ORIGINAL: ahicks
ORIGINAL: a1pcfixer
Actually that 12.5 x 14 is BELOW what DLE recommends for the DLE20 (14 x 10), which will put it in excess of 10,000+ rpm's, and often!
An 18 x 6 is ABOVE (17 x 6) what's recommended. So I'd vote on the smaller prop &/or a mid-air as being the demise of that model.
As for lubrication, he'd do good to increase it to say 25:1.....but if he's using Lawncrap all bets are on eng seizure.
It's about the load the prop is putting on the engine. He's running a TON of pitch, making the load significantly higher than one might first consider when looking at only the dia. of the prop he's running...................
Yes, the pitch increases the load, but
he's STILL going to be high reving with that small of a prop!