G'day Blokes, I always climb out in fine pitch for local flights to save our prop mechanism from unnecessary wear. No problems with temps but sometimes need to speed up/ throttle back a bit to stay below 200 degrees.
Our Dimona H36 with a L2400 motor on climb out after take off the other day to Mudgee was DEFINITELY detonating in course pitch cruise climb. Not badly but sufficient to cause damage in the long term. Just a faint "tic......tic tic............tic" etc etc. Conditions were 2000', CHT 190 degrees IAS 70kts and around 2400rpm (I think.... maybe a bit lower). When I pushed the throttle harder it didn't run rough but certainly noticeably "lumpier" due to higher manifold pressure. I think it would have run rough if I had continued. Back in fine pitch the problem went straight away and it ran beautifully. I tried it again at altitude with a cooler CHT and the detonation wasn't there but still a little lumpy running due to higher manifold pressure. Our Hoffman prop has a big difference between fine and course So, I would recommend being very careful about cruise climbing in course pitch. I find that if we are cruising, it is OK to drop back to 75kts and add a bit more power to gain height but for any serious climbing, fine pitch at 60kts and about 2900 are good for the engine as long as you watch CHT and maximum RPM. regards Rob Rob Thompson 0429 493 828
