dickj

My Feedback: (1)

Do I read the instructions correctly which state to fill the fuel tank and then check lateral and fore/aft CG for proper balance? I have always checked the CG with the tank empty in the past.

What prop would you use for this airplane with a GMS-47?

Any answers appreciated from some of you Knife experts! So far you have helped me out a lot and its almost done! Should fly this week.

Hacker

dickj,
i don't know about the tank empty or full...i always balance it with tank empty...as long as you are close it wont matter.after you get used to it your going to want to fiddel with the cg anyway. these planes fly best (3-D) tail heavy. do a search and you will find lots of helpful info about triming and flying the knife.
dont know about your gms...my os46fx is most happy with 11.5x4 or 12.25x3.75 apc. little slow too spool up (some day you will be old and slow to spool up) but not bad. i am also running a moose can pipe. hope this helps

Texas 3D

My Feedback: (16)

I have never checked the CG on any of my planes with a full tank. Always balance dry.
As for propping the engine, I would give the 11.5x4 APC a try ! Should haul it thru 3D nicely. The 12.25x3.75 might not spool up and down fast enough. The 12x4 APC probably will work out OK too. You will have to experience what suits you the best.
As for me, I have always liked the 11.5x4 better in the 40 size engines.

dickj

My Feedback: (1)

Thanks guys due to ground clearance I will go with the apc 11 1/2 X 4 and try that. One more question. My plane appears tail heavy as I have to move the engine all the way forward on the rails to balance with no lead. Has this happened to yours? Is this OK the plans show it just behing the spinner however mine would have to have too much lead added and this way no lead. Please advise me on this one anyone. Thanks for all the expert help here on RCU. I appreciate the good responses.

Texas 3D

My Feedback: (16)

I would set the CG as per indications of the plans or manual. If you have some experience with these kind of planes, you could probably set them towards the aft recommended CG, otherwise keep it as recommended for the beginning. You can always move the CG back later. Make sure you balance you Knife with the whole equipment on it. That should include all radio gear, tank, spinner, prop, landing gear etc. The engine should be the last thing mounted.
Do yourself also a favor and order some Crazy Legs from [email protected] . I believe they are $12.95 plus shipping. The supplied aluminum gear will bend very easy. The crazy legs will also give you a couple more inches of ground clearance.