RE: saito 220 KMP bf 109
The ESM me-109 73" can swing an 18" prop just fine. I actually fly my electric one with a 20x10 prop. My other one has a saito 180 in it and I have a graupner 16x10x3 on it.
I have a saito 220 in an 80" H9 P-51. I was running a 17x10 to get the best speed in the air, however, it didn't have a lot of runtime on the motor aside from a few gallons of breakin.
An 18x10 3 blade may work ok as long as the motor is strong. You might try running a higher nitro content glow fuel to see if the power output can be obtained for good rpms on an 18x10 3 blade. What prop manufacturer were you thinking? A biela prop looks really nice, and they do have an 18x10 3 blade, just not sure if its a bit much weight wise for the 220 to spin at good rpms. The motor needs to be above 7500rpms to be in the sweet spot power wise. If you can get to 8000 or so, your golden on the 220.
kurrikan, you might try running a 17x10 3 blade first. Biela also makes that size, although again, not sure what brand of prop you have access. Im sure you could order several different brands from quite a number of places in Europe.
Just to show.....my electric version of the 73" me-109 is in this pic that has the 20x10 prop(2 blade) on it. Fly it frequently. Its sitting over on the left side of the pic with the prop straight up and down to the ground. With the tail up, there is still a good amount of room under it...a couple of inches.