well, I'm not a newbie but I am sorta...
I've been flying since I was 8 and am now 22 but I haven't been in the hobby for the past 5 years...

Now that I have returned the first thing I did was go out and get an RTF so I could get back in as quickly as possible, it is an extra easy rtf from hangar 9....

Now I here is the question, Back when i was in it before I left the "old timers" at our field wouldn't dare change prop sizes...
a 40 size engine uses a 10X6 and thats it nothing else will work...

But now after reading these post on here I see what happens if you change a prop the affects and such but here is what I ask..

currently the engine has a mds .40 on it and a 10x6 prop...
the plane flys way to fast for a trainer setup it is constantly climibing even at idle almost and enough down trim where it shouldn't.. Also on take off I noticed it took it a while to "build up" speed for takeoof, a little longer/distance than it should.

What would happen if I put an 11x5 prop on it? would it slow the plane down + give better take off performance??
I guess basically what i'm asking is how do I know wich prop to go with? the 11x5 or a 10x7 or what??

I've even seen post on here about using 12x3.75 on 40 size engines?? If it would work I would have loved to use on on my old airmadillo with the .46sf so it could hover

well sorry for the long post its my first one on here, and trust me there are many more to come!
THanks!