Speaking of ST 51's

I made a couple discoveries about my T&L ST 51 that I am using in the USA-1. At The Huntersville meet, I ran the 12 x 4 1/2 Eather 3 blade on 10% nitro 25% all castor Sig Fuel. It ran great. I had broken it in per Tom's instructions on 24%-25% all castor. Back home after the meet, I switched to Sig 10% nitro, 20% oil 1/2&1/2 due to not wanting to cause the ring to stick. After turning in the needle to get the engine up to where it needed to be rpm wise, I started getting less dependable runs. Something this engine had NEVER done! After much thought (man THAT hurt) Aaron suggested cutting the prop down to 11 1/2 dia. That was all it took. Engine is back to being happy again,the break is back to excellent, and I could tell a little difference in the turn rate! My hypothesis is the the all castor was cooling the engine more, allowing the 1/2" greater diameter for the prop, and that by going to the 1/2 & 1/2 castor/synthetic it was building up a little too much heat to be happy. The engine would speed up in consecutive manuevers and it took a few level laps to settle back down. Does this make sense?
TIA
Bill <><

Bill,

Perfect sense. Same as mine. Except that I'm running a 3 blade 12X5.2 Bolly and using more castor to smoothe the run out. I'm using about 25-26% total oil and it likes that just fine!

YEP!

Scott(not a new thing)Riese

Makes perfect sense to me because that's what I found with my box stock G51. With 20% all castor it was a dog, it would go from a nice rich 4 stroke into a howling 2 stroke then take several laps to go back to 4 stroking (on a good day). A switch to 25% all castor let it growl all day long with no hint of a break (my preferred way). I suspect that slowly decreasing the oil content would allow me to adjust for any desired amount of break.

Thanks, all.
I think I will add a 'little' castor to the Sig 20% and go with that. I was getting concerned about the ring sticking with the all castor.
Good/bad idea?
Bill <><

Bill,

Add enough to get to 25% the sythetic will take care of the rest
Have a great day!

Thanks, Jim!
Hope to see you at KOI, the WC's, Brodak's or somewhere this year!
Bill <><

Bill,

My plans right now are to be at the Nats and Brodak's. I can't get to the KOI from where I am now though! 3 degrees north and 151 degrees west! I wanted to get to KOI but things worked out differently.

Hi Bill,
That Eather 12-4 1/2 3B is a lot of prop. I think you did the right thing.
I ran into something similar. I am running a Fox chrome case sport 36 with a stunt 35 sleeve. Tornado 10-4 3 blade. This is my attempt to get more power than a Fox Stunt 35. It's on a Bill Noyes Challenger. Great plane.
Anyway it ran great once, then subsequent flights it began to sag.. When I enrichened it the rpm/speed was too slow. My point is that there is a limit to what an engine can turn and still retain that sweet stunt 4-2-4 break.
Jim Armour has cut down on a Tornado 10-4 3blade on his Aerotiger 36. Runs great. I may have to do the same to get CONSISTANT stunt runs instead or occasional good stunt runs. That extra prop load must build up a lot of heat.
Happy Landings