Thanks gentlemen for your wisdom.

I'll get a 12.25 x 3.75 as you suggest![8D]

Save your 13x4W prop for when you get slightly stronger engine... or even if you decide to upgrade to a throttle pipe.

I think the 13 x 4 W would be ideal for the irvine with the thottle pipe..... the 13x4 combined with a Thottle pipe revs wayyy to much as it is.
Tried the 12.25x3.75....and i thought it was horrible! revved like parking warden's pen top and the noise was terrible!Good vertical and superb throttling though....

It wont punch out of the hover with this set-up though....might be worth trying a Just Engines purple pipe.
Substantial power increase. My mate gets a MASSIVE 11,500 rpm out of his irvine 53 swinging an APC 13x6 on 5% nitro club fuel!!!!

I use a 12.25 x 3.75 on my irvine .53, its the best performance prop but as luke says, its noisy, and irvines are quite noisy engines anyway.

I've since discovered that the ASP .52 can turn a 12x7 far better than the irvine can, throttles brilliantly and flies the same model so much better, plus it's almost silent.. more satisfying to fly. Needless to say, I shaln't be buying too many more irvines!

Seriously lads... when you think high pitch is no good for 3d, the model in this case is absolutely transformed.. you can come out of a knife edge loop on perfect 90deg just above idle.. theres so much wash over the tail... awesome! Some might not like that but I do!

They supposidly fly better if you take the Extreme tail off and replace it with a Lazer 3D tail and elevators. Better 3D????

Just started flying mine again after initial disappointment a couple of years ago. Just threw out the hugely heavy alloy undercarriage and replaced it with a carbon job and changed the throttle servo for a micro. All this has bought the weight down to 5 pounds 3 ounces with a SC .53 two stroke. It'll hover okay now and pull out but I'm expecting more improvement when I can get hold of a decent prop. Currently using a two quid Graupner 12x5.

CG is a bit far back with these mods as the nose wants to climb or dive depending what you breathed on last, but I'm enjoying flying it. Forget the manual as far as control surface movements are concerned and go for everything you can get, especially on rudder.

Also modded the nose when I built it as I'm not keen on inverted engines. So I have a nice Spitfireish nose with the engine sidewinder. Pix below are from before u/c mode etc.

I know this is a old thread but does anyone have the manual I am looking for the cg of the model cannot find it anywhere I have flown it but I believe the cg is of as is a bit noticeable but I do not know we’re the real cg is so hard to judge without knowing properly

The starting CG's listed by the manual/instructions are notoriously inaccurate. If you've flown the plane, that "suggested" CG is a moot point that can do you no good.

The REAL/correct CG location can be found by test flying only. Anything else is at best an "educated guess".

Does anyone have the manual for this as I have one but need the manual to figure out some things to see were this model stands would much appreciate it

For anyone interested: I went through a few engines on this one but ended up with a sidewinder ASP .91 four stroke turning an APC 15x4. A really nice combination. I still have it but haven't flown it for a while. A good solid airplane but not in the same class as, say, Funtana, Fliton Extra or H9 Extra 260 and others I guess, but tough as an old boot and great fun.