Building a twin engine model (56") and have the four-stroke bug just 'cause I like the sound. It just seems appropriate.
Problem is..... I'm not 4-stroke aware.
I have recently been looking at OS 30 & OS 40 engines. But none of advertising gives a hint about propellor size.
Eleven inches of propellor, shallow pitch, at 10K would move the required air. Bigger diameters would be more "scale-ish."

Anyone know what these Surpass 30's & 40's will turn, prop-wise? 

Vince

Hi Vince

You maybe want to choose  the OS 40 over  the 30  , If the plane  will take the  weight of the engines.It will turn a much larger  prop. You can  use  a 12 to 12 1/2 x 5 ..or whatever pitch works best for that particlular  plane prop, you maybe could  use as high as a 13 inch if it was a prop that was very easy to turn
The 40 weighs  12.5 ounces  the  30  only weighs  10 ounces, How much do you think  the  plane  will weigh  finished?
What type of plane is it  and  how  are  you going to use it?  If it isn't  that large of a wing  you maybe  better off with  the lighter 30s and  may not  need to use  larger diameter props.
You maybe able to use 11 x 5 props on the 30 and they might work well on the plane. also.

Regards

Randy

Hi Bob

Vince didn't say this was a "stuntship". Only hinted that he wanted to run larger props, and said they would be more scale looking...
That is  why  I asked him what type of plane this will be.
I would really like to know that  before recomending  engines. It maybe that he doesn't want to run 9 inch props


Vince  tell us  what  type of plane this will be 

Regards
Randy

So far....More information then I hoped. These boards are getting to be a great resource. Thanks everyone!
Have you ever wondered why the "best" stuff (Like the Saito 30) is always made of "un-obtainium?"

More on my model. I started with 56" span, but I am really leaning toward going to a 68 inch span for a variety of reasons (AutoCAD is a wonderful thing). 

'Building a twin engine stand off scale model..... Well, I WILL be building it after I sort out a few more details...700 sq in .... Weight to be (hopefully) under 100 oz. Four stroke(s), retracts, electronic controls and a few dis n' dats.

Why? I have had this in project mind since the early 1950's. I am not gonna compete with it.... it’s just something I wanna do. My Pop picked up a DFC, the Air Medal and a couple of Purple Hearts drivin one of these...(Europe, Pacific & Korea) My son picked up a national championship a few years ago with Pop's last A-26 as a plastic model.

Normally I would run twin 29-40's in something like this and would probably end up with the 40-size because basically I "trust in thrust" and can prop it for the tasks at hand.

Soooo.... I am after that tick-over idle....the sound .... smooth transition to good thrust & not necessarily having to cruise around at max rpm, but having it available.

Years ago I built one of those Sterling PT 17 kits.... all 65 1/2 inches of both wings. (this is my "big  model" experience)I flew it with a Fox 59 that had the prop diameter just peeking over the dummy engine /fuse.  Essentially it looked stupid, but it flew very well. I was a dB shattering mismatch to any "scale sound" and at rest, the prop always looked like someone clipped in half. I ended up with more weight in the nose then any of my other models weighted! Arse-ee guys get to balance by shoving around recievers, batteries and all kinds of stuff. The Stearman ended up with lead in the nose (a lot of lead).
I fiddled with a two chamber diverter, which could be plumbed to exhaust stacks on each side of a fuselage. Why? "Cause the exhaust "puffed" here & there at the 6 stacks and it did emit a staccato engine noise. Even though it looked cool & sounded cool running, there was no place to put it in the PT 17 it was too heavy to fly around with on anything else. I can't imagine making two of them for the A-26! 'Course weight-wise, something like this is usually plum full of recievers, batteries and stuff..... But I think I'll stick to 4-strokes & make life simpler.
I'd appreciate your thoughts,

Vince