

Bmax... As I do not have YOUR plane in front of me I could not be so presumptions as to say "fix this" .. If I may suggest tho, from reading your post which says :
If the engine has decent/proper trust angles, and the vertical fin has proper angle<point straight> that would eliminate crabbing..
Then you mention it wants to drop right wing on t/o.. I had this once on a plane I bought from someone.. It took me a while to figure it out.. Same damn symtoms.. For some silly reason I decided to take a CLOSE look at the horizonal.. I had already checked the elevator, but not the horizonal.. When I did, I noticed a slight warp from left/right.. I used heat gun, bent radically the angle in opposite direction.. Then upon trying it out <next day> the damn plane flew fantastik! The bad news, it didn't hold the reset and I ended up recovering the horizonal but did it so it was equal match side to side..
I hope this is of some help for you..
Robby

Hello Robby,
Thanks for your help.

I don't have a manual so I will need to find out from somewhere, what the angles should be.

We looked at the stab and horizontal and they look like they are straight. Didn't really notice anything out of whack. However, I will put my incidence meter on it to confirm. The tail does have bracing wires on it and maybe one side is pulling it down just enough to make it crab.

Anyway, thanks again for you help.
Bill