ORIGINAL: Yellowsierra02
I have a OS .55ax in my pulse xt 40. Its a pretty quick plane. It radared in at 103mph in a slight dive. I am using a APC 10 x 8 and 15%nitro fuel and it turns 13,600 with this combo. I'm wanting a little more speed. I just ordered a Ultra thrust tuned pipe which should wake it up alittle. I was wondering if I could use 30% nitro to get some more rpms/speed out of it. I was also thinking about using a 10 x 10 apc prop to get more air speed. I was also thinking about trying a APC 9 x 10 prop. What do you guys thinK? I would like to get 120-130 moh out of this plane. Is this possible? Is the higher nitro a good idea? Ive heard its alittle harder on the glow plugs and you will have reduced flight times.
Thanks
Justin
The OS 55 is a heck of a good engine. With the right prop it runs great. Some guys are SERIOUSLY over-propping the engine. And the engine really enjoys the tuned exhaust. Its not agressively timed, so do not look for monster rpm. But it does develop power very well at reasonable rpm.
Keep the 10x8 and bolt on the ultrathrust.
You want the OS55 engine turning between 14,500 and 15,000 peak ground rpm.
If you have 13,600 rpm now, you will be right in that range with the 10x8. (Gain is typically 1200-1500 rpm -- just like the jett-stream muffler)
More prop and the muffler will not be in its best rpm range. So more prop is not the correct approach right up front.
Don't change the fuel.
After running the 10x8, you can try something like a 9x9 for a little speed. Maybe try a 10x9 if the rpm range seems consistant.
You will definately gain in speed and the engine will run great. But I think gaining 30 mph beyond where the plane flys today may be asking for a lot.