Large Model Association Forum

I have built a pegasus models laser 200 which i flew a couple of times with a laser 150 and it was way under powered ,but I knew it would be. I always intended to put a petrol up front, I have just bought a 55cc boxer engine CRRC pro and I like the Biela 20x 10 three blade props. What I would like advice on is do I bother to put in right thrust and down thrust and if so how much?

depends on airframe. you will deffinatly need right thrust, 2 deg is a good start point. as for down thrust. you will find some aerobatic planes need up thrust! some zero some down. do you have much of a pitch change when throtling when the laser was fitted?

Thanks Allan I dont remember any pitch change, so maybe i will just put in the right thrust to start with. How do I work out where the mounting holes will be on the firewall so that the prop is central at the front of the cowl. I need to put about 12mm of packing in to get the prop clear of the cowl. I guess if I draw it out on paper using a protractor I will find out out how thick the packing needs to be on the right side to throw it over 2deg. Also I dont have a lot of room for the fuel tank what would be considered a good size for a 55cc petrol allowing say a 15 min flight time
Thanks